Wednesday, December 18, 2013

Saving your memories save your brain

The brain’s ability to preserve memories lies at the heart of our human experience and also of our identity. This is why forgetting is one of our most dangerous enemies. Diseases like Alzheimer delete our identity and make our life impossible. But we don’t have to get some of these debilitating illnesses to have problems. We are our memories and anytime we are not able to remember some experiences we lived in the past we feel like losing parts of our life. Recent findings show the fate of memories and also suggest the possible role of psychotherapy. And more…

But where in the brain do those old memories go? Despite decades studying how the brain transforms memories over time, neuroscientists remain divided over the answer. This month, researchers from Johns Hopkins University have come up with a new theory that might clear up this controversy. They claim that what we do with a memory determines where it is stored in the brain. Their theory, called Competitive Trace Theory (or CTT), suggests that what really matters is how often we revisit the memory. Memories they say are transformed each time we revisit them. A memory is first encoded by the activity of neurons from one part of the brain called the hippocampus. The hippocampus acts like as the brain’s director, telling the cortex which particular neurons to activate (see in the bellow image the structures presented in green – hippocampus and cortex). Each time we recall that memory, a similar but not identical set of neurons are activated. Neurons that are frequently activated became part of the permanent memory trace in the cortex, while the rarely activated ones are lost. Every reactivation re-encodes the memory, and depending on what cortical neurons are engaged, can strengthen, weaken or up-date particular memory features. With each memory reactivation, some features are reinforced while others disappear, explaining why the memory seems to get fuzzy over time. And the more details that are lost, the less “episodic” and the more “semantic” the memory becomes, explaining the sense of personal detachment often associated with very old memories. As memories get older, they are decontextualized due to competition among partially overlapping traces and become more semantic and reliant on cortex storage. Consolidation that leads to the strengthening of memories enhances conceptual knowledge (and becoming semantic memories) at the expense of vivid contextual details (or episodic memories).

Therapists working with traumatic patients know this very well – there is a clear distinction between recent traumas and distant traumas. Actually psychotherapy helps in this way : when a memory is recalled often it will more rapidly become stored in the cortex, become less episodic and independent of the hippocampus while a memory that’s rarely revisited will remain dependent on the hippocampus. As a result, remote memories are more likely to have a stronger semantic representation but also to be less vivid and more likely to include illusory details. And this is how it can incorporate a new perspective, a less emotional and more rational one, built by the joined efforts of the patient and the therapist.
Above I pointed out that each time we recall a memory a  set of neurons are activated, and neurons that are frequently activated became part of the permanent memory trace in the cortex, while the rarely activated ones are lost. In a recently published review, I present evidence that learning based on hippocampus seems to trigger the DNA repair pathways inside those hippocampal neurons, if the subject is re-exposed to the previously learnt information. So every time we encounter (or generally recall) some previously experienced contextual memories (a memory linked with a specific situation) the neurons involved in that memories seems to repair themselves and become healthier. And hence live longer. The new theory described above suggests that this process also save the memories stored in those neurons, the hippocampus activating the cortex and sending that data to it. Maybe the DNA repair process associated with this data transfer helps to clean up the hippocampus in order to be ready to learn something new. Something like a refresh process. Refresh that doesn’t happened in Alzheimer patients and other forms of dementia.

So revisiting your past can save your memories and also your brain.

Friday, December 6, 2013

The creative brain

Everybody knows that the left hemisphere of the brain is realistic, analytical, organized and logical, and the right hemisphere is creative, emotional, and intuitive. But in reality there is no such thing. These are only myths. In the early days of neuroscience some people claim that there are specific centers for creativity in the brain - like the temporal lobe, while other voices said is critical the interconnectivity between the two hemispheres made by the corpus callosum. But there are more speculations than scientific data. So, is there a place in the brain for creativity? And why should I be interested in the answer of these questions?

The latest findings from neuroscience suggest that the right brain/left brain distinction is not correct when it comes to understanding how creativity works in the brain. Creativity does not involve a single brain region or a single side of the brain. The entire creative process from preparation to incubation to illumination and verification consists of many interacting cognitive processes and emotions. Creation is a multi-step process not “an insight”. It takes time, sometimes weeks or even months, and depends by many factors, starting with your experiences and ending with the environment where you create. Depending on the stage of the creative process, and what you are actually trying to create, different brain networks are recruited to handle the task. Furthermore, many of these brain networks play as a team to get the job done, and recruit brain structures from both the left and right hemisphere.
And now I will be more specific. Let’s talk about some brain networks. Converging research do suggest that creativity recruits brain regions that are involved in many stuff like daydreaming, imagining the future, remembering personal memories, making meaning, and social cognition. It is known that all these processes are implemented by a specific neural network called Default network distributed on vast areas within the prefrontal, parietal and temporal lobes (see the picture bellow with yellow the Default network). Different studies documented that this network is responsible for constructing mental simulations based on personal experiences, thinking about the future, and generally when imaging alternative perspectives and scenarios to the present. It’s interesting that this Default network is associated with everything that the subjective Self entails. Hence, it is involved in introspection – when people are asked to describe their personality traits or present emotional state (disgust, fear, sadness, fury, happiness), to recall a past personal experience or to talk about their attitudes or preferences. This network is emotional by excellence, being implicated in the evaluation of objects described as positive/desirable or negative/undesirable, and the evaluation of emotionally-charged movie sequences. Also it is involved in social cognition. Studies revealed that one common element between the processes occurring within the Default network is the analysis of complex interactions between humans perceived as social, interactive and emotional in the same way as we perceive ourselves to be. It is involved in deducing the mental states of other people and is active when people make attributions regarding another person’s behavior, when they form a first impression about someone or when playing competitive games against another person (but not against a computer).
Well, imagistic studies (using fMRI) made on jazz musicians and rappers engaging in creative improvisation revealed that this Default network is highly active. When you want to loosen your associations, allow your mind to roam free, imagine new possibilities is good to increase activation in this network. So, let’s called this Default network the Imagination network.


