Intracellular and computational evidence for a
dominant role of internal network activity in
cortical computations.
Alain Destexhe
Current Opinion in Neurobiology 21: 717-725, 2011.
Special issue "Networks, Circuits and Computation"
(edited by Feldman D., Feller M. and Dayan P.)
Abstract
The mammalian cerebral cortex is characterized by intense
spontaneous activity, depending on brain region, age and
behavioral state. Classically, the cortex is considered as being
driven by the senses, a paradigm which corresponds well to
experiments in quiescent or deeply anesthetized states. In awake
animals, however, the spontaneous activity cannot be considered
as "background noise'', but is of comparable -- or even higher --
amplitude than evoked sensory responses. Recent evidence suggests
that this internal activity is not only dominant, but it shares many
properties with the responses to natural sensory inputs, suggesting
that the spontaneous activity is not independent of the sensory
input. Such evidences are reviewed here, with an emphasis on
intracellular and computational aspects. Statistical measures,
such as the spike-triggered average of synaptic conductances, show
that the impact of internal network state on spiking activity is
major in awake animals. Thus, cortical activity cannot be
considered as being driven by the senses, but sensory inputs rather
seem to modulate and modify the internal dynamics of cerebral
cortex. This view offers an attractive interpretation not only of
dreaming activity (absence of sensory input), but also of several
mental disorders.
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