Human Electrophysiology Core

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The Human Electrophysiology Core Facility has the goals of providing, a) innovative services that move the field fonward, b) extensive training for research personnel in quantitative noninvasive recording as well as brain stimulation in human subjects, and c) reliable and reproducible results based on sound experimental design and standardized experimentation. This (Ziore includes pioneering Recording and Stimulation methodologies with a strong history of innovation. The P50 potential is a sleep-state-dependent midlatency auditory evoked response that provides a quantitative measure of, a) the level of arousal through the amplitude of the first response of a pair of stimuli, and b) the level of habituation, and the process of sensory gating, through the amplitude of the response to the second stimulus as a percent of the response to the first. That is, the P50 potential is a noninvasive measure of brainstem-thalamus processing of arousal/preattentional mechanisms. The P50 potential has higher amplitude and/or reduced habituation in disorders that manifest hyperarousal, e.g. schizophrenia, anxiety disorder, depression, Parkinson's disease (PD). The P50 potential has lower amplitude in disorders that manifest hypoarousal, e.g. autism, Alzheimer's disease, Huntington's disease, coma. The psychomotor vigilance task (PVT) is a test of behavioral alertness and involves a simple reaction time (RT) designed to evaluate the ability to sustain attention and respond in a timely manner to salient signals. That is, the PVT is a noninvasive measure of thalamocortical processing of attentional mechanisms. We also have capacity for electroencephalographic (EEG) and electromyographic (EMG) recordings and analysis, usually used in conjunction with TMS studies to determine motor evoked potentials. Other tests, including an operant test battery (measures timing behavior, short-term memory, learning behavior, etc.) and near infrared spectroscopy (NIRS) (measures changes in hemoglobin concentration and redox state of cytochrome oxidase, as well as the ratio of oxygenated to total tissue hemoglobin in the frontal lobes from sensors affixed to the forehead) are also available. This Core allows the rapid (<1 hr) assessment of various levels of the neuraxis, from the brainstem to the thalamus to the cortex to the frontal lobes in human subjects. This Core also supports the common goal of making transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) (both non-invasive forms of brain stimulation) tools for studying disease processes, treating symptoms, and ultimately making them available as a treatment; although, the studies themselves represent different applications and different stages of the translational research cycle. TMS is regarded by the FDA as an investigational device, and it was only recently granted limited approval for the treatment of depression. Our clinical trials using repetitive TMS (rTMS) to treat tinnitus are specifically designed to translate clinical findings into general medical practice by laying the foundation for a large-scale trial that can gain FDA approval for this application. For example, our initial efforts to apply rTMS for the treatment of tinnitus prompted this Core to develop a realistic placebo or sham rTMS technique, one of the best in the field, and described below. In general, the clinical usefulness of rTMS has outpaced knowledge of its neural mechanisms of action and there is a great need for basic science studies of rTMS. For example, we conducted a clinical trial of TMS to alter cognition and behavior in persons who are tobacco-dependent. This study examined whether and how TMS influences reward systems in smokers who are either satiated or withdrawn from nicotine. We carried out a parallel study in the Animal Electrophysiology Core of rTMS effects in rodents exposed to smoke that afforded a greater opportunity to examine neural mechanisms of action. Other ongoing studies that use brain stimulation as a clinical treatment include the use of tDCS to augment gait recovery in stroke patients by increasing cortical activation prior to training, and will inform the design of future clinical trials in human subjects that are necessary to translate TMS and tDCS into clinical practice.