Knowledge of concept meanings in Alzheimer's disease

Deterioration of semantic associative relationships in mild cognitive impairment and Alzheimer Disease

The aim of this research was to study semantic abilities and their loss in mild cognitive impairment (MCI) and in dementia, while analyzing efficiency in the use of associative relations, within verbal and visuoperceptual modalities. Participants were split into 4 groups: 19 participants with amnestic MCI, 16 patients with mild Alzheimer disease (AD), 20 patients with moderate AD, and 20 healthy controls (HCs). All participants performed standardized neuropsychological tests and experimental (naming and semantic associations) tasks to evaluate verbal and visuoperceptual semantic abilities. We analyzed 4 associative relations (part/whole, function, superordinate, and contiguity) in both verbal and visuoperceptual code. Our results suggest a progressive impairment in semantic categorization knowledge, with worse performance in the AD groups relative to the MCI and HC groups. Our data show a different pattern in the 4 associative relations and the involvement of associative semantic relations already in the early stage of disease, as well as a different pattern of deterioration between verbal and visuoperceptual modalities. Our data indicate that the visuoperceptual semantic network appears to be less deteriorated than the verbal network in AD. The verbal semantic network may be more sensitive in detecting patients at an early stage of the disease.

Learning and forgetting new names and objects in MCI and AD

We studied how subjects with mild cognitive impairment (MCI), early Alzheimer's disease (AD) and age-matched controls learned and maintained the names of unfamiliar objects that were trained with or without semantic support (object definitions). Naming performance, phonological cueing, incidental learning of the definitions and recognition of the objects were tested during follow-up. We found that word learning was significantly impaired in MCI and AD patients, whereas forgetting patterns were similar across groups. Semantic support showed a beneficial effect on object name retrieval in the MCI group 8 weeks after training, suggesting that the MCI patients' preserved semantic memory can compensate for impaired episodic memory. The MCI group performed equally well as the controls in the tasks measuring incidental learning and recognition memory, whereas the AD group showed impairment in this respect. Both the MCI and the AD group benefited less from phonological cueing than the controls. Our findings indicate that word learning is compromised in both MCI and AD, whereas long-term retention of newly learned words is not affected to the same extent. Incidental learning and recognition memory seem to be well preserved in MCI.

Semantic memory impairment in the earliest phases of Alzheimer's disease

The presence and the nature of semantic memory dysfunction in Alzheimer's disease (AD) have been widely debated. This study aimed to determine the frequency of impaired semantic test performances in mild AD and to study whether incipient semantic impairments could be identified in predementia AD. Five short neuropsychological tests sensitive to semantic memory and easily applicable in routine practice were administered to 102 patients with mild AD (Mini-Mental State Examination score above 19), 22 predementia AD patients and 58 healthy subjects. 'Category fluency' and 'naming of famous faces' were the most frequently impaired tests in both patient groups. The study demonstrated that impairments on semantically related tests are common in mild AD and may exist prior to the clinical diagnosis. The results imply that assessment of semantic memory is relevant in the evaluation of patients with suspected AD.

CERAD test performances in amnestic mild cognitive impairment and Alzheimer's disease

OBJECTIVES

The aim of the study was to examine the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) test performances cross-sectionally in patients suffering from amnestic mild cognitive impairment (MCI) and mild Alzheimer's disease (AD). Moreover, we wanted to determine the sensitivity to amnestic MCI and mild AD, as well as the specificity of different CERAD subtests in our study groups.

MATERIAL AND METHODS

Fifteen healthy elderly individuals, 15 amnestic MCI patients and 15 probable AD patients suffering from mild dementia were tested with the CERAD neurocognitive dementia screening test.

RESULTS

Significant differences were found in all CERAD tests except Constructional praxis (copy) and Clock drawing between the controls and the AD group. The MCI group was differentiated from the controls only in the Wordlist learning test. In the language tests the sensitivity to MCI and AD was quite low and the specificity very high. In the savings scores the sensitivity to AD was high, but the specificity rather low. The Wordlist recognition test screened no false positives using the current cut-off score and the sensitivity to AD was 0.6, but only one MCI patient was detected using the current cut-off score. Raising the cut-off score also raised the sensitivity to MCI without dramatic loss of specificity. Cut-off scores for the Wordlist learning test and Wordlist delayed recall, which have been found to differentiate normal aging from dementia, are lacking in the Finnish CERAD. The current data indicates that the Wordlist learning test might be relatively sensitive to MCI.

