Layer 3 of the @entity550 is a major gateway from the neocortex to the hippocampus. Here we addressed structure-function relationships in @entity550 layer 3 by combining anatomical analysis with juxtacellular identification of single neurons in freely behaving @entity35 . Anatomically, layer 3 appears as a relatively homogeneous cell sheet. Dual-retrograde neuronal tracing experiments indicate a large overlap between layer 3 pyramidal populations, which project to ipsilateral hippocampus, and the contralateral @entity550 . These cells were intermingled within layer 3, and had similar morphological and intrinsic electrophysiological properties. Dendritic trees of layer 3 neurons largely avoided the calbindin-positive patches in layer 2. Identification of layer 3 neurons during spatial exploration (n = 17) and extracellular recordings (n = 52) pointed to homogeneous spatial discharge patterns. Layer 3 neurons showed only weak spiking theta rhythmicity and sparse head-direction selectivity. A majority of cells (50 of 69) showed no significant spatial modulation. All of the    28% of neurons that carried significant amounts of spatial information (19 of 69) discharged in irregular spatial patterns. Thus, layer 3 spatiotemporal firing properties are remarkably different from those of layer 2, where theta rhythmicity is prominent and spatially modulated cells often discharge in grid or border patterns. SIGNIFICANCE STATEMENT: Neurons within the superficial layers of the @entity550 ( @entity550 ) often discharge in border, head-direction, and theta-modulated grid patterns. It is still largely unknown how defined discharge patterns relate to cellular diversity in the superficial layers of the @entity550 . In the present study, we addressed this issue by combining anatomical analysis with juxtacellular identification of single layer 3 neurons in freely behaving @entity35 . We provide evidence that the anatomical organization and spatiotemporal firing properties of layer 3 neurons are remarkably different from those in layer 2. Specifically, most layer 3 neurons discharged in spatially irregular firing patterns, with weak theta-modulation and head-directional selectivity. This work thus poses constraints on the spatiotemporal patterns reaching downstream targets, like the hippocampus.

Anatomical Organization and Spatiotemporal Firing Patterns of Layer 3 Neurons in the XXXX Medial Entorhinal Cortex.

@entity35 :: ('10116', 'Species') :: ['rats'] @entity550 :: ('MESH:D000303', 'Disease') :: ['medial entorhinal cortex', 'MEC']
@entity35 :: (10116,Species) :: ['Rat']
