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Abstract:
The congenitally blind are slower than the sighted at mental
rotation and mirror-image discrimination of tactile stimuli,
suggesting that visual imagery may facilitate performance of these
tasks (1). We asked whether visual cortical processing is normally
recruited under such conditions. Positron emission tomography,
using O-15 water, was performed while normal male subjects verbally
reported whether a letter pressed onto the right index fingertip at
various orientations was mirror-reversed or not. Debriefing
indicated that subjects mentally visualized the tactile stimuli.
Relative to a control condition with verbal output but no tactile
stimulation, this task significantly increased regional cerebral
blood flow in areas of somatosensory, posterior parietal and
parieto-occipital cortex in the left hemisphere. Some of the
posterior parietal foci were near those recruited by mirror-image
discrimination of visual alphanumeric stimuli (2). This posterior
parietal activation during both visual and tactile mirror-image
discrimination is consistent with earlier reports of
parieto-occipital cortical involvement during visual (3) and
tactile (4,5) discrimination of orientation. These findings could
reflect either use of visual imagery during tactile spatial
operations, or modality-independent recruitment of parietal
multisensory areas for spatial processing. 1. Marmor & Zaback,
JEP:HPP 2:515-21,1976 2. Alivisatos & Petrides,
Neuropsychologia 35:111-8,1997 3. Sergent et al., Brain
115:15-36,1992 4. Sathian et al., NeuroReport 8:3877-81,1997 5.
Zangaladze et al., Nature 401:587-90,1999
Supported by NEI.
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