Posts tagged prefrontal cortex
Articles and news from the latest research reports.
Schizophrenia linked to abnormal brain waves
Neuroscientists discover neurological hyperactivity that produces disordered thinking
Schizophrenia patients usually suffer from a breakdown of organized thought, often accompanied by delusions or hallucinations. For the first time, MIT neuroscientists have observed the neural activity that appears to produce this disordered thinking.
The researchers found that mice lacking the brain protein calcineurin have hyperactive brain-wave oscillations in the hippocampus while resting, and are unable to mentally replay a route they have just run, as normal mice do.
Mutations in the gene for calcineurin have previously been found in some schizophrenia patients. Ten years ago, MIT researchers led by Susumu Tonegawa, the Picower Professor of Biology and Neuroscience, created mice lacking the gene for calcineurin in the forebrain; these mice displayed several behavioral symptoms of schizophrenia, including impaired short-term memory, attention deficits, and abnormal social behavior.
In the new study, which appears in the Oct. 16 issue of the journal Neuron, Tonegawa and colleagues at the RIKEN-MIT Center for Neural Circuit Genetics at MIT’s Picower Institute for Learning and Memory recorded the electrical activity of individual neurons in the hippocampus of these knockout mice as they ran along a track.
Previous studies have shown that in normal mice, “place cells” in the hippocampus, which are linked to specific locations along the track, fire in sequence when the mice take breaks from running the course. This mental replay also occurs when the mice are sleeping. These replays occur in association with very high frequency brain-wave oscillations known as ripple events.
In mice lacking calcineurin, the researchers found that brain activity was normal as the mice ran the course, but when they paused, their ripple events were much stronger and more frequent. Furthermore, the firing of the place cells was abnormally augmented and in no particular order, indicating that the mice were not replaying the route they had just run.
This pattern helps to explain some of the symptoms seen in schizophrenia, the researchers say.
“We think that in this mouse model, we may have some kind of indication that there’s a disorganized thinking process going on,” says Junghyup Suh, a research scientist at the Picower Institute and one of the paper’s lead authors. “During ripple events in normal mice we know there is a sequential replay event. This mutant mouse doesn’t seem to have that kind of replay of a previous experience.”
The paper’s other lead author is David Foster, a former MIT postdoc. Other authors are Heydar Davoudi and Matthew Wilson, the Sherman Fairchild Professor of Neuroscience at MIT and a member of the Picower Institute.
The researchers speculate that in normal mice, the role of calcineurin is to suppress the connections between neurons, known as synapses, in the hippocampus. In mice without calcineurin, a phenomenon known as long-term potentiation (LTP) becomes more prevalent, making synapses stronger. Also, the opposite effect, known as long-term depression (LTD), is suppressed.
“It looks like this abnormally high LTP has an impact on activity of these cells specifically during resting periods, or post exploration periods. That’s a very interesting specificity,” Tonegawa says. “We don’t know why it’s so specific.”
The researchers believe the abnormal hyperactivity they found in the hippocampus may represent a disruption of the brain’s “default mode network” — a communication network that connects the hippocampus, prefrontal cortex (where most thought and planning occurs), and other parts of the cortex.
This network is more active when a person (or mouse) is resting between goal-oriented tasks. When the brain is focusing on a specific goal or activity, the default mode network gets turned down. However, this network is hyperactive in schizophrenic patients before and during tasks that require the brain to focus, and patients do not perform well in these tasks.
Further studies of these mice could help reveal more about the role of the default mode network in schizophrenia, Tonegawa says.
Primate brain development follows a predictable pattern
In a breakthrough for understanding brain evolution, neuroscientists have shown that differences between primate brains - from the tiny marmoset to human – can be largely explained as consequences of the same genetic program.
In research published in the Journal of Neuroscience, Professor Marcello Rosa and his team at Monash University’s School of Biomedical Sciences and colleagues at Universidade Federal do Rio de Janeiro, in Brazil, used computer modelling to demonstrate that the substantial enlargement of some areas of the human brain, vital to advanced cognition, reflected a consistent pattern that is seen across primate species of all sizes.
