Retrieval Demands Adaptively Change Striatal Old/New Signals and Boost Subsequent Long-Term Memory

The testing effect for visual materials depends on preexisting knowledge

Remembering facilitates future remembering. This benefit of practicing by active retrieval, as compared to more passive relearning, is known as the testing effect and is one of the most robust findings in the memory literature. It has typically been assessed using verbal materials such as word pairs, sentences, or educational texts. We here investigate if memory for visual materials equally benefits from retrieval-mediated learning. Based on cognitive and neuroscientific theories, we hypothesize that testing effects will be limited to meaningful visual images that can be related to preexisting knowledge. In a series of four experiments, we systematically varied the type of material (meaningless "squiggle" shapes vs. meaningful object images) and the format of the test used to probe memory (a visually driven alternative forced-choice test vs. a remember/know recognition test). Within each experiment, we assessed the effects of practice type (retrieval or restudy) and the delay of the final test (immediate vs. 1 week) on the resulting practice benefits. Abstract shapes never showed a significant testing benefit, irrespective of test format. Meaningful object images did benefit from testing, particularly at long delays, and with a test format probing the recollective component of recognition memory. Together, our results indicate that retrieval can facilitate the recollection of visual images when they represent meaningful semantic units. This pattern of results is predicted by cognitive and neurobiologically motivated theories proposing that retrieval's benefits emerge through spreading activation in semantic networks, producing more easily accessible and longer-lasting memory traces. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Differential effects of expectancy on memory formation in young and older adults

Novelty can promote subsequent long-term memory via the mesolimbic system, including the medial temporal lobe and midbrain structures. Importantly, these and other brain regions typically degenerate during healthy aging, which suggests a reduced impact of novelty on learning. However, evidence in favor of such a hypothesis is scarce. Thus, we used functional MRI in combination with an established paradigm in healthy young (19-32 years, n = 30) and older (51-81 years, n = 32) humans. During encoding, colored cues predicted the subsequent presentation of either a novel or previously familiarized image (75% cue validity), and approximately 24 h later, recognition memory for novel images was tested. Behaviorally, expected novel images, as compared to unexpected novel images, were better recognized in young and, to a lesser degree, older subjects. At the neural level, familiar cues activated memory related areas, especially the medial temporal lobe, whereas novelty cues activated the angular gyrus and inferior parietal lobe, which may reflect enhanced attentional processing. During outcome processing, expected novel images activated the medial temporal lobe, angular gyrus and inferior parietal lobe. Importantly, a similar activation pattern was observed for subsequently recognized novel items, which helps to explain the behavioral effect of novelty on long-term memory. Finally, age-effects were pronounced for successfully recognized novel images with relatively stronger activations in attention-related brain regions in older adults; younger adults, on the other hand, showed stronger hippocampal activation. Together, expectancy promotes memory formation for novel items via neural activity in medial temporal lobe structures and this effect appears to be reduced with age.

Patterns of retrieval-related cortico-striatal connectivity are stable across the adult lifespan

Memory retrieval effects in the striatum are well documented and robust across experimental paradigms. However, the functional significance of these effects, and whether they are moderated by age, remains unclear. We used functional magnetic resonance imaging paired with an associative recognition task to examine retrieval effects in the striatum in a sample of healthy young, middle-aged, and older adults. We identified anatomically segregated patterns of enhanced striatal blood oxygen level-dependent (BOLD) activity during recollection- and familiarity-based memory judgments. Successful recollection was associated with enhanced BOLD activity in bilateral putamen and nucleus accumbens, and neither of these effects were reliably moderated by age. Familiarity effects were evident in the head of the caudate nucleus bilaterally, and these effects were attenuated in middle-aged and older adults. Using psychophysiological interaction analyses, we observed a monitoring-related increase in functional connectivity between the caudate and regions of the frontoparietal control network, and between the putamen and bilateral retrosplenial cortex and intraparietal sulcus. In all instances, monitoring-related increases in cortico-striatal connectivity were unmoderated by age. These results suggest that the striatum, and the caudate in particular, couples with the frontoparietal control network to support top-down retrieval-monitoring operations, and that the strength of these inter-regional interactions is preserved in later life.

OUP accepted manuscript

Retrieval practice improves retention of information in long-term memory more than restudy, but the underlying neural mechanisms of this “retrieval practice effect” (RPE) remain poorly understood. Therefore, we investigated the behavioral and neural differences between previously retrieved versus restudied items at final retrieval. Thirty younger (20–30 years old) and twenty-five older (50+ years old) adults learned familiar and new picture stimuli either through retrieval or restudy. At final recognition, hemodynamic activity was measured using functional magnetic resonance imaging (fMRI). Behaviorally, younger and older adults showed similar benefits of retrieval practice, with higher recollection, but unchanged familiarity rates. In a univariate analysis of the fMRI data, activation in medial prefrontal cortex and left temporal regions correlated with an individual’s amount of behavioral benefit from retrieval practice, irrespective of age. Compatible with this observation, in a multivariate representational similarity analysis (RSA), retrieval practice led to an increase in pattern similarity for retested items in a priori defined regions of interest, including the medial temporal lobe, as well as prefrontal and parietal cortex. Our findings demonstrate that retrieval practice leads to enhanced long-term memories in younger and older adults alike, and this effect may be driven by fast consolidation processes.

