Midbrain-Hippocampus Structural Connectivity Selectively Predicts Motivated Memory Encoding.

Motivation is a powerful driver of learning and memory. Functional MRI studies show that interactions among the dopaminergic midbrain substantia nigra/ventral tegmental area (SN/VTA), hippocampus, and nucleus accumbens (NAc) are critical for motivated memory encoding. However, it is not known whether these effects are transient and purely functional, or whether individual differences in the structure of this circuit underlie motivated memory encoding. To quantify individual differences in structure, diffusion-weighted MRI and probabilistic tractography were used to quantify SN/VTA-striatum and SN/VTA-hippocampus pathways associated with motivated memory encoding in humans. Male and female participants completed a motivated source memory paradigm. During encoding, words were randomly assigned to one of three conditions, reward ($1.00), control ($0.00), or punishment (-$1.00). During retrieval, participants were asked to retrieve item and source information of the previously studied words and were rewarded or penalized according to their performance. Source memory for words assigned to both reward and punishment conditions was greater than those for control words, but there were no differences in item memory based on value. Anatomically, probabilistic tractography results revealed a heterogeneous, topological arrangement of the SN/VTA. Tract density measures of SN/VTA-hippocampus pathways were positively correlated with individual differences in reward-and-punishment-modulated memory performance, whereas density of SN/VTA-striatum pathways showed no association. This novel finding suggests that pathways emerging from the human SV/VTA are anatomically separable and functionally heterogeneous. Individual differences in structural connectivity of the dopaminergic hippocampus-VTA loop are selectively associated with motivated memory encoding.SIGNIFICANCE STATEMENT Functional MRI studies show that interactions among the SN/VTA, hippocampus, and NAc are critical for motivated memory encoding. This has led to competing theories that posit either SN/VTA-NAc reward prediction errors or SN/VTA-hippocampus signals underlie motivated memory encoding. Additionally, it is not known whether these effects are transient and purely functional or whether individual differences in the structure of these circuits underlie motivated memory encoding. Using diffusion-weighted MRI and probabilistic tractography, we show that tract density measures of SN/VTA-hippocampus pathways are positively correlated with motivated memory performance, whereas density of SN/VTA-striatum pathways show no association. This finding suggests that anatomic individual differences of the dopaminergic hippocampus-VTA loop are selectively associated with motivated memory encoding.

Testing locus coeruleus-norepinephrine accounts of working memory, attention control, and fluid intelligence.

The current set of studies examined the relationship among working memory capacity, attention control, fluid intelligence, and pupillary correlates of tonic arousal regulation and phasic responsiveness in a combined sample of more than 1,000 participants in two different age ranges (young adults and adolescents). Each study was designed to test predictions made by two recent theories regarding the role of the locus coeruleus-norepinephrine (LC-NE) system in determining individual differences in cognitive ability. The first theory, proposed by Unsworth and Robison (2017a), posits two important individual differences: the moment-to-moment regulation of tonic arousal, and the phasic responsiveness of the system to goal-relevant stimuli. The second theory, proposed by Tsukahara and Engle (2021a), argues that people with higher cognitive abilities have greater functional connectivity between the LC-NE system and cortical networks at rest. These two theories are not mutually exclusive, but they make different predictions. Overall, we found no evidence consistent with a resting-state theory. However, phasic responsiveness was consistently correlated with working memory capacity, attention control, and fluid intelligence, supporting a prediction made by Unsworth and Robison (2017a). Tonic arousal regulation was not correlated with working memory or fluid intelligence and was inconsistently correlated with attention control, which offers only partial support for Unsworth and Robison's (2017a) second prediction.

The effect of binaural beat stimulation on sustained attention.

