History of Transcranial Stimulation
Believe it or not...
The first clinical application of electrical stimulation involved utilizing electricity derived from electric torpedo fish, catfish, and eels!
The use of electricity as a therapeutic medical application is not a recent discovery. The knowledge of electricity dates back to Ancient Egypt – ancient Egyptians were familiar with the Nile catfish’s ability to generate electricity although it is unclear whether electricity was used in clinical settings (Sarmiento, San-Juan, & Prasath, 2016). Ancient Greek philosophers Plato and Aristotle were both aware of the torpedo fish’s capacity for electrical stimulation and both were knowledgeable about its potential for therapeutic use (Sarmiento, San-Juan, & Prasath, 2016; Althaus, 1873; Rockwell, 1896; Harris, 1908). The first official documented use of electrical stimulation applied to the brain was made by Ancient Roman physician Scribonius Largus. In his works, he described how placing a torpedo fish on a patient’s scalp could relieve headache. The clinical use of electricity from fish continued to be used for over 10 centuries, its applications including use for treatment of epilepsy, demonic possessions, headaches, and even gout (Fridriksson, Hubbard, & Hudspeth, 2012).
The clinical application of applied electricity evolved as knowledge about electricity evolved. The first electricity-producing device involved a crank-controlled machine that was developed in 1660 by German Scientist Otto von Guericke (Fridriksson et al., 2012; Comroe & Dripps, 1976). The first capacitor, a device used to store electricity, was created in 1745 by Ewald Georg von Kleist. He termed his creation the “Leyden Jar” (Keithley, 1999). Later in 1757, Benjamin Franklin would combine the Leyden jar with electric generator for use in clinical applications (Fridriksson et al., 2012).
Up to this period of time, the type of electricity used was electrostatic energy. DC electricity came about in the 18th century when Luigi Galvani developed the first DC battery. DC stands for ‘direct current,’ and involves the flow of electricity without fluctuations in current (electrical charge). Galvani’s nephew, Giovanni Aldini, was the first person to apply this DC battery in a clinical setting. He initially experimented on himself. In 1801, he describes a detailed account of using DC current applied to the scalp of a 27 year old farmer who had been institutionalized for major depression (called ‘melancholy madness’ at the time). Over progressive sessions of use, the farmer’s mood progressively improved, and after several weeks of treatment, his depressive symptoms resolved completely (Fridriksson et al., 2012; Parent, 2004).
Aldini’s findings produced increased interest in the clinical use of DC electricity, specifically amongst German psychiatrists who studies the use of an early version of transcranial direct current stimulation (tDCS) device on neurologic and psychiatric conditions. Probably in part due to insufficient knowledge about the effects of polarization, varying stimulation parameters and sub-par detailed accounts published, the results of these studies were inconclusive. Thus, tDCS was abandoned until the 1950s and 1960s, the most famous results arising from a study performed by Lippold and Redfeam in 1964 who demonstrated that 50-500uA of direct current applied to the scalps of 32 healthy subjects could lead to behavioral changes. More specifically, anodal stimulation lead to increased mood, attention, and motor activity; while cathodal stimulation lead to increased quietness and apathy. Experiments with tDCS slowed to a halt after the 1970s, likely in part due to the emergence of new psychiatric medications that were introduced into the medical market (Dubljevic, Saigle, & Racine, 2014; Sarmiento et al., 2016).
Interest in transcranial stimulation as a clinical application was re-ignited in 1998 by Priori et. al who showed that transcranial magnetic stimulation applied to the scalp could alter cerebral cortical activity (Priori, 2003; Brunoni et al. 2012). This sparked interest which continues and evolves to this day. The development of more streamlined tDCS and TMS devices by biomedical engineers allow for more convenient and accurate use. There is a growing body of evidence that these applications are effective in the treatment of neurological diseases such as stroke, epilepsy, chronic pain, and migraine; the treatment of psychiatric diseases such as depression, anxiety, and bipolar disorder (Schlaug & Renga, 2008) ; and for enhancement of various cognitive functions in healthy people (Dubljević et al. 2014) . This growing body of evidence also supports that the devices used in research protocols are safe and have minimal side effect profiles. However, there is a growing concern regarding the increasing use of ‘do-it-yourself’ transcranial electric (tES) devices, which potentially be harmful if used by non-clinically trained individuals. Recent studies support that devices that are improperly built and applied may actually worsen memory function, and there is an increasing concern for adverse structural effects when tES is applied incorrectly over time (IFCN 2015 Statement regarding DIY tES). For this reason, the International Federation of Clinical Neurophsyiology has issued a statement against the use of DIY tES.
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