Facial vibrotactile stimulation activates the parasympathetic nervous system: study of salivary secretion, heart rate, pupillary reflex, and functional near-infrared spectroscopy activity.

We previously found that the greatest salivation response in healthy human subjects is produced by facial vibrotactile stimulation of 89 Hz frequency with 1.9 µ m amplitude (89 Hz-S), as reported by Hiraba et al. (2012, 20011, and 2008). We assessed relationships between the blood flow to brain via functional near-infrared spectroscopy (fNIRS) in the frontal cortex and autonomic parameters. We used the heart rate (HRV: heart rate variability analysis in RR intervals), pupil reflex, and salivation as parameters, but the interrelation between each parameter and fNIRS measures remains unknown. We were to investigate the relationship in response to established paradigms using simultaneously each parameter-fNIRS recording in healthy human subjects. Analysis of fNIRS was examined by a comparison of various values between before and after various stimuli (89 Hz-S, 114 Hz-S, listen to classic music, and "Ahh" vocalization). We confirmed that vibrotactile stimulation (89 Hz) of the parotid glands led to the greatest salivation, greatest increase in heart rate variability, and the most constricted pupils. Furthermore, there were almost no detectable differences between fNIRS during 89 Hz-S and fNIRS during listening to classical music of fans. Thus, vibrotactile stimulation of 89 Hz seems to evoke parasympathetic activity.

Cortical control of tongue protrusion and lateral movements in the cat.

Based on area P lesion experiments, we hypothesized that tongue protrusion adapted for licking might be regulated by the lateral wall of the presylvian sulcus (bilateral areas P) of the cerebral cortex (Hiraba H, Sato T, Nakakawa K, Ueda K. 2009. Cortical control of appropriate tongue protrusion during licking in cats--Increase in regional cerebral blood flow (rCBF) of the contralateral area P and in tongue protrusion after the unilateral area P lesion. Somatosens Mot Res 26:82-89). We propose that the right and left lingual muscles are dominated by the right and left hypoglossal nucleus, respectively, and that right and left pyramidal cells projecting to the right and left hypoglossal nucleus, respectively, exist in unilateral area P. These cells project via an inhibitory interneuron relay to the lateral branches toward the left or right pyramidal cells in contralateral area P. In this study, we aimed to demonstrate the existence of inhibitory interneurons using injections of a gamma-aminobutyric acid (GABA) agonist (muscimol), a GABA antagonist (bicuculline), and kainic acid into unilateral area P, followed by examination of tongue protrusion and lateral movements during trained licking and changes in regional cerebral blood flow (rCBF) values in the contralateral area P. We found disordered protrusion toward both sides and a marked decrease in rCBF values in the contralateral area P after bicuculline injection. We also found abnormal tongue protrusion toward the front and a marked increase in rCBF values after muscimol and kainic acid injections. These results suggest that cortical networks between the bilateral areas P are relayed by inhibitory interneurons.

Changes in localized arrangement into the hypoglossal nucleus after the neurectomy of unilateral hypoglossal nerve (medial branch) in cats.

We studied changes in orofacial behavior and the arrangement of bilateral hypoglossal nuclei after the neurectomy of the medial branch of the unilateral hypoglossal nerve in cats. After recovery from surgery in a head holder, the animals were acclimated to take and chew fish paste (1.8 g) from a spoon and lick milk from a wetted paintbrush. Next we performed a neurectomy in the unilateral hypoglossal nerve after training. We firstly recorded behavior during the taking of fish paste and licking of milk, and then performed a neurectomy in the unilateral hypoglossal nerve. After nerve cutting, the cats' tongue deviated toward the cut side when they licked food, and bilateral activities of EMGs in the genioglossus muscles became stable in about 1 month. After that, we injected two kinds of fluorescent dye (10% Evans blue, EB, and 3% Fast blue, FB) into the bilateral genioglossus muscles using syringes (0.15 ml in each), respectively. Although each injection of FB and EB into the bilateral genioglossus muscles in normal cats revealed cells positively stained with each dye in the hypoglossal nuclei of each injection site, in cats 1 month after nerve cutting, fluorescent dye was only observed in positive cells in the hypoglossal nucleus of the intact side and the dye injected into the neurectomy side showed a mixture into positive cells of the intact side. The findings suggest that muscles in the neurectomy side may be compensated by regeneration of the peripheral nerves on the intact side.

Cortical control of appropriate tongue protrusion during licking in cats--increase in regional cerebral blood flow (rCBF) of the contralateral area P and in tongue protrusion after the unilateral area P lesion.

