High reward makes items easier to remember, but harder to bind to a new temporal context

Learning through reward is central to adaptive behavior. Indeed, items are remembered better if they are experienced while participants expect a reward, and people can deliberately prioritize memory for high- over low-valued items. Do memory advantages for high-valued items only emerge after deliberate prioritization in encoding? Or, do reward-based memory enhancements also apply to unrewarded memory tests and to implicit memory? First, we tested for a high-value memory advantage in unrewarded implicit- and explicit-tests (Experiment 1). Participants first learned high or low-reward values of 36 words, followed by unrewarded lexical decision and free-recall tests. High-value words were judged faster in lexical decision, and more often recalled in free recall. These two memory advantages for high-value words were negatively correlated suggesting at least two mechanisms by which reward value can influence later item-memorability. The ease with which the values were originally acquired explained the negative correlation: people who learned values earlier showed reward effects in implicit memory whereas people who learned values later showed reward effects in explicit memory. We then asked whether a high-value advantage would persist if trained items were linked to a new context (Experiments 2a and 2b). Following the same value training as in Experiment 1, participants learned lists composed of previously trained words mixed with new words, each followed by free recall. Thus, participants had to retrieve words only from the most recent list, irrespective of their values. High- and low-value words were recalled equally, but low-value words were recalled earlier than high-value words and high-value words were more often intruded (proactive interference). Thus, the high-value advantage holds for implicit- and explicit-memory, but comes with a side effect: High-value items are more difficult to relearn in a new context. Similar to emotional arousal, reward value can both enhance and impair memory

Emotional arousal impairs association-memory: roles of amygdala and hippocampus

Emotional arousal is well-known to enhance memory for individual items or events, whereas it can impair association memory. The neural mechanism of this association memory impairment by emotion is not known: In response to emotionally arousing information, amygdala activity may interfere with hippocampal associative encoding (e.g., via prefrontal cortex). Alternatively, emotional information may be harder to unitize, resulting in reduced availability of extra-hippocampal medial temporal lobe support for emotional than neutral associations. To test these opposing hypotheses, we compared neural processes underlying successful and unsuccessful encoding of emotional and neutral associations. Participants intentionally studied pairs of neutral and negative pictures (Experiments 1–3). We found reduced association-memory for negative pictures in all experiments, accompanied by item-memory increases in Experiment 2. High-resolution fMRI (Experiment 3) indicated that reductions in associative encoding of emotional information are localizable to an area in ventral-lateral amygdala, driven by attentional/salience effects in the central amygdala. Hippocampal activity was similar during both pair types, but a left hippocampal cluster related to successful encoding was observed only for negative pairs. Extra-hippocampal associative memory processes (e.g., unitization) were more effective for neutral than emotional materials. Our findings suggest that reduced emotional association memory is accompanied by increases in activity and functional coupling within the amygdala. This did not disrupt hippocampal association-memory processes, which indeed were critical for successful emotional association memory formation

Reduced associative memory for negative information: impact of confidence and interactive imagery during study

Although item-memory for emotional information is enhanced, memory for associations between items is often impaired for negative, emotionally arousing compared to neutral information. We tested two possible mechanisms underlying this impairment, using picture pairs: 1) higher confidence in one’s own ability to memorise negative information may cause participants to under-study negative pairs; 2) better interactive imagery for neutral pairs could facilitate associative memory for neutral pairs more than for negative pairs. Tested with associative recognition, we replicated the impairment of associative memory for negative pairs. We also replicated the result that confidence in future memory (judgments of learning) was higher for negative than neutral pairs. Inflated confidence could not explain the impairment of associative recognition memory: Judgements of learning were positively correlated with associative memory success for both negative and neutral pairs. However, neutral pairs were rated higher in their conduciveness to interactive imagery than negative pairs, and this difference in interactive imagery showed a robust relationship to the associative memory difference. Thus, associative memory reductions for negative information are not due to differences in encoding effort. Instead, interactive imagery may be less effective for encoding of negative than neutral pairs

