Interactive reportLong-term changes in motor cortical organisation after recovery from subcortical stroke1
Introduction
The mechanisms responsible for the recovery of motor function after stroke are poorly understood. Previous studies employing transcranial magnetic cortical stimulation (TMCS) have shown that the early motor recovery which occurs in the hand during the first 3 months after a stroke can be related to improvement in conduction in the corticospinal pathway, but that there may also be changes in corticomotor excitability and in the organisation of the corticomotor projection to the hand during this early period [7], [12], [13], [40], [41]. These changes have been found both in patients with cortical and subcortical lesions, and it has been postulated that they are part of a process of reorganisation in the motor cortex which occurs as a result of the loss of cortical motoneurones or corticospinal fibres in the lesion [7], [41]. In addition, evidence of larger scale changes in the activity of cortical motor centres in both the affected and unaffected cerebral hemisphere has been derived from positron emission tomographic (PET) studies of patients with subcortical infarcts who had recovered motor function [11], [44], [45]. However, as yet there is little information on the natural history of cortical reorganisation after stroke and its long-term role in motor recovery remains uncertain.
In the present study we performed TMCS and motor cortex mapping in a group of subjects who had recovered normal or near-normal motor function in the hand following a subcortical stroke up to 15 years previously, to determine to what extent changes in motor cortex excitability and organisation persist after motor recovery.
Section snippets
Subjects
Ten patients (24–67 years of age, three female) who had suffered a single subcortical stroke 6 months to 15 years previously resulting in a motor or sensorimotor deficit in the contralateral upper limb were included in the study (Table 1). The motor deficit had recovered fully in all but two patients who had mild residual weakness and impairment of finger dexterity in the affected hand on clinical testing. The rate of recovery was variable in different cases but, in all, was maximal within the
Results
Details of interhemispheric MEP latency and threshold differences, MEP amplitude and silent period duration ratios, and interhemispheric differences in MEP and SP map position in the control and stroke subjects are given in Table 2, Table 3.
Discussion
The present findings indicate that long-term changes in the physiological properties of the corticomotor projection to the hand are frequently present in patients who have recovered motor function after a subcortical stroke. The changes found in this group of subjects point to a process of functional reorganisation in the motor cortex which occurs as part of the recovery process after a lesion of the descending motor pathways. Evidence of reorganisation was found even many years after the
Acknowledgements
The study was supported by grants from the National Health & Medical Research Council of Australia and the Neuromuscular Foundation of Western Australia. The authors are grateful to the neurologists who referred subjects for the study and to Dr. S. Ghosh for helpful discussions.
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Published on the World Wide Web on 1 December 2000.