Todd, Faraday

12/15/12 Ev ernote Web Todd, Faraday Saturday, December 15 2012, 11:25 AM Todd, Faraday and the Electrical Basis of Brain Activity Citation: Reynolds, E (2007) History of Neuroscience: Todd, Faraday and the Electrical Basis of Brain Activity, IBRO History of Neuroscience [http://www.ibro.info/Pub/Pub_Main_Display.asp?LC_Docs_ID=3486] Accessed: date Edward Reynolds This article is based on a paper, "Todd, Faraday and the Electrical Basis of Brain Activity", published in August 2007 by Practical Neurology in association with the Journal of Neurology, Neurosurgery and Psychiatry, with kind permission of the Journal. Introduction Before the 19th century, ideas of how the brain functioned were dominated by the concept of hollow nerves through which were thought to flow, at different historical periods, "animal spirits", "nervous fluid", "nervous force" ("vis nervosa") and, by the turn of the 19th century, "animal electricity" (Clarke and Jacyna, 1987). Galvani developed the concept of animal electricity by eliciting muscle contraction by the application of atmospheric or frictional electricity to a frog nerve-muscle preparation. However, this concept was challenged by Volta, who maintained that Galvani was generating chemical electricity by the approximation of two dissimilar metals in the fluid of the frog's tissues. Volta's observations led to the Voltaic pile, the forerunner of today's batteries. Our modern understanding of the electrical basis of brain activity can be traced to the early 19th century and especially to the studies of Todd and Faraday (Reynolds, 2004 a, b). Robert Bentley Todd and Michael Faraday Robert Bentley Todd (1809-1850) (Figure 1) is best remembered today for the post-ictal paralysis which bears his name (Todd's Paralysis), but this was only a small fraction of his contribution to neurology and neuroscience, and far from being his most important. He was born in Dublin, the second son of a large and distinguished Irish family, whose father, Charles Hawkes Todd, was Professor of Anatomy and Surgery at the Royal College of Surgeons in Ireland, of which he was also President in 1821. Robert entered Trinity College, Dublin and trained in medicine at the Richmond Hospital, where he was influenced by the famous Robert Graves, and at his father's College, where he qualified in 1831. He proceeded to London and Oxford, where he obtained a Bachelor of Medicine degree, and at the remarkable age of 27 years in 1836 he was appointed to the Chair of Physiology and Morbid Anatomy at King's College in London, which had been founded just a few years earlier in 1829. He was elected a Fellow of the Royal Society in 1838. 1/6 12/15/12 Ev ernote Web Figure 1: Robert Bentley Todd (1809–1860). Todd was a clinical scientist who applied anatomy, including microscopy, and physiology to clinical medicine, especially to disorders of the nervous system. He was also a gifted administrator and was the prime mover in founding King's College Hospital in 1840, where he became its most eminent physician. He revitalised King's College Medical School, of which he became the first Dean in 1842, and he was an outstanding teacher. He also founded in 1855 the first Nursing School in London, St. John's House, five years before the more famous School founded by Florence Nightingale at St. Thomas's Hospital (Reynolds, 2005). Michael Faraday (1791-1867) (Figure 2) was born in London into a poor blacksmith's family of Yorkshire origin. He had very little education but as an apprentice bookbinder he devoured the scientific books he was binding. Through his own initiative and good fortune he was appointed in 1813 as a Laboratory Assistant to Sir Humphry Davy, Professor of Chemistry and Director at the Royal Institution in Albemarle Street, London, not far from King's College. Davy was the greatest scientist of his era in the UK. Among his achievements he invented the "Davy" Miner's Safety Lamp but, more importantly from the neurological perspective, he discovered sodium, potassium, chlorine, calcium and magnesium, among other elements, utilising the Voltaic pile. Figure 2: Michael Faraday (1791–1867). https://www.ev ernote.com/edit/5c5e8388-7bb9-4ecb-9f dd-6c7a0843a466#st=p&n=5c5e8388-7bb9-4… 2/6 12/15/12 Ev ernote Web Faraday remained at the Royal Institution for more than 50 years, rising to surpass Davy and to become one of the greatest experimental philosophers of all time. In the process he declined the Presidency of the Royal Society, the Presidency of the Royal Institution and a Knighthood. According to Einstein he was responsible, along with Clerk Maxwell (also of King's College) for the greatest change in the theoretical basis of physics since Newton. The practical consequences of his discoveries have profoundly influenced the nature of civilised life (Thomas, 1991). During the 1830s and 1840s, when Todd was developing his ideas of brain function at King's College, Faraday was laying the foundations of our modern understanding of electromagnetism at the Royal