Neuropsychologia

The ability to generate novel creative ideas (divergent thinking) is closely linked with our ability to imagine novel future events (episodic simulation). Here, we employed an individual differences approach to examine whether divergent thinking and episodic simulation are differentially associated with episodic and semantic retrieval ability. In response to object word cues, participants generated meanings and definitions (semantic memory), remembered a past event (episodic memory), imagined a novel future event (episodic simulation), or generated novel uses (divergent thinking). Replicating previous findings, divergent thinking ability was predicted by the number of episodic details generated during episodic simulation. When directly comparing episodic and semantic memory, the strongest predictor of divergent thinking was semantic memory. In contrast, episodic simulation ability was predicted by both episodic and semantic memory. We interpret these findings as support for the semantic scaffold hypothesis of imagination, according to which semantic memory provides the necessary scaffold or framework for flexible expressions of cognition such as divergent thinking and episodic simulation. As episodic simulation, relative to divergent thinking, was associated with both episodic and semantic retrieval, these findings are taken to reflect common reliance on event construction processes recruited during both episodic remembering and imagining.

Visual imagery refers to the mental generation of visual representations of stimuli, while visual working memory involves retaining visual information for a short period without external input. Due to the conceptual overlap between these two constructs, successful performance on visual working memory tasks may rely on the use of visual imagery to rehearse items during the retention interval. Consequently, individuals with aphantasia, who lack voluntary visual imagery, may experience difficulties with such tasks. However, prior research has suggested that some individuals with aphantasia might employ non-visual strategies to compensate for this deficit. In two experiments, we examined visual working memory performance in aphantasic and control participants across a range of stimulus types. In Experiment 1, participants completed a change localization task using color squares and complex fractals; in Experiment 2, stimuli included real words, phonologically valid pseudowords, and phonologically invalid pseudowords. Across both experiments, aphantasic participants demonstrated significantly impaired visual working memory compared to controls. Notably, their performance was equally impaired for stimuli that were easily verbalizable (i.e., colors and words) and those that were not (i.e., fractals and pseudowords). Furthermore, individual differences in visual imagery ability, as measured by the Vividness of Visual Imagery Questionnaire (VVIQ), significantly predicted working memory performance across all stimulus types. These findings provide direct evidence for the critical role of visual imagery in supporting visual working memory.

Despite extensive investigation, the neural correlates of metaphor processing remain debated. Poor theoretical and experimental control of variables that drive metaphor activation-- particularly the constructs of novelty and familiarity--may be the reason for past discrepancies between studies. To address this issue, we used functional near-infrared spectroscopy (fNIRS) and a carefully designed paradigm modified from Cardillo et al. (2012) to investigate how neural activation varies by sentence type (metaphorical versus literal sentences) and novelty (completely novel versus familiarized phrases). Activity was significantly greater for metaphorical over literal sentences in the left inferior frontal gyrus, pars triangularis (LIFGtri), left inferior parietal cortex, right IFG, pars opercularis (RIFGop), and right angular gyrus (RAG). Novel metaphors to which participants had no prior exposure had significantly higher (albeit weak) effects within RIFGop, RAG, and right middle temporal gyrus (RMTG) compared to novel metaphors to which participants were exposed just prior to the fNIRS experiment. Pre-exposed, more familiar metaphors significantly activated a wider network of regions compared to novel metaphors, including bilateral middle frontal gyrus (MFG), bilateral IFGtri, and LMTG. A greater response time difference between conditions was associated with less LMFG activity for metaphors over literal sentences but higher LMTG activity for novel over more familiar metaphors. Taken together, these findings suggest that metaphors--particularly novel metaphors--do engage right hemisphere cortex more than other phrase types (literal sentences, more familiar metaphors) but that the effects are weaker than condition differences within canonical left language network and domain-general multiple demand network regions.

