Fractal Features of Dark, Maintained, and Driven Neural Discharges in the Cat
Visual System
S. B. Lowen, T. Ozaki, E. Kaplan, B. E. A. Saleh, and M. C. Teich
Methods: A Companion to Methods in Enzymology, in press (2000) [PS]
[E-PRINT (Biological Physics)]
Download from: http://people.bu.edu/teich/enz/paper.ps
or from: http://xxx.lanl.gov/abs/physics/9910025
ABSTRACT
We employ a number of statistical measures to characterize neural discharge
activity in cat retinal ganglion cells
(RGCs) and in their target lateral geniculate nucleus (LGN) neurons under
various stimulus conditions, and we
develop a new measure to examine correlations in fractal activity between
spike-train pairs. In the absence of
stimulation (i.e., in the dark), RGC and LGN discharges exhibit similar
properties. The presentation of a constant,
uniform luminance to the eye reduces the fractal fluctuations in the RGC
maintained discharge but enhances them in
the target LGN discharge, so that neural activity in the pair no longer
mirror each other. A drifting-grating stimulus
yields RGC and LGN driven spike trains similar in character to those
observed in the maintained discharge, with
two notable distinctions: action potentials are reorganized along the time
axis so that they occur only during certain
phases of the stimulus waveform, and fractal activity is suppressed. Under
both uniform-luminance and
drifting-grating stimulus conditions (but not in the dark), the discharges
of pairs of LGN cells are highly correlated
over long time scales; in contrast discharges of RGCs are nearly
uncorrelated with each other. This indicates that
action-potential activity at the LGN is subject to a common fractal
modulation to which the RGCs are not
subjected.
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Malvin Carl Teich, Professor
Departments of Electrical & Computer Engineering,
Physics, Biomedical Engineering, and
Cognitive & Neural Systems
Boston University
8 Saint Mary's Street
Boston, Massachusetts 02215-2421, USA
EMAIL: teich@bu.edu
TEL: (617)-353-1236; FAX: (617)-353-1459
URL: http://people.bu.edu/teich
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