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.
Highlights
When a major lesion of the nervous system – such as stroke, amputation or spinal cord injury - interrupts the normal flow of sensory inputs from the body to the brain, the corresponding sensory function is obviously dramatically affected
We simultaneously recorded local field potentials (LFPs) and multiunit activity (MUA) from the hindpaw representation and the forepaw representation of the primary somatosensory cortex (n=12 rats) in response to somatosensory stimuli delivered to the contralateral forepaw and hindpaw, under three experimental conditions in the same animals: (1) intact animals under relatively light anesthesia, (2) intact animals under deeper anesthesia, (3) immediately after spinal cord transection (Figure 2C)
To confirm the absence of global changes in cortical state after spinal cord transection under deep anesthesia, we measured the peak frequency of rectified multiunit activity (rMUA) spectrum, which did not change after spinal cord transection in both the intact forepaw cortex and the deafferented hindpaw cortex (time factor: F(1,10)=0.8, p=0.40)
Summary
When a major lesion of the nervous system – such as stroke, amputation or spinal cord injury - interrupts the normal flow of sensory inputs from the body to the brain, the corresponding sensory function is obviously dramatically affected. In addition to the direct loss of function, sensory deafferentation produces extensive long-term reorganization of brain structures up to the cortex [1,2,3,4,5]. Cortical reorganization after deafferentation is typically described in terms of the deafferented cortex becoming more responsive to stimulation of the surrounding intact body regions. In a recent study [19], we indirectly pointed toward a different – and much overlooked (but see e.g. 20) – cortical reorganization, characterized by the intact cortex adjacent to the deafferented cortex becoming more responsive to stimulation of intact body regions. After complete thoracic transection of the spinal cord in anesthetized rats, the intact forepaw cortex immediately became more responsive to stimuli delivered to the forepaw, above the lesion level
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