Humanity has always admired and created artwork, but the neurocognitive mechanisms behind artistic experience are still elusive. Professional artists and their intimate relationship with their artworks provide a unique opportunity to study the nature of art experience due to their expertise in both art making and art appreciation. During two fMRI tasks, professional artists (N=20) made aesthetic judgments on their own and other artists paintings (aesthetic appreciation task); they also mentally reconstructed the moments when they conceived their artworks or, as a control condition, when they visited now-familiar places for the first time (reconstruction by imagery task). During art appreciation of their own (as compared to other artists) paintings, participants showed stronger recruitment of bilateral posterior parietal cortices, the left lateral occipitotemporal cortex, and the dorso-central sector of the right insula, that is, action-related brain regions also involved in encoding the emotional components of movements. The reconstruction of their own artistic creation (as compared to episodic memory retrieval) involved the left fronto-parietal network associated with motor cognition. Altogether, these results suggest that the mental representations of the actions involved in creating art are integral to the overall artistic experience of painters, supporting an embodied view of the artists experience of art.

Motor and declarative memory systems have been traditionally considered distinct. However, a study by Mosha and Robertson (2016) reported striking evidence of generalisation between motor and declarative learning. Specifically, learning improved if the current task (e.g. motor sequence) shared the same high-level ordinal structure as an earlier task (e.g. word list), demonstrating cross-domain transfer of unstable memories. This finding has significant implications for our understanding and conceptualisation of memory taxonomies but has not been replicated. Here, healthy adult participants (N = 125) completed a word list and motor sequence task in counterbalanced order with either a shared or distinct sequence structure. In contrast to Mosha & Robertson (2016), we found that a shared ordinal structure between the declarative and motor sequence tasks did not facilitate performance. Overall, our results challenge the robustness of cross-domain generalisation, and underscore the complexity of cross-memory interactions.

Creative thought enables humans to flexibly generate, evaluate and select novel and adaptive ideas according to different contexts. Decades of creativity research indicates that it involves at least two aspects: retrieval of previously acquired knowledge and manipulation of that knowledge. However, the cognitive processes underpinning these two aspects of creative thought remain underspecified. The broader clinical-cognitive neuroscience literature suggests that retrieval and manipulation of knowledge is underpinned by general purpose cognitive mechanisms supporting semantic cognition, controlled episodic memory retrieval, and executive mechanisms. To identify commonalities from converging evidence that points towards a unifying theory for the neurocognitive bases of creative thought, we reviewed and meta-analysed 152 studies from creativity and the relevant parallel cognitive neuroscience literature using transcranial direct current stimulation (tDCS). The results revealed three things: 1) current tDCS studies are heavily biased towards the frontal cortex (459/591 effect sizes; 77.7%); 2) only anodal tDCS over the left lateral frontal cortex promotes creativity (p <.01); and 3) anodal tDCS stimulation over the same region also promotes improvement in many other cognitive processes. The latter includes more efficient processing of semantic knowledge (p <.05), more accurate episodic memory retrieval (p <.05), better and more efficient manipulation of buffered knowledge (all p <.001), and more efficient response selection amongst competing options (i.e., task-setting; p <.01). By merging these previously separate literatures, tDCS studies support the notion that creative thought arises from general purpose cognitive mechanisms including controlled retrieval and temporary storage of semantic and episodic information, as well as executive mechanisms.

This study examines cortical responses to chromatic and luminance stimuli in individuals with normal trichromatic vision, Daltonism, and achromatopsia. Functional magnetic resonance imaging (fMRI) data were collected using stimuli modeled after Wade et al. (2008) to evaluate the differential activation of visual cortical areas. In normal trichromats, hV4 demonstrated the highest chromatic sensitivity, while ventral areas showed stronger responses to color compared to dorsal regions. In Daltonic and achromatopsia participants, cortical activation was observed under combined chromatic and luminance conditions; however, no significant color-specific activity was detected, even in hV4. This work establishes a baseline for understanding cortical responses in color vision deficiencies and preceded gene therapy studies in the same achromatopsia patients (Fischer et al., 2020; Seitz et al., 2022). These findings contribute to ongoing research into neural plasticity and targeted therapeutic interventions.

