In chronic injury, this leads to afferent information from neighboring regions activating neurons in deafferented cortex and driving phantom sensations rather than functional recovery ( Jain et al., 1997). Over time, there is a reactivation of portions of the hand representation, likely mediated by sparse surviving primary afferents, second-order spinal neurons, and reorganization at each relay of somatosensory path: spinal cord, dorsal column nuclei (nucleus cuneatus), thalamus (ventral posterolateral nucleus, VPL), and cortex (S1) ( Figure 1 Moxon et al., 2014). In contrast, complete dorsal column injuries immediately deactivate the hand representation in contralateral S1 area 3b ( Jain et al., 1997, 2008). In contrast to the effects on fine motor control, dorsal column lesion does not significantly impair locomotion, indicating that cortical sensory processing is not necessary for gross motor movements ( Kaas et al., 2008).Īfter incomplete lesions of the dorsal column, reactivation of S1 occurs with almost normal somatotopy ( Yang et al., 2014 Qi et al., 2019). This loss of afferent input results in tactile deficits in the deprived forelimb and impaired performance on a reach-to-grasp task ( Qi et al., 2013). In non-human primates, complete unilateral lesion of the ascending dorsal columns deactivates hand representations in area 3b of contralateral cortex ( Jain et al., 1997, 2008). SCI disrupts afferent input to the central nervous system and results in the reorganization of cortical sensory representations, or maps ( Kaas et al., 2008 Moxon et al., 2014). Thus, the underlying cellular mechanisms of somatosensory map plasticity and its consequences for cortical processing are highly relevant for shaping appropriate recovery of function after injury. Cortical reorganization is a complex phenomenon that has been associated with both improved functional recovery and aberrant phantom sensations ( Moxon et al., 2014). Representations of somatosensory responses in S1 are highly plastic in response to nervous system damage, sensory experience, and learning. Sensory Cortex Responses to Spinal Cord Injury A detailed understanding of the circuit mechanisms of rehabilitation-dependent S1 cortical plasticity is not known and further studies are required to address this mechanism that could provide critical data for designing therapeutic strategies for the recovery of movement after SCI. These findings suggest that rehabilitation can improve sensory function as well as sensorimotor-dependent movement recovery after SCI. The reactivation of S1 responses to cutaneous stimulation correlates with tactile recovery ( Martinez et al., 2009). Sensory function is not simply a passive byproduct of motor rehabilitation sensorimotor training on discrete tactile substrates can improve recovery of locomotor function and tactile sensitivity after SCI ( Martinez et al., 2009). Furthermore, ablation of proprioceptive afferents after spontaneous locomotor recovery leads to a deterioration of the regained activity, indicating that proprioception is indispensable for both driving functional recovery as well as for maintaining that recovered function ( Takeoka and Arber, 2019). Level-specific ablation of proprioceptive neurons demonstrated that locomotor recovery depends upon afferent input from below, but not above, the lesion ( Takeoka and Arber, 2019). After a lateral hemisection of the thoracic spinal cord, mice show spontaneous recovery of ipsilesional hindlimb control, whereas transgenic mice lacking muscle spindle-mediated proprioceptive input fail to recover locomotor function ( Takeoka et al., 2014). Within the spinal cord, proprioceptive and mechanoreceptive circuits are known to remodel below the level of SCI, providing an alternative circuit for transmission of afferent information ( Hollis et al., 2015 Granier et al., 2020). Proprioceptive feedback transmitted through the dorsal column-medial lemniscal system is essential for movement control in healthy and injury conditions ( Pearson, 1995 Windhorst, 2007 Tuthill and Azim, 2018). Sensorimotor integration is disrupted in spinal cord injury (SCI) ( Edwards et al., 2019) and the recovery of sensory function will be a critical aspect in the recovery of movement. ![]() Additionally, sensory feedback during motor performance is required to refine ongoing movements. Sensory inputs for goal-directed movements provide information about location, size, weight, and shape of an object therefore, successful integration of sensory inputs is key for generating a motor plan to execute a given movement. Sensory circuits provide essential components for accurate movement, including texture discrimination, spatial awareness, object perception, and tactile feedback ( Abraira and Ginty, 2013).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |