Projection of the lateral part of the entorhinal area to the hippocampus and fascia dentata

Abstract

The hippocampus and fascia dentata receive their major extrinsic input from the entorhinal area through the so‐called perforant path. This pathway is now shown to be composed of at least two distinct fiber systems: (1) A medial perforant path coming from the medial part of the entorhinal area and terminating in the middle of the dentate molecular layer and in the deep half of the stratum lacunosum‐moleculare of the hippocampal subfield CA3. (2) A lateral perforant path from the lateral part of the entorhinal area to a superficial zone in the dentate molecular layer and to the superfcial part of the stratum lacunosum‐moleculare of CA3. This paper deals specifically with the lateral perforant path. A third group of perforant fibers, bing intermediate to the others with regard to both origin and termination has been noticed in one animal. The fiber‐course of the lateral perforant path is found to be identical to that previously described for the medial path. The terminal field is present along the whole axial extent of the hippocampus and fascia dentata, i.e., from the temporal tip to the subsplenial portion. No sings of degeneration corresponding to the so‐called alvear path were observed following lesions of either the medial or the lateral part of the entorhinal cortex. Terminal degeneration appeared in the molecular layer of the subiculum and CA1 and in the anterior continuation of the hippocampal formation subsequent to lesions including the prepyriform cortex.