Aging reduces EEG markers of recognition despite intact performance: Implications for forensic memory detection

The Impact of the Natural Level of Blood Biochemicals on Electroencephalographic Markers in Healthy People

This study aims to investigate the association between the natural level of blood biomarkers and electroencephalographic (EEG) markers. Resting EEG theta, alpha (ABP), beta, and gamma frequency band powers were selected as linear EEG markers indicating the level of EEG power, and Higuchi's fractal dimension (HFD) as a nonlinear EEG complexity marker reflecting brain temporal dynamics. The impact of seven different blood biomarkers, i.e., glucose, protein, lipoprotein, HDL, LDL, C-reactive protein, and cystatin C, was investigated. The study was performed on a group of 52 healthy participants. The results of the current study show that one linear EEG marker, ABP, is correlated with protein. The nonlinear EEG marker (HFD) is correlated with protein, lipoprotein, C-reactive protein, and cystatin C. A positive correlation with linear EEG power markers and a negative correlation with the nonlinear complexity marker dominate in all brain areas. The results demonstrate that EEG complexity is more sensitive to the natural level of blood biomarkers than the level of EEG power. The reported novel findings demonstrate that the EEG markers of healthy people are influenced by the natural levels of their blood biomarkers related to their everyday dietary habits. This knowledge is useful in the interpretation of EEG signals and contributes to obtaining information about people quality of life and well-being.

Behavioral and electrophysiological evidence for preserved specific associative episodic memory in older adults

Aging is often linked to a decline in associative memory. Prior research has shown that older adults have difficulty retrieving specific associative memory but can retrieve gist associative memory when deliberately differentiating test pairs with different levels of specificity during associative recognition. In this study, we utilized the context reinstatement paradigm to examine whether older adults could retrieve specific memory in situations where associations do not necessarily need to be voluntarily retrieved. Thirty-five older adults were directed to intentionally link objects with unique background scenes during encoding. Subsequently, test objects were presented against either the reinstated or similar background scenes during a recognition memory task, where participants were required to identify whether the objects were old or new regardless of their background contexts. Event-related potentials (ERP) were recorded to uncover the electrophysiological correlates of specific associative episodic memory. Behavioral results revealed higher memory sensitivity for object recognition when the background scenes were reinstated than when those were similar in older adults. ERP results indicated that older adults exhibited a more prominent fronto-centrally distributed positivity during object recognition in the reinstated than in similar contexts. Our results suggest that older adults may preserve their ability to retrieve specific memory for associations through an involuntary, spontaneous recollection process, which holds important theoretical implications for age-related associative memory deficits.

Counterfactual imagination impairs memory for true actions: EEG and behavioural evidence

Imagined events can be misremembered as experienced, leading to memory distortions. However, less is known regarding how imagining counterfactual versions of past events can impair existing memories. We addressed this issue, and used EEG to investigate the neurocognitive processes involved when retrieving memories of true events that are associated with a competing imagined event. Participants first performed simple actions with everyday objects (e.g., rolling dice). A week later, they were shown pictures of some of the objects and either imagined the same action they had originally performed, or imagined a counterfactual action (e.g., stacking the dice). Subsequent tests showed that memory for performed actions was reduced after counterfactual imagination when compared to both veridical imagination and a baseline condition that had not been imagined at all, providing novel evidence that counterfactual imagination impairs true memories beyond simple forgetting over time. ERPs and EEG oscillations showed evidence of separate processes associated with memory retrieval versus post-retrieval processes that were recruited to support recall of memories that were challenging to access. The findings show that counterfactual imagination can cause impairments to sensorimotor-rich event memories, and provide new evidence regarding the neurocognitive mechanisms that are recruited when people need to distinguish memories of imagined versus true events.

