WEBINAR - BMI Progress Reports 2020 // Prof. Markam's Lab - Jane Yi: Thalamic microcircuitry: neurons, synapses, and circuit motifs in receptive field structure and sensory processing

Thalamic interneurons play a crucial role in enhancing perception by sharpening spatial and temporal features of incoming stimuli (Hirsch et al., 2015; Martinez et al., 2014; Wang et al., 2011). Despite their presence in other thalamic nuclei, thalamic interneurons are almost exclusively studied in the visual thalamic nucleus, the lateral geniculate nucleus (LGN), due to their greater numbers (Arcelli et al., 1997; Evangelio et al., 2018). The somatosensory thalamic nuclei of the rodent brain, collectively known as the ventrobasal (VB) nucleus, contain a local interneuron population percentage of less than 1% (Arcelli et al.,1997), though conflicting reports have been reported up to 4.2% (Cavdar et al., 2014). On the other hand, interneurons in the LGN represent between 5.6 and 20% of the neuronal population (Arcelli et al., 1997; Evangelio et al., 2018). Given the sparse population of these cell types in the VB, their properties and contributions to thalamic functions have been vastly overlooked. However, the morphologies of their LGN counterparts display dense dendritic arborization patterns that span hundreds of micrometers (Morgan et al., 2020; Zhu and Lo, 1999), suggesting a profound influence on thalamocortical relay (TC) excitatory tone throughout the nucleus. In this present study, we have observed for the first time, connected pairs of TCs and VB interneurons (VBin) as well as VBins with other VBins, the latter providing a source of disinhibition. We investigated this newfound microcircuitry further to infer the functionality of observed circuit motifs. Thus, we have found that VB interneurons enrich the somatosensory thalamus with a level of complexity that was previously unknown.