Acknowledgement

1

Introduction We study the transition from
discrete to continuous movements by investigating
brain activity at 21 different movement rates
ranging from 0.5 to 2.5Hz. For this purpose two
separate EEG and MEG experiments were performed
using a continuation paradigm. One of the
subjects also participated in an fMRI study with
a similar experimental setup. Independent
component analysis (ICA) was used to separate the
spatiotemporal signals resulting in either two or
three different response types for EEG and MEG,
respectively. Using the gray-white matter
boundary extracted from an MRI scan as constraint
for the locations and directions of primary
currents we localized the origins of two of the
three MEG response types and found a division of
the region of activation identified with fMRI.

Methods Fullhead EEG and MEG recording 84
electrode EEG system SAM Technologies, San
Francisco, CA), 143 SQuID MEG system (CTF Inc.,
Port Coquitlam, BC) Behavior was measured as
pressure changes in an air cushion placed under
the right index finger Continuation paradigm
20 cycles synchronization with an auditory
metronome, 20 cycles continuation at the same
rate without metronome 21 different rates
0.5-2.5Hz in steps of 0.1Hz 4 subjects in each
experiment Blind source separation was performed
using the ICA Toolbox from the Swartz Center for
Computational Neuroscience at UCSD Freesurfer
was used to construct the surface that represents
the gray-white matter boundary fMRI from the
same subject was used to identify sensory-motor
areas Regions of activity were computed as
overlap between forward solutions from the
surface normals and patterns extracted from MEG
data
Conclusions ICA is an effective method for
separating temporally and spatially overlapping
responses in complex behavioral experiments with
consistency across subjects and modalities. The
dropout of slow wave activity seen in response
type II at higher rates indicates a
simplification of the movement related activity
and may be associated with a transition between
discrete and continuous movements. Using the
gray-white matter surface as a constraint for the
location and direction of source currents
produces anatomically meaningful areas of
activity that are consistent with results from
fMRI. The distinct split between the origins of
response type I and III, and the difference of
their activation profile in time shows that
combining imaging modalities strongly enhances
the spatial and temporal resolution of brain
activity recordings.

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Acknowledgement Work supported by NINDS (grant
NS39845), NIMH (grants MH42900 and 19116) and the
Human Frontier Science Program.