| Abstract: | An electrophysiological analysis was carried out on 82 neurons in the parabrachial nuclei to study coding of gustatory stimuli. The magnitude of neural discharge evoked by two concentrations of each of 4 basic taste stimuli were subjected to two types of analyses to evaluate neuronal specificity and across-element spatial patterning in the coding of taste quality. Results were compared and contrasted to those in rodents. Profiles of taste response of individual neurons were analyzed mathematically by Q-technique principal components analysis and cluster analysis to identify basic neuronal patterns of response. Four distinct patterns emerged which, based on the average profiles of response, were characterized as: NaCl-dominant, NaClHCl, sucrose-dominant, and nonspecific. Analysis of the NaCl- and sucrose-dominant types of neurons indicated that neurons with the most narrowly tuned patterns of response to the taste stimuli could not effectively code specific taste qualities. Comparison of interstimulus correlations in magnitude of response across neurons between qualitatively different tastants and intrastimulus correlations between intensities of given tastants also revealed difficulties with the spatial pattern model of coding. The discrepant findings raise questions about an assumption utilized in the analysis of the model, viz., that all elements contribute homogeneously to the patterning code. |
