Effect of brain and spinal cord injuries on motor imagery.

The timing of mentally executed movements was measured in ten patients with hemiplegia, tetraplegia and paraplegia. In hemiplegic patients a significant difference in mental duration times was found between the paralysed and the normal "represented limb". The paralysed limb was mentally much slower than the healthy one. In contrast, movement times in tetraplegic and paraplegic patients did not differ from those in normal subjects. All patients reported a sensation of subjective effort accompanying the execution of the mental tasks. These observations are compatible with an outflow processing underlying motor imagery.