This finding suggests how the neural circuits responsible for traits that we consider uniquely human – such as the ability to plan, make complex decisions and speak – could have emerged simply as a natural consequence of the evolution of larger brains.
“We have known for a long time that certain areas of the human brain are much larger than one would expect based on how monkey brains are organised,” Professor Rosa said.
“What no one had realised is that this selective enlargement is part of a trend that has been present since the dawn of primates.”
Using publicly available brain maps, MRI imaging data and modelling software, the neuroscientists compared the sizes of different brain areasin humans and three monkey species: marmosets, capuchins and macaques. They found that two regions, the lateral prefrontal cortex and the temporal parietal junction, expand disproportionally to the rest of the brain.
The prefrontal cortex is related to long term planning, personality expression, decision-making, and behaviour modification. The temporal parietal junction is related to self-awareness and self-other distinction.
Lead author Tristan Chaplin, from the Department of Physiology will commence his PhD next year. He said the findings showed that those areas of the brain grew disproportionately in a predictable way.
“We found that the larger the brain is, the larger these areas get,” Tristan said.
“When you go from a small to big monkey - the marmoset to macaque - the prefrontal cortex and temporal parietal junction get larger relative to the rest of the cortex, and we see the same thing again when you compare macaques to humans.”
“This trend argues against the view that specific human mutations gave us these larger areas and advanced cognition and behaviour, but are a consequence of what happens in development when you grow a larger brain,” Tristan said.
Professor Rosa said the pattern held for primate species that evolved completely separately.
"If you compare the capuchin of South America and the macaque of Asia, their brains are almost identical, although they developed on opposite sides of the world. They both reflect the genetic plan of how a primate brain grows," Professor Rosa said.
This is the first computational comparative study conducted across several primate species. Tristan now hopes, in collaboration with zoos, to check if our closest primate relatives, the chimpanzees and gorillas, also have brain areas organised as his theory predicts.
(Source: monash.edu.au)
Neuroscientists identify class of cortical inhibitory neurons that specialize in disinhibition
An inhibitory neuron type is found to specifically suppress the activation of other inhibitory neurons in cerebral cortex.
The cerebral cortex contains two major types of neurons: principal neurons that are excitatory and interneurons that are inhibitory, all interconnected within the same network. New research now reveals that one class of inhibitory neurons – called VIP interneurons — specializes in inhibiting other inhibitory neurons in multiple regions of cortex, and does so under specific behavioral conditions.
The new research finds that VIP interneurons, when activated, release principal cells from inhibition, thus boosting their responses. This provides an additional layer of control over cortical processing, much like a dimmer switch can fine-tune light levels.
The discovery was made by a team of neuroscientists at Cold Spring Harbor Laboratory (CSHL) led by Associate Professor Adam Kepecs, Ph.D. Their research, published online today in Nature, shows that neurons expressing vasoactive intestinal polypeptide, or VIP, provide disinhibition in the auditory cortex and the medial prefrontal cortex.
The researchers used molecular tagging techniques developed by team member Z. Josh Huang, a CSHL Professor, to single out VIP-expressing neurons in the vast diversity of cortical neurons. This enabled Kepecs’ group, led by postdocs Hyun Jae Pi and Balazs Hangya, to employ advanced optogenetic techniques using color-coded laser light to specifically activate VIP neurons. The activity of the cells was monitored via electrophysiological recordings in behaving animals to study their function, and in vitro to probe their circuit properties.
These VIP neurons are long sought “disinhibitory” cells: they inhibit other classes of inhibitory neurons; but they do not directly cause excitation to occur in brain. Dr. Kepecs and colleagues propose that the disinhibitory control mediated by VIP neurons represents a fundamental “motif” in cerebral cortex.
The difference between neural excitation and disinhibition is akin to the difference between hitting the gas pedal and taking your foot off the breaks. Cells that specialize in releasing the brakes, Dr. Kepecs explains, provide the means for balancing between excitation and inhibition. Kepecs calls this function “gain modulation,” which brings to mind the fine control that a dimmer switch provides.
