Effects of Single-session Transcranial Direct Current Stimulation in Children With Cerebral Palsy

Hemiparesis, or weakness on one side of the body, is common following stroke early in life. The broader clinical diagnosis for this type of childhood movement impairment is unilateral cerebral palsy (UCP). Cerebral palsy effects about 3 out of every 1000 live births in the Unites States, and produces lifelong motor, sensory, and cognitive disability.

Neurorehabilitation has primarily focused on intensive motor training to encourage use of the affected extremities in an effort to produce use-dependent neuroplasticity in the brain. Such interventions are effective, but require a burdensome amount of time, 60-90 hours per week, for both the child and therapist. Furthermore, some children do not respond at all to such training.

Neuromodulation is a relatively new field that aims to influence the brain's neuronal activity through direct application of magnetic (TMS) or electric (tDCS) energy. It is thought the combination of neuromodulation and motor training may reduce the dosage of training needed, and would promote recovery to a greater extent for more individuals. Indeed, previous work in adult stroke demonstrate a benefit of combining repetitive TMS (rTMS) and tDCS with motor training, compared to training alone. These types of synergistic interventions are just beginning to be used in children with UCP, with some preliminary data showing potential benefit.

One of the many questions surrounding neuromodulatory interventions like tDCS is how to reliably predict changes in neuronal activity. The currently hypothesized effects of tDCS are polarity-specific: anodal tDCS depolarizes membranes resulting in increased in neuronal excitability; cathodal tDCS hyperpolarizes tDCS resulting in decreased neuronal excitability. Furthermore, these effects scale with the intensity of stimulation: the larger the direct current delivered, the greater the change in excitability. This framework has been used to guide almost all studies using tDCS to produce a change in brain function and resulting behavior.

More recently, the field is beginning to appreciate that this framework may be overly simplistic. For example, when a cognitive task is performed concurrently with tDCS, there are reported non-linear effects related to current intensity and direction of change in excitability. Such work has a significant impact on the use of tDCS in rehabilitation, which advocates for the pairing of stimulation with on-going activity.