Electrical brain stimulation (EBS), also referred to as focal brain stimulation (FBS), is a form of electrotherapy and

neurotherapy Neurotherapy is medical treatment that implements systemic targeted delivery of an energy stimulus or chemical agents to a specific neurological zone in the body to alter neuronal activity and stimulate neuroplasticity in a way that develops (or b ...

used as a technique in

research Research is creative and systematic work undertaken to increase the stock of knowledge. It involves the collection, organization, and analysis of evidence to increase understanding of a topic, characterized by a particular attentiveness to ...

and

clinic A clinic (or outpatient clinic or ambulatory care clinic) is a health facility that is primarily focused on the care of outpatients. Clinics can be privately operated or publicly managed and funded. They typically cover the primary care needs ...

neurobiology Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions, and its disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, ...

to stimulate a

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

neural network A neural network is a group of interconnected units called neurons that send signals to one another. Neurons can be either biological cells or signal pathways. While individual neurons are simple, many of them together in a network can perfor ...

in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

through the direct or indirect excitation of its

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

by using an

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

. EBS is used for research or for therapeutic purposes.

History

Electrical brain stimulation was first used in the first half of the 19th century by pioneering researchers such as

Luigi Rolando Luigi Rolando (16 June 1773, Turin – 20 April 1831, Turin) was an Italian anatomist known for his pioneering research in brain localization of function. He studied medicine in Turin, later continuing his education in Florence, where he studie ...

(1773–1831) and Pierre Flourens (1794–1867), to study the brain localization of function, following the discovery by Italian physician

Luigi Galvani Luigi Galvani ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...

(1737–1798) that

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

s and

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s were electrically excitable. The stimulation of the surface of the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

by using brain stimulation was used to investigate the

motor cortex The motor cortex is the region of the cerebral cortex involved in the planning, motor control, control, and execution of voluntary movements. The motor cortex is an area of the frontal lobe located in the posterior precentral gyrus immediately ...

in animals by researchers such as

Eduard Hitzig Eduard Hitzig (6 February 1838 – 20 August 1907) was a German neurologist and neuropsychiatrist of Jewish ancestryAndrew P. Wickens, ''A History of the Brain: From Stone Age Surgery to Modern Neuroscience'', Psychology Press (2014), p. 226 ...

(1838–1907),

Gustav Fritsch Gustav Theodor Fritsch (5 March 1838 – 12 June 1927) was a German anatomist, anthropologist, traveller and physiologist from Cottbus. Fritsch studied natural science and medicine in Berlin, Breslau and Heidelberg. In 1874 he became an asso ...

(1838–1927),

David Ferrier Sir David Ferrier FRS (13 January 1843 – 19 March 1928) was a pioneering Scottish neurologist and psychologist. Ferrier conducted experiments on the brains of animals such as monkeys and in 1881 became the first scientist to be prosecuted ...

(1842–1928) and Friedrich Goltz (1834–1902). The human cortex was also stimulated electrically by

neurosurgeon Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty that focuses on the surgical treatment or rehabilitation of disorders which affect any portion of the nervous system including the brain, ...

s and

neurologist Neurology (from , "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the ...

s such as Robert Bartholow (1831–1904) and Fedor Krause (1857–1937). In the following century, the technique was improved by the invention of the stereotactic method by British neurosurgeon pioneer Victor Horsley (1857–1916), and by the development of chronic electrode implants by Swiss neurophysiologist Walter Rudolf Hess (1881–1973), José Delgado (1915–2011) and others, by using

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

s manufactured by straight insulated

wire file:Sample cross-section of high tension power (pylon) line.jpg, Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample d ...

that could be inserted deep into the brain of freely-behaving animals, such as cats and

monkey Monkey is a common name that may refer to most mammals of the infraorder Simiiformes, also known as simians. Traditionally, all animals in the group now known as simians are counted as monkeys except the apes. Thus monkeys, in that sense, co ...

s. This approach was used by James Olds (1922–1976) and colleagues to discover brain stimulation reward and the pleasure center. American-Canadian neurosurgeon Wilder Penfield (1891–1976) and colleagues at the Montreal Neurological Institute used extensive electrical stimulation of the brain cortex in awake neurosurgical patients to investigate the motor and sensory

homunculus A homunculus ( , , ; "little person", : homunculi , , ) is a small human being. Popularized in 16th-century alchemy and 19th-century fiction, it has historically referred to the creation of a miniature, fully formed human. The concept has root ...