Comparison of Pupil Dilation Responses to Unexpected Sounds in Monkeys and Humans

Pupil dilation in response to unexpected stimuli has been well documented in human as well as in non-human primates; however, this phenomenon has not been systematically compared between the species. This analogy is also crucial for the role of non-human primates as an animal model to investigate neural mechanisms underlying the processing of unexpected stimuli and their evoked pupil dilation response. To assess this qualitatively, we used an auditory oddball paradigm in which we presented subjects a sequence of the same sounds followed by occasional deviants while we measured their evoked pupil dilation response (PDR). We used deviants (a frequency deviant, a pink noise burst, a monkey vocalization and a whistle sound) which differed in the spectral composition and in their ability to induce arousal from the standard. Most deviants elicited a significant pupil dilation in both species with decreased peak latency and increased peak amplitude in monkeys compared to humans. A temporal Principal Component Analysis (PCA) revealed two components underlying the PDRs in both species. The early component is likely associated to the parasympathetic nervous system and the late component to the sympathetic nervous system, respectively. Taken together, the present study demonstrates a qualitative similarity between PDRs to unexpected auditory stimuli in macaque and human subjects suggesting that macaques can be a suitable model for investigating the neuronal bases of pupil dilation. However, the quantitative differences in PDRs between species need to be investigated in further comparative studies.

Anticipation of novel environments enhances memory for incidental information

Novelty is a potent driver of learning, but little is known about whether anticipation of novelty can enhance memory for incidental information. Here, participants incidentally encountered objects while they actively navigated toward novel or previously familiarized virtual rooms. Across immediate and delayed surprise memory tests, participants showed superior recollection for incidental objects encountered while anticipating novel as compared with familiarized rooms. Furthermore, memory for incidental objects correlated positively with between-participants average curiosity about novel rooms but negatively with within-participants trial-specific curiosity. Our findings contribute to the growing literature on how salient processes impact memory for incidental material.

Expectation-driven novelty effects in episodic memory

Novel and unexpected stimuli are often prioritised in memory, given their inherent salience. Nevertheless, not all forms of novelty show such an enhancement effect. Here, we discuss the role expectation plays in modulating the way novelty affects memory processes, circuits, and subsequent performance. We first review independent effects of expectation on memory, and then consider how different types of novelty are characterised by expectation. We argue that different types of novelty defined by expectation implicate differential neurotransmission in memory formation brain regions and may also result in the creation of different types of memory. Contextual novelty, which is unexpected by definition, is often associated with better recollection, supported by dopaminergic-hippocampal interactions. On the other hand, expected stimulus novelty is supported by engagement of medial temporal cortices, as well as the hippocampus, through cholinergic modulation. Furthermore, when expected stimulus novelty results in enhanced memory, it is predominantly driven by familiarity. The literature reviewed here highlights the complexity of novelty-sensitive memory systems, the distinction between types of novelty, and how they are differentially affected by expectancy.

The gains of a 4-week cognitive training are not modulated by novelty

Cognitive training should not only improve performance of the trained task, but also untrained abilities. Exposure to novelty can improve subsequent memory performance, suggesting that novelty exposure might be a critical factor to promote the effects of cognitive training. Therefore, we combined a 4‐week working memory training with novelty exposure. Neuropsychological tests and MRI data were acquired before and after training to analyze behavior and changes in gray matter volume, myelination, and iron levels. In total, 83 healthy older humans participated in one of three groups: Two groups completed a 4‐week computerized cognitive training of a two‐back working memory task, either in combination with novel or with familiarized nature movies. A third group did not receive any training. As expected, both training groups showed improvements in task specific working memory performance and reaction times. However, there were no transfer or novelty effects on fluid intelligence, verbal memory, digit‐span, and executive functions. At the neural level, no significant micro‐ or macrostructural changes emerged in either group. Our findings suggest that working memory training in healthy older adults is associated with task‐specific improvements, but these gains do not transfer to other cognitive domains, and it does not lead to structural brain changes.

