Viewing Brain Stimulation from a Plasticity Perspective

This chapter provides an overview of key mechanisms mediating neuronal plasticity. It summarizes the initial advances in understanding how brain stimulation modalities used clinically exert enduring effects on neuronal activity. To understand how long-term potentiation (LTP) occurs, investigators focused on two key questions: what aspects of the tetanic stimulation are necessary and sufficient to elicit LTP, and what aspect of synaptic transmission is being modified to enhance the response to a single volley. Familiarity with the marked differences in the properties of two major types of ionotropic glutamate receptors helps immensely in understanding how synaptic plasticity operates. These prominent glutamate receptor subtypes are called AMPA and NMDA receptors, named for agonists that selectively activate one but not the other subtype. Recent studies have demonstrated that the ability of transcranial direct current stimulation (tDCS) to improve motor learning can be understood in terms of the NMDA receptor dependent plasticity underlying LTP.