The electrical properties of biological cells, tissues, and organs studied in electrophysiology not only provide information about the normal/abnormal activities of human bodies but also provide a means to directly restore, repair, replace, or recreate physiological functions in humans to improve quality of life. For example, cardiac pacemakers, implanted in millions of patients, deliver electrical pulses into the right atrium and/or the right/both ventricles to control abnormal heart rhythms. Electrical activities of neurons such as action potentials (specific waveforms of voltage fired by neurons) have been studied for neurodisorders. Recordings of electric signals spatially and temporally around the brain and central nervous system, such as electroencephalography [(EEG) electrical activities along the scalp from the brain] and evoked potential responses (measurement of the time and waveform changes for nerves in other parts of the body in response to electrical stimulation of the brain), help to understand brain functions and diagnose diseases such as multiple sclerosis (nerve cells in the brain and spinal cord gradually degrade causing problems in muscle control and cognition).

As activation to targeted tissues, neurostimulation triggers neurons with electrical voltages or currents to excite signal propagation in the nervous system to restore functions. Sensations such as hearing and vision can be restored by cochlear or retinal implants. Tremors can be controlled with deep brain stimulation in the subthalamic nucleus and the globus pallidus interna areas to manage Parkinson?s Disease and dystonia (both with symptoms of involuntary muscle contractions and tremors). Chronic pain can be inhibited by electrically stimulating the periaqueductal gray and periventricular gray areas in the brain for nociceptive pain, and the ventral posterolateral/posteromedial nucleus for neuropathic pain. Brain?computer interfaces have been developed for motor neuroprosthetics, such- as robotic hands, arms, or legs that can be controlled by thoughts with decoded action potentials or EEG signals from the brain for patients with paralysis. Recently, experiments on electrical stimulation in the uperolateral branch of the medial forebrain bundle have found a significant antidepressant effect for major depression, especially treatment-resistant depression.

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