(the representation of the body in the brain cortex according to the distribution of motor and sensory territories). EBS remains inextricably entwined with the work of Robert Galbraith Heath, Delgado and Penfield. It's of interest that during cerebral localization studies, neurosurgeon Penfield could not elicit emotional reactions in humans, either by observing spontaneous epilepsy or by electrically stimulating the surface of the cerebral cortex. Neurophysiologist Delgado noted a few exceptions to this rule. In contrast, EBS, via deeply implanted electrodes in localized areas of the brain ( deep brain stimulation; DBS), elicited both pleasurable and aversive responses in laboratory animals and humans as previously described. EBS could elicit the ritualistic, motor responses of sham rage in cats by stimulation of the anterior

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

, as well as more complex emotional and behavioral components of "true rage" in both experimental animals by stimulation of the lateral hypothalamus, and in human subjects by stimulating various deep areas of the brain. EBS in human patients with

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

could trigger seizures on the surface of the brain and pathologic aggression and rage with stimulation of the amygdala.

Process

Two-photon excitation microscopy has shown that microstimulation activates neurons sparsely around the electrode even at low currents (as low as 10 μA) up to distances as far as four millimeters away. This happens without particularly selecting other neurons much nearer the electrode's tip. This is due to activation of neurons being determined by whether they do or do not have

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s or

dendrite A dendrite (from Ancient Greek language, Greek δένδρον ''déndron'', "tree") or dendron is a branched cytoplasmic process that extends from a nerve cell that propagates the neurotransmission, electrochemical stimulation received from oth ...

s that pass within a radius of 15 μm near the tip of the electrode. As the current is increased the volume around the tip that activates neuron axons and dendrites increases and with this the number of neurons activated. Activation is most likely to be due to direct

depolarization In biology, depolarization or hypopolarization is a change within a cell (biology), cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolar ...

rather than synaptic activation.

Effects

A comprehensive review of EBS research compiled a list of many different acute impacts of stimulation depending on the brain region targeted. Following are some examples of the effects documented: * ''Sensory'': Feelings of body tingling, swaying, movement, suffocation, burning, shock, warmth,

paresthesia Paresthesia is a sensation of the skin that may feel like numbness (''hypoesthesia''), tingling, pricking, chilling, or burning. It can be temporary or Chronic condition, chronic and has many possible underlying causes. Paresthesia is usually p ...

, feeling of falling, oscillopsia,

dysesthesia Dysesthesia is an unpleasant, abnormal sense of touch. Its etymology comes from the Greek word "dys," meaning "bad," and "aesthesis," which means "sensation" (abnormal sensation). It often presents as pain but may also present as an inappropriate, ...

, levitation, sounds, phosphenes, hallucinations, micropsia, diplopia, etc. * ''Motor'': Eye movements, locomotion, speech arrest, automatisms, laughter, palilalia, chewing, urge to move, crying without feeling sad, etc. * ''Autonomic'': Blushing,

mydriasis Mydriasis is the Pupillary dilation, dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, Physical trauma, trauma, or the use of c ...

, change in blood pressure and breathing,

apnea Apnea (also spelled apnoea in British English) is the temporary cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the ...

, nausea,

tachycardia Tachycardia, also called tachyarrhythmia, is a heart rate that exceeds the normal resting rate. In general, a resting heart rate over 100 beats per minute is accepted as tachycardia in adults. Heart rates above the resting rate may be normal ...

