Spatial and visual learning deficits in Alzheimer's and Parkinson's disease

Experimental paradigms adopted from animal models were used to compare the neuropsychological mechanisms underlying the dementias of Alzheimer's and Parkinson's diseases. Two tasks were selected because characteristic profiles of impairment in nonhuman primates are seen following selective lesions of frontal cortex, temporal cortex, and fornix. The tasks consisted of a spatial and a visual learning problem, each with two components: (1) original learning and (2) reversal of the original learning. The Alzheimer's patients were significantly impaired on original learning and reversal learning in the visual modality compared with demented Parkinson's patients, even though both groups were equated for severity of dementia. On the spatial tasks, both the Alzheimer's and the demented Parkinson's patients were impaired on reversal learning but not on original learning. The profile of deficits on the visual tasks may serve to differentiate Alzheimer's from Parkinson's dementia and may reflect selective orbitofrontal system lesions in the former.     

Verbal learning and visuomotor attention in Alzheimer's disease and geriatric depression

We compared the verbal learning and visuomotor attention of 34 Alzheimer's patients and 18 depressive patients. Verbal learning was assessed using The Hopkins Verbal Learning Test--Revised (HVLT--R); visuomotor attention was assessed using the Trail Making Test (TMT). The Alzheimer's patients had significantly lower scores on immediate and delayed recall of a word list. There was a nonsignificant trend in this group toward a fewer number of true positives and a greater number of false positives. Alzheimer's patients were significantly slower on Trails A, with a nonsignificant trend toward slower performance on Trails B. No difference was observed in accuracy of attentional processing. The results are discussed in terms of other factors, such as stage of cognitive decline, which might have influenced the findings.     

Maze navigation by honeybees: learning path regularity

We investigated the ability of honeybees to learn mazes of four types: constant-turn mazes, in which the appropriate turn is always in the same direction in each decision chamber; zig-zag mazes, in which the appropriate turn is alternately left and right in successive decision chambers; irregular mazes, in which there is no readily apparent pattern to the turns; and variable irregular mazes, in which the bees were trained to learn several irregular mazes simultaneously. The bees were able to learn to navigate all four types of maze. Performance was best in the constant-turn mazes, somewhat poorer in the zig-zag mazes, poorer still in the irregular mazes, and poorest in the variable irregular mazes. These results demonstrate that bees do not navigate such mazes simply by memorizing the entire sequence of appropriate turns. Rather, performance in the various configurations depends on the existence of regularity in the structure of the maze and on the ease with which this regularity is recognized and learned.     

Strategic value-directed learning and memory in Alzheimer's disease and behavioural-variant frontotemporal dementia

In healthy adults, the ability to prioritize learning of highly valued information is supported by executive functions and enhances subsequent memory retrieval for this information. In Alzheimer's disease (AD) and behavioural-variant frontotemporal dementia (bvFTD), marked deficits are evident in learning and memory, presenting in the context of executive dysfunction. It is unclear whether these patients show a typical memory bias for higher valued stimuli. We administered a value-directed word-list learning task to AD (n = 10) and bvFTD (n = 21) patients and age-matched healthy controls (n = 22). Each word was assigned a low, medium or high point value, and participants were instructed to maximize the number of points earned across three learning trials. Participants’ memory for the words was assessed on a delayed recall trial, followed by a recognition test for the words and corresponding point values. Relative to controls, both patient groups showed poorer overall learning, delayed recall and recognition. Despite these impairments, patients with AD preferentially recalled high-value words on learning trials and showed significant value-directed enhancement of recognition memory for the words and points. Conversely, bvFTD patients did not prioritize recall of high-value words during learning trials, and this reduced selectivity was related to inhibitory dysfunction. Nonetheless, bvFTD patients showed value-directed enhancement of recognition memory for the point values, suggesting a mismatch between memory of high-value information and the ability to apply this in a motivationally salient context. Our findings demonstrate that value-directed enhancement of memory may persist to some degree in patients with dementia, despite pronounced deficits in learning and memory.     

Cognitive procedural learning in early Alzheimer's disease: impaired processes and compensatory mechanisms

Introduction. The aim of this study was to study cognitive procedural learning in early Alzheimer's disease (AD). Methods. Cognitive procedural learning was assessed using the Tower of Hanoi (TH) task. In order to take account of possible interactions between different systems during cognitive procedural learning, we also measured non‐verbal intellectual functions, working memory, and declarative memory. Results. Our results showed an apparent preservation of cognitive procedural learning in AD and a deleterious effect of the disease on verbal intelligence and declarative memory. Correlational analyses revealed a difference between AD patients and control participants in the type of processing they applied to the task. Conclusion. The non‐involvement of declarative memory would appear to be partly responsible for a slowdown in the cognitive procedural dynamics of AD patients. As the AD patients were unable to use their declarative memory, they were still in a problem‐solving mode at the end of the learning protocol and had to implement higher order cognitive processes (i.e., compensatory mechanisms) to perform the procedural task.     

