Publications

Visual plasticity declines sharply after the critical period, yet adults easily learn to recognize new faces and places. Such learning is often characterized by a 'moment of insight,' an abrupt and dramatic improvement in recognition. Animals were trained to perform a naturalistic 'foraging' task, in which they learned to recognize a visual image and to associate it with a rewarded location, with learning being abrupt and characterized by large performance improvements over a few trials. Simultaneous recordings from inferotemporal and prefrontal cortices revealed a transient synchronization of neural activity between these areas that peaked around the moment of insight. Synchronization was strongest between inferotemporal sites that encoded images and reward-sensitive prefrontal sites. These results suggest that rapid learning relies on temporal synchronization between cortical sites that connect relevant stimuli with task outcomes.

Applying transcranial direct current stimulation (tDCS) to the right prefrontal cortex improves monkeys' performance on an associative learning task. While firing rates do not change within the targeted area, tDCS induces large low-frequency oscillations in the underlying tissue. These oscillations alter functional connectivity, both locally and between distant brain areas, and these long-range changes correlate with tDCS's effects on behavior. The data suggest that tDCS may act by altering long-range connectivity between PFC and other brain areas. The research employed a macaque model of tDCS that allows simultaneous examination of the effects of tDCS on brain activity and behavior.