Fascinating Facts About the Human Brain

The brain may stop growing by age 18, but it produces 250,000 neurons per minute in early pregnancy!
Credit: Published by HW Neurological Institute 


Friday the 13th: Why humans are so superstitiousRituals and talismans can give us a boost of self-confidence or a sense of control.


Friday the 13th: Why humans are so superstitious
Rituals and talismans can give us a boost of self-confidence or a sense of control.

(via laboratoryequipment)



Reflecting on mirror neurons

Mirror neurons are cells that fire during both the execution and observation of a specific action. They have been linked to many behaviours and abilities, from empathy to learning by imitation, as well as implicated in conditions such as autism. Mirror neurons were discovered in monkeys, but it’s still not clear whether they also exist in the human brain.

Mirror neurons were identified in the brains of macaque monkeys by a team of Italian researchers during experiments performed in the 1990s. The researchers, who were studying how the brain controls hand and mouth movements, implanted microelectrodes into the monkeys’ brains in order to monitor the activity of single cells while the animals reached for pieces of food and put them into their mouths. These experiments revealed that the activity of certain cells increased when the monkeys performed this action.

The cells in question are located in the premotor cortex, a part of the brain involved in planning and executing movements, so the finding was not in itself particularly surprising. By chance, however, the researchers discovered that a few of the same cells also fired weakly when the animals merely observed the researchers putting food into their own mouths, and fired more strongly when they saw other monkeys performing the same action. Subsequently, the same team of researchers identified mirror neurons in several other regions of the monkey brain. They also located cells that fire when monkeys observe an action as well as when they hear the sound related to it.

But what does it all mean? The precise role of the mirror neuron system in monkeys is still not known, though the researchers who discovered them believe that they perform two functions. First, that mirror neurons are involved in understanding the actions of others – observing an action triggers the mirror neuron system to generate a motor representation of it. This corresponds to the activity produced by the action itself: in other words, the mirror neuron system transforms the visual information into knowledge of the intention of the others’ actions. The second proposed function is imitation – or learning to perform an action by observing others.

Casting a long reflection

The discovery of mirror neurons was greeted with a great deal of excitement, and some have hailed it as one of the most important discoveries of modern neuroscience. Since these neurons were discovered in monkeys, researchers have speculated that the human brain may also contain mirror neurons.

In human beings, as in monkeys, mirror neurons are hypothesized to play an important role in imitation and understanding the actions of others. Some researchers argue that they are critical for many aspects of social interactions. These include understanding the intentions of others, and inferring their mental state from their behaviour (an ability referred to as theory of mind); empathy, or putting oneself ‘into another’s shoes’; self-awareness; and the evolution of, and the ability to learn, language.

Given their purported role in social cognition, one prominent neuroscientist has proposed that a defective mirror neuron system is what causes autism, a neurodevelopmental condition characterized primarily by impairments in social interaction and communication. The same researcher argues that the discovery of mirror neurons is ‘the single most important “unreported” story of the decade’, and has even referred to the cells as ‘the neurons that shaped civilization’, because human culture involves the transfer of complex skills and knowledge from person to person.

Box: The broken mirror hypothesis

In the late 1990s, two groups of researchers independently proposed the so-called broken-mirror hypothesis, which states the social impairments characteristic of autism are caused by defects in the mirror neuron system. The broken mirror hypothesis has received considerable attention in the mass media, but has been the subject of severe criticism by many autism researchers. It is based on assumptions that mirror neurons are involved in understanding action, imitation and language acquisition, and that people with autism are insensitive to the emotions and intentions of others. Critics say both that the first assumption is actually false, and also that there is evidence that people with autism are in fact overly sensitive to others’ emotions and intentions. What’s more, the broken-mirror hypothesis does not attempt to explain how the mirror neuron system is defective, or how the defects might arise.

But do we have mirror neurons?

Mirror neurons have proven to be highly controversial. A handful of brain- scanning studies show that several regions of the brain are activated during both action execution and observation, and it has been suggested that these areas constitute the human mirror system. But while hundreds of other studies attempt to explain their results by alluding to mirror neurons, very few actually provide hard evidence.

So there is, as yet, very little convincing direct evidence that mirror neurons exist in the human brain. In fact, a number of studies have failed to find evidence of human mirror neurons altogether. In 2009, for example, Harvard researchers exploited a phenomenon called adaptation, whereby neurons reduce their activity in response to the same repetitive stimulus. The researchers showed their participants a film clip of hand gestures and asked them to mimic the action. The scans showed that the cells adapted when the gestures were observed and mimicked, but not when they were mimicked first and then observed.

One of the difficulties is that researchers rarely get the opportunity to examine the working human brain directly. In 2010, though, one research group who had just such an opportunity, while evaluating the brains of conscious epileptic patients about to undergo neurosurgery, claimed that they had obtained the first direct evidence of human mirror neurons. Some of these cells fired both when the patients performed and observed an action, but the activity of almost as many cells decreased during execution and observation, raising doubts that they are indeed mirror neurons. Furthermore, the cells were located in the hippocampus, an area involved in memory formation, and not previously thought to be part of the presumed mirror neuron system.

