Department of Experimental Psychology, Ghent University, BelgiumOn several occasions in his excellent monograph on apraxia,Georg Goldenberg points at the relation between apraxia,aphasia, and handedness (Goldenberg, 2013b). The co-occurrences of these manifestations are believed to shedlight on their cerebral organization as well as on their mutual(in)dependence.InmycommentIwouldliketoemphasizethedifficulties associated with claims regarding relations be-tween cognitive functions and their neural correlates, inparticular when it comes to their hemispheric co-lateralization. First I will outline the stance taken by Golden-berg, then I will provide some empirical and theoretical in-sights that might hint at an alternative reading of the clinicaldata.In several chapters the question is raised whether there ex-ists an obligatory relation between apraxia and aphasia, as inright handers these symptoms occur most often followingleft hemispheric lesions. Clearly, many studies have reporteda strong association between symptoms of apraxia andaphasia and their co-occurrence even increases in clinicalstudies that use dichotomous categorizations or focus onsevere types of aphasia such as global aphasia (Duffy D Goldenberg, Hartmann, & Schlott, 2003,Goldenberg, Hermsdorfer, Glindemann, Rorden, & Karnath,2007; Wang & Goodglass, 1992). Although it seems fromthese data that most patients suffering from aphasia alsotend to show apraxia, the relation is not mandatory, anddissociations are believed to be more prominent in left-handed patients. Goldenberg devotes a separate chapter toapraxia in left handers. According to his view “the absence ofright handedness leads to a reshuffling of asymmetric brainfunctions resulting in a random distribution of their later-ality” (p. 185). This experiment of nature offers the opportu-nity to investigate what functions ‘go together’ and form anobligatory link, and what functions are independent. Gold-enberg states that if two such functions “are in fact sub-components of one overarching function, they will always belocated in the same hemisphere” (p. 186). Subsequentexploration of clinical data of left-handed patients withapraxia is taken to suggest that most left-handers do notexhibit a more symmetric organization of apraxia, but revealbilateral disturbances following unilateral lesions, just likeright-handers. Goldenberg continues to demonstrate thatleft-handed patients suffer from apraxia as a consequence ofleft or right unilateral brain damage that may or may not beaccompanied by aphasia (Goldenberg, 2013a, 2013b). Heconcludes that neither the relation between apraxia andaphasia nor between apraxia and handedness is obligatoryand that “.the laterality of apraxia can vary independentlyfrom aphasia or handedness.” (p. 190).As Goldenberg elegantly demonstrates, apraxia is not amonolithic construct but consists of several (at least partiallydissociated) symptoms flagging disturbances of an over-arching cognitivefunction calledpraxis. The same can be saidfor aphasia with respect to language. In addition to thecomposed nature of these cognitive concepts, neuroimaginghas unveiled that in normal participants tasks of praxis andlanguage typically activate clusters of regions whose laterali-zation depends on the particular subcomponent and regionunder investigation. Handedness is a multifaceted concepttoo, that varies with the method of assessment and theapplied categorization. Dividing individuals in right and lefthanders might not do justice to the complex influence of thistrait, in particular when relating handedness to asymmetry ofcognitive function. Very few right handers show right hemi-spheric language dominance, but considerably more lefthanders do. As a result, left handed groups are more likely tocontain some individuals with atypical functional asymme-tries, resulting in lower mean asymmetry scores in behavioraland functional imaging studies. Given the complexity of the
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