12/15/12 Ev ernote Web Todd, Faraday

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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.

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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).

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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. The great achievement of these latter authors was in developing our concepts of cortical localisation. Paradoxically, however, Jackson did recognise Todd's description of post-ictal hemiparesis and it is to Jackson more than anyone that we owe the eponym "Todd's Paralysis". A few years later in 1877, Caton first reported electrical potentials from the cortex of animal species, mainly rabbits, but also cats and monkeys, including visual evoked potentials, but it was another 52 years before Berger (1929) first described the human electro-encephalogram. Only then were electrical theories of brain function and epilepsy widely embraced and older theories of the vascular basis of epilepsy finally laid to rest. Meanwhile in 1906, Cajal and Golgi received the Nobel Prize for their histological development of the neuron doctrine (DeFelipe, 2002) already glimpsed by Todd over 50 years earlier. Finally, in 1963 Hodgkin and Huxley received the Nobel Prize for identifying the ionic basis of the nervous polarity which Todd had proposed over a century earlier. Amazingly this theory involved the very same ions that Faraday's mentor, Sir Humphry Davy, had discovered, i.e. sodium, potassium, chlorine, calcium and magnesium.

MILESTONES IN THE HISTORY OF BRAIN ELECTRICAL ACTIVITY

SODIUM, POTASSIUM, CHLORINE, DAVY (1800s) CALCIUM, MAGNESIUM ELECTROMAGNETISM, ANIMAL FARADAY (1830s) ELECTRICITY BRAIN ELECTRICITY, NERVOUS TODD (1840s) POLARITY, DISCHARGES FRITSCH, HITZIG CORTICAL LOCALISATION AND (1870s) JACKSON, FERRIER EXCITABILITY ANIMAL ELECTROENCEPHALOGRAM (1870s) CATON SENSORY POTENTIALS NEURON DOCTRINE CAJAL, GOLGI (1890s) 1906 Nobel Prize) 12/15/12 Ev ernote Web BERGER (1920s) HUMAN ELECTROENCEPHALOGRAM IONIC BASIS OF NEUROTRANSMISSION HODGKIN, HUXLEY (1950s) (1963 Nobel Prize)

This table illustrates the remarkable progression of our knowledge about brain electricity, or nervous polarity, from Sir Humphry Davy's discovery of the appropriate ions, through the work of his pupil Faraday, who so profoundly influenced his contemporary in London, Todd, down to the Nobel Prize-winning work of Hodgkin and Huxley, involving the same ions discovered by Davy.

It is clear from these subsequent developments that Todd was way ahead of his time in developing and confirming his ideas of nervous polarity and electrical discharges in epilepsy, which may explain in part why so much of his work was overlooked. He died at the age of 50 in 1860, the very year that the National Hospital for Paralysis and Epilepsy was opened at Queen Square, close to Todd's new Hospital, King's College Hospital, in Portugal Street near Lincoln's Inn. If Todd had lived a little longer it seems likely that he would have been appointed to the National Hospital and his work would have been more widely known to the subsequent generation of physicians practising neurology in the second half of the 19th century.

Edward Reynolds MD, FRCP, FRCPsych Institute of Epileptology King's College School of Medicine Weston Education Centre Denmark Hill Campus Cutcombe Road London SE5 6PJ, UK [email protected]

Bibliography

Berger H: Uber das Elektrenkephalogramm des Menschen. Arch. Psychiatr. Nervenkr 1929;87:527- 70.

Brazier MAB. A History of Neurophysiology in the 19th Century. New York: Raven Press, 1988.

Clarke E, Jacyna LS. Nineteenth-century Origins of Neuroscientific Concepts. Berkeley: University of California Press, 1987.

DeFelipe, J. Santiago Ramón y Cajal (1852-1934). IBRO web site: History of Neuroscience, 2002. http://www.ibro.info/Pub/Pub_Main_Display.asp?LC_Docs_ID=3456

Hodgkin AL, Huxley AF. A quantitive description of membrane current and its application to conduction and excitation in nerve. J. Physiol 1952; 117: 500-44.

Reynolds EH. Todd, Faraday and the electrical basis of brain activity. Lancet Neurology 2004a;3:557-63.

Reynolds EH. Todd, Faraday and the electrical basis of epilepsy. Epilepsia 2004b;45:985-92.

Reynolds EH. Robert Bentley Todd. J. Neurol 2005; 252: 500-01.

Thomas JM. Michael Faraday and the Royal Institution. Bristol: Adam Hilger, 1991. Todd RB (1849). On the pathology and treatment of convulsive disease. London Medical Gazette 8:661-671, 724- 729, 766-772, 815-822, 837-848.

Todd RB (1854). Clinical lectures on Paralysis, Disease of the Brain and Other Affections of the Nervous System. London: J Churchill.

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Todd RB, Bowman W (1845-1856). The physiological anatomy and physiology of man. 2 volumes. London: Parker.

Selected quotations

Todd on the concept of nervous polarity

1. "Adopting the language of the illustrious Faraday, which expresses with clearness and precision the fundamental phenomena of the electric force, we may call the nervous power a polar force, generated in the centres and propagated by rapid polarisation of the neighbouring particles in various directions … " (Todd, 1849, p. 726).

2. "We can no more detect by our senses any physical change in the piece of soft iron which is rendered magnetic by the galvanic current then we can discover a change in the particles of a nerve stimulated to action by the same current. That both the iron and the nervous matter are thrown into an analogous state by the same agent seems highly probable. In the case of the iron the indication of the assumption and of the maintenance of the polar state is afforded by its power of attracting particles of iron; while in a muscular nerve the assumption and maintenance of the polar state are shown by the active contraction of certain muscles, or a more tonic state of passive contraction" (Todd, 1835-1859; vol. 3: p. 720P).

3. "We may regard each nerve vesicle and the fibres emanating from it, with the blood vessels which play around it, as a distinct apparatus for the development of nervous polarity" (Todd and Bowman, 1845-1856, p. 239).

Todd on nervous polarity and discharge in epilepsy

4. "These periodical evolutions of the nervous force may be compared to the electrical phenomena described by Faraday under the name of 'disruptive discharge' … In some instances the tension may be limited to the hemispheres of the brain. Then consciousness and intellectual action only are disturbed. In other cases the hemispheres and mesocephale pass quickly to the highest degree of tension, and a rapid discharge takes place exciting the other parts of the brain and spinal cord with all the violence of the discharge from a highly charged Leyden Jar" (Todd, 1849, p. 840).

Todd on inducing experimental seizures in rabbits with a Faraday magneto-electric machine

5. "I then tried the corpora quadrigemina and the mesocephale. Having passed fine bradawls into the cranium in such a direction as I had previously satisfied myself would lead to this organ, I subjected it to the inference of the machine; general convulsions were produced of a character essentially different from those which resulted from stimulating the spinal cord or the medulla oblongata. They were combined movements of alternate contraction and relaxation, flexion and extension, affecting the muscles of all the limbs, of the trunk and of the eyes, which rolled about just as in epilepsy" (Todd 1849, p. 821).

Faraday on nervous polarity, electricity and magnetism

6. "Wonderful as are the laws and phenomena of electricity when made evident to us in inorganic or dead matter, there interest can bear scarcely any comparison with that which attaches to the same force when connected with the nervous system and with life … I think the agents in the nervous system may be an inorganic force; and if there are reasons for supposing that magnetism is a higher relation of force than electricity, so it may well be imagined that the nervous power may be of a still more exalted character and yet within reach of experiment" (Faraday, M. Notice of the character and direction of the electric force of the Gymnotus. Philos. Trans. R. Soc. Lond. 1839;129: 1-12).

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