Brain Control of Movements in Cerebral Palsy

Although the capacity of the immature nervous system to recover after injury is superior to that of the adult brain, children with cerebral palsy carry a great burden of morbidity for their entire life. Functional outcome may be determined not only by characteristics of the lesion (size, location, and timing) but also by the response of the brain to the lesion (cortical re-organization). Little is known about how underlying limitations, such as inefficient cortical re-organization, affect functional outcome and response to therapy in children with cerebral palsy. Because of this, individual rehabilitation strategies are based solely on the level of functioning rather than on the underlying impairment. Research demonstrates that novel rehabilitation strategies can manipulate plasticity of the motor cortex and, in this way, improve functional outcome in adults who have suffered a stroke. There is preliminary evidence that these treatments may also benefit patients with cerebral palsy. However, cortical re-organization after an injury to the developing brain may not be similar to that which occurs after a stroke in the adult brain. It would be of benefit to have a greater understanding of the impairments that arise from inefficient cortical re-organization in children with cerebral palsy. It is also important to have the research methodology to assess the effect of these novel treatments in order to measure their true benefit.

Cortical re-organization can lead to enhanced participation of the unaffected hemisphere via anomalous ipsilateral corticofugal motor projections. Recent evidence suggests that this form of neural re-organization may not be efficient. Three different types of ipsilateral projections are thought to exist: 1) fast-conducting developmental ipsilateral projections that persist beyond the age at which they normally disappear; 2) slow-conducting ipsilateral tracts present in healthy subjects that become more accessible after injury; 3) fast-conducting projections that arise de novo from the ipsilateral primary motor cortex after injury to the developing brain. Each type has a distinct neurophysiologic profile that can be characterized using transcranial magnetic stimulation (TMS) and electromyography (EMG).

To date, the relationship between anomalous ipsilateral corticofugal motor projections and functional outcome has not been examined in detail. There is preliminary evidence that the presence of these anomalous ipsilateral projections is associated with poor outcome, suggesting that they represent an inefficient cortical re-organization process. In addition, the anomalous projections that arise de novo from the ipsilateral primary motor cortex appear to have the worst prognosis. The proposed research study will characterize anomalous ipsilateral corticofugal motor projections in a group of children with spastic hemiplegia and spastic diplegia subtypes of cerebral palsy using TMS and EMG. We will evaluate functional limitations of the hand in these children and will examine the relationship between each type of ipsilateral pathway and functional outcome. In this way, it will be possible to determine which anomalous ipsilateral projections are associated with poor function in patients with cerebral palsy.

This study will increase our understanding of the functional significance of these ipsilateral projections and will make it possible to identify these ipsilateral projections in individual children. The neurophysiologic techniques developed in this study will provide essential research methodology to assess brain re-organization before and after novel therapeutic approaches.