Medical career
Horsley specialised in surgery and in physiology. He was the first physician to remove a spinal tumor, in 1887, by means of a laminectomy. He developed many practical neurosurgical techniques, including the hemostatic bone wax, the skin flap, the ligation of the carotid artery to treat cerebral aneurysms, the transcranial approach to the pituitary gland and the intradural division of the trigeminal nerve root for the surgical treatment of trigeminal neuralgia.
As a neuroscientist, he carried out studies of the functions of the brain in animals and humans, particularly on the cerebral cortex. His studies on motor response to faradic electrical stimulation of the cerebral cortex, internal capsule and spinal cord became classics of the field. Those studies later translated into his pioneering work on neurosurgery for epilepsy. Between 1884 and 1886, Horsley was the first to use intraoperative electrical stimulation of the cortex for the localization of epileptic foci in humans, preceding Fedor Krause and Wilder Penfield.
He was also a pioneer in the study of the functions of the thyroid gland. He studied myxedema and cretinism, which are caused by a decreased level of the thyroid hormones (hypothyroidism), and established for the first time, in experiments with monkeys, that they could be treated with extracts of the gland.
Appointed in 1886 as secretary to a governmental commission formed to study the anti-rabies vaccine developed by Louis Pasteur, Horsley corroborated his results and created a campaign to vaccinate against rabies in the United Kingdom. As a pathologist, he carried out research on bacteria and founded the Journal of Pathology.
In June 1886, he was elected a Fellow of the Royal Society and, in 1891, jointly with his brother-in-law Francis Gotch, delivered their Croonian Lecture on the subject of the mammalian nervous system. In 1893, he was awarded the Cameron Prize for Therapeutics of the University of Edinburgh. A year later, in 1894, he won the Royal Medal for "his investigations relating to the physiology of the nervous system, and of the thyroid gland, and to their applications to the treatment of disease".
Horsley, who had been a keen rifle shot when serving in the Artists' Rifles as a medical student, also investigated the effect of gunshot wounds on the brain, experimenting with animals provided by a butcher and using the recently issued Lee-Metford rifle. He concluded that the immediate cause of death that follows was due to respiratory failure, not heart failure.
His best-known innovation is the Horsley–Clarke apparatus, developed in 1908 together with Robert H. Clarke, for performing the so-called stereotactic surgery, whereby a set of precise numerical coordinates are used to locate each brain structure. He was a pioneer in neurosurgery and operated on a total of 44 patients.
He authored the book Functions of the Marginal Convolutions (1884) and, as a co-author, Experiments upon the Functions of the Cerebral Cortex (1888) and Alcohol and the Human Body (1902).
