Working memory (WM) training has shown promise for cognitive enhancement, but the neural mechanisms underlying training effects and offline consolidation processes remain unclear. This study examined the correspondence between behavioral and neural changes during WM training and how individual differences in WM capacity influence these processes. Twenty-eight young adults completed two visual n-back training sessions separated by a 24-h interval. Behavioral measures and brain activity in bilateral dorsolateral and ventrolateral prefrontal cortices were measured using functional near-infrared spectroscopy (fNIRS), before and after each session. Participants became more proficient in performing the n-back task, with accuracy improvements occurring during active training sessions and reaction time improvements reflecting increased automaticity occurring also during the offline consolidation period. Group-level neural changes were not significant, but individual differences in behavior were associated with neural activation changes: accuracy improvements were consistently associated with increased neural activation across all training phases, while reaction time improvements showed non-significant trends with variable relationships across intervals. Interestingly, individual WM capacity shaped neural adaptation patterns: higher-capacity individuals showed greater neural activation increases during the first training session and neural activation decrease during the second session. Although we found a behavioral effect for offline consolidation at the group level, this was not associated with specific neural activation changes. Our results highlight the complex relationship between individual capacity and training-related neural plasticity, with higher-capacity individuals showing both increased and decreased activation patterns at different time points during training. These findings support personalized training approaches that consider individual cognitive profiles.
Chronic alcohol consumption is known to impair cognitive function, but its effects on specific phases of memory processing remain incompletely understood. In the present study, we examined whether prolonged ethanol exposure alters associative fear memory and hippocampal synaptic plasticity. Rats were exposed to ethanol chronically and assessed using a fear conditioning paradigm. Chronic ethanol exposure selectively reduced the long-term expression of conditioned fear, while leaving acquisition and extinction learning largely intact. Electrophysiological recordings from hippocampal slices showed the significant attenuation of early-phase synaptic potentiation at Schaffer collateral-CA1 synapses in ethanol-exposed animals, whereas activity-dependent depotentiation was preserved. These findings indicate the selective impairment of the initial strengthening of synaptic responses accompanied by intact mechanisms for synaptic weakening. The dissociation between reduced potentiation and preserved depotentiation suggests that chronic ethanol exposure disrupts processes involved in the stabilization of newly formed memory traces, while sparing the mechanisms supporting the modification of existing memories. Together, our findings suggest that prolonged ethanol exposure preferentially compromises the mechanisms supporting the persistence of fear-based associative memory, while sparing memory acquisition, extinction, and activity-dependent synaptic weakening.
The neural mechanisms supporting delayed threat memory recall in humans remain poorly understood. Animal studies indicate that the paraventricular nucleus of the thalamus (PVT) contributes to threat-memory retrieval after longer retention intervals, but whether the human PVT shows cue-related discriminability during delayed recall remains unclear. Human neuroimaging studies of threat learning have largely focused on memory assessed within 24–48 h, limiting insight into neural responses when previously threatening cues are re-encountered after longer delays. Here, adult participants completed threat acquisition on Day 1 and returned 7–10 days later (n = 28) for a delayed threat-memory recall task while undergoing fMRI. We examined activity in the dorsal midline thalamus centered on a histology-informed PVT region of interest. During Day 1 acquisition, the PVT did not discriminate between CS+ and CS-, despite differential electrodermal activity (EDA) and unconditioned stimulus expectancy ratings. In contrast, during early Day 7 recall, the PVT showed greater activation to previously reinforced CS+ than CS-. In an independent sample (n = 56), PVT activity similarly did not discriminate between CS+ and CS- during acquisition or immediate extinction, but overall PVT activation was greater during acquisition than extinction, regardless of CS type. These findings provide preliminary evidence that a human PVT-centered dorsal midline thalamic region is sensitive to prior threat reinforcement during delayed recall, while also showing engagement during acute threat-learning contexts. More broadly, they support future investigation of PVT-centered thalamic circuitry in the persistence, retrieval, and updating of threat memories, as well as in salience-related processes.
Objectives Acute stress prior to bedtime significantly alters the subsequent sleep. Although sleep is crucial for consolidating newly acquired memories, the impact of pre-sleep stress remains unclear. This experimental study examined how acute stress induction before bedtime influences overnight consolidation of emotional and neutral memories. Methods 34 healthy adults (65% females, Mage = 25.76 years, SD = 3.35) were randomly assigned to stress (SC) or control (CC) conditions, using a virtual reality stress or control paradigm. Prior to manipulation, participants encoded emotional and neutral images, followed by recognition tasks immediately and the next morning. High-density overnight electroencephalogram (EEG) assessed sleep and salivary cortisol indexed pre-sleep stress responses. Results Pre-sleep stress was associated with longer slow-wave sleep duration, elevated high-frequency EEG power during both rapid (REMS) and non-rapid eye movement sleep (NREMS), and lower slow oscillation-spindle coupling. Memory retention was comparable between groups, but stress exposure interacted with EEG power in predicting memory outcomes. In the CC, greater low-frequency power during NREMS was associated with enhanced memory retention, whereas this association was absent in the SC. Effects were most pronounced over the central EEG derivations and were driven by the emotional material. Higher evening cortisol was independently associated with enhanced emotional memory retention. Conclusions Acute pre-sleep stress modifies sleep oscillatory dynamics and alters sleep-dependent memory consolidation, particularly for emotional content. These findings suggest that pre-sleep situational context shapes overnight memory processing, challenging the premise that memory consolidation mechanisms operate independently of prior waking experiences.
Planaria, a freshwater flatworm with unique regenerative abilities, has emerged as a valuable model organism for studying learning and memory. A growing body of evidence shows that planarians can recover their learning behaviour even after decapitation and regeneration. Behavioural paradigms, including classical, operant, and threat-related conditioning responses, show the capacity of planaria in learning and expressing both appetitive and aversive memories. Evidence at the molecular level, further confirms the presence of principal neurotransmitters, including glutamate, gamma-aminobutyric acid (GABA) and dopamine, which may contribute to planarian learning, memory and behavioural expression. Importantly, the dynamic balance among glutamatergic, GABAergic and dopaminergic pathways is consistently implicated in learning, memory, neuronal expression and behavioural activity. This review summarises behavioural evidence for learning and memory and highlights the key neurotransmitter systems that regulate these processes. It outlines future research directions for planaria as a valuable model for translational studies on memory and learning.