The team wondered when VIP neurons are activated during behavior. When, in other words, is the “cortical dimmer switch” engaged? To learn the answer the scientists recorded VIP neurons while mice were making simple decisions, discriminating between sounds of different pitches. When they made correct choices, the mice earned a drop of water; for incorrect choices, a mild puff of air. Surprisingly, the team found that in auditory cortex, a region involved in processing sounds, VIP neurons were activated by rewards and punishments. Thus these neurons appeared to mediate the impact of reinforcements and “turn up the lights” on principal cells, to use the dimmer-switch analogy.
“Linking specific neuronal types to well-defined behaviors has proved extremely difficult,” says Kepecs. These results, he says, potentially link the circuit-function of VIP neurons in gain control to an important behavioral function: learning.
(Source: cshl.edu)
Brain stimulation affects compliance with social norms
Neuroeconomists at the University of Zurich have identified a specific brain region that controls compliance with social norms. They discovered that norm compliance is independent of knowledge about the norm and can be increased by means of brain stimulation.
How does the human brain control compliance with social norms? The biological mechanisms that underlie norm compliance are still poorly understood. In a new study, Christian Ruff, Giuseppe Ugazio, and Ernst Fehr from the University of Zurich show that the lateral prefrontal cortex plays a central role in norm compliance.
Prefrontal cortex controls norm behavior
For the study, 63 participants took part in an experiment in which they received money and were asked to decide how much of it they wanted to share with an anonymous partner. A prevalent fairness norm in Western cultures dictates that the money should be evenly split between the two players. However, this contrasts with the participants’ self-interest to keep as much money as possible for themselves. In another experiment, the participants were faced with the same decision, but knew in advance that they could be punished by the partner for an unfair proposal.
By means of a technique called “transcranial direct current stimulation,” which sends weak and painless electric currents through the skull, the excitability of specific brain regions can be modulated. During this experiment, the scientists used this technique to increase or decrease neural activity at the front of the brain, in the right lateral prefrontal cortex. Christian Ruff, Professor of Neuroeconomics and Decision Neuroscience at the University of Zurich, said: “We discovered that the decision to follow the fairness norm, whether voluntarily or under threat of sanctions, can be directly influenced by neural stimulation in the prefrontal cortex.”
Brain stimulation affects normative behavior
When neural activity in this part of the brain was increased via stimulation, the participants’ followed the fairness norm more strongly when sanctions were threatened, but their voluntary norm compliance in the absence of possible punishments decreased. Conversely, when the scientists decreased neural activity, participants followed the fairness norm more strongly on a voluntary basis, but complied less with the norm when sanctions were threatened. Moreover, neural stimulation influenced the participants’ behavior, but it did not affect their perception of the fairness norm. It also did not alter their expectations about whether and how much they would be punished for violating the norm.
"We found that the brain mechanism responsible for compliance with social norms is separate from the processes that represent one’s knowledge and beliefs about the social norm," says Ernst Fehr, Chairman of the Department of Economics at the University of Zurich. "This could have important implications for the legal system as the ability to distinguish between right and wrong may not be sufficient for the ability to comply with social norms." Christian Ruff adds: "Our findings show that a socially and evolutionarily important aspect of human behavior depends on a specific neural mechanism that can be both up- and down-regulated with brain stimulation."
Literature:
Christian C. Ruff, Giuseppe Ugazio und Ernst Fehr. Changing Social Norm Compliance With Noninvasive Brain Stimulation. Science. October 3, 2013.
(Image: iStockphoto)
![Maths experts are “made, not born”
A new study of the brain of a maths supremo supports Darwin’s belief that intellectual excellence is largely due to “zeal and hard work” rather than inherent ability.
University of Sussex neuroscientists took fMRI scans of champion ‘mental calculator’ Yusnier Viera during arithmetical tasks that were either familiar or unfamiliar to him and found that his brain did not behave in an extraordinary or unusual way.
