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Abstract:
Event related potentials (ERPs) are commonly used to study
the temporal dynamics of the functioning human brain. In the
interest of probing the neural response characteristics
corresponding to stimulation at many different positions across the
visual field, we have developed a new methodology which combines
two proven techniques: multi-electrode recording and pseudo-random
m-sequence analysis. A dense array of 49 electrodes were placed on
the posterior of the scalp while the subject fixated at the center
of a "dartboard" stimulus spanning the central 15 degrees of the
visual field. The cortically scaled stimulus consisted of 60
patches which were all modulated simultaneously and independently
with an orthogonal m-sequence. Four 16 minute sessions were
averaged together to obtain the voltage response across the entire
electrode array corresponding to each stimulus patch. To study the
spatial as well as temporal dynamics of neural function, we have
also developed a novel algorithm to improve the accuracy of ERP
dipole source localization procedures. This algorithm assumes
commonality in the time-courses of patches at a similar stimulus
eccentricity thereby reducing the ambiguity in the solution. Upon
localizing the neural sources corresponding to 12 patches in a
given annulus, the solution showed clear retinotopy. This result
agrees with imaging data and also yields the temporal information
associated with each neural source. By combining techniques using
multiple recording electrodes and multiple stimulus patches, we
have developed a powerful means to study the dynamics of neuronal
activation underlying cognitive or stimulus manipulations.
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