Poster B52, Sunday, March 26, 8:00 – 10:00 am, Pacific Concourse
Working memory capacity related to dorsolateral prefrontal activity in monkeys
Hua Tang1, Xue-Lian Qi1, Mitchell Riley1, Christos Constantinidis1; 1Wake Forest School of Medicine
The information that can be stored in the working memory of humans and non-human primates is severely limited. Little is known about how activity of single neurons relates to working memory capacity and the nature of this limitation. To investigate this question, we trained two monkeys to perform a spatial working memory task. The monkeys viewed a sample display with 1 to 5 white squares. After a delay period of 1 s, a second display appeared with the same number of stimuli, either at identical locations, or with one item appearing at a different location. The subjects were required to judge whether the two stimulus displays were the same or not. Overall performance declined as the number of stimuli increased. The subjects’ estimated capacity in the task reached an asymptote at approximately 3.5 and 2 items respectively. We recorded a total of 266 neurons from the dorsolateral prefrontal cortex and 71 neurons from the posterior parietal cortex. We focused particularly on neurons with significant selectivity for different stimulus locations (ANOVA, p<0.05). Prefrontal delay period activity increased as a function of the number of stimuli, for up to 3 items. For displays with 4 or more stimuli, which exceeded the subjects’ behavioral capacity, persistent activity decreased (ANOVA, p<0.01). Posterior parietal delay period activity did not show any systematic relationship with the number of stimuli. These results suggest that prefrontal delay period activity is predictive of the subjects’ capacity limit and provide mechanistic insights on the working memory capacity limitation.
Topic Area: EXECUTIVE PROCESSES: Working memory