Now I introduce to you another brain network - the Attentional Control network (see the picture above with blue). It is recruited when a task requires that the spotlight of attention is focused like a laser beam. This network is active when you’re concentrating on something challenging, or engaging in complex problem solving and reasoning that puts heavy demands on your working memory. This network is like a highway facilitating communication between frontal cortex and the posterior part of the brain. During the creative process is good to reduce activation of the Attentional Control network – or the inner critic – but, as we will see, not completely.
And here is the interesting part. Usually when you try to fix something, to solve a problem your Default network is OFF and the Attentional Control network is ON. But studies using fMRI revealed that creative people when attempting to solve a problem are able to activate both networks simultaneously, screening the environment and also letting open the door to the inner Self. This duality is critical. Why? Because an hyperactive Default network provides maximum flexibility in thinking and leads to creativity but is also a hallmark of mental illness such as manic-depression and schizophrenia. If you didn’t know, many of the artists were suffering by these diseases, especially by the first one. An hyperactive Default network gives you wings but also destroys you. In order to be really fruitful, the creative process has to be anchored in reality. You must be able to critically analyze the results of the creative process and to judge their relevance. But also to protect yourself, or in other words, to remain connected with this world. And this is done by the Attentional Control network which acts like a film critic.
            The good news is that both networks can be developed. The Default network actually grows if you exposed yourself to new experiences, but also can be trained by some meditation techniques like mindfulness. Attentional Control network can also be trained by using specific cognitive exercises like focused attention and working memory tasks. Knowing how your brain works gives you the advantage of choosing the wright path of personal development.

Thursday, November 14, 2013

The secret stuff that protects us from stress


Chronic stress affects large areas of the brain, especially the hippocampus, frontal lobe and other parts of the brain.  It affects the connectivity between neuronal hubs of the brain, and thus informational exchange between distal areas. Furthermore, it exerts a negative effect on non-emotional learning mechanisms, which are responsible with exploring and learning novel and complex aspects, different to the ones already known. New studies found that chronic stress accelerates aging by shortening some components of the chromosomes from our DNA. Can we protect ourselves from these deleterious effects?

Imaging studies conducted on Afghanistan veterans, before and after their deployment, revealed that prolonged stress reduces the activity and integrity of the mesencephalon (a structure at the base of the brain, in proximity of the spinal cord) and this alteration affects sustained attention. These changes seem to reverse to normal 1.5 years later after stress cessation. Conversely, combat stress induces persistent reduction of the connectivity between the mesencephalon and frontal cortex. Therefore, stress-induced alterations are only partially reversible. Also, stress-generated enhancement of stress hormones affects working memory process in the medial prefrontal cortex. This data clarifies why subjects with post-traumatic stress like Veterans of the Vietnam war fail to recall personal memories, and why this failure is more accentuated after exposure to traumatic scenes. We might even say that what we call chronic depression is a degenerative disease that affects the brain’s capacity to adapt to novel environments.

The stress response is generally transient, because its effects (immunosuppression, inhibition of growth and enhanced catabolism) yield long-lasting damage. Nonetheless, when stress becomes chronic, it is accompanied by digestive and cardiovascular problems. Furthermore, it affects DNA. This consequence may prompt genesis of tumors, neuropsychiatric disorders and accelerated aging. People suffering from depression may be aging faster than other people, according to a new study. Hence in a Netherlands Study of Depression and Anxiety involving about 1,900 people ranged from 18 to 65 year old who had major depressive disorders at some point during their lives, along with 500 people who had not had depression, scientists found that patients with major depressive disorder (MDD) have an increased onset risk of aging-related somatic diseases such as heart disease, diabetes, obesity and cancer. This suggests mechanisms of accelerated biological aging among the depressed, which can be indicated by a shorter length of telomeres. Telomeres are "caps" at the end of chromosomes that protect the DNA during cell division. Normally, telomeres shorten slightly each time cells divide, and their length is thought to be an index of a cell's aging.

The researchers found telomeres were shorter in people who had experienced depression compared with people in the control group. The length of telomeres is measured in terms of their number of DNA building blocks, called base pairs (bp). In the study, the telomeres in healthy people were about 5,540 bp long on average, whereas people with depression had telomeres about 5,460 bp long. In line with previous studies, the researchers found that with each year of age, telomeres shortened by 14 bp, on average. This suggests cellular aging in people with depression is accelerated by several years. Furthermore, the severity of a person's depression as well as a longer duration of symptoms were linked with shorter telomere length those with the most severe and chronic MDD showed the shortest telomeres, and those with remitted MDD had shorter telomere than controls) and the results held after controlling for weight, smoking, drinking and several other factors that may contribute to aging. The authors said that it is possible that telomere shortening is a consequence of impairment in the body's stress system.

These findings might help explain the variety of health complaints often experienced by people with major depression.  Other studies have shown that people with depression are at increased risk for diseases that tend to come with aging — for example, dementia, cancer and type 2 diabetes — even when health and lifestyle factors are taken into account. This has raised the question whether depression accelerates aging. An important question remains whether this aging process can be reversed. It is possible that lifestyle changes could lengthen telomeres. A healthy lifestyle, such as enough physical exercise, not smoking and a healthy diet, might be of even greater importance in depressed individuals than it is in the non-depressed. But can we be more specific? Yes. A few years ago scientists discover a protein which seems to have the property to offer us protection against stress. It is called Delta Fos B. Studies made on animals shown that a higher concentration of this protein in the brain regions associated with pleasure and motivation plays a critical role in not developing post-traumatic stress, even when the animals were exposed to stressful stimuli. You will say: “Ok, but if I don’t have a high concentration of Delta Fos B, what should I do? Can I take it by spoon?” No you can. But you can do something else. Exposure to an enriched environment stimulates the secretion of this protein. What is “enriched environment”? Is a combination of new places, were you can play or work with new tools or objects, interact with new people and make physical exercise. Not one day, but several months.

If you don’t want to get depressed, lose your memory, attention, and age fast you should learn how to explore, in the same way you have done when you were a child. So, try to be a child with the mind of an adult if you want to keep your mind.





Monday, October 28, 2013

Learning how to learn

Some study techniques accelerate learning, whereas others are just a waste of time – but which ones are which? Scientific American Mind magazine reviewed more than 700 scientific articles on 10 commonly used learning techniques. And this is what they found.

Most students report rereading and highlighting, yet these techniques do not boost performance, and they distract students from more productive strategies. Underlining, highlighting or otherwise marking material is simple and quick – but it does little to improve performance. In fact, it may actually hurt performance on some higher-level tasks. It may be that underlining draws attention to individual items rather than to connections across items. 84 % of the students said they reread textbooks or notes during study. It requires no training, makes modest demands on time, and shows some benefits on recall and fill-in-the-blank-style tests. Yet the evidence is muddy that rereading strengthens comprehension. Most of the benefit of rereading appears to accrue from the second reading, with diminishing returns from additional repetitions. Don’t waste your time! In head-to-head comparisons, rereading fares poorly against more active strategies. But which are these?


