Investigating the production of emotional facial expressions: a combined electroencephalographic (EEG) and electromyographic (EMG) response.

Korb, S., Grandjean, D., & Scherer, K.R. (2008)

Proceedings of the 8th IEEE International Conference on Automatic Face and Gesture Recognition (FG 2008), September 17-19, 2008, Amsterdam, the Netherlands, ISBN 978-1-4244-2154, 1-6.

Describes dichotomy between spontaneous & posed expression and blends of these.  A blend may be the result of emotional regulation for example decreasing intensity or duration.  Ekman ( refs  7 & 8 from this paper) suggest that spontaeous emotional facial expressions show less irregularities ( pauses & stepwise intensity changes) 

facial mimicry  - Dimberg paper. EMG & EEG used to demonstrate muscle involvement in mimicry ( Achaibou et al downloaded) Mcintosh et al, printed)

neural basis 

innervation of facial muscles

temporalis, masseter,  internal & external pterygoid, are innervated by the 5th

eye muscles innervated by 3,4 & 6

facial nerve ( 7) innervate most of the muscles. 

'facial nucleus ( pons)  similar across man, non-human primates, and lower animals with the difference that it contains more neurons innervating muscles of the mouth and lower face in man, allowing for a high degree of fine and controlled movement as required for speech, and more neurons innervate the upper face and auricular muscles in lower animals'

motor control of facial muscle

voluntary movements of the lower face muscles  ( allowing for mouth movements) originate in the contralateral motor areas , ( primary motor cortex (M1) & lateral premotor cortex (LPMC) or along the corticobulbar tract descending to the facial muscles.

voluntary movement of upper face originate in the same place but project ipsilatareally as well as contralaterally.

spontaneous facial expressions project from subcortical structures including the basal ganglia, innervating both ipsi & contralateral facial nuclei via extrapyramidal tracts passing through the brainstem reticular formation  ( ref 12 Gazzaniga et al 1990 & ref 29 Purves et al, 1999)

'in addition to the direct pyramidal tract, cortical motor areas also project bilaterally onto interneurons of the reticular formation ( ? KRO the mechanism that  can modulate  spontaneous expression.' 'interestingly these indirect pathways influence mainly motor neurons of the facial muscle that control the upper face'

recent tracing studies in non humans (ref 25) at least 5 cortical motor areas project directly onto the facial nuclei

MI ( primary motor cortex)

LMPC lateral premotor cortex

SMA supplementary motor area

 caudal cingulate motor area ( CMCc ) &  rostral cingulate motor area (CMCr)

M1, LPMC &CMCc project mainly to the contralateral facial nucleus via the direct cortico bulbar tract and to mainly the motor neurons of the lower face muscles.

SMA & CMCr synapse  mainly onto ipsi and contralateral upper facial facial nuclei.

nb these are the main projections rather than the only projections.

Refs 8, 11 & 12 concerned with hemisphere involvement  e.g. right hemisphere as the source for production of at least posed facial expression.

Neurological evidence

Implanted electrodes/ depth electrodes  in epilepsy (refs 10, 20 location of seizure focus) 

note : only the left side stimulated 

 left area rostral to  supplementary motor cortex (SMA) smiling and laughing repeatedly elicited in this specific area.  Smiling was produced by lower currents than laughter, suggesting that smiling and laughter 'might involve similar mechanisms and are closely related on a single continuum' (ref 10).

Double dissociation between emotional facial paresis and voluntary facial paresis (ref 16 Hopf et al 1992 for spontaneous  also refs 17&25)  Spontaneous involves lesions of thalamus, striatocapsular area, frontal subcortical white matter, insula, and medial frontal lobe including the supplementary motor area (SMA)

refs to the article in Brain topography on the Beritschaftspotential