Spring 2005 Physics Colloquium
April 29; Friday, PAS 220, 3pm
James Kakalios
University of Minnesota
Conductance Fluctuations: From Amorphous Silicon to the Cerebral Cortex
Studies of conductance fluctuations can reveal important information
concerning defect kinetics and transport mechanisms not revealed in
conventional electronic techniques. Studies of conductance fluctuations
(1/f noise) in hydrogenated amorphous silicon (a-Si:H) by my laboratory
have been interpreted as reflecting the dynamics of inhomogeneous
current filaments, believed to arise from medium and long-ranged
structural disorder. The non-Gaussian statistics of the 1/f noise is
characterized by measurements of the second spectra, obtained from
Fourier transforms of the time-dependent fluctuations of the 1/f noise
power. The second spectra in a-Si:H films itself displays a 1/f
frequency dependence, reflecting electronic correlations between
differing current microchannels. That is, in a-Si:H, the 1/f noise has
1/f noise! These studies have been extended to analyze local field
potentials recorded from rats perfroming neurological studies. Brains
consist of non-linear neurons linked together in complex networks,
suggesting that neural systems will show cooperative dynamics. We have
discovered that the correlation coefficients of the power spectra of the
voltage fluctuations recoded while the rat is performing a variety of
tasks are highly sensitive to transient coherent oscillations that can
typically only be discerned by filtering techniques. These results are
consistent with the observed non-Gaussian second spectra (obtained from
Fourier transforms of the noise power fluctuations) and indicate that
this novel technique may be useful in measuring functional interactions
in neural systems.