, sweating, etc. * ''Emotional'': Anxiety, mirth, feeling of unreality, fear, happiness, anger, sadness, transient acute depression,

hypomania Hypomania (literally "under mania" or "less than mania") is a Psychiatry, psychiatric Abnormality (behavior), behavioral syndrome characterized essentially by an apparently non-contextual elevation of Mood (psychology), mood (i.e., euphoria) th ...

, etc. * ''Cognitive'':

Acalculia Acalculia is an acquired impairment in which people have difficulty performing simple mathematical tasks, such as adding, subtracting, multiplying, and even simply stating which of two numbers is larger. Acalculia is distinguished from dyscalcu ...

paraphasia Paraphasia is a type of language output error commonly associated with aphasia and characterized by the production of unintended syllables, words, or phrases during the effort to speak. Paraphasic errors are most common in patients with fluent for ...

anomic aphasia Anomic aphasia, also known as dysnomia, nominal aphasia, and amnesic aphasia, is a mild, fluent type of aphasia where individuals have word retrieval failures and cannot express the words they want to say (particularly nouns and verbs). By cont ...

, recalling memories, "going into a trance", "out of this world",

conduction aphasia Conduction aphasia, also called associative aphasia, is an uncommon form of aphasia caused by damage to the parietal lobe of the brain. An acquired language disorder, it is characterized by intact auditory comprehension, coherent (yet paraphasi ...

, hemispatial neglect, alexia,

déjà vu ''Déjà vu'' ( , ; "already seen") is the phenomenon of feeling like one has lived through the present situation in the past.Schnider, Armin. (2008). ''The Confabulating Mind: How the Brain Creates Reality''. Oxford University Press. pp. 167–1 ...

, reliving past experiences,

agraphia Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neuro ...

apraxia Apraxia is a motor disorder caused by damage to the brain (specifically the posterior parietal cortex or corpus callosum), which causes difficulty with motor planning to perform tasks or movements. The nature of the damage determines the di ...

, etc. EBS in face-sensitive regions of the

fusiform gyrus The fusiform gyrus, also known as the ''lateral occipitotemporal gyrus'','' ''is part of the temporal lobe and occipital lobe in Brodmann area 37. The fusiform gyrus is located between the lingual gyrus and parahippocampal gyrus above, and ...

caused a patient to report that the faces of the people in the room with him had "metamorphosed" and became distorted: "Your nose got saggy, went to the left. ..Only your face changed, everything else was the same."

Therapeutic applications

Examples of therapeutic EBS are: * Cranial electrotherapy stimulation (CES) * Deep brain stimulation (DBS) * Transcranial direct current stimulation (tDCS) *

Electroconvulsive therapy Electroconvulsive therapy (ECT) is a psychiatry, psychiatric treatment that causes a generalized seizure by passing electrical current through the brain. ECT is often used as an intervention for mental disorders when other treatments are inadequ ...

(ECT) * Low field magnetic stimulation (LFMS) * Functional electrical stimulation (FES) * Magnetic seizure therapy (MST) * Vagus nerve stimulation (VNS) * Deep transcranial magnetic stimulation (Deep TMS) * Responsive nerve stimulation (RNS) Strong electric currents may cause a localized lesion in the nervous tissue, instead of a functional reversible stimulation. This property has been used for neurosurgical procedures in a variety of treatments, such as for

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

, focal

and psychosurgery. Sometimes the same electrode is used to probe the brain for finding defective functions, before passing the lesioning current (

electrocoagulation Electrocoagulation (EC) is a technique used for wastewater treatment, wash water treatment, industrially processed water, and medical treatment. Electrocoagulation has become a rapidly growing area of wastewater treatment due to its ability to remo ...

References

{{Reflist Brain–computer interface Neurophysiology Neurology procedures Electrotherapy Physical psychiatric treatments Human subject research in psychiatry