Commuting is never fun, and is almost always stressful, in part because we often have no control over what happens to us. But everyday we get in our car, or board the train or bus, and make our way to work, having become accustomed to this stress, not realizing that this stress may have a measurable affect on our brain.

Although we do not yet know if this is the case for humans, new research in rats from the laboratory of Rockefeller University’s Bruce McEwen, Ph.D., shows that chronic, uncontrollable stress of repeated confinement leads to gradual changes in brain structure over weeks. Yet, even a single acute stress of putting a rat in a tube where it cannot move freely also causes a structural change in the brain, not immediately but over days, along with higher levels of anxiety. These results may help scientists understand what is happening in the human brain during post-traumatic stress disorder and other anxiety disorders and depressive illness.

In earlier studies, McEwen and colleagues had looked at changes in the hippocampus and the prefrontal cortex, areas of the brain that respond to repeated, confinement stress and which are important in memory storage and retrieval. Turning to a different area of the brain called the amygdala, which is thought to play a role in fear and anxiety memories, they wanted to see if it too was involved in processing stressful experiences. Indeed they found that repeated stress increased anxiety as well as a form of aggression.

“Understanding how the whole nervous system functions, how the different areas of the brain interact, is vital to understanding the neurological basis of depressive illness and anxiety disorders,” says McEwen, who is the Alfred E. Mirsky Professor and head of the Harold and Margaret Milliken Hatch Laboratory of Neuroendocrinology at Rockefeller. “And we knew of some evidence that the neurons in the amygdala are more active in depression and anxiety disorders.”

“The new paper, conducted in collaboration with Dr. Sumantra Chattarji’s laboratory in Bangalore, India, and MIT, shows that even a single stressful event in these animals can have a measurable and delayed influence on the architecture of their brains, and on their behavior,” adds McEwen. “We would like to think that these findings might become relevant in understanding conditions like post-traumatic stress disorder and depression.”

The follow-up of this paper is under investigation in collaborative studies with investigators at the Weill Medical College of Cornell University, Mt. Sinai School of Medicine and New York University under a National Institute of Mental Health Conte Center Grant for the Neurobiology of Fear and Anxiety. Further studies in the McEwen lab seek to understand the cellular and molecular mechanisms for these changes, including the role of stress hormones.

The research, published in the June 28 issue of the Proceedings of the National Academy of Science, was supported by The Wellcome Trust.

The figure is famous: a deceptively simple line drawing that at first glance resembles a vase and, at the next, a pair of human faces in profile. When you look at this figure, your brain must rapidly decide what the various lines denote. Are they the outlines of the vase or the borders of two faces? How does your brain decide?

It does so in a fraction of a second via special nerve circuits in the brain's visual center that automatically organize information into a "whole" even as an individual's gaze and attention are focused on only one part, according to Johns Hopkins researchers writing in a recent issue of the journal Neuron.

"Our paper answers the century-old question of the basis of subconscious processes in visual perception, specifically, the phenomenon of figure-ground organization," said Rudiger von der Heydt, a professor in the Zanvyl Krieger Mind-Brain Institute. "Early in the 20th century, the Gestalt psychologists postulated the existence of mechanisms that process visual information automatically and independently of what we know, think or expect. Since then, there has always been the question as to whether these mechanisms actually exist. They do. Our work suggests that the system continuously organizes the whole scene, even though we usually are attending only to a small part of it."

The report, based on recordings of nerve cells in the visual cortex of macaque monkeys, suggests that this automatic processing of images is repeated each time an individual looks at something new, usually three to four times per second. What's more, the brain provides what von der Heydt calls "a sophisticated program" to select and process the information that is relevant at any given moment.

"The result of this organization is an internal data structure, quite similar to a database, that allows the attention mechanism to work efficiently," von der Heydt said. "An image can be compared with a bag of thousands of little Lego blocks in chaotic order. To pay attention to an object in space, the visual system first has to arrange this bag of blocks into useful 'chunks' and provide threads by which one or the other chunk can be pulled out for further processing."

He noted that the research provides the theoretical foundation that might one day lead to better diagnosis and treatment of human brain disorders.

"The last decades have seen rapid progress in the neurosciences at a very broad front, particularly at the molecular and cellular levels, and this progress makes it increasingly clear that we still lack sufficient understanding of brain function at the 'system level,'" he said. "We need to understand the basis of mental processes. Single cell recording in animals is only one approach to this formidable task. It is complemented by new brain imaging techniques, traditional psychophysics, psychology and computational and theoretical neuroscience. ... Understanding the function of the visual cortex will help to interpret neurological symptoms in diseases that produce disorders of vision."

This work was funded by grants from the National Institutes of Health.

The paper, "Figure and Ground in Visual Cortex: V2 Combines Stereoscopic Cues with Gestalt Rules" appeared in the July 7, 2005, issue of Neuron (Volume 47).