Discussion forum Apraxia e The cognitive side of motor control Georg Goldenberg* Krankenhaus Munchen-Bogenhausen, Neuropsychologische Abteilung, D-81925 Munchen, Germany 1. History The beginning of research on apraxia is usually identified with the seminal writings of the German psychiatrist Hugo Karl Liepmann in the first decades of the 20th century, but disturbed mental control of deliberate movements had been subject to clinical observation and theorizing before Liep- mann. The clinical literature of the late 19th century recog- nized three syndromes characterized by wrong or awkward actions in spite of preserved motor strength and coordination: Mind-palsy, Asymbolia, and Apraxia. The theoretical fundament of mind-palsy was the associ- ationist reduction of mental processes to the anatomy of modality specific cortical areas and their connections. Mind- palsy was expected to arise when cortical areas storing memory traces of previous actions were either destroyed or disconnected from cortical areas directing the muscles that implement the intended actions. The concepts of “asymbolia” and “apraxia” were grounded in linguistics and psychology rather than in the anatomy of motor control. The psychiatrist Finkelnburg described diffi- culties of aphasic patients with the production and compre- hension of non-verbal signs like musical notes, numbers, or meaningful gestures. He postulated that aphasia is regularly accompanied by such problems because they are, like aphasia itself, expression of an overarching “asymbolia”. The linguist Steinthal described an aphasic patient who grasped the pen upside-down and took hold of spoon and fork as if he had never used them before. Steinthal explicitly excluded defi- cient motor control as the source of these difficulties. He wrote: “It is not the movement of the limbs which is inhibited, but the relationship between the movements and the object used”. His conclusion that “this apraxia is an obvious amplification of aphasia” seems to be the first printed appearance of the word “apraxia”. Liepmann’s seminal model of apraxia unified the anatomical with the psychological approach to apraxia. He suggested that fibres connecting posterior brain regions with the motor cortex are the substrate of a posterior to anterior stream of action control that converts conscious mental im- ages into motor commands. The stream thus leads from the realm of psychology to the physiology of motor control. Liepmann characterized its function as the “government of the limbs by the mind”. He envisioned two possible loci of breakdown: Disturbed mental images of intended actions would lead to “ideational”, and interruption of the stream from mental images to motor cortex to “ideo e kinetic” apraxia. In the middle of the 20th century Liepmann’s theories of apraxia were overridden by “holistic” theories which denied the validity of anatomical localisation for explaining mental symptoms of brain damage. Explanations referred to univer- sal psychological principles rather than to the anatomical implementation of motor control. Apraxia was considered as a weakness of voluntary control which undermines the au- tonomy of action and renders the patient victim of stereotypic routines and environmental influences. In the last third of the 20th century the pendulum swung back again and holism gave way to a renaissance of the localising approach. Norman Geschwind resuscitated Liep- mann’s model of apraxia but replaced the multi-modal mental images of intended actions by a stock of learned motor skills and thus degraded the posterior to anterior stream from a mechanism for the government of the limbs by the mind to a path for the transport of motor skills from their storehouse to the place of execution. * Krankenhaus Munchen-Bogenhausen, Neuropsychologische Abteilung, Englschalkingerstrasse 77, D-81925 Munchen, Germany. E-mail address: Georg.Goldenberg@extern.lrz-muenchen.de. Available online at www.sciencedirect.com Journal homepage: www.elsevier.com/locate/cortex cortex xxx (2013) 1 e5 Please cite this article in press as: Goldenberg, G., Apraxia e The cognitive side of motor control, Cortex (2013), http://dx.doi.org/ 10.1016/j.cortex.2013.07.016 0010-9452/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cortex.2013.07.016