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

Animal Models for Dysphagia Studies: What Have We Learnt So Far

Research using animal models has contributed significantly to realizing the goal of understanding dysfunction and improving the care of patients who suffer from dysphagia. But why should other researchers and the clinicians who see patients day in and day out care about this work? Results from studies of animal models have the potential to change and grow how we think about dysphagia research and practice in general, well beyond applying specific results to human studies. Animal research provides two key contributions to our understanding of dysphagia. The first is a more complete characterization of the physiology of both normal and pathological swallow than is possible in human subjects. The second is suggesting of specific, physiological, targets for development and testing of treatment interventions to improve dysphagia outcomes.

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.

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 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.