Hierarchical clustering also revealed that at a finer grain of analysis, there were three prominent sub-groups ( Figure 1D, LOW hierarchical level partition).
The existence of these two groups was confirmed by a hierarchical clustering analysis ( Figure 1D, HIGH hierarchical level partition). This analysis revealed two main groups that corresponded to postures and movements, respectively ( Figure 1C). To do that, we first applied mutual information (MI) to quantify linear and nonlinear correlations between all pairs. Therefore, we set out to identify relevant groupings among behavioral state variables. Given biomechanical constraints, we expect some postures and movements to correlate with each other. Finally, we quantified overall motion ( Figure1B OM, overall motion) by measuring the 3D Euclidean distance between all body points in consecutive frames. Locomotion was quantified by speed of movement on the x-y plane of the arena ( Figure 1B Video S2 Lc, locomotion). Six movements were quantified by the temporal derivative of the above postures (dHel, dHlr, dBar, dBlr, dBlu, and dRe). Full-body postures were quantified by projection on the first 3 eigenposes ( Figure 1B Video S2 Bar, body arch Blr, body left/right bend and Blu, body lunge), sufficient to explain 80% of changes in the body shape, and by rearing ( Figure 1B Video S2 Re, rearing). Head postures were quantified by head elevation and left/right angles ( Figure 1B Video S2 Hel, head elevation Hlr, head left/right). Hereafter, we will define this set of variables as the behavioral state of the animal. Results Spontaneous exploration in freely moving animals is defined by independent sets of postures and movementsįrom the 3D reconstruction, we quantified the postures and movements of the mouse in terms of fourteen behavioral variables. Our discovery that electrophysiological activity in the primary visual thalamus is influenced by posture during natural exploration raises the possibility that thalamic processing of visual information can be flexibly modulated according to specific visuomotor behaviors.
Moreover, although movement provides a general increase in firing, the impact of postures is more specific, with a subset of neurons excited by poses characterized by looking upward (“look-up” neurons), whereas a different set are excited by poses associated with looking downward (“look-down” neurons). Thus, although we confirm that high levels of motor activity (including but not limited to the locomotion available to head-fixed animals) excites the primary visual thalamus, we find that head and body postures are at least as influential in defining neuronal activity in this region. We find that the higher dimensional description of behavior enabled by this approach is key to understanding motor influences on the early visual system. KeywordsĪnd here, we extend it to measure a wide variety of 3D movements and postures. Our results demonstrate that the primary visual thalamus, beyond global modulations by sleep/awake states, is potentially involved in specific visuomotor integration and reveal two distinct couplings between up/down postures and neuronal activity. These results were observed in the dark, thus representing a genuine behavioral modulation, and were amplified in a lit arena. Thus, although most units were excited during full-body movements, some expressed highest firing when the animal was looking up (“look-up” neurons), whereas others expressed highest firing when the animal was looking down (“look-down” neurons). Importantly, up/down postures and full-body movements were largely independent and jointly coupled to neuronal activity. By contrast, thalamic activity was minimally correlated with other postures or movements (e.g., left/right head and body torsions). In particular, postures associated with the animal looking up/down correlated with activity in >50% neurons, and the extent of this effect was comparable with that induced by full-body movements (typically locomotion). Unbiased evaluation of a wide range of postures and movements revealed a widespread coupling between neuronal activity and few behavioral parameters. We addressed this question by developing robust 3D video reconstruction of mouse head and body during spontaneous exploration paired with simultaneous neuronal recordings from dLGN. However, its potential for more specific visuomotor integration is largely unexplored. dLGN activity is modulated by global sleep/wake states and arousal, indicating that it is not simply a passive relay station. Visual information reaches cortex via the thalamic dorsal lateral geniculate nucleus (dLGN).
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