Cortico-Cortical Coherence in the Orofacial Cortex Changes Following Sensory Loss

Objectives: Functional connectivity is when cortico-cortical interactions between neurons within and across different regions of the brain show synchronized or coherent activity during neurophysiological events. Functional connectivity of the somatosensory and motor cortex for orofacial behavior (feeding and breathing) is mostly unexplored and how that relates to normal function (and thus loss of function) has yet to be determined. This project will focus on how neurons in the orofacial sensorimotor cortex interact to create effective feeding and how loss of oral sensation impacts functional connectivity.
Methods: Data were collected from two adult male rhesus macaques (Macaca mulatta). Macaques were fed foods presented by the experimenter via a long stylus. On some days, animals engaged in the feeding task following bilateral injections of nerve block to specific sensory branches of the trigeminal nerve. Neurons were tracked with microelectrode arrays that were chronically implanted in four regions of the orofacial cortex. The neural data spike waveforms are sorted offline using Offline Sorter. Spectral coherence analysis was performed.
Results: The Theta band has the largest neural network and greatest magnitude of coherence overall between both monkeys and control/nerve block. Nerve blocks caused a change in coherence; one subject had a compensatory increase in coherent activity, while the other had an overall decrease in all areas. Neuronal pairs whose peak coherences were significantly higher than noise in the control condition either ceased to exhibit significant coherence or had a reduced coherence in the nerve block. The time of peak coherence was also shifted from the control to the nerve block. The time of peak coherences as a function of frequency bands (Alpha, Beta, Gamma, Theta) showed changes following loss of sensation.
Conclusions: Functional connectivity in the orofacial sensorimotor cortex is affected by loss of sensation in oral structures during feeding. Somatosensory research involving touch with the hands find similar conclusions in that nerve blocks impact somatosensation. Future studies could inform treatment strategies for sensory impairments associated with dental implants, trigeminal neuralgia, temporomandibular disorders, orofacial pain, and for the restoration of sensory feedback.