Input-output relationships of the primary face motor cortex in the monkey (Macaca fascicularis)

Abstract

1. Somatosensory afferent input and its relationship with efferent output were examined in the primary face motor cortex (MI) and adjacent cerebral cortical areas. Excitatory afferent inputs were tested in a total of 1,654 single neurons recorded in awake or anesthetized monkeys (Macaca fascicularis), and output was characterized in these same monkeys by the movement and EMG responses evoked by intracortical microstimulation (ICMS) at the neuronal recording sites. 2. Most neurons in the MI area responded to light tactile stimulation of the orofacial region, especially the upper lip, lower lip, and tongue. Although contralateral afferent inputs predominated, 21% of the neurons received ipsilateral or bilateral orofacial inputs. The afferent input evoked by tactile stimulation of the upper and lower lips was represented especially at the medial border and the input from the tongue at the lateral border of MI. However, in most regions of MI between the medial and lateral borders, an intermingling of tactile inputs from different orofacial areas occurred. Multiple representation of tactile input from the same orofacial area was found in several, often quite separate, intracortical sites in MI. 3. Only a small proportion of the MI neurons could be activated by the deep stimuli used (e.g., stretch and pressure applied to muscle, passive jaw movement, low-intensity stimulation of hypoglossal nerve) from the orofacial region. Those neurons which did respond to these low-threshold deep inputs were not clearly segregated from those which responded to tactile input, although most of the neurons receiving deep input were located in the rostral part of MI. 4. A somatotopic pattern of representation of orofacial tactile input was more obvious in the primary face somatosensory cortex (SI). At the medial border of SI, the periorbital area was represented, then followed laterally in sequence the tactile representation of the upper lip, lower lip, and intraoral area. Contralateral afferent inputs predominated, but as in MI, a considerable proportion of SI neurons received ipsilateral or bilateral orofacial inputs. Few neurons in the region explored (areas 3b, 1, and 2) responded to deep orofacial stimuli. 5. Tactile input also dominated the input patterns of neurons in the premotor cortex (PM). Most neurons received ipsilateral or bilateral orofacial afferent inputs and no clear somatotopic pattern was noted. Several PM neurons were also activated by visual stimuli. 6. Muscle twitches evoked by ICMS were limited to MI.(ABSTRACT TRUNCATED AT 400 WORDS)

Noxious Lingual Stimulation Influences the Excitability of the Face Primary Motor Cerebral Cortex (Face MI) in the Rat

“…We have already reported a close input-output coupling within the face MI with regard to the low-threshold mechanoreceptive fields of face MI neurons and the ICMSevoked motor effects at the face MI neuronal recording sites (Huang et al 1989;Murray and Sessle 1992). This evidence pointing to a close match between the site of noxious stimulation and the face MI site of depressed evoked motor response is also consistent with recent findings from studies of the effects of noxious stimuli on the excitability of the forelimb MI (Farina et al 2001;Urban et al 2004).…”

“…Glass-insulated tungsten microelectrodes were used for ICMS (12 pulses of width 0.2 ms, 333 Hz, total train duration 33.2 ms) as previously described (Adachi et al 2007;Huang et al 1989;Murray and Sessle 1992). The face MI (see following text) was grossly mapped by applying ICMS through the microelectrode at Յ60 A at every 200 m of depth in each transdural microelectrode penetration track in a systematic series of penetrations (each separated by 0.5 mm, maximum penetration depth: 6,200 m) made by a micropositioner.…”

Neurobiological Mechanisms Involved in Sleep Bruxism

“…In recent years, mapping of specific cortical masticatory sensorimotor areas has improved our understanding of the neuronal masticatory network (Nakamura et al, 1976;Lund et al, 1984b;Huang et al, 1989a). In primates, RJMs are triggered by microstimulation of the primary face motor cortex (MI), primary face somatosensory cortex (SI), and cortical masticatory areas (CMA) (Lund and Lamarre, 1974;Huang et al, 1989a). It should also be noted that the CMA is not exclusive to the genesis of rhythmic chewing, since micro-stimulation in these other cortical areas in awake monkeys also triggers swallowing, an activity that has also been observed in close to 60% of SB and sleep RMMA episodes in humans (Martin et al, 1999;Miyawaki et al, 2002 ([accepted]).…”

Modulation Dynamics in the Orofacial Sensorimotor Cortex during Motor Skill Acquisition

“…The orofacial sensorimotor cortex is crucial for orofacial motor control (Lowe, 1980;Huang et al, 1989b;Murray and Sessle, 1992a;Lin et al, 1994;Yao et al, 2002;Hatanaka et al, 2005;Sessle, 2006;Arce et al, 2013). Specifically, the orofacial primary motor cortex (MIo) and somatosensory cortex (SIo) exhibit neuroplasticity related to acquisition of novel oromotor skills, intraoral manipulations, and pain (Murray et al, 1991;Lin et al, 1993;Svensson et al, 2003Svensson et al, , 2006Sessle et al, 2005Sessle et al, , 2007AviviArber et al, 2010AviviArber et al, , 2011Arima et al, 2011).…”