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Modulation of dLGN firing mode across multiple timescales is predicted by pupil size dynamics

The way in which sensory systems encode information, even at early processing stages, is modulated according to the internal state of the animal. Internal states, such as arousal, are often characterized by relating neural variables to a single “level” of arousal, defined using a behavioral variable such as locomotion or pupil size. Here, we extend the notion of arousal-related modulation by showing that multifaceted aspects of pupil size dynamics can predict changes in neural activity. Specifically, we show that the phases of pupil size fluctuations occurring over multiple timescales modulate firing mode in the dorsal lateral geniculate nucleus (dLGN) of mice. Increased firing rates, driven by a preponderance of tonic spiking, occurred during pupil dilations, while burst spikes preferentially occurred during contractions. We further find that these activity modulations could not be explained solely by pupil size per se, or by transitions between overt locomotion and quiescence, and extend to periods of patterned stimulus viewing. We conclude that dLGN spiking activity is modulated by pupil-indexed arousal processes on various timescales, with implications for the determination of arousal-related cortical rhythms, and for the transfer of sensory information to the cortex.