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Abstract:
According to previous experiments and to literature data,
taste cortical areas were shown to lie in the peri Sylvian region,
including insula, inferior parts of pre and postcentral gyri, and
the opercular part of superior temporal gyrus (Cerf et al.,
abstracts de congrès, Kinomura, Murayama, Kobayakawa). The
two studies presented here assess the lateralization and plasticity
of gustatory processing. We used a 3 Tesla whole body MR scanner
allowing echo planar imaging. Stimulation consisted of 5 minutes
experiments including 2 periods with tastant alternating with
water. Solutions were presented via plastic tubes as bolus of
50µl every 3 s and were freely swallowed by the subjects. We
processed the data using the correlation of MR signal to a
psychophysical indicator, the subject's perception profile,
recorded with the finger-span method. Ten subjects, 5 left-handed
and 5 right-handed (laterality was assessed with the Dellatolas
test, derived from Edinbourgh inventory) participated in the
lateralization study. We found a bilateral activation of the
superior level of insula (according to our bilateral stimulation)
associated to a unilateral activation of the inferior level of
insula in the subject's dominant hemisphere (e.g. the right
hemisphere of left-handed and the left hemisphere of right-handed
subjects). This unilateral activation is the first evidence of a
functional lateralization of gustatory processing. Four subjects
participated in the plasticity study. They were subjects for two
parallel experiments, a learning experiment on novel tastes, and
the fMRI study. Learning study consisted in repeated psychophysical
measurements of subjets' sensitivity for novel tastes. Some tastes
were neophobic, some were good "at first sight". Each subject
underwent 3 fMRI experiments, one before any learning process, one
between the second and third learning sessions, one after the
learning completion. Voxels in peri insular .... Pourcentage of
activation in peri insular region (compared to the whole brain) was
correlated to subject's hedonic value evolution.
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