Motor cortex neuroplasticity associated with lingual nerve injury in rats

The aim of this study was to determine if lingual nerve trauma affects the features of face primary motor cortex (MI) defined by intracortical microstimulation (ICMS). The left lingual nerve was transected in adult male rats by an oral surgical procedure; sham rats (oral surgery but no nerve transection) as well as naive intact rats served as control groups. ICMS was applied at post-operative days 0, 7, 14, 21, and 28 to map the jaw and tongue motor representations in face MI by analyzing ICMS-evoked movements and electromyographic activity recorded in the genioglossus (GG) and anterior digastric (AD) muscles. There were no statistically significant effects of acute (day 0) nerve transection or sham procedure (p > 0.05). The surgery in the sham animals was associated with limited post-operative change; this was reflected in a significant (p < 0.05) increase in the number of GG sites in left MI at post-operative day 14 compared to day 0. However, nerve transection was associated with significant increases in the total number of AD and GG sites in left or right MI or specifically the number of GG sites in rats at post-operative days 21 or 28 compared to earlier time periods. There were also significant differences between nerve-transected and sham groups at post-operative days 7, 14, or 21. These findings suggest that lingual nerve transection is associated with significant time-dependent neuroplastic changes in the tongue motor representations in face MI.     

Topographic Organization of Baboon Primary Motor Cortex: Face,Hand, Forelimb,and Shoulder Representation

(1) The fine details of the motor organization of the forelimb, face, and tongue representation of the baboon (Papio h. anubis)primary motor cortex were studied in four adult animals, using intracortical microstimulation (ICMS). (2) A total of 293 electrode penetrations were made. ICMS was delivered to 10,052 sites, and of these, 6,186 sites were verified to have been located within the grey matter. Motor effects were evoked from 30% of these sites. (3)The baboon motor cortex is confined, in large part, to the cortical tissue lying along the anterior bank of the central sulcus. When the electrode penetrations were confined to the precentral gyrus, few sites were capable of evoking movement when stimulated by currents of 40 μA or less. (4)The details of the motor maps varied among the four animals; nonetheless, a general topographic organization existed, with the tongue musculature being represented most laterally, followed by a medial progression of the face, digits, wrist, forearm, and shoulder. Within the representation of a given body part, the muscles were organized as a mosaic, wherein the same muscle was multiply represented. (5) A zone of unresponsive cortex was observed to lie consistently between the face and forelimb representation in all four animals. Repeated electrode penetrations within the unresponsive zone failed to elicit muscle contractions even with stimulating currents as high as 80 μA. (6) Our results suggest that the baboon motor cortex is topographically organized; however, embedded within this overall pattern lies a fine-grained mosaic incorporating multiple representations of the same muscle.     

Topographic organization of baboon primary motor cortex: face, hand, forelimb, and shoulder representation

(1) The fine details of the motor organization of the forelimb, face, and tongue representation of the baboon (Papio h. anubis) primary motor cortex were studied in four adult animals, using intracortical microstimulation (ICMS). (2) A total of 293 electrode penetrations were made. ICMS was delivered to 10,052 sites, and of these, 6,186 sites were verified to have been located within the grey matter. Motor effects were evoked from 30% of these sites. (3) The baboon motor cortex is confined, in large part, to the cortical tissue lying along the anterior bank of the central sulcus. When the electrode penetrations were confined to the precentral gyrus, few sites were capable of evoking movement when stimulated by currents of 40 microA or less. (4) The details of the motor maps varied among the four animals; nonetheless, a general topographic organization existed, with the tongue musculature being represented most laterally, followed by a medial progression of the face, digits, wrist, forearm, and shoulder. Within the representation of a given body part, the muscles were organized as a mosaic, wherein the same muscle was multiply represented. (5) A zone of unresponsive cortex was observed to lie consistently between the face and forelimb representation in all four animals. Repeated electrode penetrations within the unresponsive zone failed to elicit muscle contractions even with stimulating currents as high as 80 microA. (6) Our results suggest that the baboon motor cortex is topographically organized; however, embedded within this overall pattern lies a fine-grained mosaic incorporating multiple representations of the same muscle.     

