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mediation of both verbal and nonverbal memory (Johnson and Ojemann 2000). Dopaminergic depletion in the basal ganglia causes a disruption of these pathways and may therefore lead to lower memory performance in PD patients (see Pillon et al. 2001 for a review). As visuospatial memory has been associated with right hemispheric function, and verbal memory is believed to show a left hemisphericpreference, stimulus modality could be a discriminative factor in the memory performance of RPD and LPD patients. Visuospatial memory. Thirteen studies investigated visuospatial memory in PD. Often used tasks included the Visual Reproduction and Designs subtests of the Wechsler Memory Scale (WMS and WMS-R), and the Benton Visual Retention Test (BVRT). The Visual Reproduction subtest of the WMS wasadministered in six studies (Blonder et al. 1989; Clair et al. 1998; Hietanen and Teräväinen 1989; Huber et al. 1992; Mohr et al. 1992; Viitanen et al. 1994), of which only one exposed a disadvantage in RPD (Huber et al. 1992), whereas the other studies failed to uncover any differences.
Another commonly used task for visuospatial memory is the Designs subtest of the WMS. Four studies did not reportany differences between RPD and LPD on the latter task (Blonder et al. 1989; Clair et al. 1998; Mohr et al. 1992; Viitanen et al. 1994), whereas one revealed a disadvantage for the LPD patients (Direnfeld et al. 1984), and another exposed an impaired performance for the RPD group (Huber et al. 1992). The last frequently used visuospatial memory task is the Benton Visual Retention Test. Threestudies disclosed a worse BVRT-performance for LPD patients (Amick et al. 2006a; Starkstein et al. 1987; Tomer et al. 1993), whereas two studies reported no differences between the groups (Mohr et al. 1992; Starkstein et al. 1987).
A recent study also found a worse performance in LPD patients on a spatial delayed response task (Foster et al. 2008). Taken together, seven out of thirteen studiesinvestigating visuospatial memory in asymmetric PD reported no differences between the groups, five found a worse performance for the LPD group, and one study showed a disadvantage for the RPD group. When differences are reported, they usually consist of a disadvantage for the LPD group.
Verbal memory. Two subtests of the WMS and WMS-R were frequently used to assess verbal memory in PD patients: LogicalMemory and Associative Learning (Blonder et al. 1989; Clair et al. 1998; Hietanen and Teräväinen 1989; Huber et al. 1992; Mohr et al. 1992; Viitanen et al. 1994).
Only one study revealed a disadvantage for RPD patients on these tests (Huber et al. 1992). Worse performance of RPD patients was also detected with the Auditory Verbal Learning Test (Amick et al. 2006a; Starkstein and Leiguarda 1993;Starkstein et al. 1987).
Other verbal memory tasks that have been used are the California Verbal Learning Test (Tomer et al. 1993), the memory subtests of the Scopa-Cog (Cubo et al. 2010), Remote Memory (Huber et al. 1989), remembering three unrelated letters (Huber et al. 1989), the Supra Span test (Direnfeld et al. 1984), Blender recall (Viitanen et al. 1994), Logical Memory Passage of the WMS(Tomer et al. 1993), Selective Reminding Test (Viitanen et al. 1994), Paired Association (Huber et al. 1989), and Sentence memory (Mohr et al. 1992). None of these studies disclosed differences between RPD and LPD on verbal memory performance, except for two studies that described worse performance for LPD patients (Direnfeld et al. 1984; Tomer et al. 1993) and one study that reported adisadvantage for the RPD patients (Cubo et al. 2010). To summarise, fifteen studies assessed verbal memory in RPD and LPD patients, yielding inconsistent findings. Eight of them did not encounter any differences between the groups, five studies reported a disadvantage for the RPD group, and two studies revealed a worse performance of the LPD patients. Summary. In memory tasks, stimulus modality is indeed...