The role of prefrontal cortex in sensory memory and motor preparation: an event-related fMRI study

Delayed-response tasks are behavioral paradigms in which subjects must remember stimulus attributes across a delay to subsequently perform the appropriate motor response. Quintana and Fuster (1992), reported that there exist subpopulations of neurons in monkey lateral prefrontal cortex (PFC) whose firing rates during the delay are tuned to either sensorial attributes of the stimulus (i.e., involved in sensory memory) or the direction of a postdelay motor response associated with the stimulus (i.e., involved in motor preparation). We studied human subjects with an event-related fMRI method that would allow us to test the hypothesis that there are regions within the PFC that are recruited during both motor preparation and sensory memory. Subjects performed a delayed-response task with two types of trials that either (1) allowed subjects to prepare during a delay period for a specific motor response or (2) required that subjects maintain a sensory attribute (specifically, color) during a delay period for correct performance postdelay. It was assumed that during the delay periods, the delayed-response trials would engage motor preparation while delayed-match trials would engage sensory memory. Behavioral data supported this assumption. Imaging results support the hypothesis that the PFC is involved in both motor preparation and sensory memory. Furthermore, no selectivity (in terms of intensity of neural representation on the spatial scale of the voxel size <5 mm(3)) for motor preparation over sensory memory (or vice-versa) was detected within the PFC. This latter result fails to support a gross anatomical segregation within the PFC with respect to involvement in these two cognitive processes.