Binaural beats have been used as a way of modifying cognition via auditory stimulation. A recent meta-analysis suggests that binaural beat stimulation can have a positive effect on attention (Garcia-Argibay et al., Psychologische Forschung 83:1124-1136, 2019a, Psychological Research Psychologische Forschung 83:357-372, 2019b), with the sample-weighted average effect size being about .58. This is an intriguing and potentially useful finding, both theoretically and practically. In this study, we focus on sustained attention. We delivered beta-frequency (16 Hz) binaural beat stimulation during a sustained attention task. In "Experiment 1", reaction times were faster under beat stimulation than control stimulation in a between-subjects design. However, the effect was modest in magnitude, and model comparisons using Bayes Factors were indiscriminate between including and excluding the effect from the model. We followed this initial experiment with two concurrently administered follow-up experiments. In "Experiment 2", we added thought probes to measure any changes in task engagement associated with binaural beat stimulation. "Experiment 2" revealed a different effect from "Experiment 1": participants in the binaural beat condition exhibited a shallower vigilance decrement. However, the beat stimulation did not affect the thought probes responses. Combining data across the two experiments indicated rather strong evidence against the hypothesis that beta-frequency binaural beats can augment sustained attention, either via a general speeding of responding or a mitigation of the vigilance decrement. Finally, in "Experiment 3", we investigated whether pupillary measures of arousal and/or task engagement would be affected by binaural beat stimulation. There was no evidence for such effects. Overall, we did not observe any consistent evidence that binaural beat stimulation can augment sustained attention or its subjective and physiological correlates.

Individual Differences in Disqualifying Monitoring Underlie False Recognition of Associative and Conjunction Lures.

The current study leveraged experimental and individual differences methodology to examine whether false memories across different list-learning tasks arise from a common cause. Participants completed multiple false memory (associative and conjunction lure), working memory (operation and reading span), and source monitoring (verbal and picture) tasks. Memory discriminability in the associative and conjunction tasks loaded onto a single (general) factor and were unaffected by warnings provided at encoding. Consistent with previous research, source-monitoring ability fully mediated the relation between working memory and false memories. Moreover, individuals with higher source monitoring-ability were better able to recall contextual information from encoding to correctly reject lures. These results suggest that there are stable individual differences in false remembering across tasks. The commonality across tasks may be due, at least in part, to the ability to effectively use disqualifying monitoring processes.

Individual differences in working memory capacity predict benefits to memory from intention offloading.

Research suggests that individuals with lower working memory have difficulty remembering to fulfil delayed intentions. The current study examined whether the ability to offload intentions onto the environment mitigated these deficits. Participants (N = 268) completed three versions of a delayed intention task with and without the use of reminders, along with three measures of working memory capacity. Results showed that individuals with higher working memory fulfilled more intentions when having to rely on their own memory, but this difference was eliminated when offloading was permitted. Individuals with lower working memory chose to offload more often, suggesting that they were less willing to engage in effortful maintenance of internal representations when given the option. Working memory was not associated with metacognitive confidence or optimal offloading choices based on point value. These findings suggest offloading may help circumvent capacity limitations associated with maintaining and remembering delayed intentions.

Neural correlates underlying the effect of reward value on recognition memory.

The prioritized encoding and retrieval of valuable information is an essential aspect of human memory. We used electroencephalography (EEG) to determine which of two hypothesized processes underlies the influence of reward value on episodic memory. One hypothesis is that value engages prefrontal executive control processes, so that valuable stimuli engage an elaborative rehearsal strategy that benefits memory. A second hypothesis is that value acts through the reward-related midbrain dopamine system to modulate synaptic plasticity in hippocampal and cortical efferents, thereby benefiting memory encoding. We used a value-directed recognition memory (VDR) paradigm in which participants encoded words assigned different point values and aimed to maximize the point value of subsequently recognized words. Subjective states of recollection (i.e., "remember") and familiarity (i.e., "know") were assessed at retrieval. Words assigned higher values at study were recognized more effectively than words assigned lower values, due to increased "remember" responses but no difference in "know" responses. Greater value was also associated with larger amplitudes of an EEG component at retrieval that indexes recollection (parietal old/new component), but had no relationship with a component that indexes familiarity (FN400 component). During encoding, we assessed a late frontal positivity (frontal slow wave, FSW) that has been related to elaborative rehearsal strategies and an early parietal component (P3) thought to index dopamine driven attention allocation. Our findings indicate that the effect of value on recognition memory is primarily driven by the dopamine-driven reward valuation system (P3) with no discernible effect on rehearsal processes (FSW).

Deep Neural Network for Visual Stimulus-Based Reaction Time Estimation Using the Periodogram of Single-Trial EEG.

