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Abstract:
The perception of faces has been connected to activation of an area in the anterior lateral
part of the fusiform gyrus. Results regarding a right sided lateralisation for perception of
emotionally expressive faces however have been contradictory. We studied the activation
induced by a task which combines perception of happy, sad and neutral faces with congruent
or dissonant mouth movements of the subject.
9 healthy subjects were examined lying in a 1,5 Tesla Siemens Magnetom VISION scanner
(768 T2*-weighted echo-planar measurements, TE=39ms, 2.6926sec for 28 4mmslices,
1mm gap, flipangle 90°, 64x64 pixel (3x3mm) in axial orientation). Via a mirror
system subjects were presented fotos of happy, sad and neutral faces, 12 different ones of
each category, each 3 times, with the instruction to imagine meeting the depicted in a
neutral social situation and to move the corners of the mouth a) upwards, b) downwards,
c) not at all as indicated by arrows in the respective direction on both sides of the face.
Fotos were presented in randomized order for 5s each with 13s rest time inbetween.
Facial movements were recorded with a video camera. fMRI-data were evaluated with
SPM96. In a separate session with the same paradigm outside the scanner subjects were
asked about their emotions and the degree of difficulty of the facial movements using a
PC-aided paradigm.
Seeing faces instead of the blank screen activated bilaterally large occipital areas including
the fusiform gyrus and also the sup. temporal lobe, BA6 and the right sup. temporal
gyrus. There was no significant difference between emotionally expressive and neutral
faces on a whole. However happy faces in contrast to sad faces activated left BA 18,
BA19 and BA37 (fusiform and ligual gyrus). Amount and lateralisation of occipital activity
was strongly influenced by the task affordances. When subjects had to make no mouth
movement they showed more rightsided activation of primary and higher order visual
areas (fusiform, sup., medial and inferior occ. gyrus, the precuneus and the calcarine sulcus)
than with concomittant facial movements although seeing the same fotos. Congruent
mouth movements, i.e. similar to those depicted, increased primary visual cortex activity
bilaterally. Also bilateral occipital activation occured in positive correlation with perceived
pleasantness and happiness due to the various picture/movement combinations.
We propose that the published contradictory results regarding lateralisation of facial
expression perception are caused by differences between tasks. Our results point to a task
dependant hemispheric specialization with right sided areas being more active during
perception and left sided areas more during action demanding situations and an interaction with emotional effects induced by the stimuli.
