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Abstract Sensorimotor integration in the trunk system is poorly understood despite its importance for functional recovery after neurological injury. To address this, a series of mapping studies were performed in the rat. First, the receptive fields (RFs) of cells recorded from thoracic dorsal root ganglia were identified. Second, the RFs of cells recorded from trunk primary sensory cortex (S1) were used to assess the extent and internal organization of trunk S1. Finally, the trunk motor cortex (M1) was mapped using intracortical microstimulation to assess coactivation of trunk muscles with hindlimb and forelimb muscles, and integration with S1. Projections from trunk S1 to trunk M1 were not anatomically organized, with relatively weak sensorimotor integration between trunk S1 and M1 compared to extensive integration between hindlimb S1/M1 and trunk M1. Assessment of response latency and anatomical tracing suggest that trunk M1 is abundantly guided by hindlimb somatosensory information that is derived primarily from the thalamus. Finally, neural recordings from awake animals during unexpected postural perturbations support sensorimotor integration between hindlimb S1 and trunk M1, providing insight into the role of the trunk system in postural control that is useful when studying recovery after injury. 

Supraspinal signals play a significant role in compensatory responses to postural perturbations after spinal cord injury (SCI). SCI disrupts descending motor control signals as well as ascending somatosensory information to and from below the lesion. In intact animals, While cortical signals are not necessary for basic postural tasks, but neurons in the motor cortex have been shown to respond to periodic postural perturbations in intact animals. However, the role of the cortex in postural control after spinal cord injury in response to unexpected postural perturbations has not been studied. To better understand how spinal lesions impact cortical encoding of information about unexpected postural perturbations, the activity of single neurons in the rat hindlimb sensorimotor cortex (HLSMC) were recorded during unexpected tilts before and after a complete midthoracic spinal transection. In a subset of animals, limb ground reaction forces were collected as well. Results show that responses in the HLSMC were modulated with changes in tilt severity (i.e. tilt velocity). As initial velocity of the tilt increased, more information was conveyed by the HLSMC neurons about the perturbation due to increases in both the number of recruited neurons and the magnitude of their response. After SCI hindlimb ground reaction forces were both attenuated and delayed, and the neural responses were delayed and less likely to respond to slower tilts. This resulted in a moderate decrease inan attenuation of the information conveyed by cortical neurons about the tilts, requiring more cells to convey the same amount of information as before the transection. Given that reorganization of the hindlimb sensorimotor cortex in response to therapy after complete mid-thoracic SCI is necessary for behavioral recovery, this sustained encoding of information after SCI could be a substrate for the reorganization that uses sensory information from above the lesion to control trunk muscles that permit weight-supported stepping and postural control.