The paper, published this week (23 September 2013) in PLOS ONE, provides scientific evidence that some calculation abilities are a matter of practice. Co-author Dr Natasha Sigala says: “This is a message of hope for all of us. Experts are made, not born.”
Cuban-born Yusnier holds world records for being able to name the days of the week for any dates of the past 400 years, giving his answer in less than a second. This is the kind of ability sometimes found in those with autism, although Yusnier is not on the autistic spectrum. Unlike those with autism or the related condition Asperger’s, he is able to explain exactly how he calculates his answers – and even teaches his system and has written books on the subject.
The study, carried out at the Clinical Imaging Sciences Centre on the University of Sussex campus, suggests that Yusnier has honed his ability to create short cuts to his answers by storing information in the middle part of the brain specialised for long-term working memory (the hippocampus and surrounding cortex). This type of memory helps us carry out tasks in our area of expertise with speed and efficiency.
Although the left side of his brain was activated during mathematical problems – which is normal for all brains – the scientists observed that something slightly different happened when Yusnier was presented with unfamiliar problems.
The scans showed marked connectivity of the anterior parts of the brain (prefrontal cortex), which are involved in decision making, during the unfamiliar calculations. This supports Yusnier’s report that he was building in an extra step to his mental processes to turn an unfamiliar problem into a familiar one. His answers to the unfamiliar questions had an 80 per cent degree of accuracy (compared with more than 90 per cent for familiar questions) and his responses were slightly slower.
Dr Sigala explains: “Although this kind of ability is seen among some people with autism, it is much rarer in those not on that spectrum. Brain scans of those with autism tend to show a variety of activity patterns, and autistic people are not able to explain how they reach their answer.
“With Yusnier, however, it is clear that his expertise is a result of long-term practice – and motivation.”
She adds: “It was beyond the scope of our paper to discuss the debate on deliberate practice vs. innate ability. But our study does not provide evidence for specific innate ability for mental calculations. As put by Charles Darwin to Francis Galton: ‘ […] I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal and hard work; I still think this an eminently important difference.’”](http://40.media.tumblr.com/749a98eac0fa21f91c01da24b2bf7089/tumblr_mtqmqtOttT1rog5d1o1_500.png)
Maths experts are “made, not born”
A new study of the brain of a maths supremo supports Darwin’s belief that intellectual excellence is largely due to “zeal and hard work” rather than inherent ability.
University of Sussex neuroscientists took fMRI scans of champion ‘mental calculator’ Yusnier Viera during arithmetical tasks that were either familiar or unfamiliar to him and found that his brain did not behave in an extraordinary or unusual way.
The paper, published this week (23 September 2013) in PLOS ONE, provides scientific evidence that some calculation abilities are a matter of practice. Co-author Dr Natasha Sigala says: “This is a message of hope for all of us. Experts are made, not born.”
Cuban-born Yusnier holds world records for being able to name the days of the week for any dates of the past 400 years, giving his answer in less than a second. This is the kind of ability sometimes found in those with autism, although Yusnier is not on the autistic spectrum. Unlike those with autism or the related condition Asperger’s, he is able to explain exactly how he calculates his answers – and even teaches his system and has written books on the subject.
The study, carried out at the Clinical Imaging Sciences Centre on the University of Sussex campus, suggests that Yusnier has honed his ability to create short cuts to his answers by storing information in the middle part of the brain specialised for long-term working memory (the hippocampus and surrounding cortex). This type of memory helps us carry out tasks in our area of expertise with speed and efficiency.
Although the left side of his brain was activated during mathematical problems – which is normal for all brains – the scientists observed that something slightly different happened when Yusnier was presented with unfamiliar problems.
The scans showed marked connectivity of the anterior parts of the brain (prefrontal cortex), which are involved in decision making, during the unfamiliar calculations. This supports Yusnier’s report that he was building in an extra step to his mental processes to turn an unfamiliar problem into a familiar one. His answers to the unfamiliar questions had an 80 per cent degree of accuracy (compared with more than 90 per cent for familiar questions) and his responses were slightly slower.
