The motor cortex and facial expression: new insights from neuroscience.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing nonhuman primate neuroanatomy and human clinical and imaging observations
PubMed 15335441 · doi:10.1097/01.nrl.0000138734.45742.8d
What was done
This narrative review synthesizes findings from nonhuman primate tract-tracing and neuroanatomical studies alongside human cortical stimulation, functional neuroimaging, localized surgical resection, and clinical neurology observations to map cortical representations and corticobulbar projections controlling facial muscles.
What was found
No quantitative numerical data are reported in the abstract. Qualitatively, the review describes five distinct cortical facial representations in the frontal and anterior cingulate cortex: M1, ventral lateral premotor cortex (LPMCv), supplementary motor cortex (M2), rostral cingulate motor cortex (M3), and caudal cingulate motor cortex (M4). M2 and M3 reside in the anterior cerebral artery territory and preferentially send bilateral projections to facial motor subnuclei innervating upper facial musculature. M1, LPMCv, and M4 (with M1 and LPMCv in the middle cerebral artery territory) preferentially send contralateral projections to lower facial musculature, aligning with the classic clinical finding of contralateral lower facial paralysis with upper facial sparing after middle cerebral artery infarction.
Why it matters
This framework links neuroanatomical connectivity discovered in nonhuman primates to human stroke presentations and movement disorders, providing an anatomical mechanism for differential voluntary and emotional control of facial movements.
Limits
The abstract reports no original experimental data, sample sizes, or quantitative effect estimates. Key structural connectivity details rely predominantly on nonhuman primate tract-tracing rather than direct human neuroanatomical tracing.
Cited by
- supports The upper part of the human face displays more involuntary, truthful emotional expression than the lower part of the face, which is under greater voluntary motor control.