Abstract
The prefrontal cortex is known to be important in the short term maintenance of information. While some studies have found a domain-specific organization, with dorsolateral prefrontal neurons representing spatial information and ventrolateral prefrontal neurons representing feature information, other studies using different behavioral tasks arrived at contradictory conclusions. For this reason, we sought to determine how training affects prefrontal neuronal responses. We performed neurophysiological recordings from monkeys before and after training on a working memory task that required the integration of spatial and feature information. We evaluated spatial selectivity of neuronal responses to visual stimuli appearing on a 10-degree, 3×3 grid, and feature selectivity to eight geometric shapes. Prior to training, we recorded from 441 neurons in the dorsal prefrontal cortex (areas 8 and 46) and 542 neurons in the ventral prefrontal cortex (areas 12 and 45) of three monkeys, only required to fixate. Overall, more neurons responded to the visual stimuli in the dorsolateral PFC (42%) than in ventrolateral PFC (9%). In dorsolateral prefrontal cortex more neurons were selective for stimulus locations than features; ventrolateral neurons were more selective for features. Neurons that were selective for both locations and features were found in both regions. After training, we recorded from 127 dorsolateral neurons and 149 ventrolateral neurons. We again found more neurons to be responsive to visual stimuli in dorsolateral (55%) then ventrolateral (13%) PFC. Dorsolateral PFC was still dominated by spatially selective neurons and had significantly fewer feature selective neurons, while ventrolateral contained more feature selective neurons. The percentage of neurons selective for both locations and features was actually lower after training. Our results suggest that contrary to earlier studies, prefrontal neurons represent the locations and features of visual stimuli regardless of training. Training on a working memory task actually enhanced domain-specific organization resulting in higher regional selectivity.
Supported by NIH EY017077 and the Whitehall Foundation.