Multiplexed deep neural networks (DNN) have engendered high-performance predictive models gaining popularity for decoding brain waves, extensively collected in the form of electroencephalogram (EEG) signals. In this paper, to the best of our knowledge, we introduce a first-ever DNN-based generalized approach to estimate reaction time (RT) using the periodogram representation of single-trial EEG in a visual stimulus-response experiment with 48 participants. We have designed a Fully Connected Neural Network (FCNN) and a Convolutional Neural Network (CNN) to predict and classify RTs for each trial. Though deep neural networks are widely known for classification applications, cascading FCNN/CNN with the Random Forest model, we designed a robust regression-based estimator to predict RT. With the FCNN model, the accuracies obtained for binary and 3-class classification were 93% and 76%, respectively, which further improved with the use of CNN (94% and 78%, respectively). The regression-based approach predicted RTs with correlation coefficients (CC) of 0.78 and 0.80 for FCNN and CNN, respectively. Investigating further, we found that the left central as well as parietal and occipital lobes were crucial for predicting RT, with significant activities in the theta and alpha frequency bands.

Aiding the search: Examining individual differences in multiply-constrained problem solving.

Understanding and resolving complex problems is of vital importance in daily life. Problems can be defined by the limitations they place on the problem solver. Multiply-constrained problems are traditionally examined with the compound remote associates task (CRAT). Performance on the CRAT is partially dependent on an individual's working memory capacity (WMC). These findings suggest that executive processes are critical for problem solving and that there are reliable individual differences in multiply-constrained problem solving abilities. The goals of the current study are to replicate and further elucidate the relation between WMC and CRAT performance. To achieve these goals, we manipulated preexposure to CRAT solutions and measured WMC with complex-span tasks. In Experiment 1, we report evidence that preexposure to CRAT solutions improved problem solving accuracy, WMC was correlated with problem solving accuracy, and that WMC did not moderate the effect of preexposure on problem solving accuracy. In Experiment 2, we preexposed participants to correct and incorrect solutions. We replicated Experiment 1 and found that WMC moderates the effect of exposure to CRAT solutions such that high WMC participants benefit more from preexposure to correct solutions than low WMC (although low WMC participants have preexposure benefits as well). Broadly, these results are consistent with theories of working memory and problem solving that suggest a mediating role of attention control processes.

Individual differences in episodic memory abilities predict successful prospective memory output monitoring.

Output monitoring refers to memory for one's previously completed actions. In the context of prospective memory (PM) (e.g., remembering to take medication), failures of output monitoring can result in repetitions and omissions of planned actions (e.g., over- or under-medication). To be successful in output monitoring paradigms, participants must flexibly control attention to detect PM cues as well as engage controlled retrieval of previous actions whenever a particular cue is encountered. The current study examined individual differences in output monitoring abilities in a group of younger adults differing in attention control (AC) and episodic memory (EM) abilities. The results showed that AC ability uniquely predicted successful cue detection on the first presentation, whereas EM ability uniquely predicted successful output monitoring on the second presentation. The current study highlights the importance of examining external correlates of PM abilities and contributes to the growing body of research on individual differences in PM.

Acute pain disrupts prospective memory cue detection processes.

Prospective memory refers to the planning, retention, retrieval, and execution of intentions for future behaviours and it is integral to the enterprise of daily living. Although prospective memory relies upon retrospective memory and executive processes often disrupted by pain, limited research has explored the influence of acute or chronic pain on the ability to complete prospective memory tasks. In the present study we investigated the influence of acute pain on prospective memory tasks that varied in their demands on executive processes (i.e., non-focal versus focal prospective memory cues). Complex-span working memory tasks were also administered to examine whether individual differences in working memory capacity moderated any negative impact of pain on prospective memory. Acute pain significantly impaired prospective memory performance in conditions that encouraged non-focal strategic processing of prospective memory cues, but not in conditions that encouraged more spontaneous focal processing. Individual differences in working memory capacity did not moderate the effect of acute pain on non-focal prospective memory. These findings provide new insights into prospective memory dysfunction created by painful experiences.

Costly Signaling Increases Trust, Even Across Religious Affiliations.

