For example, it has been proposed that the mechanisms that underlie ideomotor apraxia involve disconnections buy RAD001 between parietal language and frontal motor areas (Geschwind, 1975), thereby disrupting the capacity to execute a gesture on verbal command. Alternatively, ideomotor apraxia has been attributed to the loss of stored representations of learned movement gestures
(Gonzalez Rothi et al., 1991; Poizner et al., 1995). The inability to copy a visual model, either by drawing or by physical assembly, is central to the definition of constructional apraxia. The core symptom of the disorder is made apparent when patients are presented with a model object and attempt to produce a faithful copy of it. The copies that patients produce are spatially disorganized, in the sense that components are often put into incorrect spatial relationships with respect to one another so that the spatial
structure of the object is lost (Piercy et al., 1960; Benson & Barton, 1970). The deficit is evident both when patients attempt to draw copies of simple geometric figures (e.g. a square or a triangle; Benton, 1967; Gainotti, 1985; Gainotti et al., 1985), and also when they attempt to copy a model object GDC-0449 cell line by assembling together its component parts (Benton & Fogel, 1962). The inability to produce accurate copies could be caused by a failure to either effectively analyze the spatial structure of the model or effectively orchestrate motor output to reproduce this structure through a sequence of actions (Arena & Gainotti, 1978; Mack & Levine, 1981). The deficit tends to be most severe following damage to the PPC, though it can follow
C-X-C chemokine receptor type 7 (CXCR-7) frontal damage as well (Villa et al., 1986), and although early studies pointed to a special role of the right hemisphere in constructional praxis (Piercy et al., 1960; Benton, 1967; Mack & Levine, 1981), more systematic later work (reviewed in De Renzi et al., 1982; Gainotti, 1985) supports the notion that this function is most probably encoded by both hemispheres. It should be noted that the inability to draw a figure is not by itself a sign of constructional apraxia. For example, it has been shown that the inability to draw objects from memory is a defect independent of constructional apraxia and especially common in aphasic patients with severe semantic–lexical disturbances (Gainotti et al., 1983). The above neuropsychological data indicate that constructional praxis is a distributed function, involving at a minimum parietal and prefrontal cortex. To characterize the involvement of parietal neurons in the analysis of object structure, a recent series of physiological experiments examined the neural representation of space in parietal area 7a of monkeys as they performed an object construction task (Chafee et al., 2005, 2007; Crowe et al., 2008).