You May Not Have Rhythm, But Your Brain Does

In an attempt to understand what makes us tick, researchers have been probing various regions of the brain, such as the premotor cortex, which helps make movement possible, and the auditory cortex, responsible for processing what we hear. But neuroscientists now say communication between regions - as opposed to within the areas themselves - may be the key that has eluded analysis until now, in part, because of technological obstacles.


Earl Miller, a professor of neuroscience at Massachusetts Institute of Technology's Picower Institute for Learning and Memory, says that today's faster computers and more advanced electronics may provide scientists with the tools they need to unlock the brain's mysteries.


"Multiple electrode recording techniques," he says, "offer a whole new level of brain interactions that can't be seen using the [current] piecemeal approach." He adds that deciphering the chatter between brain regions may one day allow scientists to "augment certain modes of thought and suppress others," setting the stage for new ways to combat attention disorders, depression and some forms of psychosis.


Two studies published recently in Science support that theory:


"We hypothesized that two [neuronal] groups can only communicate efficiently with each other when their rhythms are coordinated, or synchronized," wrote Pascal Fries and Thilo Womelsdorf, neuroscientists at the F. C. Donders Center for Cognitive Neuroimaging at Radboud University Nijmegen in the Netherlands, in an e-mail interview with Scientific American Online. "If the rhythms are not coordinated, then one group sends information over while the other is not ready to take it on and vice versa."


The researchers found that when the rhythms of electrical activity are synchronized between neurons in distinct brain areas, memories are made and tasks are completed more efficiently.


The other study, by scientists at the University of Melbourne in Australia, also revealed communication between the cortex - the outermost layer of the brain believed to be involved in higher order information processing like judgment and decision making - and the more workhorse-like medial temporal region.


Fries and Womelsdorf monitored the activity of nerve cells in several different brain regions (a pair at a time) in monkeys and cats, while the animals engaged in various visual, spatial and perception-based tasks. They then grouped sections where the two neuronal populations were synchronized (they peaked and ebbed in concert) and when they directly were in opposition (with one peaking as the other ebbed) to determine each region's influence on the other.


"We did indeed find that when two groups have their rhythms in phase with each other, then they influence each other stronger than when the two rhythms are in antiphase," the authors said. "Thus, the phase and precision of neuronal synchronization could be a fundamental mechanism modulating the effective strength of a given anatomical connection."


In the Australian study, researchers tasked macaque monkeys with discerning whether the spatial orientation of a stack of bars in two images that were flashed before them within one second were the same or different. While the animals worked, researchers monitored the electrical fields in each's posterior parietal cortex (suspected to be involved in directing spatial attention) and medial temporal area, a midbrain region in that handles movement perception. The researchers had hypothesized that these two areas likely communicate with one another to enable reasoning.


Researchers observed activity first in the parietal cortex, followed by synchronous action there and in the medial temporal area. The delay illustrates "a top-down" feedback from the cortex, which then signals the lower area, says study author Trichur Vidyasagar. "The parietal neurons seem to code for what is salient or relevant in the world and allocate attentional resources accordingly," he says. "The medial temporal neurons are sensory ones that process the visual signals, but due to the influence of the parietal cortex the activity across the medial temporal area is varied."


The studies were accompanied by an editorial in which Robert Knight, a cognitive neuroscientist at the University of California, Berkeley, praised the findings - and their potential significance.


"It is now widely agreed that defining network interactions is key to understanding normal cognition," he wrote. "There are also numerous psychiatric disorders, such as depression, seasonal affective disorder, mania and even some cases of psychosis that are episodic and are not associated with defined neuroanatomical damage. Might it be that some of the periodic symptoms are caused by intermittent network dysfunction, caused by disturbed oscillatory dynamics?"


"New research begins to demystify communication between brain regions, potentially paving the way to treating disorders caused by crossed signals"

By Nikhil Swaminathan

Link to article


Scientific American

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