Mastication-related neurons in the orofacial first somatosensory cortex of awake cats

Abstract

In the orofacial area of the first somatosensory cortex (SI), we recorded single unit activity from 699 neurons in 11 awake cats. Fifty-two percent (362/699) were mastication-related neurons (MRNs) showing activity related to some aspects of masticatory movements. MRNs were divided into three types by their activity patterns: (1) the rhythmical type, showing rhythmical bursts in pace with the masticatory rhythm; (2) the sustained type, showing a sustained firing during the period of taking food and (3) the transient (biting) type, showing intense discharges in coincidence with biting hard food. MRNs had mechanoreceptive fields in the perioral, tongue, periodontal and mandibular regions. The activities of perioral rhythmical-MRNs, mandibular transient-MRNs, tongue rhythmical-MRNs and periodontal transient-MRNs were correlated with food texture, while perioral rhythmical-MRNs, perioral sustained-MRNs and tongue sustained-MRMs were not. Both facial and intraoral MRNs were scattered throughout the facial and intraoral projection areas in SI. These findings provide evidence that the orofacial SI monitors masticatory movements for food ingestion.

Cortical control for mastication in cats: Changes in masticatory movements following lesions in the masticatory cortex

“…Detailed descriptions of most of the methods have already been published (Hiraba et al 1997;Hiraba et al 2000;Hiraba 2004) and so the following descriptions focus on new methodological approaches.…”

“…Based on the analysis of behaviors as shown in Figure 1, we defined the food intake period, masticatory period and period to the final swallow, as described in the previous paper (Hiraba et al 1997;Hiraba et al 2000). During the masticatory period, sustained bilateral erection of the whiskers was observed, and jaw and tongue movements were rapid, regular and rhythmic.…”

“…Mechanoreceptive fields (RF) in the orofacial region and motor effects by the continuous intracortical microstimulation (C-ICMS; 3-4 s, 200 ms pulses at 50 Hz, 20 mA) in sites of mastication related neurons (MRN) recordings were examined in the same way (Hiraba et al 1997;Hiraba 2004). Based on recording sites of MRNs with the facial or intraoral RFs, MA was divided into the facial projection area in the posterior part and intraoral one in the anterior part.…”

Neuroplasticity of face sensorimotor cortex and implications for control of orofacial movements

“…Short-train ICMS can also evoke jaw and tongue movements when applied to the face SI or face MI in subprimates [26][27][28][29][30][31]. On the other hand, longtrain ICMS can evoke semiautomatic movements such as mastication, swallowing and facial whisking from the face MI and face SI of monkeys and subprimates [19][20][21][22][32][33][34]. Single neuron recordings reveal that neurons within many of the ICMS-defined face SI as well as face MI sites show activity related to mastication and swallowing and/or to a trained jaw-closing or tongue-protrusive task in monkeys, and to mastication, licking and whisking in rats and cats [9,[23][24][25]33,[35][36][37][38][39].…”

“…On the other hand, longtrain ICMS can evoke semiautomatic movements such as mastication, swallowing and facial whisking from the face MI and face SI of monkeys and subprimates [19][20][21][22][32][33][34]. Single neuron recordings reveal that neurons within many of the ICMS-defined face SI as well as face MI sites show activity related to mastication and swallowing and/or to a trained jaw-closing or tongue-protrusive task in monkeys, and to mastication, licking and whisking in rats and cats [9,[23][24][25]33,[35][36][37][38][39]. Also, neurons in face MI as well as face SI may have an orofacial mechanoreceptive field from which they can be activated (e.g., by tactile stimulation) [19,21,23,26,35,38,40].…”