Age-related effects on perceptual and semantic encoding in memory

Observing memory encoding while it unfolds: Functional interpretation and current debates regarding ERP subsequent memory effects

Our ability to remember the past depends on neural processes set in train in the moment an event is experienced. These processes can be studied by segregating brain activity according to whether an event is later remembered or forgotten. The present review integrates a large number of studies examining this differential brain activity, labeled subsequent memory effect (SME), with the ERP technique, into a functional organization and discusses routes for further research. Based on the reviewed literature, we suggest that memory encoding is implemented by multiple processes, typically reflected in three functionally different subcomponents of the ERP SME elicited by study stimuli, which presumably interact with preparatory SME activity preceding the to be encoded event. We argue that ERPs are a valuable method in the SME paradigm because they have a sufficiently high temporal resolution to disclose the subcomponents of encoding-related brain activity. Implications of the proposed functional organization for future studies using the SME procedure in basic and applied settings will be discussed.

Semantic-based memory-encoding strategy and cognitive stimulation in enhancing cognitive function and daily task performance for older adults with mild cognitive impairment: A pilot non-randomised cluster controlled trial

AIM

To investigate the effectiveness of a semantic-based memory-encoding strategy intervention and cognitive stimulation that enhances function for older adults with mild cognitive impairment.

METHODS

A two-armed single-blind non-randomised cluster controlled trial was conducted. Participants in two centres were allocated to the semantic-based memory-encoding experimental group and those in the other two centres received cognitive stimulation. In both groups, one centre- or community-based session and one home-based session were provided weekly for 10 weeks. Outcome measures included attention, memory and general cognitive function (Word List Memory and Word List Recall of the Consortium to Establish a Registry for the Alzheimer's disease, Digit Span Forwards and Backwards and the Cognistat), and daily task performance (Disability Assessment for Dementia and Lawton Instrumental Activities of Daily Living Scale). They were administered pre- and post-intervention.

RESULTS

Thirty-nine participants completed the study. No significant differences were revealed in the demographic or baseline data. The experimental group showed significant improvements in daily task performance (Disability Assessment for Dementia; p = 0.003), memory outcomes (Word List Recall; p < 0.001), general cognitive function (Cognistat subtests of Memory and Similarity; ps = 0.002 and < 0.001). The cognitive stimulation control group did not show any significant improvement in the measures. Between-group analysis showed significant differences in favour of the experimental group for the outcome measures of the Word List Recall and Cognistat Similarity subtest (ps < 0.001).

CONCLUSIONS

This study shows that the semantic-based memory-encoding strategy is more superior than cognitive stimulation with improvements in attention, memory, general cognitive function and daily task performance for people with a mild cognitive impairment.

TRIAL REGISTRATION

ClinicalTrials.gov Protocol Registration and Results System (NCT02953964).

Neurophysiological markers of prospective memory and working memory in typical ageing and mild cognitive impairment

OBJECTIVE

Prospective memory (PM) -the memory of delayed intentions- is impacted by age-related cognitive decline. The current event-related potential study investigates neural mechanisms underpinning typical and atypical (Mild Cognitive Impairment, MCI) age-related decline in PM.

METHODS

Young adults (YA, n = 30, age = 24.7, female n = 13), healthy older adults (OA, n = 39, age = 72.87, female n = 24) and older adults with MCI (n = 27, age = 77.54, female n = 12) performed two event-based PM tasks (perceptual, conceptual) superimposed on an ongoing working memory task. Electroencephalographic data was recorded from 128 electrodes. Groups were compared for P2 (higher order perceptual processing), N300/frontal positivity (cue detection), the parietal positivity (retrieval), reorienting negativity (RON; attention shifting).

RESULTS

Participants with MCI had poorer performance (ongoing working memory task, conceptual PM), lower P2 amplitudes, and delayed RON (particularly for perceptual PM) than YA and OA. MCI had lower parietal positivity relative to YA only. YA had earlier latencies for the parietal positivity than MCI and OA, and lower amplitudes for N300 (than OA) and frontal positivity (than OA and MCI).

CONCLUSIONS

Impaired attention and working memory may underpin PM deficits in MCI.

SIGNIFICANCE

This is the first study to document the role of RON in PM and to investigate neurophysiological mechanisms underpinning PM in MCI.