Institution, especially electromagnetic induction, the polar nature of electricity and magnetism and the inter-conversion of energies, not only of electricity and magnetism, but also of light, heat and gravity, which was the basis for the later law of the conservation of energy (Thomas, 1991). Faraday studied all forms of electricity, including the "animal electricity" generated by the electric eel (Gymnotus). Faraday's meticulous diaries record that Todd was present during his experiments on the electric eel on October 22, 1838. Also present on that occasion were two of Todd's distinguished colleagues from King's College: Professor John Frederick Daniell (1790-1845, who was the first Professor of Chemistry and invented the first constant cell battery (the Daniell battery), and Professor Charles Wheatstone (1802-1875), who was the first Professor of Experimental Philosophy and developed the first electric telegraph. Both were good friends of Faraday, sharing a common interest in electricity. The electrical basis of brain activity As both a scientist and a physician Todd made important contributions to our understanding and treatment of liver disease and acute febrile illness, but his main interest was always the nervous system. His many outstanding observations in neuroanatomy, neurophysiology, neuropathology and clinical neurology were described in several major works (Todd, 1849, 1854 and 1835-1859; Todd and Bowman, 1845-1856), among others. He made original contributions to our understanding of spinal ataxias and stroke including the post-ictal hemiparesis which bears his name. Todd was the first to recognise the functions of the posterior columns of the spinal cord. Gowers credits him with the first exact account of locomotor ataxy or tabes dorsalis. However, Todd's greatest achievement was in developing the concept of the electrical basis of brain activity and applying it especially to epilepsy (Reynolds, 2004 a, b). Influenced by the new science of electromagnetism, especially that of Faraday at the Royal Institution, but also Daniell and Wheatstone at King's, batteries, circuits and telegraphs became the model adopted by Todd for brain function. Thus Todd developed the concept of "nervous polarity" as the term "expressive of the nature of the nervous force". As a pioneer histologist he recognised that individual "nerve vesicles" (i.e. cells) had one or several nerve fibres attached to them and that every nerve fibre was connected to a vesicle which was the point of departure for one or many fibres (Figure 3). This anticipated the neuron doctrine of the late 19th century (DeFelipe, 2002). Figure 3: A CNS "vesicle" and related "fibres", i.e. neuron in later terminology. From Todd RB and Bowman W (1845). a. A large caudate nerve-vesicle, with diverging and branching processes, some of which b, are seen to pass off into extremely minute filaments. c. Long fibre with white substance of Schwann, d. https://www.ev ernote.com/edit/5c5e8388-7bb9-4ecb-9f dd-6c7a0843a466#st=p&n=5c5e8388-7bb9-4… 3/6 Furthermore, Todd brilliantly foresaw that each nerve vesicle and its associated fibres (i.e. neuron) was a distinct apparatus for the development of nervous polarity. He applied these concepts to epilepsy in which he envisaged seizures as periodic evolutions of nervous polarity comparable to the electrical phenomena described by Faraday under the name "disruptive discharge". He had learned from Faraday how a rise in electrical tension could, at a certain threshold, result in a sudden change in polar state, like the spark from a battery or lightning. In convulsions he envisaged the polar tension in the hemispheres and mesocephale rising to the highest degree and a rapid discharge taking place. Using the new magneto-electric machine developed by Faraday, Todd confirmed his theory by inducing tonic-clonic seizures in rabbits by electrical stimulation of the corpora quadrigemina and mesocephale. While recognising their similarities, Todd and Faraday doubted whether "nervous polarity" was identical with electricity. They were aware that the electricity produced by electric fish, for example the Gymnotus, required a special organ, the electric organ, which was under the control of the nervous system. In an era when the inter-conversion of energies was just beginning to dawn, especially to Faraday, both Faraday and Todd viewed nervous polarity as perhaps a higher polar force that could be converted into electricity, as well as perhaps the reverse. Subsequent developments Brazier (1988) suggested that the concept of the electrical basis of brain activity began in the 1870s with the discovery of the motor cortex by Fritsch and Hitzig, soon confirmed by Ferrier. These neurophysiologists used electrical stimulation of the cortex, in Ferrier's case in support of Hughlings Jackson's clinical views of cortical localisation. But Brazier overlooked the earlier work and priority of Todd and Faraday, as did Fritsch, Hitzig, Ferrier and Jackson.

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