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Encoding of saltatory tactile velocity in the adult orofacial somatosensory system
Processing dynamic tactile inputs is a key function of somatosensory systems. Closely tied to skilled motor activity, neural velocity encoding mechanisms are crucial for both neurotypical movement production and recovery of function following neurological insult. To date, little is known about tactile velocity encoding in trigeminal networks that process complex cutaneous afferent information associated with facial sensation, proprioception, and oromotor feedback. In this project, high resolution functional magnetic resonance imaging (fMRI) was used to investigate the neural substrates of velocity encoding in the human orofacial somatosensory system during saltatory (discontinuous, “jumping”) pneumotactile inputs to the unilateral orofacial skin in 20 healthy adults. A custom multichannel, scalable pneumotactile array was used to present 5 stimulus conditions: 5 cm/s, 25 cm/s, 65 cm/s, ALL-ON synchronous activation, and ALL-OFF. The spatiotemporal organization of cortical and subcortical blood oxygen level-dependent (BOLD) response as a function of stimulus velocity was analyzed using general linear modeling (GLM) of single-subject and pooled group fMRI signal data. Results showed that unilateral, sequential saltatory inputs to the right lower face produced localized, predominantly contralateral BOLD responses in primary somatosensory (SI), secondary somatosensory (SII), posterior parietal cortex (PPC), primary motor (MI), supplemental motor area (SMA), and insula, whose spatial organization was dependent on velocity. Additionally, ipsilateral cortical and insular BOLD response was noted during slower velocity presentations (5cm/s, 25 cm/s). In 70% of the subjects (N=14), ipsilateral cerebellar BOLD response was seen during the slower velocities (5cm/s, 25cm/s) and the ALL-ON condition, in regions consistent with the dentate and interpositus nuclei. These results indicate rapid neural adaptation via a scalability of networks processing temporal cues associated with velocity. In addition to pure somatosensory response, activations of neural regions associated with motion production, perception, and planning may indicate close physiological ties with functional motor systems, and provide access to avenues for sensorimotor rehabilitation. Based on these preliminary results, the current project has the potential to create a neurotypical hemodynamic response (HRF) model of cortical velocity processing networks following a novel velocity stimulation paradigm, which in turn could lead to new neurodiagnostic and neurotherapeutic applications.
Custead, Rebecca, "Encoding of saltatory tactile velocity in the adult orofacial somatosensory system" (2016). ETD collection for University of Nebraska - Lincoln. AAI10143292.