What Disconnection Tells about Motor Imagery: Evidence from Paraplegic Patients

Abstract

Brain activation during motor imagery has been the subject of a large number of studies in healthy subjects, leading to divergent interpretations with respect to the role of descending pathways and kinesthetic feedback on the mental rehearsal of movements. We investigated patients with complete spinal cord injury (SCI) to find out how the complete disruption of motor efferents and sensory afferents influences brain activation during motor imagery of the disconnected feet. Eight SCI patients underwent behavioral assessment and functional magnetic resonance imaging. When compared to a healthy population, stronger activity was detected in primary and all non-primary motor cortical areas and subcortical regions. In paraplegic patients the primary motor cortex was consistently activated, even to the same degree as during movement execution in the controls. Motor imagery in SCI patients activated in parallel both the motor execution and motor imagery networks of healthy subjects. In paraplegics the extent of activation in the primary motor cortex and in mesial non-primary motor areas was significantly correlated with the vividness of movement imagery, as assessed by an interview. The present findings provide new insights on the neuroanatomy of motor imagery and the possible role of kinesthetic feedback in the suppression of cortical motor output required during covert movements.

Neural decoding of treadmill walking from noninvasive electroencephalographic signals

“…This view is supported by functional MRI (fMRI) studies in which cortical activation was detected when subjects imagined themselves walking (Bakker et al 2007(Bakker et al , 2008Iseki et al 2008) and when paraplegic patients imagined foot and leg movements (Alkadhi et al 2005;Cramer et al 2005;Hotz-Boendermaker et al 2008). A cortically EEG-driven BMI for the restoration or rehabilitation of walking could be also used as a strategy to harness or potentiate the remaining functionality and plasticity of spinal cord circuits isolated from the brain (Behrman et al 2006;Grasso et al 2004;Lunenburger et al 2006) and as a new tool for assessing the cortical contributions to walking in health and disease, or to study the changes in these contributions during learning and adaptation.…”

Virtual feedback for motor and pain rehabilitation after spinal cord injury

“…[25][26][27] The importance of cortical sensorimotor mechanisms underlying the effects of VF seem to be supported by the cumulative rather than independent pain-reducing effects of the combination of VF and transcranial direct current stimulation as observed in patients with neuropathic pain after SCI, 5 as well as by its simultaneous impact on motor functions and pain. 6 In addition, motor imagery abilities 20,[31][32][33][34] and cortical sensorimotor activity during movement observation, 20 motor imagery, 31,[34][35][36] or attempted movements 31,[34][35][36][37] have been shown to be intact after SCI, at least for simple movements. Still, these may not be preserved for complex movements.…”

“…Still, these may not be preserved for complex movements. 38 Moreover, reports of decreased activation levels and delayed timing, 35 as well as of additional brain regions being activated, 31,34 suggest that sensorimotor tasks may require more attention after SCI. A better understanding of the cortical sensorimotor mechanisms underlying the effects of VF in patients with SCI is therefore warranted.…”

Supernumerary phantom limbs in spinal cord injury

“…44 The patients often feel they have full motor control over the limb (opening and closing, positioning, movement), which to some extent can be objectively measured by neuropsychological testing and be shown to induce a specific activation pattern of the brain (for example, functional MRI studies). [45][46][47] Although the involved circuits have not been delineated with sufficient preciseness, supernumerary phantom limb sensations are similarly associated with changes in the brain.…”