Gustatory responses of cortical neurons in rats. I. Response characteristics

Abstract

The responses of 111 cortical neurons to the four classical taste stimuli (sucrose, NaCl, HCl, and quinine HCl) applied to the anterior part of the tongue were recorded extracellularly in lightly anesthetized rats. Basic response properties of these cortical taste neurons were analyzed. The location of 88 of 111 neurons were histologically identified. They were distributed from anterodorsal to posteroventral direction in the insular cortex just dorsal to the rhinal sulcus and ventral to the somatic sensory area I. The receptive fields of 17 cortical neurons were examined. Most (94%) of the neurons had a narrow focus on the ipsilateral, contralateral, or bilateral sides of the tongue surface. Half of the foci were surrounded by a less-sensitive receptive field of relatively wide size. No apparent relationship was detected between the location of the cortical neurons and the site or extent of the receptive fields of those neurons, indicating a lack of topographical organization in the cortical gustatory area. The mean rate of the spontaneous discharges was 7.1 impulses/3 s, which is about 3 times larger than that in a first-order taste nerve (chorda tympani). The statistically significant difference of spontaneous discharges among response types of cortical neurons was observed only between the neurons responding in an excitatory manner to only one or two kinds of basic stimuli (6.2 impulses/3 s) and the neurons responding in an inhibitory manner to more than three kinds of taste stimuli (14.2 impulses/3 s). When the net responses (spontaneous rate subtracted) to each of the four tastes were compared with the spontaneous discharges in each neuron, the magnitude of spontaneous discharges was significantly negatively correlated with the net response to sucrose. This fact indicates that a neuron with a larger spontaneous discharge rate has a tendency to respond less to sucrose. Response characteristics of cortical taste neurons were quite distinct from those of the first-order taste neurons in the following respects: 1) a decrease in the average evoked discharge rate, which resulted in a small signal-to-noise ratio; 2) a tendency toward equalization of effectiveness of the four basic taste stimuli; 3) about 27% of the neurons decreased their firing rate during the first 3 s after the onset of taste stimulation; and 4) no clear initial phasic response, with a fluctuation in impulse discharges in some neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Neural mechanisms of nociception during orthodontic treatment

“…These anatomical findings indicate that the area corresponds to the secondary somatosensory cortex (S2) and oral region of the IC (IOR), as reported by Nakamura et al (49). S2/IOR receives varied somatosensory information from oral regions, including PDL sensation, gustation (50)(51)(52), and nociception (49,53,54). Interestingly, electrical stimulation of S2/IOR induces rhythmic jaw movement (55,56).…”

Gustatory signal processing in the glossopharyngeo-hypoglossal reflex arc of the frog.

“…1, 3, 7 and 8). Studies on the phasic versus tonic response of the rat taste neurons at different brain levels have revealed that the phasic component becomes smaller in magnitude as the level of neurons varies from the medulla, pontine and thalamus, to the cortical taste area (ScoTT, 1982;YAMAMOTO et al, 1984). OGAWA et al (1985) examined the same problem along the taste pathway from the chorda tympani to the thalamic level by means of the transiency index (SCHILLER and MALPELI, 1977), and found that the index becomes smaller for the response to NaCI, larger for the responses to sucrose and HC1, and is unchanged, or always phasic, for the quinine response.…”

The Insular Cortex and the Amygdala: Shared Functions and Interactions

“…BLA stimulation affects IC neuronal responses [8] whereas BLA tetanic stimulation induces long-term potentiation in the ipsilateral IC [157,158,198]. Interestingly, induction of this long-term potentiation in the BLA-IC projection before CTA training enhances memory retention [199].…”

“…Each subdivision is believed to process particular sensory information. For example, the AI is believed to participate in nociceptive [4][5][6] and autonomic processing [3], the DI plays a role in gustatory processing [7,8] and the GI has an important role in modulating visceral function [3].…”

“…Such studies include anatomical, electrophysiological, lesion, pharmacological and imaging studies, as well as operatory stimulation techniques which have yielded plausible roles for the IC in dozens of different functions. Several studies indicate that the IC is involved in taste processing [7,8,28,41], viscerosensory information processing [3,20,26,38,42,43], temperature and pain perception [44,45], olfaction [46] auditory processing [47][48][49], somatosensory perception [49,50], drug craving [51], motor tasks [52] and post-stroke motor-recovery functions [53].…”