Control of Somatosensory Cortical Processing by Thalamic Posterior Medial Nucleus: A New Role of Thalamus in Cortical Function

Abstract

Current knowledge of thalamocortical interaction comes mainly from studying lemniscal thalamic systems. Less is known about paralemniscal thalamic nuclei function. In the vibrissae system, the posterior medial nucleus (POm) is the corresponding paralemniscal nucleus. POm neurons project to L1 and L5A of the primary somatosensory cortex (S1) in the rat brain. It is known that L1 modifies sensory-evoked responses through control of intracortical excitability suggesting that L1 exerts an influence on whisker responses. Therefore, thalamocortical pathways targeting L1 could modulate cortical firing. Here, using a combination of electrophysiology and pharmacology in vivo, we have sought to determine how POm influences cortical processing. In our experiments, single unit recordings performed in urethane-anesthetized rats showed that POm imposes precise control on the magnitude and duration of supra- and infragranular barrel cortex whisker responses. Our findings demonstrated that L1 inputs from POm imposed a time and intensity dependent regulation on cortical sensory processing. Moreover, we found that blocking L1 GABAergic inhibition or blocking P/Q-type Ca2+ channels in L1 prevents POm adjustment of whisker responses in the barrel cortex. Additionally, we found that POm was also controlling the sensory processing in S2 and this regulation was modulated by corticofugal activity from L5 in S1. Taken together, our data demonstrate the determinant role exerted by the POm in the adjustment of somatosensory cortical processing and in the regulation of cortical processing between S1 and S2. We propose that this adjustment could be a thalamocortical gain regulation mechanism also present in the processing of information between cortical areas.

Superior colliculus modulates cortical coding of somatosensory information

“…It is well established that POm not only sends a direct input to vS1, but also modulates sensory processing in vS1 (Viaene et al, 2011;Castejon et al, 2016;Mease et al, 2016;Zhang & Bruno, 2019). Consistent with these studies, activation of SC increases activity of vS1 neurons, leading to larger whisker evoked responses particularly during small whisker movements.…”

Serotonin 5‐HT1B receptor‐mediated calcium influx‐independent presynaptic inhibition of GABA release onto rat basal forebrain cholinergic neurons

“…Despite the physiological as well as morphological significance, the precise origins of GABAergic inputs as well as expression of Ca 2+ channel subtypes on their terminals in BF remains unknown. A recent study has demonstrated that P/Q‐type Ca 2+ channels are expressed on the axon terminal of parvalbumin (PV)‐containing interneurons in the cortex (Castejon et al ., ). PV‐containing neurons are also one of the important neuronal populations in the BF, sending GABAergic inputs to cholinergic neurons (Duque et al ., ; Zaborszky & Duque, ).…”

“…Numbers in parentheses indicate number of neurons examined. cortex (Castejon et al, 2016). PV-containing neurons are also one of the important neuronal populations in the BF, sending GABAergic inputs to cholinergic neurons .…”

Superior colliculus modulates cortical coding of somatosensory information

“…It is well established that POm not only sends a direct input to vS1, but also modulates sensory processing in vS1 [36][37][38][39] . Consistent with these studies, activation of SC increases activity of vS1 neurons, leading to larger whisker-evoked responses, particularly during small whisker movements.…”