The researchers who originally discovered mirror neurons in the monkey brain have recently refined their claims, and now suggest that the cells have a far more restricted role than was originally thought. Instead of being involved in understanding the actions of others, they suggest that the cells play a role in helping us to understand, ‘from the inside’, actions that we already know how to perform. Critics argue that this confirms the alternative theory that mirror neurons are involved instead in selecting and controlling actions.


“You cannot teach a man anything, you can only help him
to find it within himself.” Galileo (via psych-facts)

(Source: beautifulepitome, via psych-facts)



The Nervous System

Painted figures from Master John Banister [1533-1610], Anatomical Tables.

The fifth and sixth ‘tables’ exhibit posterior and anterior aspects of the nervous system, etc.

(via University of Glasgow :: Manuscripts)

(via neuromorphogenesis)



Unique epigenomic code identified during human brain development

Changes in the epigenome, including chemical modifications of DNA, can act as an extra layer of information in the genome, and are thought to play a role in learning and memory, as well as in age-related cognitive decline. The results of a new study by scientists at the Salk Institute for Biological Studies show that the landscape of DNA methylation, a particular type of epigenomic modification, is highly dynamic in brain cells during the transition from birth to adulthood, helping to understand how information in the genomes of cells in the brain is controlled from fetal development to adulthood. The brain is much more complex than all other organs in the body and this discovery opens the door to a deeper understanding of how the intricate patterns of connectivity in the brain are formed.

"These results extend our knowledge of the unique role of DNA methylation in brain development and function," says senior author Joseph R. Ecker, professor and director of Salk’s Genomic Analysis Laboratory and holder of the Salk International Council Chair in Genetics. “They offer a new framework for testing the role of the epigenome in healthy function and in pathological disruptions of neural circuits."

A healthy brain is the product of a long process of development. The front-most part of our brain, called the frontal cortex, plays a key role in our ability to think, decide and act. The brain accomplishes all of this through the interaction of special cells such as neurons and glia. We know that these cells have distinct functions, but what gives these cells their individual identities? The answer lies in how each cell expresses the information contained in its DNA. Epigenomic modifications, such as DNA methylation, can control which genes are turned on or off without changing letters of the DNA alphabet (A-T-C-G), and thus help distinguish different cell types.

In this new study, published July 4 in Science, the scientists found that the patterns of DNA methylation undergo widespread reconfiguration in the frontal cortex of mouse and human brains during a time of development when synapses, or connections between nerve cells, are growing rapidly. The researchers identified the exact sites of DNA methylation throughout the genome in brains from infants through adults. They found that one form of DNA methylation is present in neurons and glia from birth. Strikingly, a second form of “non-CG” DNA methylation that is almost exclusive to neurons accumulates as the brain matures, becoming the dominant form of methylation in the genome of human neurons. These results help us to understand how the intricate DNA landscape of brain cells develops during the key stages of childhood.

The genetic code in DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). DNA methylation typically occurs at so-called CpG sites, where C (cytosine) sits next to G (guanine) in the DNA alphabet. About 80 to 90 percent of CpG sites are methylated in human DNA. Salk researchers previously discovered that in human embryonic stem cells and induced pluripotent stem cells, a type of artificially derived stem cell, DNA methylation can also occur when G does not follow C, hence “non-CG methylation.” Originally, they thought that this type of methylation disappeared when stem cells differentiate into specific tissue-types such as lung or fat cells. The current study finds this is not the case in the brain, where non-CG methylation appears after cells differentiate, usually during childhood and adolescence when the brain is maturing.

By sequencing the genomes of mouse and human brain tissue as well as neurons and glia (from the frontal cortex of the brain) during early postnatal, juvenile, adolescent and adult stages, the Salk team found that non-CG methylation accumulates in neurons through early childhood and adolescence, and becomes the dominant form of DNA methylation in mature human neurons. “This shows that the period during which the neural circuits of the brain mature is accompanied by a parallel process of large-scale reconfiguration of the neural epigenome,” says Ecker, who is a Howard Hughes Medical Institute and Gordon and Betty Moore Foundation investigator.

The study provides the first comprehensive maps of how DNA methylation patterns change in the mouse and human brain during development, forming a critical foundation to now explore whether changes in methylation patterns may be linked to human diseases, including psychiatric disorders. Recent studies have demonstrated a possible role for DNA methylation in schizophrenia, depression, suicide and bipolar disorder. “Our work will let us begin to ask more detailed questions about how changes in the epigenome sculpt the complex identities of brain cells through life,” says co-first author Eran Mukamel, from Salk’s Computational Neurobiology Laboratory.

"The human brain has been called the most complex system that we know of in the universe," says Ryan Lister, co-corresponding author on the new paper, previously a postdoctoral fellow in Ecker’s laboratory at Salk and now a group leader at The University of Western Australia. “So perhaps we shouldn’t be so surprised that this complexity extends to the level of the brain epigenome. These unique features of DNA methylation that emerge during critical phases of brain development suggest the presence of previously unrecognized regulatory processes that may be critically involved in normal brain function and brain disorders."

