ELECTRODES FOR RECEPTION AND STIMULATION IN THE BODY

Electrodes for Reception and Stimulation in the Body  Electrodes can be used two basic ways in medical applications.  They can be used for reception, to receive signals from the body, such as for diagnosing carpal tunnel and other nerve disorders or for impedance imaging and monitoring.  Electrodes can also be used for stimulation, for example, delivering shocks for cardiac defibrillation or pacing, delivering pulsed electromagnetic fields for pain therapy and healing of muscle, bones, and nerves, or for stimulating the brain for control of Parkinson’s disease or mental disorders.

Cont…  They can also be used for invasive heat treatments such as cardiac ablation, and for measuring the dielectric properties of body tissues and other materials.  Electrodes for either stimulation or reception can be used over very large regions of the body, smaller regions, or very localized areas.  They can be invasive, external, in vitro, or completely separated from the body.  For all applications, maintaining good electrical contact between the electrode and the body is very important.  Conductive gels are often used (such as in ECG measurements). and specialized materials are used to prevent buildup of nonconductive fibrous tissue (scar tissue) around implantable electrodes.

Electrodes for Reception 1. Electrophysiological Assessment  Clinical electrophysiological assessment, also called electroneuromyography (ENMG; or when only associated with a muscle, electromyography [EMG]), is used to determine the function and integrity of specific parts of the neuromuscular system.  The neuromuscular junction, skeletal muscles, peripheral sensory nerve fibers, reflexes, and some central nervous system pathways can be tested using ENMG, even individual motor neurons.  Surface electrodes are the least localized and least invasive.

Cont...  Needle electrodes are more localized and more invasive.  Miniaturized needle electrodes made out of silicon are the most localized and are generally meant to be implanted in the body (and hence are the most invasive).  Sometimes both stimulation and recording electrodes are used simultaneously to determine the effect of stimulating a region and determine if the signals pass through the neural system as expected.

2. Intracellular Recording: Receiving Signals from Brain and Nerves  These studies have been used extensively for the development and assessment of neurotransmitter drugs and an overall study of the nervous system.  Until, there has been no way to perform these tests in a living organism, because the nerve cells are too small.  Recently, a number of groups have been developing very tiny electrodes and arrays of electrodes made by etching silicon, and have been able to receive signals from individual neurons.  Although still used mainly for research, this technology is rapidly progressing toward commercial applications that focus on individual nerve stimulation more than neural recording.

3.Impedance Imaging  It would be extremely useful if impedance measurements could be used to map the impedance of the interior of the body.  Such a map would provide not only morphometric information like that provided by x-ray computed tomography (CT) scans, but also additional physiological information.  One method for mapping impedance would be to use an array of electrodes around the periphery of the body, as illustrated in Figure

Cont…  These reconstruction techniques work well with x-rays because the x-rays travel in straight lines through the body.  These same reconstruction techniques do not work well with impedance imaging, however, because the currents do not travel in straight lines between the electrodes through the body.  Special techniques have been used to try to account for differing current paths, but with limited success.  If impedance imaging could be made useful, it would have the advantage of being simpler and less expensive than some other imaging techniques