CONCLUSIONS

The results indicate that the Finnish CERAD test battery with its current cut-off scores has low sensitivity to MCI, and using it as a sole cognitive screening instrument for MCI and preclinical dementia might result in false negatives.

Preserved morphological decomposition in persons with Alzheimer's disease

Persons with Alzheimer's disease (AD) demonstrate a severe lexical impairment that affects conceptual knowledge. Research into aspects of word structure and the structural relationships between words, however, has been scarce in this population. Taking advantage of the rich morphology of Hebrew, the current article examines the status of morphological decomposition in AD. Fourteen persons with AD and 48 control participants completed 2 experiments: The 1st investigated root extraction from pseudoverbs containing existing and nonexisting consonantal roots, and the 2nd looked at sensitivity to morphological priming effects. Results suggest that despite severe semantic-conceptual deficits on naming, fluency, and comprehension tasks, persons with AD engage in adequate morphological decomposition of words, in a similar manner to normal adult speakers of Hebrew.

Early visual impairment is independent of the visuocognitive and memory disturbances in Alzheimer's disease

Static and dynamic contrast sensitivity (SCS and DCS), semantic object identification, and verbal recall functions were evaluated in 20 Alzheimer's disease (AD) patients and in 20 control subjects. We found general SCS and DCS loss in the 0.48-14.34 c deg-1 spatial frequency range. In relation to the cognitive functions, semantic object identification was intact, whereas explicit memory was markedly impaired in the AD group. There was no significant correlation between the CS and the memory disturbances. The results suggest that early visual impairment and higher-level cognitive disturbances are independent in AD.

Sematic memory deficit in multiple sclerosis; impaired understanding of conceptual meanings

The aim of the present study was to determine whether a cognitive decline, related to multiple sclerosis (MS), also involves deficits in semantic memory. Semantic memory function was evaluated by studying the conscious understanding of conceptual meanings. A group of MS patients with cognitive decline was presented with four tasks concerning concepts, their attributes and relationships to other concepts. The tasks were designed to measure spontaneous, cued and recognition performance separately. The patients had difficulties in understanding conceptual meanings. Easing the retrieval demands of the tasks did not help them to improve their performance which was poorer than the control group's on every task used. The results indicate a retrieval deficit combined with an underlying storage deficit in the semantic memory of MS patients with cognitive decline.

Semantic processing of spoken words in Alzheimer's disease: an electrophysiological study

Patients suffering from Alzheimer's disease (AD) have severe difficulties in tasks requiring the use of semantic knowledge. The semantic deficits associated with AD have been extensively studied by using behavioral methods. Many of these studies indicate that AD patients have a general deficit in voluntary access to semantic representations but that the structure of the representations themselves might be preserved. However, several studies also provide evidence that to some extent semantic representations in AD may in fact be degraded. Recently, a few studies have utilized event-related brain potentials (ERPs) that are sensitive to semantic factors in order to investigate the electrophysiological correlates of the semantic impairment in AD. Interest has focused on the N400 component, which is known to reflect the on-line semantic processing of linguistic and pictorial stimuli. The results from studies of N400 changes in AD remain somewhat controversial: Some studies report normal or enlarged N400 components in AD, whereas others report diminished ones. One issue not reported in previous studies is whether word-elicited ERPs other than N400 remain normal in AD. In the present study our aim was to find out whether the ERP waveforms N1, P2, N400, and Late Positive Component (LPC) to semantically congruous and incongruous spoken words are abnormal in AD and whether such abnormalities specifically reflect deficiencies in semantic activation in AD. Auditory ERPs from 20 scalp sites to semantically congruous and incongruous final words in spoken sentences were recorded from 17 healthy elderly adults and 9 AD patients. The early ERP waveforms N1 and P2 were relatively normal for the AD patients, but the N400 and LPC effects (amplitude difference between congruous and incongruous conditions) were significantly reduced. We interpret the present results as showing that semantic-conceptual activation and other high-level integration processes are defective in AD. However, a word congruity effect earlier than N400 (phonological mismatch negativity), reflecting lexical selection processes, is at least to some extent preserved in AD.