Dr Sigala explains: “Although this kind of ability is seen among some people with autism, it is much rarer in those not on that spectrum. Brain scans of those with autism tend to show a variety of activity patterns, and autistic people are not able to explain how they reach their answer.
“With Yusnier, however, it is clear that his expertise is a result of long-term practice – and motivation.”
She adds: “It was beyond the scope of our paper to discuss the debate on deliberate practice vs. innate ability. But our study does not provide evidence for specific innate ability for mental calculations. As put by Charles Darwin to Francis Galton: ‘ […] I have always maintained that, excepting fools, men did not differ much in intellect, only in zeal and hard work; I still think this an eminently important difference.’”
Brain may rely on computer-like mechanism to make sense of novel situations
Our brains give us the remarkable ability to make sense of situations we’ve never encountered before—a familiar person in an unfamiliar place, for example, or a coworker in a different job role—but the mechanism our brains use to accomplish this has been a longstanding mystery of neuroscience.
Now, researchers at the University of Colorado Boulder have demonstrated that our brains could process these new situations by relying on a method similar to the “pointer” system used by computers. “Pointers” are used to tell a computer where to look for information stored elsewhere in the system to replace a variable.
For the study, published today in the Proceedings of the National Academy of Sciences, the research team relied on sentences with words used in unique ways to test the brain’s ability to understand the role familiar words play in a sentence even when those words are used in unfamiliar, and even nonsensical, ways.
For example, in the sentence, “I want to desk you,” we understand the word “desk” is being used as a verb even though our past experience with the word “desk” is as a noun.
“The fact that you understand that the sentence is grammatically well formed means you can process these completely novel inputs,” said Randall O’Reilly, a professor in CU-Boulder’s Department of Psychology and Neuroscience and co-author of the study. “But in the past when we’ve tried to get computer models of a brain to do that, we haven’t been successful.”
This shows that human brains are able to understand the sentence as a structure with variables—a subject, a verb and often, an object—and that the brain can assign a wide variety of words to those variables and still understand the sentence structure. But the way the brain does this has not been understood.
Computers routinely complete similar tasks. In computer science, for example, a computer program could create an email form letter that has a pointer in the greeting line. The pointer would then draw the name information for each individual recipient into the greeting being sent to that person.
In the new study, led by Trenton Kriete, a postdoctoral researcher in O’Reilly’s lab, the scientists show that the connections in the brain between the prefrontal cortex and the basal ganglia could play a similar role to the pointers used in computer science. The researchers added new information about how the connections between those two regions of the brain could work into their model.
The result was that the model could be trained to understand simple sentences using a select group of words. After the training period, the researchers fed the model new sentences using familiar words in novel ways and found that the model could still comprehend the sentence structure.
While the results show that a pointer-like system could be at play in the brain, the function is not identical to the system used in computer science, the scientists said. It’s similar to comparing an airplane’s wing and a bird’s wing, O’Reilly said. They’re both used for flying but they work differently.
In the brain, for example, the pointer-like system must still be learned. The brain has to be trained, in this case, to understand sentences while a computer can be programmed to understand sentences immediately.
“As your brain learns, it gets better and better at processing these novel kinds of information,” O’Reilly said.
(Source: colorado.edu)
Training the Older Brain in 3-D: Video Game Enhances Cognitive Control
Scientists at UC San Francisco are reporting that they have found a way to reverse some of the negative effects of aging on the brain, using a video game designed to improve cognitive control.
The findings, published on Sept. 5 in Nature, show that a specially designed 3-D video game can improve cognitive performance in healthy older adults, they said. The researchers said the study provides a measure of scientific support to the burgeoning field of brain fitness, which has been criticized for lacking evidence that such training can induce lasting and meaningful changes.
In the game, which was developed by the UCSF researchers, participants race a car around a winding track while a variety of road signs pop up. Drivers are instructed to keep an eye out for a specific type of sign, while ignoring all the rest, and to press a button whenever that particular sign appears. The need to switch rapidly from driving to responding to the signs – i.e. multitasking – generates interference in the brain that undermines performance. The researchers found that this interference increases dramatically across the adult lifespan.