Cognitive neuroscience has long sought to disentangle stimulus-driven processing from conscious perceptual processing. Some prior evidence for neural processing of perceived musical beat (periodic pulse) may be confounded by stimulus-driven activity. Notably, Nozaradan et al. (2011) controlled for stimulus factors and used frequency tagging to show increased brain activity at imagery-related frequencies when listeners imagined a beat pattern during an isochronous stimulus. However, it remains unclear whether this effect is replicable and whether it reliably reflects conscious beat perception. This registered report presents 13 independent replications using the same vetted protocol. Listeners performed the same experimental paradigm as in Nozaradan et al. (2011), with an added behavioral task on each trial to assess conscious perception of the imagined beat. Pre-registered meta-analyses revealed smaller raw effect sizes of imagery condition (Binary: 0.03 uV, Ternary: 0.03 uV) than the original study (Binary: 0.12 uV, Ternary: 0.20 uV), with confidence intervals all overlapping with 0. Differences in full-sample estimated effect sizes (this study: n = 152, eta squared = .03-.04; 2011 study: n = 8, eta squared = .62-.76) suggest larger sample sizes are necessary to detect these effects reliably, if they exist. Additionally, only neural activity at the stimulus frequency predicted imagery task accuracy, contradicting our hypothesis that beat-related frequencies would predict performance. Our findings suggest an overall failure to replicate all main effects from the original study. We discuss potential reasons for discrepancies with the original study as well as implications for the utility of frequency tagging for studying beat perception.

Human memory for recent events is believed to undergo reactivation during sleep. This process is thought to be relevant for the consolidation of both individual episodic memories and gist extraction, the formation of generalized memory representations from multiple, related memories. Which kinds of gist are actually enhanced, however, is the subject of less consensus. To address this question, we focused our design on four types of gist: inferential gist (relations extracted across non-contiguous events), statistical learning (regularities extracted from a series), summary gist (a theme abstracted from a temporally contiguous series of items), and category gist (characterization of a stimulus at a higher level in the semantic hierarchy). Sixty-nine participants (30 men, 38 women, and 1 other) completed memory encoding tasks addressing these types of gist and corresponding retrieval tasks the same evening, the morning after, and one week later. Inferential gist was retained over a week, whereas memory for category gist, summary gist, and statistical learning decayed. Higher proportions of REM were associated with worse performance in a statistical learning task controlling for time. Our results support that REM sleep is involved in schema disintegration, which works against participants ability to identify regularities within temporal series.\n\nSIGNIFICANCE STATEMENTTo gain the most from our experiences, we extract from them the most important elements, or \"gist\", with sleep believed to facilitate this process. However, what is referred to as gist varies considerably across studies. We report categorically different mnemonic trajectories of two classes of gist. In particular, we show that gist involving synthesis across relational memories is retained over time, whereas other gists were subject to substantial decay. Moreover, our evidence supports the idea that REM works to discretize, rather than synthesize experiences. Future research should test similar constructs in different tasks to determine whether these findings are generalizable. Our research suggests that patients with reduced REM sleep may experience more interference between similar memories.

Recent evidence suggests that brain activity following the offset of a stimulus during encoding contributes to long-term memory formation, however the exact mechanisms underlying offset-related encoding are still unclear. Here we used repetitive transcranial magnetic stimulation (rTMS) to investigate offset-related activity in the left ventrolateral prefrontal cortex (VLPFC). rTMS was administered at different points in time around stimulus offset while male and female participants encoded visually-presented words (first rTMS experiment) or pairs of words (second rTMS experiment) and the analyses focused on the effects of the stimulation on subsequent memory performance. The results show that rTMS administered at the offset of the stimuli, but not during online encoding, disrupted subsequent memory performance. In the first experiment we show that rTMS specifically disrupted encoding mechanisms initiated by the offset of the stimuli rather than general, post-stimulus processes. In the second experiment, we show a robust decline in associative memory performance when rTMS was delivered at the offset of the word pairs, suggesting that offset-related encoding may contribute to the binding of information into an episodic memory trace. A meta-analysis conducted on the two studies and on a previously published dataset confirmed that the involvement of the left VLPFC in memory formation is initiated by the offset of the stimulus. The offset of the stimulus may represent an event boundary that promotes the reinstatement of the previously experienced event and episodic binding.\n\nSIGNIFICANCE STATEMENTHow well an event is encoded predicts how well it is remembered, and verbal encoding is an important part of everyday memory that, if disrupted, can lead to difficulties and disorders. The timing of encoding processes relative to the presentation of an event is important for successful retrieval, and little is known about the interval immediately after an events presentation (post-stimulus offset) which is thought to involve critical encoding processes in the VLPFC and hippocampus. The current studies demonstrate that indeed, verbal encoding processes in the VLPFC that are necessary for memory formation are triggered by the offset of the word, and these processes may involve VLPFC-hippocampal interactions that promote binding of event features into a single, coherent memory trace.

