Penn researcher Michael Platt and colleagues from Yale and Duke have discovered the region of the brain that increases neuron firing rates just before divergent behavior occurs: the posterior cingulate cortex. In their study, the researchers observed the effect of two experiments, named the patch-leaving task and the traveling salesman, on rhesus macaques. 

In the first test, Dr. Platt, the James S. Riepe University Professor in Penn’s psychology, neuroscience and marketing departments, and his colleagues gave the macaques the choice between harvesting juice that depleted overtime but was immediate and guaranteed or moving to a new “patch” that offered a potentially larger reward but required more time and energy.

In the “traveling salesman” experiment, macaques had the option of visiting six different locations, two of which contained different-sized rewards. The locations containing rewards were randomized and changed each time the experiment ran. “The optimal solution is to develop a routine where you visit all of them in a circle. That’s the best you can do; you go from nearest neighbor to next neighbor. That’s what monkeys do in the wild,” Dr. Platt said, “Occasionally, these animals break off to explore for something that might be better, kind of like what people do in a grocery store. Suddenly monkeys here would break off and out of order. We didn’t know why.”

While observing the macaques’ behavior in both experiments, researchers recorded neuron behavior in the posterior cingulate cortex. Neural activity in the area built up, peaking just before the animals changed behavior. This provides evidence that this increase in brain function leads to divergent action and thinking. “If you increased activity in the area exogenously, if I put an electrode in there and stimulated, then you would break off from the routing, you would become more exploratory,” Dr. Platt said, “Similarly, if you could suppress activity, you’d see the opposite. You’d become hyper-focused on one option, and you may never make a change.”