Sensorimotor reorganization in relation to hand function following unilateral brain lesions

Abstract

Most activities of daily living require skillful use of our hands. Whatever the complexity of the task, our ability to perform any motor function largely relies on the integrity of the widely distributed corticomotor network. Damage to the central nervous system at any stage our life results in functional limitations to various extents. How the body responds in order to recover from such injuries will vary depending on the time, location and severity of the brain lesions. This is particularly true of children with early brain lesions, since an immature nervous system is known to have superior compensatory capabilities. Irrespective of the severity of impairment and the level of recovery, decreased ability in terms of effective hand function has a huge negative impact on the quality of day‐to‐day activities and personal wellbeing.

The overall aim of this thesis is to investigate the relationship between hand function and different types of unilateral brain lesions from the perspective of development, training outcomes and clinical measurements.

We have investigated children with unilateral cerebral palsy (CP) in Studies I, II and III. The aim of the Study I was to investigate the relationship between brain lesion characteristics, organization of corticomotor‐projection and hand function. Results showed a wide variation in hand function and the children with ipsilateral projection pattern showed lower ability than those with contra lateral pattern. We also found that corticomotor‐projection pattern can be influenced by lesion extent and location but not lesion type. We investigated these issues further in relation to the outcome of intensive training in Study II. In this study, we were able to show that children with unilateral CP were able to improve after intensive training, independent of their lesion characteristics and (re)organization of motor projection patterns. The results from Study III showed that, when performing asymmetric bimanual tasks, children with unilateral CP have impaired temporal and force coordination but are still able to complete these tasks through an alternative strategy compared with typically developing children. Impairment was greater when the non‐ paretic hand served as the holding hand. Interestingly, the ability of the non‐paretic hand was affected by the ability of the paretic hand.

Study IV was designed to develop and validate a method to quantitatively measure “spasticity”, which is a very common clinical symptom after an injury of the central nervous system. While investigating a group of adults with unilateral stroke, our results validated a biomechanical model that could separate and measure neural contribution in the generation of spasticity in the hand. The findings from this study have significant implications in relation to measuring spasticity directly in clinical settings.

Overall, this thesis holds direct clinical implication through our efforts to describe and assess hand function after unilateral brain lesions in both children and adults. With combined use of neurophysiology and neuroimaging methods, we could better describe both unimanual and bimanual abilities in children with reorganized corticomotor‐projection and also could indicate the potentials to improve after intensive training. A quantifiable measurement of spasticity is possible to be used in clinical settings.