Adequate tongue protrusion may be regulated by cat bilateral area P (the motor cortex for jaw and tongue movements) (Hiraba and Sato, Somatosens Mot Res 2005b;22:183-192). The ICMS (intracortical microstimulation) in the unilateral area P evoked motor effects of tongue protrusion without deviation (Hiraba and Sato, Somatosens Mot Res 2004;23:1-12), and cats with the unilateral lesion of area P showed abnormal tongue protrusion without deviation during licking (Hiraba and Sato, Somatosens Mot Res 2005b;22:183-192). Further, the measurements of the regional cerebral blood flow (rCBF) in the bilateral jaw and tongue motor cortical areas were shown to have the same activity rate during the lateral licking (Hiraba and Sato, Somatosens Mot Res 2005c;22:307-317). We assumed from these results that cortical control for tongue protrusion was executed by networks between the bilateral area P including inhibitory interneurons. We prepared the measurable cats of the rCBF in the contralateral side after the unilateral area P lesion. Changes in the rates of rCBF and tongue protrusion during licking were examined over a long time course of about 1-2 months after the unilateral area P lesion. All cats after the unilateral area P lesion showed increased rate (double or triple in comparison with the normal ones) of rCBF of the contralateral area P in the early (0-20 days) phase. On the other hand, increased rates of tongue protrusion were about 120% in the early phase, and about 180% in the middle (21-35 days) and late (36-last days) phases. The results support the organization of networks between bilateral area P including the inhibitory interneurons.

Increased secretion of salivary glands produced by facial vibrotactile stimulation.

Patients with low-back pain can be evaluated immediately by means of an electrical tool that produces bony vibration to the lumbar spinal processes (Yrjama M, Vanharanta H. Bony vibrotactile stimulation: A new, non-invasive method for examining intradiscal pain. European Spine Journal 1994;3:233-235). In the rehabilitation of masticatory disturbance and dysphagia, an electric toothbrush is commonly used as an oral motor exercise tool for the facilitation of blood flow and metabolism in the orofacial region in Japanese hospitals. However, subjects receiving vibration in the facial regions reported increased salivary secretion. We attempted to develop an oral motor exercise apparatus modified by a headphone headset that was fixed and could be used for extended periods. The vibration apparatus of the heating conductor is protected by the polyethyle methacrylate (dental mucosa protective material), and electric motors for vibration control of the PWM circuit. We examined the amount of salivation during vibration stimuli on the bilateral masseter muscle belly, using a cotton roll positioned at the opening of the secretory duct for 3 min. Although the quantity of salivation in each subject showed various and large fluctuations in the right and left sides of the parotid and submandibular and sublingual glands, one or more of the salivary glands were effectively stimulated by 89 Hz vibration. The reported apparatus will be useful as an additional method in orofacial rehabilitation.

Organization of cortical processing for facial movements during licking in cats.

We proposed that cortical organization for the execution of adequate licking in cats was processed under the control of two kinds of affiliated groups for face and jaw & tongue movements (Hiraba H, Sato T. 2005A. Cerebral control of face, jaw, and tongue movements in awake cats: Changes in regional cerebral blood flow during lateral feeding Somatosens Mot Res 22:307-317). We assumed the cortical organization for face movements from changes in MRN (mastication-related neuron) activities recorded at area M (motor cortex) and orofacial behaviors after the lesion in the facial SI (facial region in the primary somatosensory cortex). Although we showed the relationship between facial SI (area 3b) and area M (area 4delta), the property of area C (area 3a) was not fully described. The aim of this present study is to investigate the functional role of area C (the anterior part of the coronal sulcus) that transfers somatosensory information in facial SI to area M, as shown in a previous paper (Hiraba H. 2004. The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats Somatosens Mot Res 21:87-97). We examined the properties of MRNs in area C and changes in orofacial behaviors after the area C or area M lesion. MRNs in area C had in common RFs in the lingual, perioral, and mandibular parts, and activity patterns of MRNs showed both post- and pre-movement types. Furthermore, cats with the area C lesion showed similar disorders to cats with the area M lesion, such as the dropping of food from the contralateral mouth, prolongation of the period of ingestion and mastication, and so on. From these results, we believe firmly the organization of unilateral cortical processing in facial SI, area C, and area M for face movements during licking.

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

In a previous paper (Hiraba and Sato 2004) we reported that an accurate mastication might be executed by the cortical processing in bilateral masticatory area (MA)and motor cortices. The aim of this study was to determine if cats with lesion of either unilateral or bilateral MA showed changes in mastication. After exploring mechanoreceptive fields and motor effects of mastication-related neurons (MRNs) in MA using the single unit recording and intracortical microstimulation methods, we made various lesions in MAs with injections of kainic acid (0.1%, 2.0 microl). Since the MA was divided into facial (F) and intraoral (I) projection areas as reported in the previous paper, cats with the unilateral lesion in F or I, and with the bilateral lesion in F and F, I and I or F and I (F on one side and I on other side) were prepared. Cats with unilateral lesion in F or I and with bilateral lesion in F and I showed no changes in mastication except for prolongation of the food intake and masticatory periods. Cats with bilateral lesion into F and F, or I and I showed wider jaw-opening during mastication. Particularly, the latter group showed enormous jaw-opening, delay in the start of mastication and difficulty in manipulating food on the tongue. In all cats with lesions of each type, masticatory and swallowing rhythms remained normal. These findings suggest that accurate mastication is executed by the close integration between F and F and I and I of the bilateral MA.

