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Abstract:
Previous research has shown that gamma-band (20-50 Hz)
activity covaries with temporal binding of auditory stimuli
(PNAS,91:11748-51,1994). To test for similar correlations in the
somatosensory system, we recorded brain activity using
magnetoencephalography (MEG) while subjects identified two tactile
stimuli. Using a whole-head MEG system (BTi), neuromagnetic
recordings were obtained for 7 sighted and 7 congenitally blind
right-handed adults while attending to tactile "taps" delivered to
the right index finger. Taps lasting 2 msec were generated by a
flat pizeoelectric surface. Stimuli consisted of single taps or
paired taps at varying intrapair intervals
(3,6,9,12,15,18,21,24,30,36msec). Evoked responses were averaged,
analyzed by Fast Fourier Transform (FFT), and filtered. The average
response to a single stimulus consisted of at least two 20-50 Hz
oscillatory cycles. As previously observed in the auditory system,
experimental and perceptual results indicate a critical intrapair
interval of approximately 12 msec. At shorter intervals, only one
20-50 Hz response was observed. At intervals longer than 12 msec, a
second 20-50 Hz response was observed, which correlated with the
identification of two distinct taps. As in the auditory system,
these results obtained from the somatosensory system indicate that
gamma-band oscillatory activity is a neurophysiological correlate
of early temporal processing, suggesting that the CNS employs a
central gamma-band timing mechanism for cognitive binding. Support:
Charles A. Dana Foundation, McDonnell-Pew Foundation.
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