| |
Abstract:
Abstract: The present study employed a frequency analysis to
"tag" activity arising from imagined rhythmic movements and
attempted to locate approximately its cortical sources. Subjects
synchronized overt and imagined taps with the onsets of brief
visual stimuli presented at a constant rate of 1.25 Hertz (Hz). The
taps alternated between the right and left index fingers at a rate
of 0.625 Hz. We recorded event-related brain potentials (ERPs) from
59 electrode sites across the scalp and electromyographic (EMG)
activity from the finger flexor muscles. After laplacian transforms
to reduce the contribution of noncortical sources, the ERP
recordings were converted to the frequency domain, and topographic
maps were constructed of power at the frequency (0.625 Hz) of
alternation between left and right taps. Two prominent power loci
occurred in each hemisphere for both overt taps and imagined taps
without EMG, one over sensorimotor cortex and the other over
posterior parietal cortex, with the homologous loci in opposite
hemispheres arising from oscillations 180 degrees out of phase.
Power was greater over all locations for overt than imagined taps,
greater over sensorimotor than posterior parietal cortex for overt
taps, and the opposite for imagined taps. These findings
demonstrate the activation of sensorimotor cortex without EMG
during motor imagery and highlight the role of posterior parietal
cortex in both overt and imagined movement.
|