There are two clear winners: self-testing and distributed practice. How it works. Unlike a test that evaluates knowledge, practice tests are done by students on their own, outside the class. Methods might include using flash cards to test recall or answering the sample questions at the end of a textbook chapter. Although most students prefer to take as few tests as possible, hundreds of experiments show that self-testing improves learning and retention. This technique seems to trigger a mental search of long-term memory that activates related information, forming multiple memory pathways that make the information easier to access. Regarding the second technique, distributed practice, this is how it works. Students often “mass” their study. But distributed learning over time is much more effective. Longer intervals are generally more effective. 30-day delay improves performance more than lags of just one day. To remember something for one week, learning episodes should be 12 to 24 hours apart; to remember something for five years, the material should be spaced 6 to 12 months apart. Although it may not seem like it, you actually do retain information even during these long intervals, and you quickly relearn what you have forgotten. Long delays between study periods are ideal to retain fundamental concepts that form the basis for advanced knowledge.

The techniques presented above are proved to be the most practical. Along with them, there are a few with moderate utility. Elaborative interrogation requires to put yourself in the position to ask “Why?”. “Why does it make sense that ….?” or “Why is this true?”. This is effective especially if you already know something about the subject.  Another technique is self-explanation. In this case, students generate explanations of what they learn, reviewing their mental processing with questions such as “What new information does the sentence provide for me?”. Similar with elaborative interrogation, self-explanation may help integrate new information with prior knowledge. It helps in solving math problems, logical reasoning puzzles and learning from narrative texts. At the bottom of my list is interleaved practice. In this technique students alternate a variety of types of information or problems, instead of study in blocks, finishing one topic before moving on to the next. It improves performance on algebra problems and is effective to train medical students to put correct the diagnostic. But this technique is useful for those who are already reasonably competent.

Why don’t students use more effective study techniques? The research done by Scientific American Mind magazine found some explanations. It seems they are not being taught the best strategies, perhaps because teachers themselves are not schooled in them. A second problem may be that in the educational system, the emphasis is on teaching students content and maybe some critical-thinking skills. Less time is spent on teaching them how to learn. The result can be that students who do well in their early years, when learning is closely supervised, may once struggle once they are expected to regulate their own learning in high school or college.

Monday, October 21, 2013

Our genome as a memory stick

We tend to see humans as a combination of nature and nurture, nature being represented by the genes we inherit from parents and nurture by the impact of environment. But the reality is far more complex and subtle. What if the genes are only a biological data base especially built for saving the relevant changes from the environment we live?


 For people who are more or less familiar with psychology there is a well-known theory that intelligence is classified into two main categories: fluid and crystallized. Fluid intelligence is thought to deal with solving new problems, while crystallized intelligence is a sort of reservoir of knowledge. And the later are thought to be developed through the investment of fluid intelligence (hence the name “investment theory of intelligence”). But a new  study made by Dutch scientists from Tilburg and Amsterdam universities contested this view. In striking contrast with the general view that fluid intelligence would have a heavy genetic base while the crystallized one would be based on learnt knowledge or cultural load rather than genes, this new study found the exact opposite. Using an IQ test which has both culture free and culture loaded items, they found that highly culturally items had higher heritability coefficients (hence a stronger genetic component) and were also highly related to general IQ score. How to interpret these findings? The authors advanced the theory that people with more complex minds tend to seek out intellectually demanding environments, and as they develop higher levels of cognitive ability, they will be more favored to achieve higher levels of knowledge. So cognitive abilities and knowledge dynamically feed off each other. This is similar with studies which tried to find if there is an effect of brain fitness exercises on increasing the performance of working memory and attention. They found that these exercises help especially people with more powerful minds, not those with poorer cognitive abilities – which should be the main beneficiaries of this sort of training. Why? Because smart people tend to be more interested in self development, seek out more stimulation and also are more able to motivate themselves long enough (6 weeks of daily exercising) to benefit from the effect of this enduring mental training. 
It seems that societal demands influence the development and interaction of multiple cognitive abilities and knowledge, and giving rise to general intelligence factor. This is something similar to the Flynn effect. The Flynn effect is the substantial and long-sustained increase in fluid and crystallized intelligence test scores (average test scores) measured in many parts of the world from roughly 1930 to the present day. Some explanations have included improved nutrition, better education, and greater environmental complexity. The fact is that this effect tends to be strongly associated with the economic boom of a country.



As I mentioned above, brain fitness exercises increase performance of working memory and attention. In addition, another type of mental exercise – mindfulness meditation is proved to strengthen connections between regions of the brain called Default network and to increase the volume of the hippocampus (a brain structure critical for learning).  The brain’s Default network comprises several brain regions which are viewed as the biological basis of Self, storing our life experiences and contributing to introspection and other self-relevant processing, but also to creativity. Also these people which meditate 20 minutes a day for 90 days develop a more wrinkled cortex – the brain outer layer which is used for the most sophisticated mental abilities – and their brain become more efficient. Animal studies using enriched environment also discovered the effect of environment upon the brain. Enriched environment means housing mice in complex cages, where they have the possibility to play with toys, to explore, to make physical exercises and to interact with other mice. All these impact the brain’s circuits responsible with learning, increased brain plasticity and modify the expression of more than 40 genes involved in learning, building synapses and regulating blood supply in the brain.
So we have an important clue here! The environment, a new, complex environment seems to modify brain’s circuitry involved in learning and also the expression of the genes which build the brain. This process is called epigenetics, and represents the ability of the genes to be changed in their expression by the environment. And also to pass these changes to the next generation. So the environment leaves a mark on the brain, even a genetic mark, and this mark is heritable. This is the explanation for the discovery of the Dutch scientists presented at the beginning of this post. In psychology there is the assumption that genotype (meaning genes) and environment are independent and do not covary. These data suggest they very much do.

The tools we use during our lifetime, the games we play, the gadgets, the internet, all of these seems to shape our genes. Genes are not something created to build “the brain”. They are building specific brains according to the environment were that species use to live.  In the last 5000 years approx. 7 % of our genes have changed. And given that life on Earth is 3,5 billion years old, and our species is 190.000 years old, 5000 years is a blink of an eye! The human brain has adapted to the cultural information from the environment and these adaptations changed the expression of its genes. And some of these changes are passed to the next generation in order to be more adapted. Part of our culture is already in our genes and probably we can say that basically they are a biological form of culture.