Decreased hippocampal brain‐derived neurotrophic factor and impaired cognitive function by hypoglossal nerve transection in rats

The hypoglossal nerve controls tongue movements, and damages of it result in difficulty in mastication and food intake. Mastication has been reported to maintain hippocampus‐dependent cognitive function. This study was conducted to examine the effect of tongue motor loss on the hippocampus‐dependent cognitive function and its underlying mechanism. Male Sprague Dawley rats were subjected to the initial training of Morris water maze task before or after the bilateral transection of hypoglossal nerves (Hx). When the initial training was given before the surgery, the target quadrant dwelling time during the probe test performed at a week after the surgery was significantly reduced in Hx rats relative to sham‐operated controls. When the initial training was given after the surgery, Hx affected the initial and reversal trainings and probe tests. Brain‐derived neurotrophic factor (BDNF) expression, cell numbers and long‐term potentiation (LTP) were examined in the hippocampus on the 10^th day, and BrdU and doublecortin staining on the 14^th day, after the surgery. Hx decreased the hippocampal BDNF and cells in the CA1/CA3 regions and impaired LTP. BrdU and doublecortin staining was decreased in the dentate gyrus of Hx rats. Results suggest that tongue motor loss impairs hippocampus‐dependent cognitive function, and decreased BDNF expression in the hippocampus may be implicated in its underlying molecular mechanism in relation with decreased neurogenesis/proliferation and impaired LTP.     

Developmental time course of peripheral cross‐modal sensory interaction of the trigeminal and gustatory systems

Few sensory modalities appear to engage in cross‐modal interactions within the peripheral nervous system, making the integrated relationship between the peripheral gustatory and trigeminal systems an ideal model for investigating cross‐sensory support. The present study examined taste system anatomy following unilateral transection of the trigeminal lingual nerve (LX) while leaving the gustatory chorda tympani intact. At 10, 25, or 65 days of age, rats underwent LX with outcomes assessed following various survival times. Fungiform papillae were classified by morphological feature using surface analysis. Taste bud volumes were calculated from histological sections of the anterior tongue. Differences in papillae morphology were evident by 2 days post‐transection of P10 rats and by 8 days post in P25 rats. When transected at P65, animals never exhibited statistically significant morphological changes. After LX at P10, fewer taste buds were present on the transected side following 16 and 24 days survival time and remaining taste buds were smaller than on the intact side. In P25 and P65 animals, taste bud volumes were reduced on the denervated side by 8 and 16 days postsurgery, respectively. By 50 days post‐transection, taste buds of P10 animals had not recovered in size; however, all observed changes in papillae morphology and taste buds subsided in P25 and P65 rats. Results indicate that LX impacts taste receptor cells and alters epithelial morphology of fungiform papillae, particularly during early development. These findings highlight dual roles for the lingual nerve in the maintenance of both gustatory and non‐gustatory tissues on the anterior tongue. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 626–641, 2016     

Episodic hypoxia induces long-term facilitation of neural drive to tongue protrudor and retractor muscles.

Hypoxic episodes can evoke a prolonged augmentation of inspiratory motor output called long-term facilitation (LTF). Hypoglossal (XII) LTF has been assumed to represent increased tongue protrudor muscle activation and pharyngeal airway dilation. However, recent studies indicate that tongue protrudor and retractor muscles are coactivated during inspiration, a behavior that promotes upper airway patency by reducing airway compliance. These experiments tested the hypothesis that XII LTF is manifest as increased inspiratory drive to both tongue protrudor and retractor muscles. Neurograms were recorded in the medial XII nerve branch (XIIMED; contains tongue protrudor motor axons), the lateral XII nerve branch (XIILAT; contains tongue retractor motor axons), and the phrenic nerve in anesthetized, vagotomized, paralyzed, ventilated male rats. Strict isocapnia was maintained for 60 min after five 3-min hypoxic episodes (arterial Po(2) = 35 +/- 2 Torr) or sham treatment. Peak inspiratory burst amplitude showed a persistent increase in XIIMED, XIILAT, and phrenic nerves during the hour after episodic hypoxia (P < 0.05 vs. sham). This effect was present regardless of the quantification method (e.g., % baseline vs. percent maximum); however, comparisons of the relative magnitude of LTF between neurograms (e.g., XIIMED vs. XIILAT) varied with the normalization procedure. There was no persistent effect of episodic hypoxia on inspiratory burst frequency (P > 0.05 vs. sham). These data demonstrate that episodic hypoxia induces LTF of inspiratory drive to both tongue protrudor and retractor muscles and underscore the potential contribution of tongue muscle coactivation to regulation of upper airway patency.     