Posture recognition in Alzheimer's disease

BACKGROUND: Apraxia is neurologically induced deficit in the ability perform purposeful skilled movements. One of the most common forms is ideomotor apraxia (IMA) where spatial and temporal production errors are most prevalent. IMA can be associated Alzheimer's disease (AD), even early in its course, but is often not identified possibly because the evaluation of IMA by inexperienced judges using performance tests is unreliable. The purpose of this study, therefore, is to learn if the Postural Knowledge Test (PKT), a praxis discrimination test that assesses knowledge of transitive (PKT-T subtest) and intransitive (PKT-I subtest) postures and does not require extensive training, is as sensitive and specific as the praxis performance tests. METHODS: We studied 15 subjects with probable AD as well as 18 age-matched controls by having them perform transitive and intransitive gestures to command and imitation, as well as having them discriminate between correct and incorrect transitive and intransitive postures. RESULTS: Overall on all tests, the control subjects performed better than those with AD. In addition all subjects had more trouble with transitive than intransitive gestures. Using a stepwise discriminative analysis, 81.8% of the subjects could be classified according to Group (94.4% of Controls, 66.7% of AD subjects). In this analysis, the PKT-T (transitive posture subtest) was the only measure that contributed to the discrimination of subjects. CONCLUSION: We found that having subjects select the correct transitive hand postures in this "booklet test" was more sensitive than grading their praxis performances even when using judges with extensive training. This suggests that this discrimination test might be an excellent means for diagnosing and screening patients for AD. The reason why recognition of transitive postures is relatively more difficult for our AD subjects is not known. Two possibilities are that the representations for intransitive movements are stronger than those for transitive movements, and hence, more resistant to degradation, or that intransitive acts are stored in parts of the brain not affected by AD.     

Confabulation in Alzheimer's disease.

Confabulation is present when memory is disturbed, but does it occur in Alzheimer's disease (AD) where memory abnormalities are often severe? In this study, confabulation was assessed prospectively in 26 AD patients and 15 normal elderly (NE) controls using a neuropsychological battery specifically designed to assess different types of memory errors. The results indicated that the AD group made significantly more verbal intrusions than the NE group. These findings provide evidence for the feasibility of eliciting confabulatory-type behavior during clinical assessment and support previous reports which have documented verbal intrusions as a common accompaniment of the memory impairment manifested by AD patients.     

Semantic memory in Alzheimer's disease

Patients with Alzheimer's disease have been suggested to have a semantic memory impairment not present in the normal old. This article reviews the performance of Alzheimer patients on tests of various aspects of semantic memory, including word finding, knowledge of the semantic attributes, and associates of concepts, as well as their category membership. The effect that semantic context has on cognitive processes such as lexical and semantic priming and memory encoding is also reviewed. Finally, the ability of theoretical constructs such as implicit memory and automaticity to explain intertask variability in Alzheimer patients' semantic performance is discussed.     

Pantomime recognition impairment in Alzheimer's disease

This study was designed to examine whether 10 AD patients with diffuse lesions and an early semantic deficit could comprehend the meaning of pantomimes and symbolic gestures. We especially wanted to determine the relationship between pantomime recognition and production. The tasks involved naming or showing an understanding (e.g., circumlocutions) of the pantomimes executed by the examiner and producing pantomimes to verbal command or to imitation. The results showed no significant relationship between pantomime comprehension and pantomime production. However, 60% of AD patients performed poorly compared to controls on the Gesture Recognition task. Gesture comprehension was highly correlated with a measure of global cognitive impairment (3MS). The data are consistent with the proposed separation of comprehension and action production systems in a cognitive model of praxis. Gesture comprehension may be diffusely distributed and thus preserved in the early stages of AD as in circumscribed lesions of the left parietal lobe.     

Ideational action impairments in Alzheimer's disease

We report data from a group of patients with mild Alzheimer's disease on a range of tasks requiring either stored semantic knowledge about objects (e.g., naming object use) or the execution of action to objects (e.g., miming and using objects). We found that the patients were impaired at miming in response to objects, even when they could describe the object's function. On the other hand, copying gestures was not impaired relative to naming gestures, indicating that an ideomotor deficit in action execution, per se, was unlikely to explain the impairments in object use. We suggest instead that the patients had an impairment in stored motor programmes for action, over and above their deficits in semantic knowledge. Despite this, the patients were better at using than at miming to objects, consistent with the view that proprioceptive input (when using objects) can directly constrain selection of the appropriate motor programme for action.     

Syntactic comprehension deficits in Alzheimer's disease

Syntactic comprehension of German patients with dementia of the Alzheimer type was investigated and compared to healthy controls matched with respect to age, sex, and education. Special attention was directed at syntactic structures, which, in contrast to a language like English, are feasible in a grammatically rich language like German. In a sentence picture matching paradigm, only semantically reversible sentences were used. Syntactic complexity ranged from simple active voice sentences to more complex sentences like center-embedded object relative sentences. In comparison to their controls, patients showed a deficit in nearly all categories. Their performance was not influenced by age, but was heavily influenced by the degree of cognitive impairment. Patients with mild cognitive impairment, as defined by a MMSE score of 20 or higher, showed only slight difficulties in syntactic processing, whereas patients with moderate to severe impairment (MMSE < 20) did not perform above chance limits in most syntactic categories. It appears as though syntactic comprehension is only mildly affected in the early stages of Alzheimer's disease and is rather severely impaired in more advanced stages. In the present report, results are discussed in terms of working memory demands for syntactic processing.     

Visual aiming movements in Alzheimer's disease

This study examined whether AD affects the control of pointing movements. Sixteen older adults with probable AD and 10 age-matched healthy adults pointed at targets varying in size (3 and 7 mm in diameter) and located at three positions (at the midline and 33 degrees to the left and right). Results revealed the patients exhibited longer movement time, lower peak velocity and more time in deceleration, although they exhibited effects of target size and location comparable to the healthy controls. AD, then, would appear to slow down movement without affecting the motor system's ability to respond to task demands.