Convergence of afferent inputs from the chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats

The responses of single neurons in the insular cortex to electrical stimulation of the chorda tympani (CT), lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, pharyngeal branch of the glossopharyngeal (PH-IXth) nerve, and superior laryngeal (SL) nerve were recorded in anaesthetized and paralyzed rats. Ninety-four neurons responding to stimulation of at least one of the four nerves were identified from the insular cortex. Most of the neurons were located in the posterior portion of the insular cortex; the mean location was 0.8 mm anterior to the anterior edge of the joining of the anterior commissure (AC) and was 1.4 mm dorsal to the rhinal fissure (RF). Of the 94 neurons, 84 (89%) received convergent inputs from two or more nerves, and the remaining 10 (11%) received inputs from one nerve. The neurons responding to the CT stimulation were distributed more anteriorly than those responding to other three nerves in the anterior-posterior dimension. Our results indicate that the neurons recorded mainly from the posterior portion of the insular cortex receive convergent inputs from the oropharyngolaryngeal regions.