State - dependent receptive - ® eld restructuring in the visual cortex

To extract important information from the environment on a useful timescale, the visual system must be able to adapt rapidly to constantly changing scenes. This requires dynamic control of visual resolution, possibly at the level of the responses of single neurons. Individual cells in the visual cortex respond to light stimuli on particular locations (receptive ®elds) on the retina, and the structure of these receptive ®elds can change in different contexts. Here we show experimentally that the shape of receptive ®elds in the primary visual cortex of anaesthetized cats undergoes signi®cant modi®cations, which are correlated with the general state of the brain as assessed by electroencephalography: receptive ®elds are wider during synchronized states and smaller during non-synchronized states. We also show that cortical receptive ®elds shrink over time when stimulated with ̄ashing light spots. Finally, by using a network model we account for the changing size of the cortical receptive ®elds by dynamically rescaling the levels of excitation and inhibition in the visual thalamus and cortex. The observed dynamic changes in the sizes of the cortical receptive ®eld could be a re ̄ection of a process that adapts the spatial resolution within the primary visual pathway to different states of excitability. The frequency content of the electroencephalogram (EEG) is correlated to behavioural states. In a drowsy state, a-waves and some d-waves predominate, whereas mainly b-waves are observed during attentive perception. This indicates that the temporal and spatial resolution of the visual system might also change in a way that is correlated with EEG frequency content. Indeed, the temporal characteristics of the cell responses in the visual thalamus (lateral geniculate nucleus, LGN) are markedly EEG-correlated. Brief stereotyped bursts of LGN neurons are seen during an a/d-wavedominated EEG (a synchronized EEG), whereas the cells ®re in a tonic, long-lasting way during a b-wave-dominated EEG (a nonsynchronized EEG). letters to nature