Generation of information about the temporal order of events is essential for the control of memory-based behavioral tasks. We studied cellular activity in the lateral prefrontal cortex (LPFC) in two monkeys that were required to remember the temporal order in which visual objects were presented. In this report, we focus on cellular activity in response to the sequential appearance of three different objects. We identified cells that responded selectively to physical properties (color and shape) of objects (23%) in the ventral part of the LPFC and cells for which activity was selective for the numerical position (rank order) of objects (44%) in the dorsal part of the LPFC. We also identified cells for which activity was selective for both the physical properties and rank order of objects (30%). The third type of cells, distributed in the ventral LPFC, seems of importance in integrating the two categories of information, i.e., physical and temporal information about the occurrences of objects to construct sequential order information. Furthermore, we identified a distinct group of cells that exhibited selectivity for the sequence of presentation of the three objects. Our findings suggest that LPFC cells are involved in encoding temporal sequences of events when such information is required for planning forthcoming motor behavior.
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