Organization of cat anterior parietal cortex: relations among cytoarchitecture, single neuron functional properties, and interhemispheric connectivity.

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Abstract
Microelectrode penetrations are made in the anterior parietal cerebral cortex of domestic cats. Whenever possible they are placed so that long sequences of cortical neurons are encountered. At each location where the activity of a single neuron is recorded, a description of receptive-field (RF) location and submodality properties is obtained. The observations are reconstructed to a map showing the relations between anterior parietal topographical organization and cytoarchitecture. In a 2nd series of experiments the method of retrograde transport of horseradish peroxidase (HRP) is used to reveal the locations of anterior parietal neurons, projecting to the homotopic field in the opposite hemisphere. A map of the relations between cortical territories, distinguishable on the basis of interhemispheric connectivity and cytoarchitecture, is generated from the data provided in each experiment. The maps of the distribution of anterior parietal neurons having interhemispheric connections correspond closely with the map of anterior parietal topographic organization. Direct comparison of the different maps reveals the relations among cytoarchitecture, interhemispheric connectivity and functional organization. General anesthetics reduce RF size, and alter the configuration of the RF of anterior parietal neurons from that observed in the absence of general anesthesia. Other effects of these agents include elevation of the threshold for eliciting neuronal discharge with natural stimuli, and reduction of the amplitude of single-neuron response evoked by controlled natural stimulation. The RF data obtained after i.v. administration of the general anesthetics ketamine (10-40 mg/kg) and methohexital (2-4 mg/kg) appear inconsistent with the map of anterior parietal topographic organization, generated from RF data in the absence of general anesthesia; the data is also inconsistent with the proposed relations among topographic organization, interhemispheric connectivity and cytoarchitecture.