Contents



Preface

For centuries, electrical stimulation has been employed for treating neural disorders. As early as the Egyptian period, for example, medical records cite the use of electric eel shock therapy for pain, while during the eighteenth

for electrotherapy waned somewhat in the late 1800s and early 1900s as

surgery, making them an appealing therapeutic strategy.

century it was used for treating paralysis and psychiatric symptoms. Enthusiasm

For the most part, the mechanisms elicited by neurostimulation are unknown. One widely acknowledged proposal is that neurostimulation somehow affects the electrical patterning that enables information transfer, since electrical activity is known to be fundamental to brain communication. The understanding of how patterning is structured, however, has been both evolving and vigorously debated, with the result that mechanisms of neurostimulation are themselves poorly understood. In the 1990s, though, Singer proposed a new thesis premised on the combinatorial properties of brain oscillations, which were intrinsic to neural operation. This provided for virtually unlimited freedom of expression in neural communication, unlike earlier models. Impelled in part by the prospect of an improved understanding of underlying mechanisms that may modulate, facilitate, or disrupt brain activity, as well as successes in symptomatic and long-term therapeutic relief, neurostimulatory and neuromodulatory protocols have since seen rapid growth in domains other than the motor diseases. Additionally fueling recent growth are the intrinsic advantages of neurostimulation over the more commonly used pharmaceutical agents. Unlike pharmacological approaches, which are difficult to target to specific brain regions and whose temporal distribution is usually prolonged, neurostimulation is inherently better suited to address the discrete spatial and temporal variation that characterizes individual dysfunctions.

The need for surgical intervention with its risk of secondary complications has spawned, moreover, an additional and equally broad group of non-invasive applications, including transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), and repetitive TMS (rTMS), among others, which can be used both therapeutically as well as diagnostically. Diagnostically, for example, TMS can be a surrogate marker of recovery that is both sensitive and quantitative for cranial vascular disorders. TMS has also proven to be a useful tool for examining cortical and corticospinal physiology and enabling the understanding of motor dysfunction. When physiologic data are correlated with clinical function, they can assist diagnosis of underlying motor dysfunction. Operant conditioning with TMS, for instance, has been used both to assess the weakness of corticospinal connections and to promote targeted neuroplastic

change.

psychotherapies came to acquire greater prestige for treating psychiatric symptoms. In recent decades, however, interest in neurostimulation for therapy has again reignited, beginning chiefly with applications for motor disorders and pain treatment. High-frequency stimulation of the subthalamic nucleus or globus pallidus in patients with Parkinson's disease (PD) was notably found to produce clinical effects that were similar to surgical ablation, yet were reversible, unlike