But after receiving just 12 hours of training on the game, spread over a month, the 60- to 85-year-old study participants improved their performance until it surpassed that of 20-somethings who played the game for the first time.
The training also improved the participants’ performance in two other important cognitive areas: working memory and sustained attention. And participants maintained their skills at the video game six months after the training had ended.
“The finding is a powerful example of how plastic the older brain is,” said Adam Gazzaley, MD, PhD, UCSF associate professor of neurology, physiology and psychiatry and director of the Neuroscience Imaging Center. Gazzaley co-founded the company, Akili Interactive Labs, which is developing the next generation of the video game.
Gazzaley, who has made a career out of studying how distraction affects cognitive performance, said his game, NeuroRacer, does more than any ordinary game – be it bridge, a crossword puzzle, or an off-the-shelf video game – to condition the brain. Like a good teacher, he said, NeuroRacer undermines people’s natural tendency to go on automatic pilot once they’ve mastered a skill, and pushes them further than they think they can go.
“Normally, when you get better at something, it gets easier,” he said. But with this game, “when you get better, it gets harder.”
Brain Training Reverses Age-Related Decline
Evidence that the adult brain is capable of learning has been accumulating for more than a dozen years. A study of London taxi drivers, for example, found that their brains had changed as they learned to navigate the city’s notoriously complicated streets. Nevertheless, Gazzaley said the brain’s function often erodes steadily over time in many areas, with some exceptions, like wisdom.
Given this, Gazzaley said it’s encouraging that even a small amount of brain training can reverse some of the age-related decline.
Gazzaley’s group found evidence of a possible brain mechanism that may explain the improvements he saw in his older subjects, and why these gains transferred to other cognitive areas. Electroencephalograph (EEG) recordings point to changes in a neural network involved in cognitive control, which is necessary to pursue goals.
The scientists measured midline frontal theta – or low frequency oscillations – in the prefrontal cortex, as well as the coherence in these waves between frontal and posterior regions of the brain. As the older “drivers” became more adept at the multitasking challenges of NeuroRacer, their brains modulated this key neural network and its activity began to resemble that of young adults.
Both of these measures – midline frontal theta and theta coherence – are well established neural markers of cognitive control that have been associated with many of the processes that enable people to pursue their goals.
We see this as evidence that the training may have improved our study participants’ ability to stay in an engaged, active state for a longer period of time,” said Joaquin A. Anguera, the paper’s first author and a post-doctoral fellow in Gazzaley’s lab.
Indeed, the researchers found that the training-induced changes in this neural network predicted how well participants would do on a different test, called the Test of Variables of Attention (TOVA), which measures sustained attention.
“The amount that midline frontal theta went up was related to something that was untrained, this other measure, the TOVA,” Anguera said. “It implies there’s something that changed that was common to the training and to the task we tested afterwards.”
Gazzaley said these findings point toward a common neural basis of cognitive control that is enhanced by the challenging and high-interference conditions of the video game, and this might explain how racing a car in 3-D could improve something as seemingly unrelated as memory.
If the finding holds, it could have wide application. Other brain disorders like ADHD, depression and dementia are also associated with deficits in cognitive control.
“Follow up studies using functional Magnetic Resonance Imaging and transcranial electrical stimulation are still needed to better understand exactly how this network is involved in the performance changes,” Gazzaley said.
Brain imaging study reveals the wandering mind behind insomnia
Study is the first to find functional MRI differences in working memory in people with primary insomnia
A new brain imaging study may help explain why people with insomnia often complain that they struggle to concentrate during the day even when objective evidence of a cognitive problem is lacking.
"We found that insomnia subjects did not properly turn on brain regions critical to a working memory task and did not turn off ‘mind-wandering’ brain regions irrelevant to the task," said lead author Sean P.A. Drummond, PhD, associate professor in the department of psychiatry at the University of California, San Diego, and the VA San Diego Healthcare System, and Secretary/Treasurer of the Sleep Research Society. "Based on these results, it is not surprising that someone with insomnia would feel like they are working harder to do the same job as a healthy sleeper."
