The palmomental reflex, an involuntary contraction of the mentalis muscle of the chin caused by stimulation of the thenar eminence, can be tested easily and rapidly. Its presence may alert the clinician to the possibility of cerebral pathology. However, the reflex is often present in normal people and may be absent in disease states. Testing merely for the presence or absence of the reflex therefore lacks both specificity and sensitivity. A strong, sustained, and easily repeatable contraction of the mentalis muscle, which can be elicited by stimulation of areas other than the palm, is more likely to indicate cerebral damage.
Since the original description, several methods of eliciting the reflex have been proposed. Most authors suggest stroking the thenar eminence in a proximal to distal direction using a sharp object such as the pointed end of a reflex hammer, key, paper clip, or fingernail. The stimulus should cause discomfort but not pain. Contraction of the ipsilateral, contralateral, or both mentalis muscles may then be observed.