Loss of information concerning hair displacement and other somatic stimuli in the first somatic sensory cortex of unanesthetized Macaca mulatta monkeys following dorsal funiculus transections

Abstract

Metal microelectrodes were used to record extracellular potentials from single cells in the four cytoarchitectural areas 3a, 3b, 1 and 2 of the representation of the lower body of the postcentral gyrus of Macaca mulatta monkeys. The animals were paralyzed and artificially respirated while remaining awake. Non-noxious natural stimuli were employed to determine response characteristics, like the submodality, of cells. After recording from a series of normal animals, spinal cord lesions of the dorsal funiculus, were surgically performed at cervical or high thoracic spinal levels. The animals were allowed to recover, and the above-mentioned cell characterization procedures were performed. After the recording, animals were humanely sacrificed and histological reconstructions of the penetrations and the spinal lesions were made. In the postcentral gyrus of normal animals, cells in cytoarchitectural areas 3b and 1 responded predominantly to cutaneous stimuli while cells in areas 3a and 2 responded predominantly to deep stimuli. Responses to displacement of hairs were only recorded in the predominantly cutaneous areas. In these areas in animals with dorsal funiculus transections at cervical or high thoracic spinal cord levels, many fewer cells responded to somatosensory stimulation than in the same areas in normal animals. There were no longer any responses to hair displacement stimuli. In this lower body region, responses to cutaneous stimuli and responses to some deep stimuli were reduced. Cortical areas 3b and 1, that normally showed responses predominantly to cutaneous stimuli, had an increased percentage of responses to deep stimuli. Cells that did not respond to our somatic stimuli but that had a spontaneous firing pattern were found in the first somatic sensory cortex (SI). We conclude that at rostral spinal levels, the dorsal funiculus contains all of the information about hair displacement stimuli of the lower body that projects to the first somatic sensory cortex as well as much information from cutaneous receptors and some from deep receptors on the body surface. Temporal information as well as precise receptive field demarkation is also supplied to SI cells by the dorsal funiculus.