The performances of patients with dementia of the Alzheimer type (DAT), patients with Huntington's disease (HD), and demented and nondemented patients with Parkinson's disease (PD) were compared on 2 tests of implicit memory that do not require the conscious recollection of prior study episodes: (1) a pursuit-rotor motor learning task and (2) a lexical priming test. The HD patients were found to be impaired on the motor learning but not the lexical priming task, whereas the DAT patients evidenced the opposite relationship on these tasks. The demented, but not the nondemented, PD patients were found to be impaired on both tests of implicit memory. For both the HD and PD patients, deficits on the motor learning task correlated significantly with severity of dementia but not with level of primary motor dysfunction. The noted double dissociation between HD and DAT patients indicates that different forms of implicit memory, all of which are intact in amnesia, are dependent upon distinct neuroanatomic systems. Motor skill learning may be mediated by a corticostriatal system, whereas verbal priming may depend upon the integrity of the neocortical association areas involved in the storage of semantic knowledge. The results for the PD patients suggest that the demented PD patients have endured damage to the neurologic systems subserving both motor learning and lexical priming.

Neuropsychological and motor deficits in Parkinson's disease that may contribute to driving impairment were examined in a cohort study comparing patients with Parkinson's disease (PD) to patients with Alzheimer's disease (AD) and to healthy elderly controls.

The ability of patients with Huntington's disease (HD), patients with dementia of the Alzheimer's type (DAT), and amnesic patients (AMN) to acquire the motor skills underlying a pursuit rotor task was assessed. Differences between groups in initial levels of performance were minimized by adjusting the rotation speed of the disk. The HD and DAT groups were also administered a verbal recognition span test. The results showed that the DAT, AMN, and intact control groups all significantly improved their time on target over six test blocks whereas the HD group was severely impaired in the acquisition of this motor skill. On the verbal recognition span test, the DAT and HD groups were significantly and equally impaired, but the HD group evidenced better immediate and delayed recall than did the DAT group. These results provide further evidence that the basal ganglia are critically involved in the acquisition of motor skills.

We administered 3 commonly employed tests of mental status (the Information-Memory-Concentration test [IMC], the Mini-Mental State Examination [MMSE], and the Dementia Rating Scale [DRS]) to 92 patients with probable dementia of the Alzheimer type. The 3 tests were readministered to 55 of the patients (2-year subgroup) approximately 1 year later, and administered a 3rd time to 20 of the patients (3-year subgroup) approximately 2 years after their initial assessment. In all cases, scores on the 3 tests were highly correlated with each other. Examination of the annual rate of change (ARC) in score for the 2-year subgroup revealed an average decline of -3.24 error points on the IMC, 2.81 points on the MMSE, and 11.38 points on the DRS. Of the 3 tests, only the DRS evidenced greater sensitivity to change with increasing dementia severity. In the 3-year subgroup, the ARC between years 1 and 2 was not correlated with ARC between years 2 and 3 for any of the 3 tests. This finding suggests that a patient's rate of progression in 1 year may bear little relationship to future rate of decline.