title: Brain activation sequences following electrical limb stimulation of normal and paraplegic subjects.
abstract: In current clinical practice the degree of paraplegia or quadriplegia is objectively determined with transcranial magnetic stimulation (TMS) and somatosensory-evoked potentials (SSEP). We measured the MEG signal following electrical stimulation of upper and lower limbs in two normal and three clinically complete paraplegic subjects. From the MEG signal we computed distributed estimates of brain activity and identified foci just behind the central sulcus consistent in location with primary somatosensory (SI) for arm and foot and secondary somatosensory (SII) areas. Activation curves were computed from regions of interest defined around these areas. Activation of the SI foot area was observed in normal and paraplegic subjects when the upper limb was stimulated. Surprisingly, for each paraplegic subject, stimulation below the lesion was followed by cortical activations. These activations were weak, only loosely time-locked to the stimulus and were seen intermittently behind the central sulcus and nearby cortical areas. Statistical analysis of tomographic solutions and activation curves showed consistent responses following foot stimulation in one paraplegic (PS1) and intermittently in another paraplegic subject. We repeated the same experiment for PS1 in a different laboratory and the results from the analysis of foot stimulation from both laboratories revealed statistically significant focal cortical response only in the contralateral SI foot area.
authors.affiliation: Laboratory for Human Brain Dynamics, Brain Science Institute (BSI), RIKEN, 2-1 Hirosawa, Wako-shi, Saitama, 351-0198, Japan.
authors.forename: Andreas A
authors.initials: AA
authors.lastname: Ioannides
authors.forename: Lichan
authors.initials: L
authors.lastname: Liu
authors.forename: Ara
authors.initials: A
authors.lastname: Khurshudyan
authors.forename: Roger
authors.initials: R
authors.lastname: Bodley
authors.forename: Vahe
authors.initials: V
authors.lastname: Poghosyan
authors.forename: Tadahiko
authors.initials: T
authors.lastname: Shibata
authors.forename: Jürgen
authors.initials: J
authors.lastname: Dammers
authors.forename: Ali
authors.initials: A
authors.lastname: Jamous
mesh_terms: D000328:Adult; D000465:Algorithms; D000842:Ankle / Q000502:physiology; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005121:Extremities / Q000502:physiology*; D030141:Feedback, Psychological; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008875:Middle Aged; D010264:Paraplegia / Q000503:physiopathology*; D013003:Somatosensory Cortex / Q000502:physiology; D013119:Spinal Cord Injuries / Q000503:physiopathology; D014953:Wrist / Q000502:physiology