"It's like the old story about the American crossing the road in England," says Conor Liston, an M.D.-Ph.D. student at Rockefeller and Cornell, who led the research. A response-reversal requires the brain to override the habitual impulse to first look left instead of right for oncoming cars. An American in Venice might require an attention-shift, by contrast, to seek out boats instead of evading cars.
In earlier research on rats, neuroscientists found that these two tasks place demands on different circuits in the brain, and the circuits are affected in different ways by stress. In particular, collaborative work by McEwen and John Morrison at Mount Sinai Medical Center have shown that repeated stress on rats shriveled nerve cells of the medial prefrontal cortex, and that a shrunken prefrontal cortex is linked to slower performance on attention-shifting tasks. In those experiments, rats learned to dig through a certain texture, like sawdust, in the presence of an irrelevant odor to find food; then the researchers made odor, rather than texture, the clue for finding the food and measured how long it took the rats to switch their foraging strategies. But while the restricted prefrontal cortex a larger version of which is thought to play a role in the "executive function" in humans slowed the rats' performance on attention-shifts, it did not change their performance on response-reversal tasks. In fact, neurons in a different part of the brain thought to be involved in response-reversals, the orbital frontal cortex, actually grew larger from the stress.
The new research suggests that something very similar may happen to distressed humans. Liston, working with B.J. Casey at the Sackler Institute at Weill Cornell, used fMRI to explore his hunch that the brains of rats and men have some basic processes in common th
|Contact: Brett Norman|