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Objectives In the absence of sensory input, the mammalian brain exhibits a wide array of structured, state dependent spontaneous activities. In cortical networks periods of active wakefulness characterized by dilated pupils are associated with depolarized membrane potential, asynchronous firing and fast oscillations in the local field potential, whereas periods of quiet wakefulness characterized by constricted pupils are associated with hyperpolarized membrane potential, synchronized firing and large amplitude slow oscillations. Methods To characterize the state dependent activity in thalamic networks we monitored the electrical activity of various identified thalamic neurons in relation to rapid brain state changes reflected in the pupil diameter in awake head restrained mice. Results Neurons in the visual thalamus (i.e. the lateral geniculate nucleus, LGN) form two groups where the spontaneous firing is suppressed during periods of synchronous cortical activity in one group and cortical desynchronization in the other. Identified thalamocortical neurons are characterized by decreased overall firing rate, a change in firing mode from tonic to burst and hyperpolarized membrane potentials during synchronized cortical network activity. The activity of identified local circuit interneurons, on the other hand showed an opposite effect, being suppressed upon cortical desynchronization. Some properties of visual responses including orientation tuning in the LGN thalamocortical neurons were also brain state dependent. Discussion The activity of thalamic neurons can change during rapid brain state transitions in a cell-type specific manner on a rapid timescale and this results in altered sensory responses. Conclusions and significance The results could be important for understanding subcortical sensory coding. |
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