Heart rate reduction by zatebradine reduces infarct size and mortality but promotes remodeling in rats with experimental myocardial infarction

The importance of heart rate for left ventricular remodeling and prognosis after myocardial infarction is not known. We examined the contribution of heart rate reduction by zatebradine, a direct sinus node inhibitor without negative inotropic effects on left ventricular function and dilatation, on mortality, energy metabolism, and neurohormonal changes in rats with experimental myocardial infarction (MI). Thirty minutes after left coronary artery ligation or sham operation, the rats were randomized to receive either placebo or zatebradine (100 mg x kg(-1) x day(-1) per gavage) continued for 8 wk. Mortality during 8 wk was 33.3% in the placebo and 23.0% in the zatebradine group (P < 0.05); MI size was 36 +/- 2% and 30 +/- 1% (means +/- SE, P < 0.05), respectively. Zatebradine improved stroke volume index in all treated rats but increased left ventricular volume in rats with small MI (2.43 +/- 0.10 vs. 1.81 +/- 0.10 ml/kg, P < 0.05) but not in rats with large MI (2.34 +/- 0.09 vs. 2.35 +/- 0.11 ml/kg, not significant). Zatebradine reduced left and right ventricular norepinephrine and increased left and right ventricular 3,4-dihydroxyphenyl ethylene glycol-to-norepinephrine ratio suggesting aggravation of cardiac sympathetic activation by zatebradine after MI. Creatine kinase and lactate dehydrogenase isoenzymes in rats with MI remained unchanged by zatebradine. Lowering heart rate per se reduces mortality and MI size in this model but induces adverse effects on left ventricular remodeling in rats with small MI.     

Changes in evoked cortico-motor responses in the rat during aging and after partial decortication

Some changes of the organization of cortical motor representations, which were revealed by means of the intracortical microstimulation (ICMS) in aged rats after unilateral partial decortication, were true consequences of the decortication, but had no significant relationship to the aging. Distributions of latent periods of contralateral hind-leg EMG-responses to the ICMS had no significant shifts both during aging and after the surgery. Values of short-latency responses of ipsilateral proximal and axial muscles to the ICMS were in late time periods, from 8 to 16 months after surgery, significantly lower than ones of contralateral homonymous muscles. It is supposed, that ipsi- and bilateral short-latency responses to the ICMS in proximal and axial muscles of operated rats during late time periods are relayed through some pathways from the brain stem to the spinal cord.     

Experimentally cross-wired lingual taste nerves can restore normal unconditioned gaping behavior in response to quinine stimulation

Studies examining the effects of transection and regeneration of the glossopharyngeal (GL) and chorda tympani (CT) nerves on various taste-elicited behaviors in rats have demonstrated that the GL (but not the CT) nerve is essential for the maintenance of both an unconditioned protective reflex (gaping) and the neural activity observed in central gustatory structures in response to lingual application of a bitter substance. An unresolved issue, however, is whether recovery depends more on the taste nerve and the central circuits that it supplies and/or on the tongue receptor cell field being innervated. To address this question, we experimentally cross-wired these taste nerves, which, remarkably, can regenerate into parts of the tongue they normally do not innervate. We report that quinine-stimulated gaping behavior was fully restored, and neuronal activity, as assessed by Fos immunohistochemistry in the nucleus of the solitary tract and the parabrachial nucleus, was partially restored only if the posterior tongue (PT) taste receptor cell field was reinnervated; the particular taste nerve supplying the input was inconsequential to the recovery of function. Thus, PT taste receptor cells appear to play a privileged role in triggering unconditioned gaping to bitter tasting stimuli, regardless of which lingual gustatory nerve innervates them. Our findings demonstrate that even when a lingual gustatory nerve (the CT) forms connections with taste cells in a non-native receptor field (the PT), unconditioned taste rejection reflexes to quinine can be maintained. These findings underscore the extraordinary ability of the gustatory system to adapt to peripherally reorganized input for particular behaviors.     

