Medical Hypotheses
Volume 74, Issue 3 , Pages 508-509, March 2010

Facial paralysis: A critical review of accepted explanation

Department of Physical Medicine and Rehabilitation, Harvard Medical School, Spaulding Rehabilitation Hospital, 125 Nashua St., Boston, MA 02114, United States

Received 27 September 2009; accepted 4 October 2009. published online 12 November 2009.

Summary 

Historically, paralysis of facial muscles has been divided into “upper motor neuron injury” and “lower motor neuron injury”. Patients who experience a stroke in the cortex or internal capsule have UMN injury and cannot purse their lips or smile on command. They are, however, able to wrinkle their forehead, raise their eyebrows, and completely close their eyes. Patients with LMN injury, in addition to the aforementioned impairments cannot raise their eyebrows. The classical explanations for these clinical findings are that the upper facial muscles receive bilateral innervation from the cerebral cortex and the lower facial muscles receive only unilateral innervation from the contralateral cerebral cortex. However, a review of the basic science literature indicates that commonly accepted explanations and the pattern of cortical projections are not consistent with anatomical studies. Studies in monkeys demonstrate that both the upper facial nucleus and the lower facial nucleus receive bilateral cortical projections. As well, there is no direct anatomical evidence in human beings that the facial nucleus (upper or lower) receives any innervation from the cortex.

Abbreviations: M1, primary motor cortex, M2, supplementary motor area, M3, rostral cingulated motor cortex, M4, caudal cingulated motor cortex, LPMCd, dorsal lateral-premotor cortex, LPMCv, ventral lateral-premotor cortex

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PII: S0306-9877(09)00685-9

doi:10.1016/j.mehy.2009.10.010

Medical Hypotheses
Volume 74, Issue 3 , Pages 508-509, March 2010