mvcs at gramercy.ios.com (Jeff Baldwin) writes:
>I haven't the time necessary to spend obtaining and reading the book,
>but I _AM_ interested: Why just the pyramidal cells. They aren't the
>only ones with activity.... why is EEG from only those (or primarily
>those) cell types?
The apical dendrites of cortical pyramidal cells are aligned perpendicular
to the cortical surface -- this allows the PSPs in the apical dendrites
of many (millions?) cortical pyramidal cells to summate spatially, and
thus be detectable on the cortical or scalp surface. The dendrites of
other cell types are generally aligned in random directions, so that
the PSPs in these dendrites cancel each other (when observed from an
electrode that is "far" away).
This is not to say that everything in the EEG is from cortical pyramidal
cells -- for instance, auditory brain-stem evoked potentials aren't. But
to detect these potentials, you have to average thousands of EEG epochs
to improve the signal-to-noise ratio.
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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