Inverted list-strength effects in recognition

If some list items are studied strongly and others weakly, many memory models predict the effect of strength on memory will be larger when strengths are mixed within a list than between pure lists of a single strength: a list-strength effect. In explaining why list-strength effects were elusive in old/new recognition, Shiffrin et al. (1990) introduced differentiation. This gave the model a way to produce an inverted list-strength effect which they thought was usually offset by the co-existing expected “upright” list-strength effect. Alternatively, attentional subsetting theory (Caplan, 2023; Caplan & Guitard, 2024b) predicted inverted list-strength effects in some circumstances by considering how the dimensionalities of attended feature spaces might differ for strong and weak items. Inversions were indeed found in manipulations of stimulus duration (e.g., 500 ms versus 2000 ms study time/word). Here we replicated the pattern when display time was equated (Experiment 1) and with massed-repetition (Experiment 2), ruling out the relevance of visionlocked features and number of stimulus onsets. Both theoretical accounts of inverted list-strength effects, however, miss the fine structure of the data, namely, reduced hit rates for weak items in pure than mixed lists and the reverse effect (albeit less robust) for strong items. Model fits suggested the critical factor is that list composition parameterically influences the number of deep features processed at test combined with participants response bias adapting to list composition. In sum, inverted list-strength effects are robustly found in manipulations of item study time and point to differential processing of probe features depending on list composition, compatible with most models

Value bias of verbal memory

© 2019 Elsevier Inc. A common finding is that items associated with higher reward value are subsequently remembered better than items associated with lower value. A confounding factor is that when a higher value stimuli is presented, this typically signals to participants that it is now a particularly important time to engage in the task. When this was controlled, Madan, Fujiwara, Gerson, and Caplan (2012) still found a large value-bias of memory. Their value-learning procedure, however, explicitly pitted high- against low-value words. Our novel value-learning procedure trained words one at a time, avoiding direct competition between words, but with no difference in words signalling participants to engage in the task. Results converged on null effects of value on subsequent free recall accuracy. Re-analyses attributed Madan et al.’s value-bias to competition between choice items that were paired during learning. Value may not bias memory if it does not signal task importance or induce inter-item competition

Long-Term Recency in Anterograde Amnesia.

Amnesia is usually described as an impairment of a long-term memory (LTM) despite an intact short-term memory (STM). The intact recency effect in amnesia had supported this view. Although dual-store models of memory have been challenged by single-store models based on interference theory, this had relatively little influence on our understanding and treatment of amnesia, perhaps because the debate has centred on experiments in the neurologically intact population. Here we tested a key prediction of single-store models for free recall in amnesia: that people with amnesia will exhibit a memory advantage for the most recent items even when all items are stored in and retrieved from LTM, an effect called long-term recency. People with amnesia and matched controls studied, and then free-recalled, word lists with a distractor task following each word, including the last (continual distractor task, CDFR). This condition was compared to an Immediate Free Recall (IFR, no distractors) and a Delayed Free Recall (DFR, end-of-list distractor only) condition. People with amnesia demonstrated the full long-term recency pattern: the recency effect was attenuated in DFR and returned in CDFR. The advantage of recency over midlist items in CDFR was comparable to that of controls, confirming a key prediction of single-store models. Memory deficits appeared only after the first word recalled in each list, suggesting the impairment in amnesia may emerge only as the participant's recall sequence develops, perhaps due to increased susceptibility to output interference. Our findings suggest that interference mechanisms are preserved in amnesia despite the overall impairment to LTM, and challenge strict dual-store models of memory and their dominance in explaining amnesia. We discuss the implication of our findings for rehabilitation

Caudate Infarcts

Eighteen Patients Had Caudate Nucleus Infarcts (10 Left-Sided; 8 Right-Sided). Infarcts Extended into the Anterior Limb of the Internal Capsule in 9 Patients, and Also the Anterior Putamen in 5 Patients. Thirteen Patients Had Motor Signs, Most Often a Slight Transient Hemiparesis. Dysarthria Was Common (11 Patients). Cognitive and Behavioral Abnormalities Were Frequent, and Included Abulia (10 Patients), Agitation and Hyperactivity (7 Patients), Contralateral Neglect (3 Patients, All Right Caudate), and Language Abnormalities (2 Patients, Both Left Caudate). the Majority of Patients Had Risk Factors for Penetrating Artery Disease. Branch Occlusion of Heubner\u27s Artery, or Perforators from the Proximal Anterior or Middle Cerebral Arteries Were the Posited Mechanism of Infarction. © 1990, American Medical Association. All Rights Reserved

Gamma oscillations correlate with working memory load in humans

Functional imaging of human cortex implicates a diverse network of brain regions supporting working memory—the capacity to hold and manipulate information for short periods of time. Although we are beginning to map out the brain networks supporting working memory, little is known about its physiological basis. We analyzed intracranial recordings from two epileptic patients as they performed a working memory task. Spectral analyses revealed that, in both patients, gamma (30-60 Hz) oscillations increased approximately linearly with memory load, tracking closely with memory load over the course of the trial. This constitutes the first evidence that gamma oscillations, widely implicated in perceptual processes, support the maintenance of multiple items in working memory