Robust interactions between the effects of auditory and cutaneous electrical stimulations on cell activities in the thalamic reticular nucleus.

The thalamic reticular nucleus (TRN), a cluster of GABAergic cells, is thought to regulate bottom-up and top-down streams of sensory processing in the loop circuitry between the thalamus and cortex. Provided that sensory inputs of different modalities interact in the TRN, the TRN could contribute to fast and flexible cross-modal modulation of attention and perception that incessantly takes place in our everyday life. Indeed, diverse subthreshold interactions of auditory and visual inputs have been revealed in TRN cells (Kimura, 2014). To determine whether such sensory interaction could extend across modalities as a universal neural mechanism, the present study examined TRN cell activities elicited by auditory and cutaneous electrical stimulations in anesthetized rats. Juxta-cellular recording and labeling techniques were used. Recordings were obtained from 129 cells. Auditory or somatosensory responses were modulated by subthreshold electrical stimulation or sound (noise burst) in the majority of recordings (77 of 85 auditory and 13 of 15 somatosensory cells). Additionally, 22 bimodal cells and seven cells that responded only to combined stimulation were recognized. Suppression was predominant in modulation that was observed in both early and repeatedly evoked late responses. Combined stimulation also induced de novo cell activities. Further, response latency and burst spiking were modulated. Axonal projections of cells showing modulation terminated in first- or higher-order thalamic nuclei. Nine auditory cells projected to somatosensory thalamic nuclei. These results suggest that the TRN could regulate sensory processing in the loop circuitry between the thalamus and cortex through the sensory interaction pervasive across modalities.