Retrieval Practice Improves Recollection-Based Memory Over a Seven-Day Period in Younger and Older Adults

Retrieving information improves subsequent memory performance more strongly than restudying. However, despite recent evidence for this retrieval practice effect (RPE), the temporal dynamics, age-related changes, and their possible interactions remain unclear. Therefore, we tested 45 young (18–30 years) and 41 older (50 + years) participants with a previously established RP paradigm. Specifically, subjects retrieved and restudied scene images on Day 1; subsequently, their recognition memory for the presented items was tested on the same day of learning and 7 days later using a remember/know paradigm. As main findings we can show that both young and older adults benefited from RP, however, the older participants benefited to a lesser extent. Importantly, the RPE was present immediately after learning on Day 1 and 7 days later, with no significant differences between time points. Finally, RP improved recollection rates more strongly than familiarity rates, independent of age and retrieval interval. Together, our results provide evidence that the RPE is reduced but still existing in older adults, it is stable over a period of seven days and relies more strongly on hippocampus-based recollection.

Sensitivity of Reality Monitoring to Fluency: Evidence from Behavioral Performance and Event-Related Potential (ERP) Old/New Effects

Background

Item memory and source memory are differently processed with both behavioral and event-related potential (ERP) evidence. Reality monitoring, a specific type of source memory, which refers to the ability to differentiate external sources from internal sources, has been drawing much attention. Among factors that have an impact on reality monitoring, fluency has not been well-studied. Therefore, the current study aimed to investigate whether fluency could affect reality monitoring, through observations on both behavioral performance and electrophysiological patterns.

Material/Methods

Adopting ERP techniques, participants were required either to watch the presentation of a name/picture pair, or to imagine a picture for each displayed name, once (low fluency) or twice (high fluency). Later they completed a reality monitoring task of identifying names as perceived, imagined, or novel items. Behavioral performance was measured, and ERP waveforms were recorded.

Results

Behaviorally, high fluency items were faster and more accurately attributed to the sources than low fluency items. ERP waveforms revealed that late positive component (LPC) occurred for all 4 types of items, while imagined items of low fluency did not record a robust FN400 or late frontal old/new effect.

Conclusions

As results revealed, the factor of fluency does influence reality monitoring in terms of accuracy and responding speed. Meanwhile, for imagined items of low fluency, the absence of FN400 and frontal old/new effect also suggests the sensitivity of reality monitoring to fluency, because these representatives of familiarity-based processing and post-retrieval monitoring are inevitably involved in the process of differentiating internal source from external source.

Dopamine Enhances Item Novelty Detection via Hippocampal and Associative Recall via Left Lateral Prefrontal Cortex Mechanisms

The involvement of fronto-striatal circuits in item and associative memory retrieval as well as in the stabilization of memories by retrieval practice suggests that both retrieval and re-encoding of stored memories might rely on dopaminergic mechanisms in humans. We tested these hypotheses in a placebo-controlled pharmacological fMRI study using 2 mg of the D2 antagonist haloperidol administered acutely before a cued associative recall task of previously encoded picture-word pairs in 53 healthy humans of both sexes. The cued associative recall was moreover repeated 3 d later outside the scanner without pharmacological intervention. Dopaminergic modulation significantly improved associative recall performance and recognition accuracy of verbal items. Moreover, we observed a significant dopamine effect on re-encoding in terms of increased specificity of associative memories from the first to the second cued associative recall. Better association memory under haloperidol was linked with higher activity in the left lateral prefrontal cortex and right parietal cortex, suggesting that dopamine facilitates associative retrieval through increased recruitment of frontoparietal monitoring processes. In contrast, improved recognition of verbal items under haloperidol was reflected by enhanced novelty detection in the hippocampus and increased activity in saliency networks. Together, these results show distinct but concomitant positive effects of dopamine on associative recall and item recognition and suggest that the specificity of associative recall through re-encoding mechanisms is likewise augmented by dopamine.SIGNIFICANCE STATEMENT Although the neurotransmitter dopamine has been linked with learning and memory for a long time, dopaminergic effects on item recognition in humans were demonstrated only recently. The involvement of fronto-striatal monitoring processes in association retrieval suggests that associative memory might be particularly affected by dopamine. Moreover, fronto-striatal dopaminergic signals have been hypothesized to determine the updating and re-encoding of previously retrieved memories. We here demonstrate clear facilitative effects of dopamine on associative recall and item recognition mediated by prefrontal and hippocampal mechanisms respectively. Additionally, effects on re-encoding were reflected by increased specificity of associative memories. These results augment our understanding of dopaminergic processes in episodic memory retrieval and offer new perspectives on memory impairments in dopamine-related disorders and their treatment.

