Spatial Planning deficits in limb apraxia

Abstract

Geschwind (1975) proposed a disconnection model in which an apraxic subject is unable to carry out movements to command because the left hemisphere that comprehended the verbal command is disconnected from the right premotor and motor areas which controls the left hand. An alternate model, however, proposes that apraxia results from destruction of spatiotemporal representations of learned movement stored in the left hemisphere (Heilman, 1979). The disconnection hypothesis would predict that apraxic subjects should be able to correctly imitate gestures and correctly use actual tools since these tasks do not require language. The movement representation model predicts that imitation and actual tool use would also be impaired. Motion analyses were performed on the trajectories of repetitive 'slicing' gestures made in a series of conditions in which contextual cues were introduced in a graded fashion. Four cue conditions were presented: no cues (verbal command), object present, tool present and both object and tool present. Positions of the hand, wrist, elbow, and shoulder were digitized from neighbouring views, reconstructed in three dimensions and analysed with respect to specific spatiotemporal features of the trajectories. Three subjects with limb apraxia, who had lesions that included left parietal cortex, and four neurologically intact subjects participated. The apraxic subjects showed disturbances in planning the movement of the hand in space across the cue conditions. For example, they showed deficits in the plane of motion, the shape of the trajectory and in the coupling of hand speed and trajectory shape even when given full contextual cues. These data support the hypothesis that apraxia can result from the destruction of spatiotemporal representations of learned movement, rather than from a disconnection between the receptive language areas in the left hemisphere and the contralateral motor cortices.

Apraxia: a review

“…Interestingly, the patient could not prevent himself from performing the action appropriate to the tool he was holding, rather than the action that was requested. In another study however, gesture execution improved when the object of the action, but not the tool, was given (Clark, Merians, Kothari, Poizner, Macauley, Rothi and Heilman, 1994). Hence, the addition of visual and somaesthetic cues may improve certain aspects of apraxic movements, since it provides mechanical constraints and supplementary information that facilitates the selection of an adequate motor program (Hermsdörfer, Hentze and Goldenberg, 2006).…”

“…According to this model the verbal command for the movement is comprehended in Wernicke's area and is transferred to the ipsilateral motor and premotor areas that control the movement of the right hand (Clark et al, 1994;Leiguarda and Marsden, 2000). For a left hand movement, the information needs to be further transmitted to the right association cortex via the corpus callosum.…”

“…These techniques allowed to show many abnormalities in the kinematic features of apraxic movements such as for example: deficits in spatial accuracy, irregular velocity profiles, reduced maximum velocities, reduced movement amplitudes, decoupling of the relationship between instantaneous wrist velocity and trajectory curvature, improper linearity of the movement, wrong orientation of the movement in space and/or deficient joint coordination (Poizner, Mack, Verfaellie, Rothi and Heilman, 1990;Platz and Mauritz, 1995;Rapcsak et al, 1995;Poizner, Clark, Merians, Macauley, Rothi and Heilman, 1995;Poizner, Merians, Clark, Rothi and Heilman, 1997;Merians et al, 1997;Merians et al, 1999;Clark et al, 1994;Haaland et al, 1999;Binkofski et al, 2001;Hermsdörfer et al, 2006). An example of an apraxic movement with abnormal kinematics is shown in Figure 4.…”

Apraxia Impairs Intentional Retrieval of Incidentally Acquired Motor Knowledge

“…The SRT paradigm assesses incidental motor sequence learning by performance measures; in addition a subsequent free recall task allows assessing intentional retrieval of the incidentally learned motor sequence (Nissen and Bullemer, 1987;Keele et al, 2003). Because of its spatial component and the opportunity to isolate a sequence-specific learning effect, the SRT paradigm is well suited for the investigation of apraxic patients who clinically present with spatial (Poizner et al, 1990;Clark et al, 1994) as well as sequential errors (De Renzi et al, 1983;Harrington and Haaland, 1992;Buxbaum and Schwartz, 1998;Weiss et al, 2008). The neural substrate underlying motor learning deficits in apraxic patients was revealed by quantitative VLSM, thereby extending previous studies adopting the SRT paradigm to stroke patients (Pohl and McDowd, 2006;Orrell et al, 2007), which performed no or only descriptive lesion analysis.…”

Towards a computational neuropsychology of action

“…Thus, these tasks might be inadequate to elicit apraxic deficits. A caveat, however, is that patients with ideomotor apraxia have been shown to have kinematic abnormalities even for simple natural movements (Clark et al, 1994;Poizner et al, 1995). These kinematic abnormalities tend to be ignored by the neuropsychological and neurological literature (although see (Ietswaart et al, 2006)).…”