Trust is a critical aspect of social interaction. One might predict that individuals trust religious out-groups less than religious in-groups, and that costly signals performed by members of religious in-groups increase trust while costly signals performed by members of religious out-groups decrease trust. We examined how Christian participants perceived the trustworthiness of Muslim and Christian individuals who did or did not engage in religious costly signaling. Religious costly signaling, operationalized as giving to religious charities (Experiments 1 and 2) or adhering to religious dietary restrictions (Experiment 3), increased self-reported trust, regardless of target religious affiliation. Furthermore, when estimating the likelihood that trustworthy versus untrustworthy targets engaged in costly signaling, participants made systematic judgments that showed that costly signaling is associated with trust for both Muslim and Christian targets (Experiment 4). These results are novel in their suggestion that costly signals of religious commitment can increase trust both within and, crucially, across religious-group lines.

Judging the reality of others' memories.

Interpersonal reality monitoring (IRM) refers to our ability to evaluate whether other people's memories reflect real or imagined events. The current work examined IRM and whether or not it can be affected by training and feedback. We found that people are better than chance and that the ability to accurately make this judgement can be improved or reduced with appropriate and inappropriate training, respectively. Understanding IRM has implications for applied psychologists interested in how people evaluate others' descriptions of past events (e.g., eyewitness testimony).

No effects of executive control depletion on prospective memory retrieval processes.

Research has suggested that prospective memory retrieval is reliant on executive control processes, and the degree to which these processes are necessary for intention fulfillment is dependent on a host of variables related to the prospective memory task. Based on results suggesting that aspects of the prospective memory task vary in their need for executive control, the current study examined the possibility that executive control depletion from the Stroop task would negatively transfer to prospective memory performance. Depletion of executive control, measured objectively in a Stroop task, did not impair prospective memory performance in either low or high cue-target association conditions. However, participants' subjective assessments of their own cognitive fatigue correlated significantly with their prospective memory performance, regardless of the association between cues and target responses.

Investigating the subjective reports of rejection processes in the word frequency mirror effect.

We sought to systematically investigate how participants subjectively classify the basis of their recognition memory judgments for low and high word frequency items. We found that participants more often reported rejection processes related to the increased perceived memorability for unstudied low word frequency items (relative to high word frequency items), rather than classifying their decision on a lack of familiarity. Experiment 2 replicated this pattern and demonstrated context variability and word frequency independently influenced the subjective classifications for correct rejections. Results of Experiment 3 revealed that these differences are dependent upon having experience with both low and high frequency items. Overall, these data suggest participants' rejection of low frequency items is more strongly related to judgments of perceived memorability, but only when they are presented in the context of high frequency items. The results are discussed in relation to distinctiveness and expected memorability.

Strategic search from long-term memory: an examination of semantic and autobiographical recall.

Searching long-term memory is theoretically driven by both directed (search strategies) and random components. In the current study we conducted four experiments evaluating strategic search in semantic and autobiographical memory. Participants were required to generate either exemplars from the category of animals or the names of their friends for several minutes. Self-reported strategies suggested that participants typically relied on visualization strategies for both tasks and were less likely to rely on ordered strategies (e.g., alphabetic search). When participants were instructed to use particular strategies, the visualization strategy resulted in the highest levels of performance and the most efficient search, whereas ordered strategies resulted in the lowest levels of performance and fairly inefficient search. These results are consistent with the notion that retrieval from long-term memory is driven, in part, by search strategies employed by the individual, and that one particularly efficient strategy is to visualize various situational contexts that one has experienced in the past in order to constrain the search and generate the desired information.

Reservoir-computing based associative memory and itinerancy for complex dynamical attractors.

Traditional neural network models of associative memories were used to store and retrieve static patterns. We develop reservoir-computing based memories for complex dynamical attractors, under two common recalling scenarios in neuropsychology: location-addressable with an index channel and content-addressable without such a channel. We demonstrate that, for location-addressable retrieval, a single reservoir computing machine can memorize a large number of periodic and chaotic attractors, each retrievable with a specific index value. We articulate control strategies to achieve successful switching among the attractors, unveil the mechanism behind failed switching, and uncover various scaling behaviors between the number of stored attractors and the reservoir network size. For content-addressable retrieval, we exploit multistability with cue signals, where the stored attractors coexist in the high-dimensional phase space of the reservoir network. As the length of the cue signal increases through a critical value, a high success rate can be achieved. The work provides foundational insights into developing long-term memories and itinerancy for complex dynamical patterns.

Working memory capacity and retrieval from long-term memory: the role of controlled search.

