Abstract
The function of the higher-order sensory thalamus remains unclear. Here, the posterior medial (POm) nucleus of the thalamus was examined by in vivo extracellular recordings in anesthetized rats across a variety of contralateral, ipsilateral, and bilateral whisker sensory patterns. We found that POm was highly sensitive to multiwhisker stimuli involving diverse spatiotemporal interactions. Accurate increases in POm activity were produced during the overlapping time between spatial signals reflecting changes in the spatiotemporal structure of sensory patterns. In addition, our results showed for first time that POm was also able to respond to tactile stimulation of ipsilateral whiskers. This finding challenges the notion that the somatosensory thalamus only computes unilateral stimuli. We found that POm also integrates signals from both whisker pads and described how this integration is generated. Our results showed that ipsilateral activity reached one POm indirectly from the other POm and demonstrated a transmission of sensory activity between both nuclei through a functional POm-POm loop formed by thalamocortical, interhemispheric, and corticothalamic projections. The implication of different cortical areas was investigated revealing that S1 plays a central role in this POm-POm loop. Accordingly, the subcortical and cortical inputs allow POm but not the ventral posteromedial thalamic nucleus (VPM) to have sensory information from both sides of the body. This finding is in agreement with the higher-order nature of POm and can be considered to functionally differentiate and classify these thalamic nuclei. A possible functional role of these higher-order thalamic patterns of integrated activity in brain function is discussed.
Highlights
Sensory systems have mostly been studied using simple and discrete stimuli
These results showed that the dynamical spatiotemporal structure of sensory patterns and the different variety of their parts was accurately reflected in precise posteromedial thalamic nucleus (POm) activity fluctuations
Our findings show that POm capacities to sustain and integrate activity allow the representation of tactile events
Summary
Sensory systems have mostly been studied using simple and discrete stimuli. How the somatosensory system transforms these merged raw sensory signals into reliable neural representations and extracts information from that apparent noise is incompletely understood In these animals, tactile information from whiskers is processed by parallel ascending pathways toward the cortex (Chiaia et al, 1991; Diamond et al, 1992; Sherman and Guillery, 1998; Ahissar et al, 2000; Veinante et al, 2000a; Ohno et al, 2012; Clascá et al, 2016). Our observations reveal a different implication of VPM and POm in bilateral perception This finding is in agreement with the higher-order nature of POm and can be considered to functionally classify these thalamic nuclei
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