Novelty Before or After Word Learning Does Not Affect Subsequent Memory Performance

In humans, exposure to novel images and exploration of novel virtual environments before the encoding of words improved subsequent memory performance. Animal studies revealed similar effects of novelty, both before and after learning, and could show that hippocampus-dependent dopaminergic neuromodulation plays an important role. Here, we further investigated the effects of novelty on long-term memory in humans using a novel paradigm employing short sequences of nature movies presented either before or at two time points after learning of unrelated words. Since novelty processing is associated with a release of dopamine into the hippocampus, we hypothesized that novelty exposure primarily affects hippocampus-dependent memory (i.e., recollection) but not hippocampus-independent memory (i.e., familiarity). We tested 182 healthy human subjects in three experiments including a word-learning task followed by a 1-day delayed recognition task. Importantly, participants were exposed to novel (NOV) or familiar movies (FAM) at three time points: (experiment 1) directly after encoding of the word list, (experiment 2) 15 min after encoding, (experiment 3) 15 min prior to encoding. As expected, novel movies were perceived as more interesting and led to better mood. During word recognition, reaction times were faster for remember as compared to familiarity responses in all three experiments, but this effect was not modulated by novelty. In contrast to our main hypothesis, there was no effect of novelty – before or after encoding – on subsequent word recognition, including recollection and familiarity scores. Therefore, an exposure to novel movies without an active task does not affect hippocampus-dependent and hippocampus-independent long-term recognition memory for words in humans.

Cortical modulation of pupillary function: systematic review

BACKGROUND

The pupillary light reflex is the main mechanism that regulates the pupillary diameter; it is controlled by the autonomic system and mediated by subcortical pathways. In addition, cognitive and emotional processes influence pupillary function due to input from cortical innervation, but the exact circuits remain poorly understood. We performed a systematic review to evaluate the mechanisms behind pupillary changes associated with cognitive efforts and processing of emotions and to investigate the cerebral areas involved in cortical modulation of the pupillary light reflex.

METHODOLOGY

We searched multiple databases until November 2018 for studies on cortical modulation of pupillary function in humans and non-human primates. Of 8,809 papers screened, 258 studies were included.

RESULTS

Most investigators focused on pupillary dilatation and/or constriction as an index of cognitive and emotional processing, evaluating how changes in pupillary diameter reflect levels of attention and arousal. Only few tried to correlate specific cerebral areas to pupillary changes, using either cortical activation models (employing micro-stimulation of cortical structures in non-human primates) or cortical lesion models (e.g., investigating patients with stroke and damage to salient cortical and/or subcortical areas). Results suggest the involvement of several cortical regions, including the insular cortex (Brodmann areas 13 and 16), the frontal eye field (Brodmann area 8) and the prefrontal cortex (Brodmann areas 11 and 25), and of subcortical structures such as the locus coeruleus and the superior colliculus.

CONCLUSIONS

Pupillary dilatation occurs with many kinds of mental or emotional processes, following sympathetic activation or parasympathetic inhibition. Conversely, pupillary constriction may occur with anticipation of a bright stimulus (even in its absence) and relies on a parasympathetic activation. All these reactions are controlled by subcortical and cortical structures that are directly or indirectly connected to the brainstem pupillary innervation system.

Age-Related Decreases in the Retrieval Practice Effect Directly Relate to Changes in Alpha-Beta Oscillations

The retrieval (or testing) of information leads to better memory performance compared with reencoding. This phenomenon is known as "testing effect" or "retrieval practice effect" and has been primarily described in behavioral studies with healthy young subjects. However, possible age-related changes and their associated underlying neural processes, in particular neural oscillations, remain unclear. To address this issue, we used a previously established paradigm in healthy young (N = 27) and elderly (N = 28) male and female human adults while their brain activity was being recorded using EEG. Subjects viewed prefamiliarized scene images intermixed with new scenes and classified them as indoor versus outdoor (encoding task) or old versus new (retrieval task). Subsequently, subjects performed a recognition memory task 10 min and 24 h after encoding. Behaviorally, both age groups showed the testing effect at both time points but, importantly, it was less pronounced in the elderly. At the neural level, the retrieval compared with the encoding task was accompanied by power decreases in the alpha (9-12 Hz) and beta bands (13-30 Hz), possibly reflecting task demands, and this difference was more pronounced in the elderly. Finally, a correlation analysis revealed that those elderly who displayed a more pronounced testing effect exhibited a neural pattern that was more similar to the younger subjects. These findings provide evidence that the testing effect decreases across the life span, and they suggest that changes in alpha-beta oscillations play a direct role.SIGNIFICANCE STATEMENT Learning new and retrieving old information is part of everyday human life. Understanding how learning processes can be optimized therefore has direct applications in the realm of educational and rehabilitative contexts. Here, we show that retrieval practice is a strategy to optimize encoding into long-term memory in both young and elderly humans. Importantly, retrieval practice was significantly reduced in the elderly and closely related to changes in alpha (9-13 Hz) and beta band (13-30 Hz) oscillations. Our findings suggest that decreased retrieval practice effects across the life span contribute to, and may reflect, age-related declines in memory performance. They further provide new insights into the underlying neural mechanisms and point toward future avenues for neuro-modulatory interventions.