Identification of the lateral and medial perforant path of the hippocampus using single and dual random impulse train stimulation

In this paper, we present a new method to characterize the nonlinearities resulting from the co-activity of two pathways that converge on a common postsynaptic element. For this purpose, we investigated the nonlinear dynamic relationship between the lateral and the medial perforant pathway of the hippocampal dentate gyrus, and the effects of these cross-pathway interactions on granule cell output. This method is employed to identify the two pathways based on differences in the kernels calculated using the Volterra-Poisson modeling approach. The kernels present pathway specific signatures as they capture the nonlinear dynamics of each pathway individually in the form of self-kernels, and the nonlinear dynamics of the interaction between the two pathways in the form of cross-kernels. We present preliminary results using data collected in-vitro from acute slices of adult rats via a mult-electrode array recording system. The stimuli were single-site and dual-site random impulse trains with Poisson distributed inter-impulse intervals. The recorded responses from the granule cells were population spikes, simplified as discrete impulses with variable amplitudes. The results of single-site and dual-site stimulation, reported in the paper, support the use of kernels as consistent path identification signatures across all inter-impulse intervals within the memory of the biological system.