Central Facial Palsy - Examination Techniques

Examination Techniques

Through electrophysiological studies and neuronal tracing, these characteristics do not fully support the typical person with central facial palsy. Often, transcranial magnetic stimulation (TMS) is used to understand the bilateral corticonuclear projections of the lower facial motor neurons. This idea using bilateral innervation to the upper facial motor neurons is rarely tested by humans because of the afferent fibers in the trigeminal nerve are distributed over the head and face and could cause damage. Supranuclear motor innervation of the facial musculature is difficult to examine because the circuitry is quite complex, only a few cases are described in literature of central facial palsy and the absence of bilateral perioral muscle responses after TMS of the affected hemisphere. EMG responses are often used to observe the upper facial muscles, however, it is difficult to elicit by TMS, which often works by examining the motor cortex and recording the motor stroked potentials. At high stimulation strengths, this often will excite the trigeminal sensory afferents and will trigger a blink reflex. From the blink reflex, it contains the R1 ipsilateral and bilateral R2 component. The reflex can then be recorded in the lower parts of the brain. The R1 component will limit the evaluation of the ipsilateral responses in the lower facial muscles.