Friday, October 11, 2013

Status is a drug

Brain uses the same mechanisms to get attached by somebody and to get addicted to drugs. Given these strange connections, it seems that social support and social status have a strong effect upon the brain, putting us in the position of becoming “addicted to power” and “addicted to public image”. And similar to the sensation of “being high” triggered by drugs, power gives us the sentiment of being above other humans and untouchable.

In these days many people have learnt about the role of body chemicals in romantic love and bonding in general. Despite the initially shocking discovery that human brain uses almost the same circuits for falling in love and for getting addicted to drugs, this scientific knowledge entered gradually into common sense. In all the women magazines you can find now articles about the “love hormones” oxytocin and vasopressin.  But this is not the full story, not even by far. These two ancient hormones are not the solely chemical involved in attachment, and when we start to get the bigger picture some intriguing facts comes to surface.
For instance, oxytocin works together with another brain’s chemical, the famous neurotransmitter – dopamine.  Oxytocin modulates dopamine release in the brain. Dopamine has several receptors to bind in order to exert its effect. One of them is the D2 receptor. And studies have found that these receptors seem to facilitate mother-child bonding. Dopamine interacts with oxytocin especially in the same brain areas involved in drug addiction, which are full of oxytocin receptors. And, strangely, this interaction materializes in social memory and social recognition. D2 is one of the dopamine receptors, and D1 is another one. Laboratory studies  made at University of Texas have shown that dopamine D2 receptor facilitates the establishment of a pair bond, while the D1 receptor inhibits it. So are not the parents to blame? In addition, after sexual intercourse, the dopamine D1 receptor prevents the male to “move on” from the original pair bond to a new bond with another female. Subsequent to mating-induced pair bonding, D1 receptor density increases at the membrane surface of neurons and this increase maintains monogamy by transforming responses toward other females from affiliative interest into aggressiveness. We should put the picture of this receptor on the wall of the City Hall weddings room. These studies were made on rats but there are human studies too, and one of them, made at Northwestern University in Evanston Illinois, have shown that boys with a mutation of the gene responsible with dopamine D2 receptor (mutation which reduces up to 40% of D2 receptor density in the brain areas involved in drugs addiction) tend to begin their sex life earlier and are less inclined toward developing long-lasting relationships with a partner. These individuals may not want to have children or get married, hence confirming the data from animal studies. I think somebody should invent a phone application able to detect this mutation, what do you think girls?



But is more than this. It is not only attachment connected with brain’s mechanisms of addiction. Is leadership, too. A study made in 2010 at Columbia University found a positive correlation between the ability of dopamine to bind with its receptors D2 and perceived social support in humans. Again the brain region targeted was the same intensively studied in drugs addiction. Their data suggest that D2 receptor binding is associated with an individual’s social capital, which may be regarded as a balance between social status and stress reduction by means of social support. High social rank, a strong feeling of social support and low levels of social avoidance are associated with increased dopamine binding with its D2 receptor. Social rank, strong support from the people around you, and a natural tendency to approach people, and to feel comfortable in social situations….Hmm, looks like leadership to me. And which is the connection with drugs? Studies in monkeys have revealed that when a dominant figure is isolated from the group, there is a drop in D2 receptor density in this brain area, and that individual becomes predisposed toward cocaine addiction. Conversely, when an animal becomes the group leader, D2 receptor density increases, thus reflecting the role of these receptors in social reward perception. Also, monkeys that have been exposed to social stress during adolescence are more likely to take drugs and they have lower dopamine binding at D2 receptor in this part of the brain involved in addiction. So, social status is like a drug? You can become addicted to it? Others revealed the implication of other areas in social status, such as the upper region of the frontal lobe. Therefore, electrical recordings from the neurons in this area, showed a stronger activation of the excitatory synapses in rats with high positions in a group hierarchy, compared to the subordinate ones. So your brain functions better when you are the boss. At least you are more excitable.
To summarize, what do we have here? It seems to be a tight connection in the brain between attachment, social status and brain’s mechanisms involved in addiction, but also in performance. If the first are accomplished, it seems the brain enters in a “high mode”, being more excitable, more eager to explore and conquest. And here are the downsides. Studies have found that people driving expensive cars were more likely than other motorists to cut off drivers and pedestrians at a four-way-stop intersection in the San Francisco Bay Area, UC Berkeley researchers observed. Those findings led to a series of experiments that revealed that people of higher socioeconomic status were also more likely to cheat to win a prize and to have an unethical behavior in a company. Genes regulating social behavior are strongly preserved from insects to people. And the brain’s mechanisms they build seem to have a lot in common, despite the differences in size and form. But it seems that evolution takes us by surprise. What makes you fitter and healthier in animal kingdom is not necessary suitable for traffic rules or management. We have to learn how to control these mechanisms in order not to become a stoned baboon driving a Ferrari.

Friday, October 4, 2013

How to open the brain’s windows

The brain is built to learn in a massive way only during the childhood and adolescence. Specific plasticity windows - named critical and sensitive windows - are open within this time interval, which help us to rapidly adapt to the external world. But the fact is that most of our life we live outside these windows and we can see this misfortune almost every day, as adults. Nevertheless, recent studies revealed the secret recipes for re-opening these plasticity windows in adult brain, with tremendous effects on learning, repairing and postponing the old age.

A "critical period" is a time window when external stimuli are mandatory for the normal development of a certain brain circuit. An example could be the learning of language. By contrast, a sensitive period is a time window when environmental experiences have the greatest impact upon a brain circuit. An example is learning a foreign language. A critical period once closed the openness the effect is a reduced effect of sensorial experiences upon the brain. These windows explain the easy of learning which characterizes children and adolescents by contrast to the relative decrease in learning performance specific to adult people. The onset and the duration of a critical period depend on age but also on experience. If a proper exposure or activity is not provided, a brain circuit remains in a waiting state until that input is available.  Not all the brain regions have the same developmental pathway. It matures starting from back to front and from basic functions like vision and movements to more complex abilities like language, problem solving or understanding others. In the visual cortex, the critical period closed around the age of 5 in humans, after this milestone the brain’s capacity to be changed by experience being significantly reduced. It is interesting that any foreign language learned before the age of 11 is superimposed in the brain on the same area of the native language, within the Broca area of language. By contrast, any foreign language learned after this age is saved in a different area within the Broca area. Also, learning a foreign language after this age requires much more effort and good results takes more time.  If a child is not exposed to native language until age of 11, afterwards he/she can learn only the words but not the grammar, hence being impossible to speak normally. Critical periods dictate also over some learning processes like extinction of a traumatic memory or a phobia. It is known that after a successful therapeutic session, these memories are not erased, are only inhibited (this is why they can pop-up sometimes and the stressful memory reappears). At least this is happening in the adult brain. But in the child brain, during  his/her first years of life, the extinction involves the permanent erasure of that memories. In the adult brain a proteins network is developed around the neurons and this network secures the memories for a life time. So is not possible to be erased anymore. It is striking that the proteins that build this network are the same that build the cartilages from the trachea, bronchi and heart.