Effect of weak, interrupted sinusoidal low frequency magnetic field on neural regeneration in rats: functional evaluation

A study of the effect of weak, interrupted sinusoidal low frequency magnetic field (ISMF) stimulation on regeneration of the rat sciatic nerve was carried out. In the experiment, 60 Wistar rats were used: 24 rats underwent unilateral sciatic nerve transection injury and immediate surgical nerve repair, 24 rats underwent unilateral sciatic nerve crush injury, and the remaining 12 rats underwent a sham surgery. Half of the animals (n = 12) with either sciatic nerve lesion were randomly chosen and exposed between a pair of Helmholtz coils for 3 weeks post-injury, 4 h/day, to an interrupted (active period to pause ratio = 1.4 s/0.8 s) sinusoidal 50 Hz magnetic field of 0.5 mT. The other half of the animals (n = 12) and six rats with sham surgery were used for two separate controls. Functional recovery was followed for 6 weeks for the crush injuries and 7(1/2) months for the transection injuries by video assisted footprint analysis in static conditions and quantified using a recently revised static sciatic index (SSI) formula. We ascertained that the magnetic field influence was weak, but certainly detectable in both injury models. The accuracy of ISMF influence detection, determined by the one-way repeated measures ANOVA test, was better for the crush injury model: F(1, 198) = 9.0144, P = .003, than for the transection injury model: F(1, 198) = 6.4826, P = .012. The Student-Newman-Keuls range test for each response day yielded significant differences (P < .05) between the exposed and control groups early in the beginning of functional recovery and later on from the points adjacent to the beginning of the plateau, or 95% of functional recovery, and the end of observation. These differences probably reflect the ISMF systemic effect on the neuron cell bodies and increased and more efficient reinnervation of the periphery.     

The effect of two episodes of denervation and reinnervation on skeletal muscle contractile function.

Sensory or motor "baby-sitting" has been proposed as a clinical strategy to preserve muscle integrity if motion-specific axons must regenerate over a long distance to reach denervated target muscles. Denervated muscles are innervated temporarily by using axons from nearby sensory or motor nerves. After motion specific motor axons have reached the target, the baby-sitter nerve is severed and motion-specific axons are directed to the target. Although this strategy minimizes denervation time, the requisite second episode of denervation and reinnervation might be deleterious to muscle contractile function. This study was designed to test the hypothesis that two sequential episodes of skeletal muscle denervation and reinnervation result in greater force and power deficits than a single peripheral nerve injury and repair. Adult Lewis rats underwent either transection and epineurial repair or sham exposure of the left peroneal nerve. After a 4-month recovery period, the contractile properties of the extensor digitorum longus muscle of the sham exposure group (control, n = 9) and one of the nerve division and repair groups (repair group 1, n = 9) were evaluated with measurements of the maximum tetanic isometric force, peak power, and maximal sustained power. A third group of rats underwent a second cycle of nerve division and repair (repair group 2, n = 9) at this same time point. Four months postoperatively, contractile properties of the extensor digitorum longus muscles were evaluated. Maximum tetanic isometric force and peak power were significantly reduced in repair group 2 rats as compared with repair group 1 and control rats. Maximal sustained power was not significantly different between the groups. These data support our working hypothesis that skeletal muscle contractile function is adversely affected by two cycles of denervation and reinnervation as compared with a single episode of nerve division and repair.     

