Cognitive slowing in Parkinson's and Alzheimer's patients: distinguishing bradyphrenia from dementia.

The contribution of cognitive slowing to the slowed performance of patients with Parkinson's disease (PD) is a matter of long-standing debate. In this study, we contrasted the performance of PD patients on two reaction-time tasks with the performance of Alzheimer's disease (AD) patients, young normal subjects, and elderly normal subjects. Both nondemented and demented PD patients showed cognitive as well as motor slowing, and the extent of cognitive slowing varied with overall cognitive status. Moreover, by comparison with the cognitive slowing in AD patients, cognitive slowing in PD patients was disproportionate to their general level of cognitive performance. We suggest that this disproportionality be used to differentiate the concepts of bradyphrenia and nonspecific cognitive slowing.

Lexical priming by pictures and words in normal aging and in dementia of the Alzheimer's type.

Alzheimer's disease causes a progressive loss of semantic memory, one manifestation of which is a progressive language deficit. In order to delineate the relationship between cognitive processing deficits and language disturbance, word-word and picture-word lexical-decision priming tasks were administered to patients with mild dementia of the Alzheimer's type (DAT) (n = 6), very mild DATs (n = 7), and older normals (n = 23). The mild DATs differed from the other two groups in both tasks. When pictures were used as primes, significant identity priming was seen in the normals and very mild DATs, but not in the mild DATs. The mild DATs showed an aberrant pattern-responses significantly slower with picture primes than with nonsense primes in all three picture-word conditions. This may reflect residual inhibitory activity within a damaged associational network. In the word-word paradigm, the mild DAT subjects demonstrated significant priming both when the prime and target were identical (identity priming, e.g., dog-dog) and when they were semantically related (semantic priming, e.g., cat-dog). The other two groups showed no significant priming. These data reinforce other studies which have found that DAT subjects show a supranormal amount of word-word lexical-decision priming. This "hyperpriming" may occur due to partially degraded internal representations which benefit from priming more than intact representations (a cognitive crutch). Both paradigms thus exposed information-processing deficits which distinguished mild DATs from the other two groups. DAT-induced changes in selective attention are probably contributing to these results.

Dysnomia in dementia and in stroke patients: different underlying cognitive deficits.

The performance of 11 Alzheimer's (DAT) and 8 anomic aphasic stroke patients is contrasted with that of 32 normal elderly subjects on both the Boston Naming Test (BNT) and the Controlled Oral Word Association Test (COW), a letter-category verbal-fluency test. While both tests require phonological processing, only the BNT requires semantic processing (object recognition). Both DAT and anomic aphasic stroke patients were significantly impaired on the BNT, with mean z scores (based on the performance of the normals) of -4.08 and -2.57, respectively; the DAT patients were significantly farther from normal than were the anomic aphasics. Their relative levels of impairment on the COW were reversed: The anomic aphasics' performance (z = 1.79) was worse than that of the DATs (z = -0.66). This pattern of performance on the two tests is consistent with the hypothesis that impaired word finding reflects impaired processing mainly of semantic information for the DAT subjects, mainly of lexical-phonological information for the anomic aphasic subjects.