Electrocortical and behavioral effects of chronic immobility on word processing

Neuroelectrical and subjective effects of chronic motor deficits (severe immobility) on word processing were explored. A total of ten artificially ventilated patients with end-stage amyotrophic lateral sclerosis (ALS), seven patients with tetraplegia due to a high spinal cord injury (SCI), and nine matched controls were examined. Both ALS and SCI patients were almost completely paralyzed; eye, head, and face movements were intact in SCI but not in ALS patients. Event-related brain potentials (ERPs) were recorded during presentation of verbs with strong motor-action associations and nouns with strong visual associations. Subjects estimated the subjective strength of motor and visual associations for each word using a scale from 0 to 5. No between-group difference was found for subjectively rated motor associations. All patients reported much stronger visual associations for both nouns and verbs than healthy subjects. ERPs to both word classes revealed a left occipital negativity in SCI patients at a latency of 200-300 ms, and a marked decrease of the slow positive wave in the interval of 300-800 ms in the two patient groups. Both psychophysical and electrophysiological data suggest compensatory activation of visual information processing areas in severely paralyzed patients. The more pronounced effects in the SCI group as compared with the ALS group may be attributed to somatosensory deafferentation in SCI patients, while the sensory inflow in ALS remains relatively intact.