Dr Kuo-Sheng Lee - University of Geneva, Switzerland : "Emergence of tonotopic map in early somatosensory pathway: mechanoreceptors, synaptic networks and transformation of neural coding"

Speaker:

Dr Kuo-Sheng Lee
Department of Fundamental Neurosciences, University of Geneva
Switzerland

Title: "Emergence of tonotopic map in early somatosensory pathway: mechanoreceptors, synaptic networks and transformation of neural coding"

Abstract:

Perceiving substrate vibrations and location of the vibration is a fundamental component of tactile perception. In general, tactile experience could be understood as processing a cutaneous stimulus through various spectrum channels with mechanoreceptors preferring different vibration frequencies: Mercel cell, Meissner corpuscles and Pacinian corpuscles selectively respond to frequency from low to high (0.5-500 Hz, comparable to the span of human hearing range). Location (somatotopy) and frequency tuning (tonotopy) are highly important properties of neurons in somatosensory pathways. The combined organization of these particular tuning properties in the neural space will strongly shape the population response to different tactile inputs, yet it is poorly understood. In this study, we address this challenge by employing in vivo electrophysiological recordings and two-photon calcium imaging along all stages of the ascending somatosensory pathway: primary sensory afferents (mechanoreceptors), dorsal root ganglia, dorsal column nuclei (DCN), thalamus and cortex. Surprisingly, in somatosensory brainstem DCN where the synaptic integration happens for the first time, we discovered that frequency tuning for vibration stimulus was organized into highly structured maps that remained consistent across the depth of DCN, similarly to location tuning for the stimulus. Next, we found that somatotopic and tonotopic maps were intimately related at the fine spatial scale with parallel map gradients on a cellular basis. Further subcellular imaging and neural network simulation again supported that the tonotopic map partially inherits from the distribution of mechanoreceptors in the skin and deep tissue, and the synaptic networks underlying the submodality convergence in DCN contributes to the emergence of tonotopy. In addition, neither fine-scale somatotopic and tonotopic organization could be observed in dorsal root ganglia, where the cell bodies of the first-order neurons reside. We conclude that the neural circuits in DCN are the key to the emergence of these two fine-scale topological organizations in early somatosensory pathways. This finding allows modeling the underlying computational principle to reveal novel features of vibrotactile sensation.