Cortical control of mastication in cats. 2. Deficits of masticatory movements following a lesion in the motor cortex.

Our previous study suggested that area P in the lateral wall of the presylvian sulcus and MA (masticatory cortex) in the rostral part of the orbital gyrus play an important role in execution of mastication. The aim of this present study is to examine if changes in orofacial behaviors and masticatory movements occur in cats with lesions of area P. First, we explored the locations in area P through the use of single unit recording and ICMS (intracortical microstimulation). Since mastication related neurons (MRNs) with the mechanical receptive field (RF) in facial or intraoral region were intermingled in area P, we performed either a partial or entire lesion in area P by injections of 2 microl or 4 microl of 0.1% kainic acid. Cats with the entire lesion in area P showed a decrease of food intake rates associated with abnormal tongue protrusion and wide jaw-opening, fluctuation of masticatory start, and prolongation of masticatory and food intake periods. Abnormal movements of tongue and jaw did not recover, although their prolongation and fluctuation returned to normal levels in one month. On the other hand, all deficits evoked by cats with the partial lesion recovered in about one month. In cats with the partial and entire lesions, masticatory rhythm remained normal. These findings suggest that area P may regulate accurate and suitable tongue and jaw movements during mastication depending on cortical processing.

Cerebral control of face, jaw, and tongue movements in awake cats: changes in regional cerebral blood flow during lateral feeding.

Mastication is achieved by cooperation among facial, masticatory, and lingual muscles. However, cortical control in cats for the masticatory performance is processed by two systems: facial movement processed by facial SI (the first somatosensory cortex), area C, and area M (motor areas), and jaw and tongue movements performed by intraoral SI, masticatory area, and area P (motor area). In particular, outputs from area P organized in the corticobulbar tract are projected bilaterally in the brainstem. In this present study, the aim is to explore changes in the regional cerebral blood flow (rCBF) in the facial SI, area M, and area P during trained lateral feeding (licking or chewing from the right or left side) of milk, fish paste, and small dry fish. The rCBF in area M showed contralateral dominance, and rCBF in area P during chewing or licking from the right or left side was almost the same value. Furthermore, activities of genioglossus and masseter muscles in the left side showed almost the same values during licking of milk and of fish paste, and chewing of small dry fish during lateral feeding. These findings suggest that the cortical process for facial, jaw, and tongue movements may be regulated by the contralateral dominance of area M and the bilateral one of area P.

The function of sensory information from the first somatosensory cortex for facial movements during ingestion in cats.

The aim of the present study was to investigate the relationship between the facial region of the first somatosensory cortex (facial SI) and facial region of the motor cortex (facial MI), as the basis of orofacial behaviors during ingestion of fish paste. Area M in the ventral cortex of the cruciate sulcus that was defined as part of the facial MI by and, showed various facial twitches evoked by intracortical microstimulation (ICMS) and recorded many mastication-related neurons (MRNs). Many MRNs in area M had receptive fields (RFs) in lingual, perioral and mandibular regions. The 60% value of activity patterns of MRNs (n = 124) recorded in area M of normal cats, were the pre-SB type (the sustained and pre-movement type) that showed increased firing prior to the start of mastication and then tonic activity during the masticatory period. MRNs recorded in area M of cats with the facial SI lesion, showed a noticeable decrease in MRNs with RFs in the perioral and mandibular regions and with activity of the pre-SB type. These results strongly suggest that blocking facial SI sensory inputs evoked by mastication interferes with the relay of important facial sensory information to area M required for the appropriate manipulation of food during mastication.

Cortical control of mastication in the cat: properties of mastication-related neurons in motor and masticatory cortices.

The aim of this study is to examine mastication-specific activity of orofacial neurons in the motor and masticatory cortices of the awake cat. We examine properties of mastication-related neurons (MRNs) in masticatory (MA, the rostral region of the orbital gyrus) and motor (area P, the lateral wall of the presylvian sulcus) cortical areas that are related to mastication of cats. MRNs in MA and area P had in common mechanoreceptive fields (RFs) in perioral, mandibular and lingual regions, and many MRNs had bilateral RFs in the tongue and mandibular regions. Facial RF size was the largest in area P. Eleven percent of MRN recording sites in MA, and 43% in area P evoked various motor effects with the use of intracortical microstimulation (ICMS). MRNs of the pre-movement type showing activities prior to mastication, or masticatory or lingual EMG, were 14% in MA and 45% in area P. Based on wheat germ agglutinin-horseradish peroxidase (WGA-HRP) injection into area P and MA, cortico-cortical connections were examined. After the unilateral area P injection, were reciprocal connections between the contralateral area P and bilateral MA were demonstrated. After the unilateral MA injection, there were reciprocal connections between the contralateral MA, bilateral area P and bilateral orofacial SI (the orofacial region of the first somatosensory area). These findings suggest that accurate masticatory movements may be executed by the cortical processing in MA and area P.