Nandakumar, B. | Search bioRxiv

bioRxiv2020

Trunk sensory and motor cortex ispreferentially integrated with hindlimb sensoryinformation that supports trunk stabilization

Sensorimotor integration in the trunk system has been poorly studied despite its importance for examining functional recovery after neurological injury or disease. Here, we mapped the relationship between thoracic dorsal root ganglia and trunk sensory cortex (S1) to create a detailed map of the extent and internal organization of trunk primary sensory cortex, and trunk primary motor cortex (M1) and showed that both cortices are somatotopically complex structures that are larger than previously described. Surprisingly, projections from trunk S1 to trunk M1 were not anatomically organized. We found relatively weak sensorimotor integration between trunk M1 and S1 and between trunk M1 and forelimb S1 compared to extensive integration between trunk M1 and hindlimb S1 and M1. This strong trunk/hindlimb connection was identified for high intensity stimuli that activated proprioceptive pathways. To assess the implication of this integration, the responses in sensorimotor cortex were examined during a postural control task and supported sensorimotor integration between hindlimb sensory and lower trunk motor cortex. Together, these data suggest that trunk M1 is guided predominately by hindlimb proprioceptive information that reached the cortex directly via the thalamus. This unique sensorimotor integration suggests an essential role for the trunk system in postural control, and its consideration could be important for understanding studies regarding recovery of function after spinal cord injury. SignificanceThis work identifies extensive sensorimotor integration between trunk and hindlimb cortices, demonstrating that sensorimotor integration is an operational mode of the trunk cortex in intact animals. The functional role of this integration was demonstrated for postural control when the animal was subjected to lateral tilts. Furthermore, these results provide insight into cortical reorganization after spinal cord injury making clear that sensorimotor integration after SCI is an attempt to restore sensorimotor integration that existed in the intact system. These results could be used to tailor rehabilitative strategies to optimize sensorimotor integration for functional recovery.

neuroscience↗

bioRxiv2020

At-level allodynia after mid-thoracic contusion in the rat

The rat mid-thoracic contusion model has been used to study at-level tactile allodynia after spinal cord injury (SCI), one of the more common types of allodynia. An important advantage of this model is that not all animals develop allodynia and, therefore, it could be used to more clearly examine mechanisms that are strictly related to pain development separately from mechanisms related to the injury itself. However, how to separate those that develop allodynia from those that do not is unclear. The aims of the current study were to identify where allodynia and spasticity develop and use this information to identify metrics that separate animals that develop allodynia from those that do not in order study difference in their behavior. To accomplish these aims, a standardized grid was used to localize pain on the dorsal trunk and map it to thoracic dermatomes, providing for the development of a pain score that relied on supraspinal responses and separated subgroups of animals. Similar to human studies, the development of allodynia often occurred with the development of spasticity or hyperreflexia. Moreover, the time course and prevalence of pain phenotypes (at-, above-, or below level) produced by this model were similar to that observed in humans who have sustained an SCI. However, the amount of spared spinal matter in the injured cord did not explain the development of allodynia, as was previously reported. This approach can be used to study the mechanism underlying the development of allodynia separately from mechanisms related to the injury alone.

physiology↗