| Recent experiments demonstrate that neural activity in brain tissue has statistical properties expected near the critical point of a phase transition. These observations raise the question, why might the brain operate near a phase transition? Does this state give the brain functional advantages? Here, we approach this question with experiments; we quantify the ability of living neural tissue to process stimuli as we tune the tissue through a phase transition. We tune a network of living neurons through a phase transition by altering the relative influence of excitatory and inhibitory interactions between neurons using drugs. In agreement with a simple model, the critical point of the phase transition corresponds to the situation where excitatory and inhibitory interactions balance each other. Our main finding is that the dynamic range of the tissue is maximized at the critical point of the phase transition. The dynamic range is defined as the range of stimulus amplitudes that the tissue is capable of responding to without saturating. We stimulate the tissue with electrical shocks and record the resulting neural activity with an array of 60 microelectrodes. This finding supports the hypothesis that a brain operating near a phase transition may be better able to process stimuli arriving from the senses. |
|