Optic nerve regeneration after intravitreal peripheral nerve implants: trajectories of axons regrowing through the optic chiasm into the optic tracts

We have studied axon regeneration through the optic chiasm of adult rats 30 days after prechiasmatic intracranial optic nerve crush and serial intravitreal sciatic nerve grafting on day 0 and 14 post-lesion. The experiments comprised three groups of treated rats and three groups of controls. All treated animals received intravitreal grafts either into the left eye after both left sided (unilateral) and bilateral optic nerve transection, or into both eyes after bilateral optic nerve transection. Control eyes were all sham grafted on day 0 and 14 post-lesion, and the optic nerves either unlesioned, or crushed unilaterally or bilaterally. No regeneration through the chiasm was seen in any of the lesioned control optic nerves. In all experimental groups, large numbers of axons regenerated across the optic nerve lesions ipsilateral to the grafted eyes, traversed the short distal segment of the optic nerve and invaded the chiasm without deflection. Regeneration was correlated with the absence of the mesodermal components in the scar. In all cases, axon regrowth through the chiasm appeared to establish a major crossed and a minor uncrossed projection into both optic tracts, with some aberrant growth into the contralateral optic nerve. Axons preferentially regenerated within the degenerating trajectories from their own eye, through fragmented myelin and axonal debris, and reactive astrocytes, oligodendrocytes, microglia and macrophages. In bilaterally lesioned animals, no regeneration was detected in the optic nerve of the unimplanted eye. Although astrocytes became reactive and their processes proliferated, the architecture of their intrafascicular processes was little perturbed after optic nerve transection within either the distal optic nerve segment or the chiasm. The re-establishment of a comparatively normal pattern of passage through the chiasm by regenerating axons in the adult might therefore be organised by this relatively immutable scaffold of astrocyte processes. Binocular interactions between regenerating axons from both nerves (after bilateral optic nerve transection and intravitreal grafting), and between regenerating axons and the intact transchiasmatic projections from the unlesioned eye (after unilateral optic nerve lesions and after ipsilateral grafting) may not be important in establishing the divergent trajectories, since regenerating axons behave similarly in the presence and absence of an intact projection from the other eye.     

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.     

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.     

The roles of visual and proprioceptive information during motor program choice in frogs

Previous studies have shown that leopard frogs, Rana pipiens, use tongue prehension to capture small prey and jaw prehension to capture large prey. After hypoglossal nerve transection, the frogs fail to open their mouths when attempting to feed on small prey, but open their mouths and capture large prey. Here, we investigate how visual information about the prey and proprioceptive information from the tongue interact to influence the motor program choice. Using pieces of earthworm of various sizes, we found that Rana exhibits two different behavior patterns based on prey size. The frogs captured the 1.5-cm prey using tongue prehension, whereas 2.0-cm and larger prey were captured using jaw prehension. After hypoglossal transection, the frogs never opened their mouths when they tried to feed on 1.5-cm prey. When feeding on 3.0-cm and larger prey after transection, they always opened their mouths and captured the prey using jaw prehension. When offered 2.0-cm prey, they alternated randomly between opening and not opening the mouth. Therefore, deafferentation changed the pattern of motor program choice at the behavioral border. This implies that afferents from the tongue interact with visual input to influence motor program choice.     

Functional status of the regenerated chorda tympani nerve as assessed in a salt taste discrimination task

We tested whether the recovered ability of rats to discriminate NaCl from KCl after chorda tympani nerve transection (CTX) is causally linked to nerve regeneration or some other compensatory process. Rats were presurgically trained in an operant NaCl vs. KCl discrimination task. Rats with regenerated nerves, histologically confirmed by anterior tongue taste pore counts and tested 62 days after CTX (CTX-62R; n = 5), performed as well as those tested 62 days after sham surgery (Sham-62; n = 5), but both of these groups initially performed slightly worse than animals tested 7 days after sham surgery (Sham-7; n = 4). Performance of rats tested either 7 (CTX-7P; n = 5) or 62 (CTX-62P; n = 4) days after CTX in which nerve regeneration was prevented was severely disrupted. Adulteration of the stimuli with amiloride, an epithelial sodium channel blocker, impaired discrimination performance in a similar dose-dependent manner in the Sham-7 (n = 2), Sham-62 (n = 5), and CTX-62R (n = 5) groups, suggesting that the functional status of the amiloride-sensitive transduction pathway returns to normal in rats with regenerated chorda tympani nerves. Performance of CTX rats without regenerated nerves (CTX-7P, n = 2; CTX-62P, n = 4) was further degraded by amiloride treatment, suggesting that taste receptors innervated by other nerves are sensitive to amiloride. In conclusion, nerve regeneration is an essential component underlying full recovery of salt discrimination function after CTX.     

