Marcus <73370.2242 at CompuServe.COM> writes:
>How far into the cortex does a scalp electrode detect electrical
>activity ? That is, what is the resistance of brain tissue, and
>how far does and action potential or a epsp "travel" through the
>brain (apart from its propagation along neural processes) ? Any
>ideas ?
To answer your question briefly, the scalp-recorded EEG at a given
electrode site represents the temporal and spatial summation of PSPs
from many cortical pyramidal cells. The EEG "sources" may not all
necessarily be in the cortex under the electrode; volume conduction
through the brain allows sources at other [distant] locations to be
detected at that given electrode. A good reference on this topic is
Paul Nunez's book, "Electric Fields of the Brain".
Kevin
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Kevin Spencer
Cognitive Psychophysiology Laboratory and Beckman Institute
University of Illinois at Urbana-Champaign
kspencer at s.psych.uiuc.edu
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