Palmomental reflex and palmosubmental reflex

Background: Palmomental reflex response is considered as a primitive reflex and associated with pathological states. Reflex activation of mental and submental muscles with median nerve stimulation in the healthy aged and demented population has not been reported before, nor have there been any reports pertaining to reflex response of the orbicularis oris and masseter muscles.Method: In this study, we recorded activity from mental, submental, orbicularis oris and masseter muscles with bipolar surface electrodes by means of sub-threshold stimulation of the median and radial nerves in a population of dementia (n=18) and healthy-aged controls (n=20).Results: All subjects displayed palmosubmental and palmomental reflex responses at approximately the same latency (80-90 msec). The orbicularis oris and masseter muscles reflex responses were slightly longer in their latencies and the amplitude of the reflex responses less when comparing the mental and submental reflex responses. Needle electrode recordings from 2 patients resulted in mental and submental reflex responses at the same latency (with clear-cut responses). Radial nerve stimulation at the wrist evoked muscle reflex responses with later latency and less amplitude.Conclusion: Palmomental reflex response might be associated with functions such as mouth-opening or swallowing rather than being a primitive reflex. These reflexes may open a venue to investigate the physiology of hand and mouth coordination.