Effects of Lacticaseibacillus paracasei Strain Shirota on Daytime Performance in Healthy Office Workers: A Double-Blind, Randomized, Crossover, Placebo-Controlled Trial

Lacticaseibacillus paracasei strain Shirota (LcS) modulates psychological homeostasis via the gut-brain axis. To explore the possible efficacy of LcS for improving daytime performance, we conducted a double-blind, randomized, crossover, placebo-controlled study of 12 healthy office workers with sleep complaints. The participants received fermented milk containing viable LcS (daily intake of 1 × 1011 colony-forming units) and non-fermented placebo milk, each for a 4-week period. In the last week of each period, the participants underwent assessments of their subjective mood and measurements of physiological state indicators via an electroencephalogram (EEG) and heart rate variability in the morning and afternoon. The attention score in the afternoon as assessed by the visual analog scale was higher in the LcS intake period than in the placebo intake period (p = 0.041). Theta power on EEG measured at rest or during an auditory oddball task in the afternoon was significantly lower in the LcS period than in the placebo period (p = 0.025 and 0.009, respectively). The change rate of theta power was associated with the change in attention score. Treatment-associated changes were also observed in heart rate and the sympathetic nerve activity index. These results indicate that LcS has possible efficacy for improving daytime performance, supported by observations of the related physiological state indicators.

Can neural correlates of encoding explain the context dependence of reward-enhanced memory?

Selective encoding can be studied by manipulating how valuable it is for participants to remember specific stimuli, for instance, by varying the monetary reward participants receive for recalling a particular stimulus in a subsequent memory test. It would be reasonable for participants to strategically attend more to high-reward items compared to low-reward items in mixed list contexts, but to attend both types of items equally in pure list contexts, where all items are of equal value. Reward-enhanced memory may be driven by automatic dopaminergic interactions between reward circuitry and the hippocampus and thus be insensitive to list context; or it may be driven by meta-cognitive strategies, and thus context-dependent. We contrasted these alternatives by manipulating list composition and tracked selective encoding through multiple EEG measures of attention and rehearsal. Behavioral results were context-dependent, such that recall of high-reward items was increased only in mixed lists. This result and aspects of the recall dynamics confirm predictions of the eCMR (emotional Context Maintenance and Retrieval) model. The power of ssVEPs was lower for high-reward items regardless of list composition, suggesting decreased visual processing of high-reward stimuli and that ssVEPs may index the modulation of context-to-item associations predicted by eCMR. By contrast, reward modulated the amplitude of Late Positive Potential and Frontal Slow Wave only in mixed lists. Taken together, the results provide evidence that reward-enhanced memory is caused by an interplay between strategic processes applied when high- and low-reward items compete for cognitive resources during encoding and context-dependent mechanisms operating during recall.

EEG evidence that morally relevant autobiographical memories can be suppressed

Remembering unpleasant events can trigger negative feelings. Fortunately, research indicates that unwanted retrieval can be suppressed to prevent memories from intruding into awareness, improving our mental state. The current scientific understanding of retrieval suppression, however, is based mostly on simpler memories, such as associations between words or pictures, which may not reflect how people control unpleasant memory intrusions in everyday life. Here, we investigated the neural and behavioural dynamics of suppressing personal and emotional autobiographical memories using a modified version of the Think/No-Think task. We asked participants to suppress memories of their own past immoral actions, which were hypothesised to be both highly intrusive and motivating to suppress. We report novel evidence from behavioural, ERP, and EEG oscillation measures that autobiographical memory retrieval can be suppressed and suggest that autobiographical suppression recruits similar neurocognitive mechanisms as suppression of simple laboratory associations. Suppression did fail sometimes, and EEG oscillations indicated that such memory intrusions occurred from lapses in sustained control. Importantly, however, participants improved at limiting intrusions with repeated practice. Furthermore, both behavioural and EEG evidence indicated that intentional suppression may be more difficult for memories of our morally wrong actions than memories of our morally right actions. The findings elucidate the neurocognitive correlates of autobiographical retrieval suppression and have implications for theories of morally motivated memory control.