BACKGROUND AND AIMS: Medial sector of posterior complex (PoM) of the thalamus receives two driving somatosensory inputs – from the periphery and from the cortical layer 5b and their functional significance was proposed to depend on arousal level. In anesthetized rats sensory evoked potentials in PoM revealed only late latency, cortex-dependent responses while in wakefulness they contained also fast latency components. In aroused animals this early activity is effectively transmitted to the sensory cortex. The current experiments were set up to record activity of single PoM neurons from conscious rats in order to confirm the field recording data and characterize the role of PoM in fast transmission of somatosensory information. METHODS: Rats were habituated to head fixation and body restrain, then implanted with chronic electrodes located in primary and higher order cortical somatosensory and motor areas. For extracellular recordings from PoM, microelectrodes were implanted on movable microdrives or the cranial window was opened for semichronic recording with silicon probe multichannel electrodes. Continuous signal containing field potentials and unitary activity was recorded for offline analysis. Single and multi-unit activity was extracted with template matching and clustering methods by Spike 2 software. The average evoked potentials and peristimulus time histograms were calculated to analyze the responses to whisker stimulations. RESULTS: Our preliminary results indicate that in awake rats PoM neurons respond to whisker stimulation with short-latency (5–6 ms) discharges followed by later, more dispersed activity CONCLUSIONS: Short-latency action potentials generated by PoM cells after vibrissae stimulation suggest that this nucleus participate in fast detection of tactile stimuli. Further research should elaborate the role of early response of this mixed-order somatosensory thalamic nucleus in more detail. Supported by National Science Centre grant DEC-2013/08/W/ NZ4/00691.
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