Figure 1.

The experimental paradigm and dlPFC neural circuitry underlying spatial working memory. A. The ODR spatial working memory task. Trials began when the monkey fixated on a central point for 0.5 sec. A cue was present in 1 of 8 possible locations for 0.5 sec and was followed by a delay period of 2.5 sec. When the fixation point was extinguished, the monkey made a saccade to the location of the remembered cue. The position of the cue changed on each trial in a quasi-random manner, thus requiring the constant updating of working memory stores. B. The region of monkey dlPFC where recordings occurred. PS=principal sulcus; AS=arcuate sulcus. C. An example of a Delay cell with spatially tuned, persistent firing during the delay period. Rasters and histograms are arranged to indicate the location of the corresponding cue. The neuron’s preferred direction and the opposing, nonpreferred direction are indicated; subsequent figures will show neuronal responses to only these two directions. This cell exhibited significant delay-related activity for the 180° location but not other directions. D. An illustration of the deep layer III microcircuits subserving spatially tuned, persistent firing during the delay period, based on Goldman-Rakic, 1995. B = GABAergic Basket cell. E. Working model of glutamate actions at NMDAR and AMPARs on long, thin dendritic spines of layer III pyramidal cells in monkey dlPFC.