Increased sensitivity to proactive interference in amnestic mild cognitive impairment is independent of associative and semantic impairment

Episodic memory deficit is the hallmark of amnestic mild cognitive impairment (aMCI). There is, however, an overlap in performance among patients with aMCI and elderly controls (EC). The memory deficit in aMCI therefore needs to be better characterized. Studies have shown that associative memory is selectively impaired in aMCI, and recent work suggested that aMCI may be hypersensitive to semantic proactive interference (PI). It is not known whether this increased PI is related to associative or semantic impairment. EC (n = 44) and patients with aMCI (n = 30) performed two tasks presenting a gradually increasing PI effect across four lists. One task used semantic cueing, the other phonological cueing. We controlled for associative memory by introducing it as a covariate and by matching our subjects for it. Patients with aMCI had a greater PI effect than EC matched for associative memory, regardless of the type of cueing. The increased PI effect in patients with aMCI is independent of their associative and semantic impairment.     

The assessment of recognition memory using the Remember/Know procedure in amnestic mild cognitive impairment and probable Alzheimer’s disease

This study used the Remember/Know (R/K) procedure combined with signal detection analyses to assess recognition memory in 20 elders with amnestic mild cognitive impairment (aMCI), 10 patients with probable Alzheimer’s disease (AD) as well as matched healthy older adults. Signal detection analyses first indicated that aMCI and control participants were comparable on general recognition performance. As regards AD patients, they were impaired relative to both aMCI and healthy elders. When assessing Remember and Know responses the aMCI group showed diminished sensitivity for Remember responses but intact Know responses compared to healthy elders. In contrast, AD patients showed decreased sensitivity for both Remember and Know responses compared to control and aMCI participants. The response bias index revealed that AD patients were more liberal than aMCI and control participants when providing Know responses. On the other measures, response bias was comparable between the groups. Overall, this study indicates that the R/K procedure can characterize different aspects of recognition memory performance in persons with aMCI or AD.     

Response speed, contingent negative variation and P300 in Alzheimer’s disease and MCI

Background

Decreased speed of information processing is a hallmark of Alzheimer’s disease (AD) and mild cognitive impairment (MCI). Recent studies suggest that response speed (RS) measures are very sensitive indicators of changes in longitudinal follow-up studies. Insight into the psycho-physiological underpinnings of slowed RS can be provided by measuring the associated event-related potentials (ERP).

Aims

The current study aims to investigate the relation between RS and its psycho-physiological correlates in AD and MCI.

Methods

Fifteen psychoactive drug-naïve AD patients, 20 MCI patients and twenty age-matched, healthy control subjects participated. Response speed was measured during a simple (SRT) and choice reaction time task (CRT). An oddball and contingent negative variation (CNV) paradigm were used to elicit ERP. To evaluate test-retest reliability (TRR), subjects underwent a similar assessment one week after the first.

Results

The SRT and CRT distinguished the patient groups significantly. The P300 amplitude and latency also distinguished the groups and showed a significant correlation with response speed. The CNV amplitude did not reveal a significant difference between groups and also showed a low TRR.The TRR of the SRT, CRT and P300 amplitude and latency in general was moderate to high.The current study suggests that response speed measures on a behavioural and psycho-physiological level deserve attention as a possible marker in the diagnosis and follow-up of AD.