Henry Head and His Nerve Regeneration Self-Experiment

Sir Henry Head was an English neurologist in the late 19th and early 20th centuries, known for his methodical research on the nervous system. His work provided insights into how nerves function and perceive the world, establishing him as a prominent figure in neurology. Head’s approach combined clinical observation with a deep theoretical curiosity, driving him to explore the complexities of sensation and brain function.

Early Life and Career

Born in 1861, Henry Head pursued his education at Trinity College, Cambridge, where he excelled in natural sciences. His early academic path included time in Germany and Prague, where he studied physiology under Ewald Hering, an experience that shaped his scientific outlook.

Upon returning to England, Head completed his medical training at University College Hospital in London and qualified as a doctor in 1890. He settled at the London Hospital, where he was appointed assistant physician in 1896. It was here he began the neurological research that would define his legacy.

The Nerve Regeneration Experiment

At the turn of the 20th century, the understanding of how sensory nerves recover from injury was limited. Head found that information gathered from patients was often imprecise, so he began a self-experiment to document the process of nerve healing and sensory return.

On April 25, 1903, a surgeon made an incision in Head’s left forearm, severing the superficial radial and external cutaneous nerves. The ends were sutured together to facilitate regeneration. This procedure initiated a multi-year study, during which Head subjected his arm to numerous sensory tests. He was 42 years old and in excellent health, having abstained from alcohol and tobacco to ensure the purity of his observations.

The experiment was a collaboration with psychologist W.H.R. Rivers, who conducted the objective sensory evaluations. Over five years, Rivers systematically tested Head’s arm, mapping the gradual return of sensation. The findings, published in the journal Brain in 1908, provided a detailed account of nerve regeneration.

Protopathic and Epicritic Sensation

From his self-experiment, Head developed a theory dividing sensation into two systems: protopathic and epicritic. He observed that as his nerves healed, different types of feelings returned at different stages, suggesting they were governed by separate neural mechanisms. This model proposed a novel hierarchical organization of the sensory system.

The first system to recover was what Head termed “protopathic” sensation. This primitive system is responsible for detecting basic stimuli like pain and extreme temperatures. Protopathic sensations are poorly localized and generate an “all-or-nothing” response that is often unpleasant.

Following the return of protopathic sensation, the “epicritic” system began to recover. This more refined system is responsible for discerning fine gradations of touch and temperature. Epicritic sensation allows for the localization of stimuli, the ability to distinguish between two points of contact on the skin, and the perception of light touch. Head’s identification of these two regenerating sensory pathways was a contribution to understanding the peripheral nervous system.

Other Neurological Contributions

Beyond his work on sensory nerves, Head contributed to other areas of neurology. He conducted extensive research on aphasia, the loss of language ability due to brain injury. His 1926 work on the subject offered a detailed classification of language disorders and treated aphasia as a complex psychological issue, not just a matter of brain localization.

Earlier in his career, Head investigated referred pain, where pain from an internal organ is perceived on the skin. Through observing patients with conditions like herpes zoster, he mapped these areas, which became known as “Head’s zones.” His research also extended to studying spinal cord injuries in soldiers during World War I.