At present, there is consensus among neuroscientists that many mental disorders have a neurodevelopmental origin and arise from an interaction between genetic predisposition and environmental influences (for example, early-life stress or drug abuse), the outcome of which is altered activity of brain networks. The building and shaping of these brain networks requires a long maturation process in which central nervous system cell types (neurons and glia) need to fine-tune the way they express their genetic code.

"DNA methylation fulfills this role," says study co-author Terrence J. Sejnowski, a Howard Hughes Medical Institute Investigator, holder of the Francis Crick Chair and head of Salk’s Computational Neurobiology Laboratory. “We found that patterns of methylation are dynamic during brain development, in particular for non-CG methylation during early childhood and adolescence, which changes the way that we think about normal brain function and dysfunction."

By disrupting the transcriptional expression of neurons, adds co-corresponding author M. Margarita Behrens, a staff scientist in the Computational Neurobiology Laboratory, “the alterations of these methylation patterns will change the way in which networks are formed, which could, in turn, lead to the appearance of mental disorders later in life.”

Image2: A new study by Salk researchers provides the first comprehensive maps of epigenomic changes in the brain known as “DNA methylation,” a chemical modification of a cell’s DNA that can act as an extra layer of information in the genome. The study provides clues as to how specific genes are regulated in fetal, juvenile and adult brain cells, and the findings form a critical foundation to explore whether changes in methylation patterns may be linked to human diseases, including psychiatric disorders.

Brain DNA 

“In a morbid condition of the brain, dreams often have an extraordinary distinctiveness, vividness, and extraordinary semblance of reality. At times monstrous images are created, but the setting and the entire process of imagining are so truth-like and filled with details so delicate, so unexpected, but so artistically consistent with the picture as a whole, that the dreamer, were he an artist like Pushkin or Turgenev even, could never have invented them in the waking state. Such sick dreams always remain long in the memory and make a powerful impression on the overwrought and excited nervous system.” Crime And Punishment by Fryodor Dostoevsky (via psych-facts)

Gut Bacteria We Pick Up As Kids Stick With Us For Decades

Most of the microbes in our guts appear to remain stable for years, perhaps even most of our lives, researchers reported Thursday.
An analysis of the bacteria in the digestive systems of 37 healthy women over a period of about five years found, for the most part, little variation over time, says molecular biologist Jeffrey Gordon of the Washington University School of Medicine, who led the research. As decades-long internal companions, Gordon says, many microbes “are in a position to shape our lives, to promote our health or, in certain circumstances, contribute to risk for disease.”
Scientists have known for a long time that we all carry around bacteria that help us digest our food. But they apparently do lots of other things for us too.
"These are cells that are important parts of ourselves," Gordon says. “And they contribute to our health."
There’s always been one big question about the microbes, he says: “Once these communities are formed, how long do they endure? What is the stability in healthy individuals?”
To try to get a sense of that, Gordon and his colleagues developed a new type of “gut check”: a genetic analysis Gordon calls “a bar code of life.” The technique involves repeatedly analyzing all the variations in a particular bacterial gene. Because each strain of bacteria carries a slightly different form of the gene, the forms act almost like name tags or “bar codes” that identify which strains are present.
The method is “a way of classifying organisms represented in an individual’s gut community in a moment of time and over time,” Gordon says.
Being able to test gut microbes from time to time could eventually prove to be a useful part of a checkup, Gordon says. For example, in the current study, published in this week’s issue of the journal Science, Gordon and his team found that when several women lost weight, the makeup of their gut bacteria slightly shifted (though the scientists couldn’t tell which came first — the weight loss, or the bacterial shift).
"By looking at someone’s intestine we could pretty much tell how much weight they had lost or gained without having to put them on a scale," says Jeremiah Faith of Mount Sinai Hospital in New York, who helped conduct the study.
Another intriguing finding was that people’s microbes seem to run in families — much as genes do. The researchers found more similarities in the gut microbes of related women — such as sisters, or a mother and her daughter — than among women who were not related.
"For everyone that we checked we were able to identify strains of bacteria that were shared between related individuals, which suggests that [they] had these microbes for a long time because many of these [relatives] lived far apart from each other now," Faith says.
The finding corroborates earlier work suggesting that our microbial communities tend to form early in life, largely from microbes we get from our mothers and other close relatives when we are young.
"In the same way our genome defines who we are, one could say that the microbial populations that inhabit us define who we are," says Eric Pamer of Memorial Sloan-Kettering Cancer Center in New York.
Because all the women in the study were healthy, the researchers did not examine what happens to our microbes when we do things like take antibiotics or probiotics. Stay tuned for future research.
Image: Streptococcus bacteria, like this strain, can be found in our guts.


Gut Bacteria We Pick Up As Kids Stick With Us For Decades


(Source: psych-facts)

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