George K. York and David A. Steinberg
The Såa Institute, Fiddletown, CA USA, and Kaiser Stockton Medical Center, Stockton CA USA
Postictal paralysis, in which focal tonic and myoclonic movements are followed by temporary paralysis in the same distribution, presents the conceptual problem of apparent sequential increased and decreased function in the same anatomic area. Any adequate theory of cerebral localisation must explain the anatomy and pathophysiology of postictal paralysis, and conversely the explanation of it reflects contemporaneous theories. Though descriptions of postictal paralysis can be found in medical writings since Babylonian times, when writers attributed it the hand of the fever demon, it was not until the nineteenth century that Todd's paralysis was shown to be the result of focal cortical disease. In 1854 Robert Bentley Todd proposed that a seizure is the result of the gradual accumulation of morbid material in the blood, When this material reaches a critical level it provokes a discharge of nervous power, and leaves the brain in an exhausted state, as if malnourished. If this process was confined to the cortex, only mental exhaustion occurs; if it extends to the striatum, temporary hemiplegla ensues. Postictal paralysis provoked a disagreement between John Hughlings Jackson and William Gowers. Hughlings Jackson, adapting Todd's hypothesis to his theory of the nervous system as an evolutionary hierarchy of discrete centers, claimed that postictal paralysis was due to exhaustion of the highest and middle motor centers. Since the corticospinal tract was his middle motor level, paralysis results from exhaustion of this level. Gowers observed that Todd's paralysis could occur after an exclusively sensory seizure, and inferred that postictal paralysis could also occur by active inhibition of motor centers by epileptic discharges located in sensory centers. In response, Hughlings Jackson allowed that such a thing could occur, but he had difficulty understanding how to fit it into his theory. The history of postictal paralysis demonstrates that scientific explanations are constrained by the assumptions under which observations are made. Todd's explanation was constrained by his assumption that the function of the cortex is exclusively mental, not motor. Hughlings Jackson was limited by his assumption that exhaustion of one level lead to dis-inhibition of the next lower level; he could not fit the idea of active inhibition into this scheme. Gowers's explanation was strengthened by his acceptance of two complementary mechanisms, Jacksonian exhaustion and active inhibition.
Friday, 20 June 1997, 16.45-17.05
Second Annual Meeting of the International Society for the History of the Neurosciences (ISHN) and 6th Meeting of the European Club on the History of Neurology (ECHN)
Leiden, The Netherlands