ABSTRACTRecalling the past, thinking about the future and navigating in the world are linked with a brain structure called the hippocampus. Precisely how the hippocampus enables these critical cognitive functions is still debated. The strategies people use to perform tasks associated with these functions have been under-studied, and yet such information could augment our understanding of the associated cognitive processes and neural substrates. Here, we devised and deployed an in-depth protocol to examine the explicit strategies used by 217 participants to perform four naturalistic tasks widely acknowledged to be hippocampal-dependent, namely, those assessing scene imagination, autobiographical memory recall, future thinking and spatial navigation. In addition, we also investigated strategy use for three laboratory-based memory tasks, one of which is held to be hippocampal-dependent – concrete verbal paired associates – and two tasks which are likely hippocampal-independent – abstract verbal paired associates and the dead or alive semantic memory test. We found that scene visual imagery was the dominant strategy not only when mentally imagining scenes, but also during autobiographical memory recall, when thinking about the future and during navigation. Moreover, scene visual imagery strategies were used most frequently during the concrete verbal paired associates task, whereas verbal strategies were most prevalent for the abstract verbal paired associates task and the dead or alive semantic memory task. The ubiquity of specifically scene visual imagery use across a range of tasks may attest to its, perhaps underappreciated, importance in facilitating cognition, whilst also aligning with perspectives that emphasise a key role for the hippocampus in constructing scene imagery.Competing Interest StatementThe authors have declared no competing interest.View Full Text

Retrieval training (i.e., cued recall) is theorised to induce rapid memory consolidation, similarly to sleep. Across consolidation, related neural representations become increasingly similar; yet, this representational change has never been directly compared between sleep and retrieval training. In this study, 30 subjects (27F, 18-34, M=22.17) completed four separate sessions in which they (1) learnt object-word pairs, followed by (2) immediate recognition testing, (3) one of four 120-min interventions (retrieval training, restudy, sleep, or wake), and (4) delayed recognition testing. We compared EEG phase similarity between similar and different objects to assess the time, frequency, and anatomical distribution of representational similarity across encoding (learning to immediate recognition), and each intervention (immediate to delayed recognition). We hypothesised that EEG phase patterns for similar objects would become more similar (i.e., representational merging) across retrieval training and sleep interventions, and predict a greater endorsement of similar-object lures. Indeed, we found increased representational similarity between similar objects across the encoding shift in the theta-band and occipital sources. Crucially, additional representational merging was only observed across the retrieval training intervention, in the alpha-band and parieto-occipital sources. Despite retrieval training leading to reduced performance in discriminating similar-objects lures, greater representational merging across retrieval training predicted greater discrimination of similar-object lures. Together, these findings suggest that sleep and retrieval training induce different memory transformations across the same timescale. Retrieval training may generally provoke rapid gist extraction, with greater neocortical integration supporting episodic discrimination. Conversely, sleep may selectively maintain task-relevant episodic and semantic details in the short-term.

The formation of associative representations and their retrieval from episodic memory are vital cognitive functions. However, it is unclear to what extent retrieval of the basic component relations of episodic memory - identity, time, and space - requires different or shared brain mechanisms. In the current study, we employed EEG to track the time courses of electrophysiological correlates of retrieval processes of memory for identity relations, temporal order, and spatial configuration. Participants engaged in pair-associate learning of serially presented and spatially configured object picture pairs, followed by discrimination of identity, spatially, or temporally intact and rearranged pairs. Event-related brain potentials (ERPs) revealed distinct patterns of activity during successful retrieval of identity, spatial, and temporal relations that differed by the status of association, across the three retrieval time windows examined (300-500, 500-800, and 800-1000 ms). The identity relations condition was distinguished by a widespread greater negative-going deflection for rearranged relative to intact pairs in all three time windows. For the temporal relations condition, we observed a widespread more negative-going deflection for rearranged than intact pairs, significant in the second time window only. For the spatial relations condition, there was a widespread positive-going deflection greater for rearranged than for intact pairs, significant in the early and in middle time windows. These patterns of activity suggest that retrieval of associative memory traces for identity, spatial, and temporal relationships involve dynamically different processes, which may partially rely on different sets of basic associative mechanisms.