The protein network which protect our memories from erasure (with red)(from Gogolla et al., 2009. Science, 325:1258-1261)

Given the fact that most of our life we spend as adults and the environment around us is changing all the time, is critical for an adult to preserve the learning abilities he/she use to have as an adolescent. Accidents that happened  to an adult brain are harder to be repaired and sometimes the repair process is not totally  successful. And the closure of the critical and sensitive periods are to be blamed for this. But it is possible to re-open these windows in an adult brain?  Experiments revealed that several factors are involved in triggering a critical or a sensitive period.  For instance, the therapy with antidepressant medication, such Prozac, seems to facilitate the plasticity of adult brain and it is prescribed, along with the physiotherapy, for the stroke victims. Also, enriched environment it is documented to have the same beneficial effects with the antidepressant medication, at least for the animals suffering of amblyopia.  Enriched environment provides a combination of multisensory stimulation, physical activity, social interactions and facilitation of exploratory behavior.   Enriched environment impacts the brain leading to an enhancement of cognitive  functions (especially learning and memory) but also positively impacts emotional reactivity and stress response.   Also it facilitates the growth of the grey matter hence influencing the weight of the brain, the number of synapses and the birth of new neurons. It also stimulates the expression of 41 genes known to be involved in learning and memory, plasticity, cellular growth, the genesis of blood vessels, and neuronal excitability. Even more ,  enriched environment seems to stimulates the anti-oxidative mechanisms of the organism, decreasing the inflammation and boosting immunity. It is interesting that enriched environment facilitates the maturation of visual system even in the case of total absence of visual experiences! Studies made on rats have shown that housing the pregnant female in this type of environment during the last semester of pregnancy leads to a more rapid development of pups’ visual system.    Furthermore, running in a wheel leads to a 2-fold increase in the number of neurons in their pups’ brain and also a better working memory for them, once they give birth.
A critical period can be induced in adult humans through non-invasive techniques such as enriched environment (as I already mentioned) but also by incremental training and educational video games, all of these putting the brain into a “learning mode”. Studies have shown that people which use to train themselves with action videogames, present an enhancement in visual acuity, effect not possible to be obtained by playing non-action video games. This emphasizes the role of some specific features of action games in maintaining attention and stimulating some neurotransmitters like dopamine and noradrenaline which are critical for brain plasticity. Studies made on animals found that the modification of the training protocols in order to contain incremental changes of the sensorial experiences leads to enhancement of the learning ability. The same results have been seen on human subjects exposed 2-3 weeks on various learning experiences previous to the exposure to the target material to be learned. This is called metaplasticity, or the intentionally process of inducing plasticity in the brain.

  All of this data show that our brain is a life time project; it can help us only if we help it. It’s a sort of symbiosis. In addition, the brain is the only organ in our body we can keep young, at least for a while. The “know-how” of this process is not written in our genes, it depends by the knowledge we gathered with the technology it helps us to develop. So we can say neuroscience is the brain’s effort to discover how it is built, how to repair itself and how to enjoy the world as much as is possible.

Wednesday, September 25, 2013

The technology for rewriting the memories

Every time we retrieve something from our memory it can be changed, rewritten with new info and re-consolidated in the brain as a new, up-dated memory. There are specific time windows of this process that could be implemented into the extinction procedures used for the therapy of phobia and addiction.
The traditional view in psychology and also in neuroscience is a module-oriented approach: the amygdala relates to emotions, the hippocampus to memory, and the visual cortex to perception. Subsequently, the brain has been regarded as a “Swiss penknife”, each anatomical part being a specialized tool for a certain function. And these functions are ascertained by the psychology as “psychological processes” or “mental faculties”. Psychology textbooks are organized into chapters  according to these taxonomies – one chapter for emotions, one for perception, and one for memory. But what if this paradigm is wrong? Based on the acquired data in neuroscience various authors have implied that the mental faculties approach should be altered, pointing out the inaccuracy of this module-oriented organization of the brain.



From the very beginning, psychology and cognitive sciences in general, have investigated memory, dividing it into various subcomponents: sensory, short and long term, procedural and declarative, implicit and explicit, episodic and semantic. All these paradigms are based on the same definition of memory: the ability to encode, store and recall information. One fundamental aspect in this definition is that information is initially stored and subsequently revealed, in the same way a “refrigerator” assumes that a certain temperature prevents food from going bad. Nonetheless, experimental data has revealed that the ability to recall information is not independent from what we traditionally call “perception”, “imagination” or “attention”, but rather shares an intimate relation with them. The “perceptual-mnemonic” theory of the brain implies that it may not be constructive to make a distinction between “perception” and “memory” as mental functions, as they may seem to be from introspection. Instead, they should be regarded as different manifestations of a common neural substrate. There is a dynamic interaction between “perception” and “retrieval”. Subsequently, retrieval of information is similar to perception because it involves the identification and understanding of current stimuli according to past experiences. Some argue that we cannot see something if it does not resemble information from memory. An anecdotic example supporting this contention is the story of the native Americans that could not see the Spanish ships anchored onshore because they did not know anything about ships.
Experimental studies have shown that is possible to rewrite an old memory with new info, but first you have to be exposed to the context where that old memory was initially created. Actually this is happening when people who were witess to an accident or murder are exposed to information about that incident covered by the media, during the time interval they wait to testify in Court. Their original memories become automatically compromised by these new info. This re-exposure trigger a special labile state in the brain and memory updating is made only when the brain enters in this labile state and the new info is presented particulary in this state. It is fascinating ! It’s like a magic key from the Indiana Jones movies. Hence memory retrieval leads to new memories formation on the foundation of the stored and reactivated previous experience. Actually the reality is even more dramatic, being impossible to create new memories without reactivating past memories. Old memories act like an atractor which capture info from the same category with them and fix it like a superglue. Even more fascinating, studies revealed that there are specific time windows when it comes to change an existing memory. Most of this sort of studies were made for treating phobia and addiction. In order to overcome a phobia or an addiction, the brain has to re-learn rather than to erase the undesirable aversive or appetitive memories. This re-learning is called extinction and consist in the association of the context previously associated with the drugs of abuse or the unpleasant stimulus, with lack of drugs respectively with safeness. But in order to be effective, this extinction technique must obeys some specific rules. Hence, performing a spatial or contextual learning task 1 or 2 hours before the extinction training facilitates the effect of training. But not if the exposure was 3 hours before. Why ? Because this sort of learning produces proteins in the neurons and this proteins are captured by the synapses and used to consolidate the new memory created during the extinction training. The process is named tag-and-capture.  Furthermore, the extinction is effective only if procedes between 10 minutes and maximum 2 hours after the exposure to the traumatic context respectively the reactivation of the traumatic memory. Note the labile state of the brain induced by remembering/recognition, mentioned above. This is the time interval it stays labile and can incorporate new info into the existing one. Fructose or glucose consumption 30 minutes after the exposure/reactivation also helps. It is important to say that 2 hours after exposure/reactivation, the time window for the reconsolidation of the new memory is closing, and the behavioral effect could be noticed only after 2 days when the reconsolidation process is finished. This procedure could be resumed several times if is necesary, but the results obtained are garanteed at least 180 days. As you can see it’s a kind of engineering.

