Recently it has been proposed that corticobulbar innervation of the lower facial muscles is bilateral, that is from both right and left sides of the motor cortex. The objectives of this study were, i) to evaluate the corticonuclear descending fibers to the perioral muscles and, ii) to determine how central facial palsy (CFP) occurs and often recovers rapidly following a stroke. Eighteen healthy volunteers and 28 patients with a previous history of a stroke and CFP (mean ages: 51 and 61 years) were investigated by TMS (transcranial magnetic stimulation) with a figure of eight coil. Intracranial facial nerve and cortical motor evoked potentials (MEPs) were recorded from the perioral muscles. The periorbital MEPs were also studied. The absence of MEPs in both perioral muscles with TMS of the affected hemisphere was the most obvious abnormality. Also, central conduction time was significantly prolonged in the remaining patients. The mean amplitude of the affected hemisphere MEPs was diminished. The amplitudes of the unaffected hemisphere MEPs recorded from the intact side were enhanced especially in the first week following the stroke. During TMS, only the blink reflexes were elicited from the periorbital muscles due to stimulus spreading to trigeminal afferent nerve fibers. It is concluded that perioral muscles are innervated by the corticobulbar tract bilaterally. CFP caused by a stroke is generally incomplete and mild because of the ipsilateral cortical and multiple innervations out of the infarction area, and recovers fast through cortical reorganisation.
Hand motor representation area expands towards the area of the perioral facial motor cortex in patients with peripheral facial paralysis (PFP) and in hemifacial spasm cases treated with botulinum toxin. In this current study, we aimed to investigate the changes both in the ipsilateral and contralateral facial motor cortex areas in patients with PFP with transcranial magnetic stimulation (TMS). Thirty healthy individuals and 41 patients with unilateral PFP with partial or total axonal degeneration participated in this study. Motor evoked potentials (MEPs) of perioral muscles elicited by TMS of the intracranial portion of the facial nerve and motor cortex, were recorded. TMS was delivered through a figure-of-eight coil. Mapping of the cortical representation of perioral muscles were also studied in 13 of 41 patients and in 10 of control subjects. Mean amplitude of the intact perioral MEPs elicited by the ipsilateral hemisphere TMS, was significantly higher in patients than the control subjects. There was also a mild enlargement of the mean cortical representation area of intact perioral muscles on both hemispheres though it was not significant. We have concluded that there was a cortical reorganization in the hemisphere contralateral to the paralytic side resulting in an increase at corticofugal output related to intact perioral muscles.
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