Spatialization in working memory refers to the spatial coding of non-spatial information along a mental horizontal line when encoding verbal material. This phenomenon is thought to support working memory by facilitating order encoding. Although it has been observed for both visually and auditorily presented stimuli, no direct comparison has yet examined whether these modalities rely on similar neural mechanisms. In this study, we investigated whether spatialization in visual and auditory modalities involves shared or distinct patterns of activity within the working-memory network. Forty-nine participants performed both a visual and an auditory working memory SPoARC task of the same verbal material, allowing to study the cortical patterns associated with distinct serial positions at both encoding and recognition across sensory modalities. Whole-brain analyses revealed similar frontoparietal networks across conditions. In addition, a representational similarity analysis (RSA) was conducted to assess the similarity of neural patterns between early and late serial positions in a sequence and across sensory modalities. This multivoxel pattern analysis revealed modality-dependent patterns distinguishing early and late positions in the inferior frontal gyrus. Additional modality-specific effects were observed in the anterior intraparietal sulcus in the visual modality and in the posterior hippocampus in the auditory modality. Drawing on the framework proposed by Bottini & Doeller (2020), we propose that order decoding in the IPS might reflect a low-dimensional spatial coding of order (e.g., along a horizontal axis), whereas order decoding in the hippocampus might reflect higher-dimensional spatial representations or temporal representations.

Auditory working memory is often conceived of as a unitary capacity, with memory for different auditory materials (syllables, pitches, rhythms) thought to rely on similar neural mechanisms. One spontaneous behavior observed in working memory studies is chunking. For example, individuals often recount digit sequences in groups, or chunks, of 3 to 4 digits, and this chunking improves performance. Chunking may also operate in musical rhythm, with beats acting as chunk boundaries for tones in rhythmic sequences. Similar to chunking, beat-based structure in rhythms also improves performance. Thus, beat processing may rely on the same mechanisms that underlie chunking of verbal material. The current fMRI study examined whether beat perception is a type of chunking, measuring brain responses to chunked and unchunked letter sequences relative to beat-based and nonbeat-based rhythmic sequences. Participants completed a sequence discrimination task, and comparisons between stimulus encoding, maintenance, and discrimination were made for both rhythmic and verbal sequences. Overall, rhythm and verbal working memory networks overlapped substantially. When comparing rhythmic and verbal conditions, rhythms activated basal ganglia, supplementary motor area, and anterior insula, compared to letter strings, during encoding and discrimination. Letter strings compared to rhythms activated bilateral auditory cortex during encoding, and parietal cortex, precuneus, and middle frontal gyri during discrimination. Importantly, there was a significant interaction in the basal ganglia during encoding: activation for beat-based rhythms was greater than for nonbeat-based rhythms, but verbal chunked and unchunked conditions did not differ. The significant interaction indicates that beat perception is not simply a case of chunking, suggesting a dissociation between beat processing and grouping mechanisms that warrants further exploration.

Gender has been investigated in psycholinguistics research both with respect to how it is retrieved when a noun is encountered and the computation of its agreement dependencies between different elements in a sentence. The literature is abound with differences as to the processing of gender agreement computations across languages and constructs. Similarly, neurophysiological evidence with respect to gender retrieval mechanisms differ wherein languages differ in the way the gender feature is retrieved when a noun is encountered based on different properties. The present study aims to scrutinize gender agreement computations in verb-agreement relations in Hindi and to ascertain if the intrinsic property (i.e. the animacy) of a noun participating in the relation plays a role in processing agreement dependencies. In addition, it also looks into the issue of whether the gender retrieval mechanism in the language influences agreement comprehension. Results revealed a positivity for the animate subject agreement and a negativity for the inanimate subject agreement violations at the position of the verb respectively. The results are suggestive of distinct processing mechanisms underlying semantic and syntactic gender. Further, the results also suggest that gender agreement computation in Hindi is modulated by the way gender is retrieved at the position of the noun.