I conclude that knowing the real functional organization of the brain is a must if we want to explain the mind but especially if we want to positively impact its performance such as improving learning and re-learning.


Friday, July 5, 2013

Best of 2013

Aşa cum face toată lumea in iulie-august şi blogul meu va intra in vacanţă. Vom reveni probabil doar in septembrie, dar cu o supriză semnificativă (sper să imi şi iasă). Pȃnă atunci, mulţumesc cititorilor mei şi vă ofer un “best of” al postărilor din acest an. Vă doresc şi vouă vacanţă plăcută!

Terapie prin patternuri. Toată lumea a auzit de călugării sihaştrii care se izolează in pesteri sau chili in vȃrful muntelui pentru a-l găsi pe Dumnezeu. Şi chiar il aud sau il văd. Pe el sau pe alte personaje gen Satana, duhurile strămoşilor sau Fecioara Maria. Pur şi simplu pentru că aşa reacţionează creierul la izolare şi deprivare senzorială. Activează compensator patternuri din cele stocate in memorie. De la amintiri autobiografice şi pȃnă la halucinaţii şi delir. De aceea există inţelepţi şi guru doar in mănăstiri izolate şi sihăstrii, nu şi in mall-uri sau in trafic. Dar tot din acelaşi motiv invăţăturile lor nu se pot aplica la oamenii care trăiesc intre target-uri, deadline-uri şi hypermarket. Oarecum fenomenul ăsta are loc şi cȃnd se face psihoterapie. Oamenii cu depresie sau anxietate, sau cei cu senzaţia de gol existential au o problemă cu găsirea şi invăţarea de patternuri. Iar creierul lor suferă din acest motiv. Terapeutul incearcă să-i ajute să le găsească din nou. Lucrează cu ei in a le da un sens, a le explica simptomele si a-i invaţa patternuri de actiune. De genul, “cand te mai simti aşa, trebuie să faci sau să gȃndeşti următoarele”. Sau “asta se intȃmplă din cauză că…..”. 

Mereu am făcut glume pe seama terapeuţilor. Le spuneam că neuroştiinţele incă nu au găsit toate cauzele depresiei după zeci de ani de studii iar un terapeut iti spune de ce esti depresiv după jumate de oră de discuţie cu tine. Chestia este că el nu trebuie să ştie care sunt cauzele reale ale depresiei tale. El invata niste scheme explicative care trebuie să ţi se pară cȃt mai plauzibile şi să vorbească pe limba ta. Ce spune trebuie să facă sens pentru tine, conform experienţei tale de viaţă. În felul acesta se reporneştemotorul de găsit patternuri (Doctore, dă-mi ceva să facă sens!).


Conştiinţa este un face-lift al memoriilor. Totuşi, ce inseamnă “a fi conştient”?  Din ce s-a descoperit pȃnă acum, inseamnă suma cunoştinţelor noastre care sunt conectate intre ele la un moment dat. Adică, dacă am cunoştinţe despre un lucru anume, cȃnd il văd undeva il recunosc, stiu dacă imi place sau nu, mă prind dacă contextul in care apare e normal pentru el, ştiu ce aş putea face cu el sau ar putea să imi facă el mie, ce istoric am cu el, cum ar trebui să reacţionez in faţa lui, in functie de situatia in care sunt singur sau impreună cu altii, şi aşa mai departe. De ce se activează toate informaţiile astea? Cercetătorii de la University of California Berkeley au realizat o hartă a locurilor unde sunt stocate informaţiile in creier despre tot felul de categorii: părţi ale corpului, animale, vehicule, texte, peisajem drumuri sau clădiri. După cum vedeţi din imaginea de mai jos, ele sunt răspȃndite imprăştiat pe toată suprafaţa creierului. Ei, de fiecare dată cȃnd ne intalnim cu lucruri sau oameni cunoscuţi, memoriile noastre isi fac up-date. Şi dat fiind imprătierea lor, ele trebuie cumva conectate, pentru că o experienţă de viaţă  e compusă din tot felul de detalii diferite, stocate in locaţii diferite. Iar informaţia nouă cu care ne intȃlnim trebuie să fie confruntată cu tot ce există similar prin creier.  În plus, se pare că acest proces de up-date este critic pentru sănătatea neuronilor noştrii. Dacă el nu are loc ei se degradează mai rapid, adică ne sclerozăm. Atunci cȃnd ne recunoaştem un fost coleg pe stradă, au loc in creier lucruri mult mai complicate decȃt am crede. Mai intȃi că se activează informaţiile pe care le avem despre el, apoi se pornesc niste simulări mentale despre cum va reacţiona el, cum ar trebui să ne purtăm cu el, ce ar trebui să ii spunem si ce nu, etc. Studiile au arătat că oamenii sunt mai puţin impulsivi in decizii, cu cȃt sunt mai capabili să realize aceste simulări ale variantelor de viitor posibile. Deci, in limbaj comun, putem spune că sunt mai conştienţi atunci cȃnd iau decizii, sau mai responsabili. Toate aceste reamintiri şi simulări fac parte din ceea ce numim CONŞTIINŢĂ. Dar, de fapt sunt doar un system de refresh al memoriilor noastre. Cu cȃt refreshul implică mai multe memorii, cu atȃt suntem mai conştienţi de ce ni se intȃmplă şi de lumea din jurul nostru. De aceea copiii şi oamenii cu Alzheimer sunt “mai puţin conştienţi” - pentru că au mai puţine amintiri la dispoziţie (De ce avem conştiinţă).

