Effects of tDCS in cortical plasticity and motor learning in children with cerebral palsy

Abstract

Cerebral Palsy (CP) is the most prevalent severe disability in childhood, with a birth incidence of approximately two in 1000 live births (Platt, Krageloh-Mann, & Cans, 2009). CP describes a group of disorders of development and posture, causing activity limitations that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of CP are often accompanied by disturbances of sensation, cognition, communication, perception, and/or behavior, and/or by a seizure disorder (Rosenbaum et al., 2007). Motor learning involves more than motor processes; it involves learning new strategies for sensing as well as for moving. Thus, motor learning, like motor control, emerges from an interplay of perception/cognition/action processes. To promote motor learning in CP, an ideal treatment would be one that targets specific dysfunctional areas of the brain with mild or no adverse effects. By combining motor training with a technique of Neuromodulation, this may be able to enhance the motor learning for those individuals, and therefore enhance neural plasticity. Following these criteria, transcranial direct current stimulation (tDCS) may have clinically relevant impact in the field of neurological and neuropsychological restoration for these patients.While tDCS has been used to improve motor function in pathologies such as Parkinson's disease or stroke, little has been to explore the beneficial effects of this neuromodulatory technique in children with CP. To investigate more than just physical improvements, the cognitive sphere needs to be evaluated as well to distinguish the possible benefits of tDCS as an intervention to enhance cognitive function such as executive function, working memory, and attention. Additionally, evaluation of neural plasticity in the motor cortex will provide objective measurements of the changes that take place during motor learning, and also increase the knowledge base for this population.tDCS is one of these non-invasive techniques able to modulate cortical excitability. The transcranial application of weak direct currents to the human primary motor cortex is capable of eliciting cortical excitability changes. In summary, cerebral excitability is diminished by cathodal stimulation, which hyperpolarizes neurons. Anodal stimulation causes neuronal depolarization, leading to an increase in excitability (Bindman, Lippold, & Redfearn, 1962).Further, tDCS is capable of inducing duration-dependent, long-lasting modulatory effects that outlast the duration of the stimulation period. This method of stimulation has been shown to affect a range of motor, somatosensory, visual, affective, and cognitive functions (Norris, Degabriele, & Lagopoulos, 2010). Brain stimulation with weak direct currents is a promising tool in human neuroscience and neurobehavioral research; preliminary data suggest that it can induce beneficial effects in brain disorders (Michael A. Nitsche et al., 2008). tDCS has emerged as a great tool to modulate cortical plasticity in the brain's motor area (Fregni et al., 2005), and non-invasively enhance motor restoration and learning. This non-invasive device releases a small electrical current (1 to 2mA) which flows through the scalp from anode to cathode. In the process, the current changes electrical activity in the brain.Indeed, most brain stimulation studies focus on the primary motor cortex as the main stimulation site. tDCS is shown to be safe in human safety studies and a recent meta-analysis (Brunoni et al., 2011), inducing only mild effects such as itching, tingling, headache, or burning sensation under the site of the electrodes. (AU)