Divergent Findings in Brain Reorganization After Spinal Cord Injury: A Review

Abstract

Spinal cord injury (SCI) leads to a general lack of sensory and motor functions below the level of injury and may promote deafferentation‐induced brain reorganization. Functional magnetic resonance imaging (fMRI) has been established as an essential tool in neuroscience research and can precisely map the spatiotemporal distribution of brain activity. Task‐based fMRI experiments associated with the tongue, upper limbs, or lower limbs have been used as the primary paradigms to study brain reorganization following SCI. A review of the current literature on the subject shows one common trait: while most articles agree that brain networks are usually preserved after SCI, and that is not the case as some articles describe possible alterations in brain activation after the lesion. There is no consensus if those alterations indeed occur. In articles that show alterations, there is no agreement if they are transient or permanent. Besides, there is no consensus on which areas are most prone to activation changes, or on the intensity and direction (increase vs. decrease) of those possible changes. In this article, we present a critical review of the literature and trace possible reasons for those contradictory findings on brain reorganization following SCI. fMRI studies based on the ankle dorsiflexion, upper‐limb, and tongue paradigms are used as case studies for the analyses.

Impact of fractional amplitude of low‐frequency fluctuations in motor‐ and sensory‐related brain networks on spinal cord injury severity

“…The resting‐state cortex or subcortex reorganization and plastic changes found in the current study appear to be related to brain dysregulation and alteration in SCI patients, which can be used as a strategy for neurorehabilitation 29 . SCI rehabilitation aims to minimize further damage while restoring as much function as possible by attempting to induce spinal and supraspinal neuroplasticity 30 . Compared with healthy controls, patients with SCI (complete and incomplete) showed low fALFF values in the superior medial frontal gyrus.…”

“…29 SCI rehabilitation aims to minimize further damage while restoring as much function as possible by attempting to induce spinal and supraspinal neuroplasticity. 30 Compared with healthy controls, patients with SCI (complete and incomplete) showed low fALFF values in the superior medial frontal gyrus. In addition, fALFF values of this brain area were positively correlated with the motor and sensory scores in SCI patients.…”

Sense of agency for intracortical brain–machine interfaces

“…Finally, given the long-term spinal cord lesion suffered by this participant, we cannot exclude that some plastic changes have occurred in his motor representations in M1, his somatosensory representations in S1, or the connectivity between the two. There is still no consensus about plasticity following spinal cord injury, with some evidence of preserved network organization, some possible changes in grey matter density 45,46 or activation in the sensorimotor cortices 47,48 . It is also not clear how these results at the population level of SCI patients are predictive of changes at the single patient level.…”

Rethinking the Body in the Brain after Spinal Cord Injury

“…Importantly, recent studies have shown that sensory connections are spared in approximately half of the lesions considered to be complete [50,51]. The purpose of these brief considerations is to highlight the risk of relevant biases that occur in most studies regarding the consequences of an SCI on the CNS, in line with a recent review [52].…”