The research team led by Drummond and co-principal investigator Matthew Walker, PhD, studied 25 people with primary insomnia and 25 good sleepers. Participants had an average age of 32 years. The study subjects underwent a functional magnetic resonance imaging scan while performing a working memory task.
Results published in the September issue of the journal Sleep show that participants with insomnia did not differ from good sleepers in objective cognitive performance on the working memory task. However, the MRI scans revealed that people with insomnia could not modulate activity in brain regions typically used to perform the task.
As the task got harder, good sleepers used more resources within the working memory network of the brain, especially the dorsolateral prefrontal cortex. Insomnia subjects, however, were unable to recruit more resources in these brain regions. Furthermore, as the task got harder, participants with insomnia did not dial down the “default mode” regions of the brain that are normally only active when our minds are wandering.
"The data help us understand that people with insomnia not only have trouble sleeping at night, but their brains are not functioning as efficiently during the day," said Drummond. "Some aspects of insomnia are as much of a daytime problem as a nighttime problem. These daytime problems are associated with organic, measurable abnormalities of brain activity, giving us a biological marker for treatment success."
According to the authors, the study is the largest to examine cerebral activation with functional MRI during cognitive performance in people with primary insomnia, relative to well-matched good sleepers. It also is the first to characterize functional MRI differences in working memory in people with primary insomnia.
The American Academy of Sleep Medicine reports that about 10 to 15 percent of adults have an insomnia disorder with distress or daytime impairment. Most often insomnia is a comorbid disorder occurring with another problem such as depression or chronic pain, or caused by a medication or substance. Fewer people suffering from insomnia are considered to have primary insomnia, which is defined as a difficulty falling asleep or maintaining sleep in the absence of a coexisting condition.
(Source: eurekalert.org)
Perception of Marijuana as a “Safe Drug” Is Scientifically Inaccurate
The nature of the teenage brain makes users of cannabis amongst this population particularly at risk of developing addictive behaviors and suffering other long-term negative effects, according to researchers at the University of Montreal and New York’s Icahn School of Medicine at Mount Sinai.
“Of the illicit drugs, cannabis is most used by teenagers since it is perceived by many to be of little harm. This perception has led to a growing number of states approving its legalization and increased accessibility. Most of the debates and ensuing policies regarding cannabis were done without consideration of its impact on one of the most vulnerable population, namely teens, or without consideration of scientific data,” wrote Professor Didier Jutras-Aswad of the University of Montreal and Yasmin Hurd, MD, PhD, of Mount Sinai. “While it is clear that more systematic scientific studies are needed to understand the long-term impact of adolescent cannabis exposure on brain and behavior, the current evidence suggests that it has a far-reaching influence on adult addictive behaviors particularly for certain subsets of vulnerable individuals.”
The researchers reviewed over 120 studies that looked at different aspects of the relationship between cannabis and the adolescent brain, including the biology of the brain, chemical reaction that occurs in the brain when the drug is used, the influence of genetics and environmental factors, in addition to studies into the “gateway drug” phenomenon. “Data from epidemiological studies have repeatedly shown an association between cannabis use and subsequent addiction to heavy drugs and psychosis (i.e. schizophrenia). Interestingly, the risk to develop such disorders after cannabis exposure is not the same for all individuals and is correlated with genetic factors, the intensity of cannabis use and the age at which it occurs. When the first exposure occurs in younger versus older adolescents, the impact of cannabis seems to be worse in regard to many outcomes such as mental health, education attainment, delinquency and ability to conform to adult role,” Dr Jutras-Aswad said.
Although it is difficult to confirm in all certainty a causal link between drug consumption and the resulting behavior, the researchers note that rat models enable scientists to explore and directly observe the same chemical reactions that happen in human brains. Cannabis interacts with our brain through chemical receptors (namely cannabinoid receptors such as CB1 and CB2.) These receptors are situated in the areas of our brain that govern our learning and management of rewards, motivated behavior, decision-making, habit formation and motor function. As the structure of the brain changes rapidly during adolescence (before settling in adulthood), scientists believe that the cannabis consumption at this time greatly influences the way these parts of the user’s personality develop. In adolescent rat models, scientists have been able to observe differences in the chemical pathways that govern addiction and vulnerability – a receptor in the brain known as the dopamine D2 receptor is well known to be less present in cases of substance abuse.
