Sensory mapping of the septal area of the rat

Abstract

The purpose of this investigation was the localization of cells in the septal area of the rat which respond to sensory stimulation and the types of responses which are present. The suggestion of a possible sensory involvement of the septal area is indicated by observations that both lesions and stimulation of the septal area of the rat can alter the behavioral and electrophysiological responsiveness of the rat to sensory stimulation. Previous studies have demonstrated the existence of sensory-responsive cells in the septal area, and the present study attempted to extend these findings by determining the localization of the responsive units within the septal area. Fifty male Sprague Dawley albino rats were used in the study. Subjects were paralyzed with gallamine triethiodide and single unit activity was sampled in six planes transecting the longitudinal axis of the septal area. Units were tested for responsiveness to visual, auditory, somatosensory, gustatory, and olfactory stimuli. Responsive units were localized in the anterior area of the septum, in the dorsomedial area, and in the posterior ventral-medial area. The anterior region contained units responsive primarily to auditory, gustatory, and olfactory stimuli. The dorsomedial region contained mostly visual- and auditory-responsive units. The posterior ventral-medial region was responsive to somatosensory and visual stimuli with slight responsiveness to gustatory and olfactory stimuli. An analysis of the number of stimuli to which cells responded indicated a considerable number of units responding to only one stimulus. The results of the experiment suggest that the sensory responsiveness in the septal area is relatively modality-specific and is found predominantly in the medial areas. The importance of the specificity and localization of the responsive units was discussed in terms of possible afferent pathways critical for the sensory responsiveness of the septal units and of possible efferent points of convergence of the information from the septal regions of sensory-responsive cells.