Cortical layer-specific modulation of neuronal activity after sensory deprivation due to spinal cord injury

Abstract

Cortical areas have the capacity of large-scale reorganization following sensory deprivation. However, it remains unclear whether this phenomenon is a unique process that homogenously affects an entire deprived cortical region or it is suitable to changes depending on neuronal networks across distinct cortical layers. Here, we studied how local circuitries within each layer of the deprived cortex set the basis for neuroplastic changes after immediate sensory deprivation due to thoracic spinal cord injury (SCI) in anaesthetised rats. In vivo electrophysiological recordings from deprived hindlimb somatosensory cortex showed that SCI induces layer-specific changes mediating evoked and spontaneous activity. In supragranular layers 2/3, sensory deprivation increased gamma oscillations and the ability of these neurons to initiate up-states during spontaneous activity, suggesting altered corticocortical network and/or intrinsic properties that may serve to maintain the excitability of the cortical column after deprivation. On the other hand, sensory deprivation enhanced infragranular layers ability to integrate evoked-sensory inputs leading to increased and faster neuronal responses. Delayed evoked-responses onset were also observed in layers 5/6, suggesting alterations in thalamocortical connectivity. Altogether, our data indicate that SCI immediately modifies local circuitries within the deprived cortex allowing supragranular layers to better integrate spontaneous corticocortical information, and thus modifying column excitability, and infragranular layers to better integrate evoked-sensory inputs to preserve subcortical outputs. These layer-specific neuronal changes may guide the long-term alterations in neuronal excitability and plasticity associated to the rearrangements of somatosensory networks and the appearance of central sensory pathologies usually associated with spinal cord injury.