Revoluţiile solare. Sub influenţa filmelor Ice Age mulţi cred că epoca de gheaţă le-a venit de hac dinozaurilor (era şi o reclamă parcă cu ceva in genul ăsta). Adevărul este că ultima epocă de gheaţă (mai corect spus Glaciaţiunea) s-a terminat acum 12.000 de ani, iar dinozaurii dispăruseră de mult, de vreo 65 de milioane de ani. Chestia este că soarele a avut o perioadă de maximă activitate la finalul Glaciaţiunii, acum 16-11.000 de ani. Iar odată cu terminarea ei, au inflorit primele aşezări urbane şi a apărut agricultura. Iar omul a inceput să se schimbe rapid. Gȃndiţi-vă că acum 10.000 de ani nu existau oameni cu ochi albaştrii, oamenii nu puteau mȃnca carne friptă şi nici lapte adulţi fiind. Acestea se datorează unor mutaţii la care a fost expusă specia umană. În cazul acesta nu e clar ce le-a produs, dar au coincis cu activitatea Soarelui şi au condus la evoluţie. Activitatea Soarelui nu a impactat doar evoluţia omului in trecut, ci se pare că o face şi in zilele noastre. Există o stranie corelaţie intre perioadele de maximă activitate solară şi unele activităţi umane precum revoluţiile, cuceririle şi descoperirile geografice. Unii cercetători de la observatorul astronomic din Cracovia au realizat o statistică in care se vede o corelaţie intre Soare şi evenimente precum declararea independenţei coloniilor americane de sub dominaţia britanică, revoluţia franceză, inlăturarea ţarului şi instaurarea comunismului in Rusia, revoluţia cubaneză, “primăvara de la Praga”, infinţarea sindicatului Solidaritatea din Polonia sau căderea comunismului. Se pare că activităţile umane tind să marcheze fluctuaţiile din activitatea Soarelui, la fel cum se invigorează zborul fluturilor de noapte in jurul lămpii atunci cȃnd o aprindem. Şi 2012-2013 este din nou o perioadă de maximă activitate solară…

Religiile şi filosofiile au incercat in toata istoria existenţei lor să explice sensul vieţii omului pe Pămȃnt. Poate că rolul vieţii in general, a tuturor formelor ei, este de a inregistra activitatea Soarelui şi de a o salva sub diferite forme – de la gene la civilizaţie (În slujba soarelui).

Cablajele comportamentului. Conexiunile dintre diverse zone ale creierului dictează ce stil de viaţă avem. Din datele privind conexiunile a rezultat că creierul bărbaţilor homo şi al femeilor hetero este mai sensibil la stimuli emoţionali, la stres şi anxietate. De altfel se ştie că femeile sunt de 2-3 ori mai expuse la tulburări afective decȃt barbaţii, iar incidenţa depresiei şi a tentativelor de suicid este crescută la bărbaţii homosexuali. Pe de altă parte, creierul bărbaţilor hetero şi al femeilor homo este mai atent la mediul din jur şi mai orientat spre acţiune – aşa numitele fight or flight reactions. Şi se ştie că bărbaţii dar şi femeile homo tind să fie mai agresivi. Cu alte cuvinte, la stres bărbaţii homo reacţionează mai uşor şi mai emotional, fie prin anxietate fie prin depresie, in timp ce bărbaţii hetero nu sunt chiar aşa sensibili, iar cȃnd reacţionează o fac mai activ, sau chiar agresiv. Aceste diferenţe anatomice sunt prezente la naştere, chiar şi la fetus deci trebuie să fie ceva legat de mecanismele care construiesc creierul. Cu toate acestea, se ştie că nu există o “genă” a homosexualităţii. Deci trebuie să fie altceva (Homosexualitatea – efect secundar al evoluţiei).

Licenţa de părinte. Acum cȃţiva ani se punea in parlamentul englez problema introducerii unei legi prin care cei care doreau să devină pentru prima dată părinţi să aibă obligaţia de a face un curs de parenting in urma căruia să primească un fel de licenţă prin care să li se dea dreptul să aibă copii. Dacă luau examenul. Dacă nu, să nu li se dea. Initiaţiva, incă neadoptată pȃnă in prezent, s-ar justifica – spuneau cei din partidul laburist iniţiatorii proiectului – prin numărul mare de copii abandonaţi, neglijaţi, abuzaţi, precum şi procentului ridicat al delicvenţei juvenile, toate puse pe socoteala proastei educaţii primite, in special de către cei din mediile defavorizate. Această idee dă apă la moară unor evoluţionişti care au observat că omul ar fi dezavantajat spre deosebire de animale cȃnd e vorba de creşterea progeniturilor. Adică, el are nevoie de sfaturi – fie ale celor mai in vȃrstă fie profesioniste (cum ar fi cursurile de parenting sau sfaturile pediatrului şi psihologului de copii) – pentru a-şi creşte corespunzător urmaşii, in timp ce animalele fac totul “din instinct”. Adică au scris in genele lor pachetul respectiv. Lucru in bună măsură adevărat. Dar se poate pune problema şi DE CE există această diferenţă, aş zice eu fundamentală? De ce fundamentală? O sa vedeţi unde ajungem cȃnd căutăm explicaţiile…(Copilăria – laborator de experienţe genetice).

