The Complexity Effect as an Indicator for the Parkinson Plus Syndrome

Abstract

Given the manifest slowing of motor functions in parkinsonian patients, it would seem only logical to measure reaction time and to take this as a basis for developing a scoring system to assess the pathological impairment caused by the disease. This has, of course, been done before, yet with contradictory results, since the nature of the stimulus-response situation affects the behavioral response in parkinsonian patients in a quite distinct manner [1]. Cognitive and motor elements are confounded in the reaction time, and separating the one from the other calls for sophisticated methods of mental chronometry [6,7]. Parkinsonian patients have particular problems with motor reactions if the situation is effort-demanding and self-directed, movements have to be initiated and organized in space, or the necessary movements are sequential, simultaneous, complex, or without visual feedback [2,3]. While other cerebrally impaired patients with focal or diffuse lesions and, notably, demented display marked deficits of varying degrees in all reaction tasks, parkinsonian patients are, under certain conditions, perfectly able to react in the same way as normal controls, providing the degenerative disease process does not exceed the nigrostriatal system and no additional cerebral lesions (“Parkinson plus” (PLUS)) exist [4,9–11].