Only a minority (approximately one in four) of teenage users of cannabis will develop an abusive or dependant relationship with the drug. This suggests to the researchers that specific genetic and behavioral factors influence the likelihood that the drug use will continue. Studies have also shown that cannabis dependence can be inherited through the genes that produce the cannabinoid receptors and an enzyme involved in the processing of THC. Other psychological factors are also likely involved. “Individuals who will develop cannabis dependence generally report a temperament characterized by negative affect, aggressivity and impulsivity, from an early age. Some of these traits are often exacerbated with years of cannabis use, which suggests that users become trapped in a vicious cycle of self-medication, which in turn becomes a dependence” Jutras-Aswad said.
The researchers stress that while a lot remains unknown about the mechanics of cannabis abuse, the body of existing research has clear implications for society. “It is now clear from the scientific data that cannabis is not harmless to the adolescent brain, specifically those who are most vulnerable from a genetic or psychological standpoint. Identifying these vulnerable adolescents, including through genetic or psychological screening, may be critical for prevention and early intervention of addiction and psychiatric disorders related to cannabis use. The objective is not to fuel the debate about whether cannabis is good or bad, but instead to identify those individuals who might most suffer from its deleterious effects and provide adequate measures to prevent this risk” Jutras-Aswad said. “Continuing research should be performed to inform public policy in this area. Without such systematic, evidenced-based research to understand the long-term effects of cannabis on the developing brain, not only the legal status of cannabis will be determined on uncertain ground, but we will not be able to innovate effective treatments such as the medicinal use of cannabis plant components that might be beneficial for treating specific disorders,” Dr Hurd said.
(Image: AP)
Remembering to Remember Supported by Two Distinct Brain Processes
You plan on shopping for groceries later and you tell yourself that you have to remember to take the grocery bags with you when you leave the house. Lo and behold, you reach the check-out counter and you realize you’ve forgotten the bags.
Remembering to remember — whether it’s grocery bags, appointments, or taking medications — is essential to our everyday lives. New research sheds light on two distinct brain processes that underlie this type of memory, known as prospective memory.
The research is published in Psychological Science, a journal of the Association for Psychological Science.
To investigate how prospective memory is processed in the brain, psychological scientist Mark McDaniel of Washington University in St. Louis and colleagues had participants lie in an fMRI scanner and asked them to press one of two buttons to indicate whether a word that popped up on a screen was a member of a designated category. In addition to this ongoing activity, participants were asked to try to remember to press a third button whenever a special target popped up. The task was designed to tap into participants’ prospective memory, or their ability to remember to take certain actions in response to specific future events.
When McDaniel and colleagues analyzed the fMRI data, they observed that two distinct brain activation patterns emerged when participants made the correct button press for a special target.
When the special target was not relevant to the ongoing activity — such as a syllable like “tor” — participants seemed to rely on top-down brain processes supported by the prefrontal cortex. In order to answer correctly when the special syllable flashed up on the screen, the participants had to sustain their attention and monitor for the special syllable throughout the entire task. In the grocery bag scenario, this would be like remembering to bring the grocery bags by constantly reminding yourself that you can’t forget them.
When the special target was integral to the ongoing activity—such as a whole word, like “table” — participants recruited a different set of brain regions, and they didn’t show sustained activation in these regions. The findings suggest that remembering what to do when the special target was a whole word didn’t require the same type of top-down monitoring. Instead, the target word seemed to act as an environmental cue that prompted participants to make the appropriate response – like reminding yourself to bring the grocery bags by leaving them near the front door.
“These findings suggest that people could make use of several different strategies to accomplish prospective memory tasks,” says McDaniel.
McDaniel and colleagues are continuing their research on prospective memory, examining how this phenomenon might change with age.
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