The number of neurons in the different laminae of the binocular and monocular regions of area 17 in the cat

Abstract

The number of neurons in individual laminae of area 17 was determined separately for both the binocular and the monocular regions in the left hemisphere of six cats. The number of neurons/mm3 of tissue was obtained for each lamina by using the method of size-frequency distribution applied to neuronal nuclei. The number of neurons per unit of cortical surface could then be calculated from measurements of layer thickness. The number of neurons/mm3 of tissue for the total cortical thickness is on the order of 48,000 to 50,000 neurons, with no statistically significant differences between binocular and monocular regions. There are no significant differences for any of the layers except layer IV, in which the numerical density is 20% higher in the monocular region. The thickness of the cortex and of many of its layers, however, do vary between the two regions. Consequently there are significant differences in the number of neurons under 1 mm2 of surface. For the total cortical thickness there are significantly more (27%) neurons in the binocular (78,440) than in the monocular region (61,900). This overall difference is due to significant changes in layers 11, IIIA, IVA, and especially in layers V and VIA where neurons are 40% more numerous in the binocular region. These findings could signify either that the binocular region contains additional interneurons specifically related to binocular interactions or that it has a greater number of neurons projecting to other cortical and subcortical areas, or both.

The Relationship Between Synchronization Among Neuronal Populations and Their Mean Activity Levels

“…Feedback connections were 5%, from the infragranular excitatory cells of the second cortical area to the modulatory NMDA synapses of supragranular cells in the rst cortical area. The synapse-to-neuron ratio in this model was consistent with experimental ndings (Beaulieu & Colonnier, 1983, 1985. The extrinsic, interareal connections were exclusively excitatory.…”

Correlations between morphology and electrophysiology of pyramidal neurons in slices of rat visual cortex. I. Establishment of cell classes

“…These authors concluded that tissue shrinkage under such conditions was minimal (< I%), and a recent study of rat hippocampus has reached a similar conclusion (West et al, 1988). However, other authors have reported and corrected for substantial shrinkage in similar studies (e.g., Beaulieu and Colonnier, 1983). Shrinkage may affect various components of the tissue unequally, and the processes of injected and filled cells may corrugate rather than reducing in length if shrinkage occurs.…”

A Quantitative Map of the Circuit of Cat Primary Visual Cortex

“…Anatomical studies indicate that the total number of synapses formed by the chandelier cells on the axon initial segment is between 20 and 43 (Somogyi et al, 1982;Farinas and DeFelipe, 1991 (Beaulieu and Colonnier, 1983;Gabbott and Somogyi, 1986), and S j u axo2/3 ϭ 3300 ϫ n j axo2/3 because a chandelier cell forms ϳ3300 synapses in layer 2/3 (Somogyi et al, 1982;Freund et al, 1983). …”

“…Beaulieu and Colonnier (1983) counted for each cortical layer the number of cell bodies under a square millimeter of cortical surface in cat area 17. Multiplying these numbers with the total surface area of one cortical hemisphere, which for the cat is 399 mm 2 (Anderson et al, 1988), we obtained the total number of neurons per layer.…”