POTENTIALS-EVOKED BY ALVEAR TRACT IN HIPPOCAMPAL CA1 REGION OF RATS .2. SPATIAL FIELD ANALYSIS

This paper rigorously applies the CSD technique to the potentials evoked by the alvear tract. Data indicated that the optimal experimental method was to sample averaged evoked potentials (AEPs) at 100-μm intervals in a 2-dimensional grid on a plane. Maps of the AEP, current flow, and CSD were constructed to illustrate the events at each instant of time. These maps allow localization of the active populations of neurons or parts of these neurons since pyramidal and interneurons and their processes are distributed in different depths in the regularly stratified hippocampal CA1 region. Previous work has identified sources and sinks with the maximum or minimum of the potential in a single track for a particular instant of time. According to the theory of CSD, this interpretation is not necessarily correct, particularly because of the curved geometry of some parts of the hippocampus. The previous paper reported that the AEPs consisted of at least 3 components in a sequential order: the antidromic action potentials (APs), the excitatory postsynaptic potentials (EPSPs), and the inhibitory postsynaptic potentials (IPSPs). Source-sink analysis then permits a quantitative calculation of the spatial distribution of the active locus of each component and the spatial divergence of the neural signal. Preliminary results have been reported.