From the List Universe -- Top 10 Bizarre Mental [/neurological] Disorders

The theory explains how the brain compensates for damage from injuries such as stroke

Carnegie Mellon University neuroscientist Marcel Just and Stanford postdoctoral fellow Sashank Varma have put forward a new computational theory of brain function that provides answers to one of the central questions of modern science: How does the human brain organize itself to give rise to complex cognitive tasks such as reading, problem solving and spatial reasoning? Just and Varma's theory, called 4CAPS, is described in the fall issue of the journal Cognitive, Affective, and Behavioral Neuroscience.

More than a decade of research involving functional Magnetic Resonance Imaging brain scans in hundreds of laboratories has yielded a tremendous amount of information about what parts of the brain are activated when a person performs various tasks. Some researchers have been tempted to conclude that a simple one-to-one relationship exists between high-level mental tasks and brain areas. For example, some believe that a specific brain area is responsible for a specific cognitive task, such as identifying a face.

Just and Varma, however, propose that the evidence reveals a more complex picture in which thinking is a network function - a collaboration of several brain areas that is constantly adapting itself, based on the task at hand and the brain's own resources and biological limitations. The collaborating parts of the brain, according to Just, are like members of a sports team whose players substitute in and out of the action. 4CAPS (an acronym for Capacity Constrained Concurrent Cortical Activation-based Production System), proposes a decentralized process by which members of the cortical team volunteer themselves when their strengths are called for, but also permits less efficient but capable members to step forward when the primary player is injured or disabled, as might occur as a result of a stroke. Just and Varma have constructed a number of computational models to demonstrate this process, such as a model that understands English sentences.

A unique characteristic of the theory is that it can accurately predict the change in brain activation that results from some types of brain damage or disease. For example, if a stroke damages the part of the brain known as Broca's area - which is located in the left prefrontal cortex and is involved in language processing - the corresponding site on the right side of the brain often becomes activated during language processing, even within hours after a stroke. According to 4CAPS, the same dynamic allocation mechanism that allows brain areas to volunteer themselves on a moment-by-moment basis would also come into play if Broca's area were damaged, and would allow any excess computational load to spill over to the right hemisphere mirror site on a more permanent basis. Another example occurs with Alzheimer's disease, where the damage to some brain areas causes additional "helper" areas to be recruited to perform a task, additional areas that are not typically used by control subjects who do not have the disease.

"Many brain-imaging studies have shown as the nature of the task changes, so does the set of activating brain areas," said Just, the D.O. Hebb Professor of Psychology. "It is as though substitutions of team players are being made dynamically in response to changes in the game."

"We credit this dynamic mechanism with the fluidity or adaptability of human intelligence, and with much of the plasticity that occurs with learning or with recovery from brain damage," Just said.

4CAPS provides a framework for scientists and medical researchers to better understand nascent topics in neuroscience, such as how brain areas communicate and collaborate with one another during the thought process and how this can go awry. For example, Just and his colleagues have proposed an influential theory of autism, called the underconnectivity theory, that attributes the disorder to poor connectivity and hence communication between frontal areas of the brain and more posterior areas. The individual areas still have their specializations, according to the theory, but they cannot communicate as well with each other, and may develop a tendency to operate more independently of each. The theory also provides an account of what limits our ability to do multitasking.

"The thousands of facts that scientists have learned from brain imaging studies cry out for some sort of organization, some way to impose coherence, and ultimately to understand the brain system that is producing the results," Just said. "The theory provides a new conceptual framework for understanding how the fluidity of thought arises from the dynamics of brain activity.

"As neurological issues arise in education, aging and development, and as a basis for a knowledge-based economy, it will become increasingly important that human brain function be understood by students, parents and educators, patients and doctors, trainees and managers, citizens and policy-makers."

Carnegie Mellon Press Release
15 November 2007

Scientists are finding new evidence that a good night's rest plays a crucial role in cementing memories formed during the day.

One new study has identified a brain region involved, along with the hippocampus, in creating memories of the day's activities during sleep. Another study suggests melatonin, a hormone involved in regulating our day-night cycle, or "circadian rhythm," acts to suppress the formation of new memories as bedtime nears, perhaps in an effort to give memories made earlier in the day a chance to be prepared for long-term storage.

Both studies are detailed in the Nov. 16 issue of the journal Science.

Duke University Medical Center neuroscientists say the places a memory is processed in the brain may determine how someone can be absolutely certain of a past event that never occurred. These findings could help physicians better appreciate the memory changes that accompany normal aging or even lead to tools for the early diagnosis of Alzheimer's disease, according to Duke neuroscientist Roberto Cabeza, Ph.D.

Information retrieved from memory is simultaneously processed in two specific regions of the brain, each of which focuses on a different aspect of an past event. The medial temporal lobe (MTL), located at the base of the brain, focuses on specific facts about the event. The frontal parietal network (FPN), located at the top of the brain, is more likely to process the global gist of the event. The specific brain area accessed when one tries to remember something can ultimately determine whether or not we think the memory is true or false, the researchers found.

"Human memory is not like computer memory -- it isn't completely right all the time," said Cabeza, senior author of a paper appearing in the Journal of Neuroscience. "There are many occasions when people feel strongly about past events, even though they might not have occurred." Cabeza wanted to understand why someone could have such strong feelings of confidence about false memories. In his experiments, he scanned the brains of healthy volunteers with functional MRI as they took well-established tests of memory and false memory. Functional MRI is an imaging technique that shows what areas of the brain are used during specific mental tasks.

During the brain scans, Cabeza found that volunteers who were highly confident in memories that were indeed true showed increased activity in the fact-oriented MTL region. "This would make sense, because the MTL, with its wealth of specific details, would make the memory seem more vivid," Cabeza said. "For example, thinking about your breakfast this morning, you remember what you had, the taste of the food, the people you were with. The added richness of these details makes one more confident about the memory's truth."

On the other hand, volunteers who showed high confidence in memories that turned out to be false exhibited increased activity in the impressionistic FPN. The people drawing from this area of the brain recalled the gist or general idea of the event, and while they felt confident about their memories, they were often mistaken, since they could not recall the details of the memory.

These findings, coupled with the findings of other studies, can help explain what happens to the human brain as it ages, Cabeza said. "Specific memories don't last forever, but what ends up lasting are not specific details, but more general or global impressions," Cabeza said. "Past studies have shown that as normal brains age, they tend to lose the ability to recollect specifics faster than they lose the ability recall impressions. However, patients with Alzheimer's disease tend to lose both types of memories equally, which may prove to be a tool for early diagnosis."

Cabeza's colleague for this research was Hongkeun Kim at Daegu University in South Korea. The research was supported by the National Institutes of Health and Daegu University.

By activating multiple fluorescent proteins in neurons, neuroscientists at Harvard University are imaging the brain and nervous system as never before, rendering their cells in a riotous spray of colors dubbed a "Brainbow."

The technique, described in the cover story of the Nov. 1 issue of the journal Nature, has been developed by a team led by Harvard's Jean Livet, Joshua R. Sanes, and Jeff W. Lichtman and  allows researchers to tag neurons with roughly 90 distinct colors, a huge leap over the mere handful of shades possible with current fluorescent labeling. (read article; view slide show)