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Physics Colloquium - Monday, Feb. 2nd, 2009,
Center; Refreshments at 3:30 P.M. in
Phase transitions and stimulus processing in the brain
National Institutes of Health
Recent experiments demonstrate that the activity of neurons in
the brain has statistical properties expected near the critical point of
a phase transition. These observations raise the question; why might
the brain operate at such a critical point? Theories and models predict
optimized information processing, but experimental support for these
ideas has been lacking.
Here, we experimentally test the prediction that the dynamic range, i.e.
the range of stimulus intensities the neural network can process, is
greatest at a critical point. We study brain tissue cultures and
compare our results to a simple numerical model. We tuned the system
through a phase transition using drugs that alter the relative influence
of excitatory and inhibitory interactions between neurons. In agreement
with our model, the critical point of the phase transition corresponds
to the situation where excitatory and inhibitory interactions balance
each other. We find that dynamic range is indeed maximized when the
neural tissue is closest to the phase transition.