In two experiments, the role of working memory capacity (WMC) in the controlled search of long-term memory was examined. Participants performed a prolonged category fluency task that required them to retrieve as many animals as possible in 5 min. The results suggested that WMC differences arose in the numbers of animals retrieved, the numbers of clusters retrieved, and the rates of the retrieval (Exp. 1). However, no differences were found in terms of how participants initiated retrieval or in the nature of the clusters generated. Furthermore, an examination of differences in retrieval strategies suggested that high-WMC individuals were more strategic than low-WMC individuals and that these differences in retrieval strategies accounted for the overall differences in the numbers of animals retrieved. Additionally, presenting participants with retrieval cues eliminated WMC differences in the numbers of animals retrieved (Exp. 2). These results suggest that low-WMC individuals are less able than high-WMC individuals to select and utilize appropriate retrieval strategies to self-generate cues to access information in long-term memory. Collectively, the results are consistent with research suggesting that WMC is important for controlled search from long-term memory.

An assessment of learning rates in habitual prospective memory.

Most laboratory research in the field of prospective memory has focused on newly formed (episodic) intentions that are carried out in the experimental context once or only a small number of times. However, many naturalistic prospective memories are carried out many times and these types of (habitual) intentions have been studied much less in the laboratory. In the current study, our aim was to extend prior work examining habitual intentions in laboratory prospective memory paradigms. Participants formed a typical prospective memory intention and then completed an ongoing task in which the intention could be executed up to 63 times. We examined changes in performance across trials in three traditionally important prospective memory metrics: cue detection, task interference, and cue interference. Across repeated performance of the prospective memory task, we observed an increase in cue detection, elimination of task interference, and elimination of cue interference. These results provide key insights into the operation of learning mechanisms in prospective memory paradigms and promote theory development by showing that many of the resource-demanding processes that are theorized to be necessary for successful prospective memory play much less of a role when intentions are repeatedly completed.

Task sequencing does not systematically affect the factor structure of cognitive abilities.

Latent variable analyses of cognitive abilities are among the major means by which cognitive psychologists test theories regarding the structure of human cognition. Models are fit to observed variance-covariance structures, and the fit of those models are compared to assess the merits of competing theories. However, an often unconsidered and potentially important methodological issue is the precise sequence in which tasks are delivered to participants. Here we empirically tested whether differences in task sequences systematically affect the observed factor structure. A large sample (N = 587) completed a battery of 12 cognitive tasks measuring four constructs: working memory, long-term memory, attention control, and fluid intelligence. Participants were assigned to complete the assessment in one of three sequences: fixed and grouped by construct vs. fixed and interleaved across constructs vs. random by participant. We generated and tested two hypotheses: grouping task sequences by construct (i.e., administering clusters of tasks measuring a cognitive construct consecutively) would (1) systematically increase factor loadings and (2) systematically decrease interfactor correlations. Neither hypothesis was supported. The measurement models were largely invariant across the three conditions, suggesting that latent variable analyses are robust to such subtle methodological differences as task sequencing.

Noradrenaline tracks emotional modulation of attention in human amygdala.

The noradrenaline (NA) system is one of the brain's major neuromodulatory systems; it originates in a small midbrain nucleus, the locus coeruleus (LC), and projects widely throughout the brain.1,2 The LC-NA system is believed to regulate arousal and attention3,4 and is a pharmacological target in multiple clinical conditions.5,6,7 Yet our understanding of its role in health and disease has been impeded by a lack of direct recordings in humans. Here, we address this problem by showing that electrochemical estimates of sub-second NA dynamics can be obtained using clinical depth electrodes implanted for epilepsy monitoring. We made these recordings in the amygdala, an evolutionarily ancient structure that supports emotional processing8,9 and receives dense LC-NA projections,10 while patients (n = 3) performed a visual affective oddball task. The task was designed to induce different cognitive states, with the oddball stimuli involving emotionally evocative images,11 which varied in terms of arousal (low versus high) and valence (negative versus positive). Consistent with theory, the NA estimates tracked the emotional modulation of attention, with a stronger oddball response in a high-arousal state. Parallel estimates of pupil dilation, a common behavioral proxy for LC-NA activity,12 supported a hypothesis that pupil-NA coupling changes with cognitive state,13,14 with the pupil and NA estimates being positively correlated for oddball stimuli in a high-arousal but not a low-arousal state. Our study provides proof of concept that neuromodulator monitoring is now possible using depth electrodes in standard clinical use.