Figure 2.

The cellular basis of working memory, as discovered by Goldman-Rakic. (a) The oculomotor delayed response (ODR) task. A monkey fixates on a central spot while a cue is briefly lit at one of eight locations. The monkey must remember that location over a delay period while maintaining fixation. At the end of the delay, the fixation point is extinguished and the monkey can move its eyes to the remembered location for juice reward. The cue location constantly changes over hundreds of trials, requiring the constant updating of working memory. (b) The physiology and microcircuitry of the primate dlPFC. Delay cells maintain persistent firing across the delay period for their preferred location, but not other locations. The persistent firing is generated by the recurrent excitation of pyramidal cells with shared preferred directions, likely receiving their information from area 7 of the parietal association cortex. These pyramidal cells excite each other via NMDAR NR2B synapses on spines; there are only subtle influences of AMPARs. The spatial tuning of delay cells is enhanced via lateral inhibition from GABA (G) interneurons. Delay-cell microcircuits reside in deep layer III and possibly superficial layer V. Delay cells are modulated by dopamine actions at D1R but not D2R. In contrast, response cells are modulated by D2R but not D1R and likely reside in layer V. Perisaccadic response cells fire immediately before the motor response and likely convey orders to the motor system, while postsaccadic response cells convey feedback (corollary discharge) about the response. Some response cells show both pre- and postsaccadic firing; that is, both motor and feedback characteristics. Postsaccadic response cell firing relies on AMPAR as well as NMDAR stimulation. Response cells are what are most common in rodent PFC, which has a very large layer V.