Terapie emisferică. Ca şi evoluţii ale funcţiilor lor iniţiale, la om emisfera stȃngă este responsabilă de a genera sentimentul de “sens al vieţii”, iar o slabă activitate a ei este asociată cu depresia. Iar dreapta este responsabilă de a genera vigilenţă şi nevoie de control, o activitate prea ridicată a ei fiind asociată cu stresul şi anxietatea. De aceea oamenilor care suferă de simptome de depresie şi lipsă de motivaţie in viaţă le prinde bine o terapie care pune accentul pe a povesti cuiva sau in scris cum ii este viaţa şi de ce crede că este aşa, pe a-i oferi un sens, o explicaţie pentru ce se intȃmplă cu ea, dar şi pe rutine casnice (cum e să facă ordine), pe organizare (cum sunt planurile de viitor), pe reintoarcerea la lucruri şi persoane familiare, la familie, la locurile copilăriei, revederea filmelor preferate, re-ascultarea muzicii din adolescenţă şi chiar şi mȃncarea “ca la mama acasă”. Toate acestea “re-pornesc”emisfera stȃngă. Iar oamenilor stresaţi şi anxioşi le face bine antrenarea răspunsurilor comportamentale in situaţii noi, incerte, in care nu au controlul, sau terapia gen reţetă: “În situaţia X trebuie să faci …. şi să eviţi a face…” Şi repetarea acestora pȃnă devin rutine, adică trec in emisfera stȃngă (De ce trebuie să ştii evolutionism ca să scapi de depresie).

Chemistry-ul dintre noi. Am lăsat la urmă simţul feromonal. El nu are legătură cu mirosul, aşa cum aţi putea crede, deşi informaţia pătrunde prin nas. Doar că nu ajunge in centrul mirosului, ci intr-un organ numit vomeronazal. Feromonii sunt nişte molecule care transmit inconştient informaţii privind o groază de lucruri. Nu cum miroase cel de lȃngă tine, ci dacă este mai dominant sau mai servil, dacă este mai sociabil sau nu, dacă este mai stresat şi fricos sau mai relaxat, dacă este gay sau heterosexual. Este interesant că unele informaţii sunt chiar mai corect transmise prin aceste molecule, decȃt prin văz. Studiile realizate la University of Wroclaw din Polonia au arătat că feromonii impregnaţi in tricourile purtate 3 zile de nişte oameni şi mirosite apoi de alţii au fost un indicator mai exact privind trăsăturile de personalitate ale purtătorilor decȃt inregistrările video cu comportamentul acestora. Alte studii realizate la Monell Chemical Senses Center au arătat că feromonii conţin informaţii privind genele care controlează sistemul imunitar. Toţi avem acelaşi gene imunitare, dar nu toţi aceeaşi variantă a genei respective. E fascinant că ne simţim mai atraşi sexual dacă persoana de lȃngă noi de sex opus are gene diferite de ale noastre. De ce? Pentru că dacă am face copii impreună, ei ar avea un set mai complet de gene care gestionează imunitatea, care ar acoperi o gamă mai largă de amenintări. Acest senzor al capacităţii imunitare nu mai funcţionează insă dacă femeile iau anticoncepţionale, strict pe perioada cȃnd o fac. Asta explică de ce le plac un gen de bărbaţi cȃnd nu luau anticoncepţionalele şi alt gen, ulterior.  Feromonii sunt probabil cel mai important instrument de comunicare socială din lumea vie, de la viermi şi insecte şi pȃnă la om (O specie ignorantă şi indiferentă).


X şi …O. Ce e mai interesant (şi cu aplicaţii practice aş zice eu) e că atunci cȃnd un băiat moşteneşte inteligenţa, e posibil ca el să aibă inteligenţa bunicii şi nu a mamei. De ce bunica şi nu mama? Pentru că mama s-ar putea să nu aibă funcţională gena de pe cromozomul X moştenit de la mama ei pentru că ea moşteneşte şi un cromozom X de la tatăl ei (aşa cum am arătat mai sus), iar acesta poate afecta prin imprinting (vezi mai sus) cromozomul X moştenit de la mamă. Adică il inhibă şi se manifestă el in locul lui. Iar cȃnd femeia face un copil, ea poate să ii dea mai departe X-ul bun de la maică-sa sau X-ul rău de la taică-său. Dacă acest copil se naşte fată ea mai are o şansă (poate lua un X bun de la tată chiar dacă a avut ghinionul să il ia pe cel rău de la mamă) in schimb dacă este băiat şansele sunt mai mici, pentru că se bazează doar pe X-ul matern (Ce moştenesc copiii de la noi).

Orgasmul ca la şcoală. În ce priveşte orgasmul, există o groază de studii in ultima vreme. Astfel, se ştie că bărbaţii ajung mai repede acolo – cam in 10-12 minute – in timp ce femeile mai greu – cam după 20 de minute. De aceea multe pierd ocazia să il mai aibă. Apoi, odată declanşat, el durează mai mult la femei decȃt la bărbaţi ceea ce complică foarte mult viaţa celor care studiază fenomenul masculin cu instrumente de imagistică medicală. În plus, femeile pot avea şi orgasme multiple, in cazul in care nu ai apucat să il “prinzi” pe aparat pe primul dintre ele…Mai sunt şi alte diferenţe. Astfel, orgasmul la bărbaţi este strict dependent de senzaţiile pe care le simt in organul sexual, iar diferenţele dintre orgasmul obţinut prin masturbare nu este foarte diferit de cel obţinut prin act sexual (era şi un banc despre care e diferenţa dintre cele două, iar răspunsul era că nici una, doar că făcȃnd sex mai cunoşti lume). În creierul lor este foarte activat in timpul orgasmului cortexul somato-senzorial. În schimb la femei diferă semnificativ orgasmul obţinut prin act sexual, el fiind semnificativ mai intens decȃt cel obţinut prin masturbare. Creierul femeilor in timpul orgasmului diferă de al bărbaţilor, activarea in cortexul somato-senzorial fiind mai redusă decȃt la bărbaţi, iar in plus are loc o “decuplare” a lobului frontal precum şi a unor structuri limbice precum amigdala şi hipocampul. Cu alte cuvinte, ele sunt ca şi intr-un fel de transă, se rup de lume, nu mai simt frică, raţiune, iar calitatea orgasmului depinde de context, atmosferă, tipul partenerului, etc. Chiar şi de purtatul ciorapilor! Dacă au ciorapi in picioare se simt mai bine (!?). Iar cu cȃt orgasmul este mai intens şi şansele să rămȃnă insărcinate sunt mai mari. Ce au in comun cele două sexe? Orgasmul produce in zone de la baza creierului descărcare de dopamină similară cu cea obţinută de o doză de heroină. Practic pȃnă la un punct, orgasmul şi heroina sunt similare in creier, ceea ce explică caracterul de adicţie pe care il are sexul (dacă nu ştiaţi există “dependenţă de sex” ca şi tulburare psihică)( Ştiinţa sexului).