Cat parahippocampal unit discharge patterns during limbic stimulation.

The cat parahippocampal gyrus, a part of the limbic lobe of Broca 4, includes the subicular and entorhinal areas 14,19. The septum, hippocampus, and cingulate gyrus may project fibers directly to these areasl,6-s,15-18, z4 in various animals including cat. Commissural fibers from one entorhinal area pass to the contralateral homotopic cortex 3. These anatomical studies suggest paths from different limbic structures transmit signals which converge on parahippocampal units. The influences on unit spike patterns are not known. The intent of this study was to investigate the types of input (excitatory, inhibitory) resulting from a regional limbic stimulation. Patterns resulting from inputs simultaneously arising in different limbic structures and the stimulus parameters affecting the inputs are subjects for future study. Specifically, units were tested for stimulus time-locking or entrainment of their firings to electrical stimuli.