Expression of MHC-beta and MCT1 in cardiac muscle after exercise training in myocardial-infarcted rats.

To evaluate the hypothesis that increasing the potential for glycolytic metabolism would benefit the functioning of infarcted myocardium, we investigated whether mild exercise training would increase the activities of oxidative enzymes, expression of carbohydrate-related transport proteins (monocarboxylate transporter MCT1 and glucose transporter GLUT4), and myosin heavy chain (MHC) isoforms. Myocardial infarction (MI) was produced by occluding the proximal left coronary artery in rat hearts for 30 min. After the rats performed 6 wk of run training on a treadmill, the wall of the left ventricle was dissected and divided into the anterior wall (AW; infarcted region) and posterior wall (PW; noninfarcted region). MI impaired citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities in the AW (P < 0.01) but not in the noninfarcted PW. No differences in the expression of MCT1 were found in either tissues of AW and PW after MI, whereas exercise training significantly increased the MCT1 expression in all conditions, except AW in the MI rats. Exercise training resulted in an increased expression of GLUT4 protein in the AW in the sham rats and in the PW in the MI rats. The relative amount of MHC-beta was significantly increased in the AW and PW in MI rats compared with sham rats. However, exercise training resulted in a significant increase of MHC-alpha expression in both AW and PW in both sham and MI rats (P < 0.01). These findings suggest that mild exercise training enhanced the potential for glycolytic metabolism and ATPase activity of the myocardium, even in the MI rats, ensuring a beneficial role in the remodeling of the heart.     

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 Hiraba et al. (1992 and 1993), 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.     

Repetitive microstimulation alters the cortical representation of movements in adult rats

In order to examine the effects of repetitive stimulation on functional cortical organization, standard intracortical microstimulation (ICMS) techniques were used to generate maps of movement representations in motor cortex of rat. After identification of caudal and rostral forelimb fields and adjacent vibrissae and neck fields, one or more representational borders were defined in greater detail. Then a microelectrode was introduced into one of these representational fields, and ICMS current pulses were delivered at a rate of 1/sec for 1 to 3 hr. Following repetitive ICMS, significant changes in movement representations were observed using current levels that were either suprathreshold or subthreshold for evoking the site-specific movement. Electromyographic activity could be evoked at suprathreshold and near-threshold current levels, but not at the subthreshold current levels used here. Significant border shifts ranged from 210 to 670 microns. In each case in which shifts occurred, there appeared to be expansion of the movement represented at the repetitively stimulated site. The effects were progressive and reversible. These results suggest that at least under these unusual experimental circumstances, large representational changes can be generated very rapidly within motor cortex in the absence of any evident peripheral feedback.     

Repetitive Microstimulation Alters the Cortical Representation of Movements in Adult Rats

In order to examine the effects of repetitive stimulation on functional cortical organization, standard intracortical microstimulation (ICMS) techniques were used to generate maps of movement representations in motor cortex of rat. After identification of caudal and rostral forelimb fields and adjacent vibrissae and neck fields, one or more representational borders were defined in greater detail. Then a microelectrode was introduced into one of these representational fields, and ICMS current pulses were delivered at a rate of 1/sec for 1 to 3 hr. Following repetitive ICMS, significant changes in movement representations were observed using current levels that were either suprathreshold or subthreshold for evoking the site-specific movement. Electromyographic activity could be evoked at suprathreshold and near-threshold current levels, but not at the subthreshold current levels used here. Significant border shifts ranged from 210 to 670 μm. In each case in which shifts occurred, there appeared to be expansion of the movement represented at the repetitively stimulated site. The effects were progressive and reversible. These results suggest that at least under these unusual experimental circumstances, large representational changes can be generated very rapidly within motor cortex in the absence of any evident peripheral feedback.