Posterior insular cortex in rats: response characteristics and function.

Since the first report by Cechetto and Saper (1987) showing the viscerotopic sensory representation in the insular cortex, various studies on the posterior insular cortex have been performed. We previously studied the response properties of neurons in the rat insular cortex to gustatory, visceral and nociceptive stimulation, and to electrical stimulation of the various sensory nerves (chorda tympani, CT; lingual-tonsillar branch of the glossopharyngeal nerve, LT-IXth; pharyngeal branch of the glossopharyngeal nerve, PHIXth; superior laryngeal nerve; SL), using single unit recordings (Hanamori et al., 1997a,b, 1998a,b). The results from these studies indicated that neurons in the posterior insular cortex (posterior to the region where the CT projects) receive convergent inputs from various sensory organs. In the present study, first, we summarized the data from previous our studies concerning response properties and convergence in the insular cortex. Previously several studies (e.g. Ruggiero et al., 1987) have shown that electrical or chemical stimulation of the posterior insular cortex induces changes in the cardiovascular system [increase or decrease in heart rate (HR) or blood pressure (BP)]. In addition, it has been shown that neuronal activity in the posterior insular cortex was increased or decreased by chemoreceptor or baroreceptor stimulation. In the present study, we found neurons in the posterior insular cortex that show fluctuations in the spontaneous discharge. The fluctuations were also observed in BP and HR recorded simultaneously. The relationships among fluctuations in neuronal activity of the insular cortex, mean arterial pressure (MAP), and HR were analyzed using the Pearson correlation coefficient (r).