The temporal and spatial processing of face perception in normal subjects w
as traced by magnetoencephalography (MEG) and electroencephalography (EEG).
We used 5 different visual stimuli: (1) face with opened eyes, (2) face wi
th closed eyes, (3) eyes, (4) scrambled face, and (5) hand, and they were s
hown in random order. Subjects were asked to count the number of hand stimu
li. To analyze the complicated brain responses to visual stimuli, we used b
rain electric source analysis (BESA) as the spatio-temporal multiple source
model. In MEG recording, the 1M and 2M components were identified in all s
ubjects. The 1M component was recorded to all kinds of stimuli. The 2M comp
onent was clearly identified only to face stimulation in all subjects, but
to eyes stimulation in only 3 subjects with a small amplitude. The 2M compo
nent was not identified to scrambled face nor hand stimulation. The 2M comp
onent was recorded from the right hemisphere in all subjects, but in only 5
of 10 subjects from the left hemisphere. The mean peak latencies of the 1M
and 2M components were approximately 132 and 179 ms, respectively. The int
erpeak latency between 1M and 2M was approximately 47 ms on average but the
interindividual difference was large. There was no significant difference
of the 2M latency between face with opened eyes and face with closed eyes.
The IM component was generated in the primary visual cortex in the bilatera
l hemispheres, and the 2M component was generated in the inferior temporal
cortex, around the fusiform gyrus. In the EEG recording, face-specific comp
onents, positive at the vertex, P200 (Cz), and the negative at the temporal
areas, N190 (T5') and N190 (T6'), were clearly recorded. The EEG results w
ere fundamentally compatible with the MEG results. The amplitude of the com
ponent recorded from the right hemisphere was significantly larger than tha
t from the left hemisphere. These findings suggest that the fusiform gyrus
is considered to play an important role in face perception in humans, and t
hat the right hemisphere is more dominant. Face perception takes place appr
oximately 47 ms after the primary response to visual stimulation in the pri
mary visual cortex, but the period of information transfer to the fusiform
gyrus is variable among subjects. Detailed temporal and spatial analyses of
the processing of face perception can be achieved with MEG. (C) 1999 Elsev
ier Science B.V. All rights reserved.