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| The thalamus and the cerebral cortex are reciprocally connected brain structures. In the physiological realm, the path of information flow during spontaneous activity is still being debated. Here we investigate information flow within the cortical-thalamo-cortical loop during slow oscillations ($\leq$1Hz), i. e. spontaneous activity emerging during slow wave sleep and anaesthesia. We apply information directionality measures within the framework of the Ordinal Symbolic Dynamics to local field potential recordings simultaneously obtained from the visual thalamus and visual cortex layers 2/3 and 5. We compared across two types of waves, spontaneous and evoked by visual stimulation. In the case of spontaneous activity, we find evidence that supports models triggered by the cortical layer 5. Thus, in the absence of external stimuli cortical layer 5 leads the flow of information towards other cortical layers and thalamus. In the evoked waves, the thalamus plays a more important role, triggering activity on cortical layers 2/3 as expected from the anatomical connectivity. However, our information flow measurements reveal that cortical layer 5 has still a prominent role inducing activity on the remaining cortical layers. We will discuss how this information measurement matches and enhances the current understanding of the anatomical/physiological models of connectivity. |
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