Across sleep-based and retrieval-mediated consolidation, memories typically become generalised and less dependent on their episodic components for their recollection. However, memory transformations across sleep and retrieval training have not been directly compared. The current study aims to compare how sleep and retrieval training impact the endorsement of semantically similar and different lures, as well as their episodic recollection using the parietal old/new effect on the late positive component (LPC) in subjects EEG. Thirty subjects (27F, 18-34, M=22.17) attended four sessions where they learnt different sets of 104 object-word pairs and completed one of four 120-minute memory interventions: retrieval training (i.e., cued recall practice), restudy (i.e., pair re-exposure), a nap opportunity, or a wakeful rest. EEG was recorded while subjects were tested on their recognition accuracy in an old/new paradigm with similar- and different-object lures. Our results revealed that retrieval training, but not sleep, lead to greater accuracy for identifying old pairs, but worse similar-lure discrimination. Whilst the parietal old/new effect did not differ between conditions, retrieval had lower LPC amplitudes for similar- than different-object false alarms, whilst restudy demonstrated the opposite. Sleep and wake demonstrated no differences in LPC amplitudes between hits and different false alarm types. Together, our study demonstrates evidence for gist-abstraction across retrieval training, and a task-relevant selective maintenance of episodic details across sleep. These results challenge theories that retrieval training replicates sleep-based consolidation mechanisms, instead acting as a fast route to semanticization regardless of the context.

Ergativity marks subject arguments as agents of a transitive event and thereby signals verbal transitivity and influences language comprehension. We report here on an event-related brain potentials (ERP) study in Hindi, in which we investigated this interconnection to ascertain whether the ergative case as a processing cue and its ERP correlates can be generalized across and within ergative languages. The case marking on the subject argument (ergative or nominative case) in our study either matched or mismatched with the transitivity of the light verb (transitive or intransitive) in compound light verb constructions. Ergative case violations due to an intransitive light verb evoked an N400 effect, whereas nominative case violations due to a transitive light verb elicited a P600 effect. The results reveal neurophysiological differences in the processing of ergative and nominative case alignment modulated by the transitivity of the light verbs. The findings highlight the need for cross-linguistic research to aim beyond universality and elucidate the mechanism underlying the processing of language-specific structural variations.

Individual differences in second language (L2) learning can offer insights into the neurobiological bases of learning aptitude. One neurophysiological marker of inter-individual differences in cognition is the individual alpha frequency (IAF), a trait-like measure correlated with cognition. Further, the N400 is an electrophysiological marker indexing stimulus irregularity and has been used to study L2 learning; however, its relationship with IAF and L2 learning remains unknown. To examine the relation between IAF and L2 learning (indexed by N400 amplitude), we report data from a modified miniature language learning study. After a vocabulary learning period, participants (N = 38, Mage = 25.3, SD = 7.13) judged the grammaticality of classifier-noun pairs, with mixed-effects modelling revealing lower IAF individuals were better than higher IAF individuals at grammaticality judgements. N400 amplitude also reduced across the experiment in low relative to high IAF individuals, indicating the relationship between IAF and language learning is more complex than initially postulated.

Memories that differ in content or duration differ in the extent to which they depend on the hippocampus, and also the part of the hippocampus, posterior (pHPC) or anterior (aHPC), that they implicate. Inter-individual differences in learning-related activation in different hippocampal subregions have been found to predict specific differences in memory abilities. The complexity of these relationships creates a setting that is ripe for theoretically informative investigation, but that can also lead to reports of spurious relationships that do not reflect underlying neurobiological associations. Across-study replication is therefore a critical first step toward understanding how differences in hippocampal activity drive individual differences in memory ability. In the domain of verbal memory, Wig et al. (2008) identified a negative relationship between task-induced activation in pHPC and out-of-scanner verbal memory test performance. Replicating this result in an independent sample of 86 participants, we identified the same negative correlation between pHPC activation during a Lithuanian word learning task and out-of-scanner California Verbal Learning Test (CVLT-II) performance. This replication represents a critical step toward understanding how pHPC supports verbal memory by answering the basic question of whether the relationship can be reliably observed.