Yayoi Yamaguchi

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

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.

Deficits of masticatory movements caused by lesions in the orofacial somatosensory cortex of the awake cat

The purpose of this study was to determine the role of somatosensory cortex (SI) in the control of orofacial movements during eating. We identified perioral and tongue projection regions of the cat SI and destroyed cells in one region by injecting kainic acid. The effects on orofacial behavior were then studied over a period of 4-6 weeks. Cats with unilateral lesions in the perioral region (PL-cats) dropped food from the contralateral side of the mouth in the early phase. Failure in erection of the contralateral whisker hairs during masticatory movements and delay of the masticatory start were observed throughout the experimental period. Furthermore, in the late phase, PL-cats showed prolongations of the masticatory and food intake periods, which were accompanied by the increase in the number of swallows and chewing cycles. Cats with unilateral lesions in the tongue region (TL-cats) showed the prolongation of the masticatory period in the early phase, which was accompanied by the increase in the number of swallows and chewing cycles. TL-cats did not show the prolongation of the food intake period and failure in erection of the contralateral whisker hairs. In both PL- and TL-cats, masticatory and swallowing rhythms were normal.The purpose of this study was to determine the role of somatosensory cortex (SI) in the control of orofacial movements during eating.We identified perioral and tongue projection regions of the cat SI and destroyed cells in one region by injecting kainic acid. The effects on orofacial behavior were then studied over a period of 4-6 weeks. Cats with unilateral lesions in the perioral region (PL-cats) dropped food from the contralateral side of the mouth in the early phase. Failure in erection of the contralateral whisker hairs during masticatory movements and delay of the masticatory start were observed throughout the experimental period. Furthermore, in the late phase, PL-cats showed prolongations of the masticatory and food intake periods, which were accompanied by the increase in the number of swallows and chewing cycles. Cats with unilateral lesions in the tongue region (TL-cats) showed the prolongation of the masticatory period in the early phase, which was accompanied by the increase in the number of swallows and chewing cycles. TL-cats did not show the prolongation of the food intake period and failure in erection of the contralateral whisker hairs. In both PL- and TL-cats, masticatory and swallowing rhythms were normal.

Low-threshold motor effects produced by stimulation of the facial area of the fifth somatosensory cortex in the cat

The motor effective sites of the fifth somatosensory cortex (SV) in the cat were mapped in detail by using unit recording and intracortical microstimulation (ICMS) techniques. The motor effective sites for facial muscle contraction were identified using stimulus currents of less than 30 microA. Of the 257 effective sites detected, 49% were activated by stimulus currents of less than 20 microA and of these, 51% responded to stimulus currents of less than 10 microA. ICMS within the facial area of the SV neuron produced contralateral eye-blinking, the lowest threshold current for which was 2 microA and ICMS within the SV neurons produced whisker movements, the minimum threshold current for which was 4 microA. Furthermore, stimulation of some SV neurons at a threshold current as low as 4 microA produced whisker movements and some responded to both visual and cutaneous stimuli. Ablation of areas 6a beta, 3a, SII, SIII and the motor cortex did not eliminate or reduce the low-threshold responses elicited by this weak stimulation of the SV. These motor effective areas receive input from the contralateral cutaneous of the surrounding muscle motor effective region. Our results suggest that the described effect is independent of motor effective areas.

1646 Changes in masticatory movements induced by a lesion in the first somatosensory (SI) or masticatory cortex (MA) in conscious cats

Direct projections from the dorsal (PMd) and ventral (PMv) divisions of the premotor cortex to the subthalamic nucleus (SIN) were investigated in the Japanese monkey (Mucacufuscara) by using double anterograde tracing with WGAHRP and biotinylated dextran amine (BDA). Under the guidance of intracortical microstimulation, WGA-IIRP was injected into the forelimb region of PMd, and BDA was injected into the forelimb region of PMv. Anterogradely-labeled axon terminals from PMd and PMv were distributed mainly in the medial half of STN, and their distribution areas were overlapped with each other. These areas further corresponded well to the terminal field of the corticosubthalamic projection from the supplementary motor area @MA). Some labeled axon terminals from PMd and PMv were also found in the lateral half of STN that received projection fibers from the primary motor cortex. The present results indicate that the medial SIN receives convergent inputs from PMd, PMv and SMA, and support our previous observation that STN has double somatotopical representation in both medial and lateral STN.

Cortico-cortical connections to the fifth somatosensory area (SV) in the cat's cerebral cortex: a horseradish peroxidase study

It is known that there are at least four separate somatosensory cortical representations in the cats cortex. These areas had many cortico-cortical connections in the cerebral cortex. Furthermore, Mori et al. found a new and complete somatosensory representation of the body surface located rostro-caudally along the medial bank of the anterior suprasylvian sulcus (ASSS-m), the fifth somatosensory cortex (SV). These neurons had large receptive fields (RFs). In the present study, we used the HRP technique to identify the cortico-cortical neurons which project to the facial or trunk-hindlimb regions of SV.