Brain research provides clues to what makes people think and behave differently

Differences in the physical connections of the brain are at the root of what make people think and behave differently from one another. Researchers reporting in the February 6 issue of the Cell Press journal Neuron shed new light on the details of this phenomenon, mapping the exact brain regions where individual differences occur. Their findings reveal that individuals’ brain connectivity varies more in areas that relate to integrating information than in areas for initial perception of the world.

"Understanding the normal range of individual variability in the human brain will help us identify and potentially treat regions likely to form abnormal circuitry, as manifested in neuropsychiatric disorders," says senior author Dr. Hesheng Liu, of the Massachusetts General Hospital.

Dr. Liu and his colleagues used an imaging technique called resting-state functional magnetic resonance imaging to examine person-to-person variability of brain connectivity in 23 healthy individuals five times over the course of six months.

The researchers discovered that the brain regions devoted to control and attention displayed a greater difference in connectivity across individuals than the regions dedicated to our senses like touch and sight. When they looked at other published studies, the investigators found that brain regions previously shown to relate to individual differences in cognition and behavior overlap with the regions identified in this study to have high variability among individuals. The researchers were therefore able to pinpoint the areas of the brain where variable connectivity causes people to think and behave differently from one another.

Higher rates of variability across individuals were also displayed in regions of the brain that have undergone greater expansion during evolution. “Our findings have potential implications for understanding brain evolution and development,” says Dr. Liu. “This study provides a possible linkage between the diversity of human abilities and evolutionary expansion of specific brain regions,” he adds.

Stress-Resilience/Susceptibility Traced to Neurons in Reward Circuit

A specific pattern of neuronal firing in a brain reward circuit instantly rendered mice vulnerable to depression-like behavior induced by acute severe stress, a study supported by the National Institutes of Health has found. When researchers used a high-tech method to mimic the pattern, previously resilient mice instantly succumbed to a depression-like syndrome of social withdrawal and reduced pleasure-seeking – they avoided other animals and lost their sweet tooth. When the firing pattern was inhibited in vulnerable mice, they instantly became resilient.

“For the first time, we have shown that split-second control of specific brain circuitry can switch depression-related behavior on and off with flashes of an LED light,” explained Ming-Hu Han, Ph.D., of the Mount Sinai School of Medicine, New York City, a grantee of NIH’s National Institute of Mental Health (NIMH). “These results add to mounting clues about the mechanism of fast-acting antidepressant responses.” Han, Eric Nestler, M.D., Ph.D., of Mount Sinai, and colleagues, report on their study online, Dec. 12, 2012, in the journal Nature.

In a companion article, NIMH grantees Kay Tye, Ph.D., of the Massachusetts Institute of Technology, Cambridge, Mass., and Karl Deisseroth, M.D., Ph.D., of Stanford University, Stanford, Calif., used the same cutting-edge technique to control mouse brain activity in real time. Their study reveals that the same reward circuit neuronal activity pattern had the opposite effect when the depression-like behavior was induced by daily presentations of chronic, unpredictable mild physical stressors, instead of by shorter-term exposure to severe social stress.

Prior to the new studies, Han’s team suspected that a telltale pattern – rapid firing of neurons that secrete the chemical messenger dopamine in a key circuit hub – makes an animal vulnerable to the depression-like effects of acute severe stress, and that slower firing supports resilience. But they lacked direct, real-time evidence.

To pinpoint cause-and-effect, they turned to a research technology pioneered by Deisseroth, called optogenetics. It melds fiber optics and genetic engineering to precisely control the activity of a specific brain circuit in a living, behaving animal. Genetically modified viruses are used to inject light-reactive proteins, borrowed from primitive organisms like algae, to make the circuitry similarly light-responsive.