Reorganization of the Intact Somatosensory Cortex Immediately after Spinal Cord Injury

Abstract

Sensory deafferentation produces extensive reorganization of the corresponding deafferented cortex. Little is known, however, about the role of the adjacent intact cortex in this reorganization. Here we show that a complete thoracic transection of the spinal cord immediately increases the responses of the intact forepaw cortex to forepaw stimuli (above the level of the lesion) in anesthetized rats. These increased forepaw responses were independent of the global changes in cortical state induced by the spinal cord transection described in our previous work (Aguilar et al., J Neurosci 2010), as the responses increased both when the cortex was in a silent state (down-state) or in an active state (up-state). The increased responses in the intact forepaw cortex correlated with increased responses in the deafferented hindpaw cortex, suggesting that they could represent different points of view of the same immediate state-independent functional reorganization of the primary somatosensory cortex after spinal cord injury. Collectively, the results of the present study and of our previous study suggest that both state-dependent and state-independent mechanisms can jointly contribute to cortical reorganization immediately after spinal cord injury.

Increased cortical responses to forepaw stimuli immediately after peripheral deafferentation of hindpaw inputs

“…Similarly, hindpaw stimuli also evoked small responses in the forepaw cortex (Table 1). These observations are consistent with our previous results6710.…”

“…We first studied the cortical evoked responses, measured by the local field potentials (LFPs) as in our previous works671819. In intact animals (P0), the responses evoked in the forepaw cortex by forepaw stimuli displayed greater amplitude than the responses evoked in the hindpaw cortex by hindpaw stimuli (Fig.…”

“…Focusing in models of spinal cord injury, we recently characterized the cortical responses to peripheral stimulation above the level of the lesion immediately after a complete thoracic transection67 or thoracic hemisection8. Our results show an increment in the amplitude of the responses evoked in the somatosensory cortex by stimuli delivered to the forepaw, above the lesion level.…”

“…Our results show an increment in the amplitude of the responses evoked in the somatosensory cortex by stimuli delivered to the forepaw, above the lesion level. These changes in the responses have both a state-dependent component, due to a global change in cortical state6, and a state-independent component, due to more classical unmasking mechanisms at cortico-subcortical level78. Interestingly, these increased responses to forepaw stimuli are not observed only in the hindpaw cortex, which is deafferented by the thoracic spinal cord injury, but also in the forepaw cortex, which would be classically considered as non-deafferented.…”

Cortical reorganization after spinal cord injury: Always for good?

“…But if cortical spontaneous activity is carefully monitored, cortical responses immediately after spinal cord transection still increase, even without a change in cortical state (Humanes-Valera et al, 2013; Yagüe et al, 2014). These increased responses could be due to a change in the equilibrium between excitation and inhibition at cortical and subcortical level.…”