Entrainment enhances theta oscillations and improves episodic memory

Synchronous Theta Networks Characterize Successful Memory Retrieval

Memory retrieval activates regions across the brain, including not only the hippocampus and medial temporal lobe (MTL), but also frontal, parietal, and lateral temporal cortical regions. What remains unclear, however, is how these regions communicate to organize retrieval-specific processing. Here, we elucidate the role of theta (3-8 Hz) synchronization, broadly implicated in memory function, during the spontaneous retrieval of episodic memories. Analyzing a dataset of 382 neurosurgical patients (213 males, 168 females, and 1 unknown) implanted with intracranial electrodes who completed a free-recall task, we find that synchronous networks of theta phase synchrony span the brain in the moments before spontaneous recall, in comparison to periods of deliberation and incorrect recalls. Hubs of the retrieval network, which systematically synchronize with other regions, appear throughout the prefrontal cortex and lateral and medial temporal lobes, as well as other areas. Theta synchrony increases appear more prominently for slow (3 Hz) theta than for fast (8 Hz) theta in the recall-deliberation contrast, but not in the encoding or recall-intrusion contrasts, and theta power and synchrony correlate positively throughout the theta band. These results implicate diffuse brain-wide synchronization of theta rhythms, especially slow theta, in episodic memory retrieval.

The strength of neural entrainment to electronic music correlates with proxies of altered states of consciousness

In electronic music events, the driving four-on-the-floor music appears pivotal for inducing altered states of consciousness (ASCs). While various physiological mechanisms link repetitive auditory stimuli to ASCs, entrainment-a brainwave synchronization through periodic external stimuli-has garnered primary focus. However, there are no studies systematically exploring the relationship between entrainment and ASCs. In the present study, we depart from the finding that entrainment to auditory stimuli peaks for stimulation rates around 2 Hz compared to others. Nineteen participants listened to six one-minute electronic music excerpts at different tempos (1.65 Hz, 2.25 Hz, and 2.85 Hz). For each excerpt, they performed cognitive tasks and reported phenomenological experiences related to ASCs through questionnaires. Brain activity was recorded with electroencephalography to assess whether a modulation in entrainment by the beat of electronic music affected objective and subjective proxies of ASCs. Our results revealed a tempo-driven modulation of entrainment at the group level, with entrainment being higher for stimulation rates at 1.65 Hz compared to 2.85 Hz. Similarly, music at 1.65 Hz aroused more feelings of unity compared to music at 2.85 Hz. However, at the individual level, no significant relationship was found between entrainment magnitude and phenomenological experience. Instead, a positive relationship was observed between entrainment and participants' reaction time. The results suggest that brainwave entrainment modulate processes relevant to rhythm-induced ASCs. While we cannot determine whether participants entered an ASC due to design constraints, the observed relationship between entrainment and reaction time at the individual level supports its functional significance.

Evaluating the combined effects of mobile computerized CBT and post-learning oscillatory modulation on self-esteem: a randomized controlled trial

Self-esteem, crucial for psychological well-being, can be enhanced through targeted interventions like cognitive behavioral therapy (CBT). However, traditional CBT faces various accessibility barriers. Digital health interventions such as computerized CBT and mobile health (mHealth) applications offer potential solutions. Recent research suggests that brain oscillations, particularly theta rhythms, play a key role in memory consolidation. Combining computerized CBT with post-learning theta rhythm modulation may optimize and stabilize improvements in self-esteem and promote neuro-wellbeing. This six-month longitudinal study aimed to evaluate the synergistic effects of a computerized CBT intervention (GGSE) combined with post-training theta rhythm brain modulation on improving self-esteem in young adults with low self-esteem. Participants were randomly allocated to three groups: GGSE + theta audio-visual entrainment (AVE) with Cranio-Electro Stimulation (CES), GGSE + beta AVE + CES (active control), and GGSE only (control). The intervention lasted three weeks. Assessments of self-esteem, maladaptive beliefs, and mood were conducted at baseline, 21 days, 42 days, and six months post-baseline. Although post-treatment oscillatory entrainment did not enhance the long-term efficacy of the intervention, significant treatment effects persisted for six months across all groups. These results support the potential long-term efficacy of brief, game-like, digital CBT approaches for improving self-esteem.

Response coupling with an auxiliary neural signal for enhancing brain signal detection

Brain-computer interfaces (BCIs) offer an implicit, non-linguistic communication channel between users and machines. Despite their potential, BCIs are far from becoming a mainstream communication modality like text and speech. While non-invasive BCIs, such as Electroencephalography, are favored for their ease of use, their broader adoption is limited by challenges related to signal noise, artifacts, and variability across users. In this paper, we propose a novel method called response coupling, aimed at enhancing brain signal detection and reliability by pairing a brain signal with an artificially induced auxiliary signal and leveraging their interaction. Specifically, we use error-related potentials (ErrPs) as the primary signal and steady-state visual evoked potentials (SSVEPs) as the auxiliary signal. SSVEPs, known for their phase-locked responses to rhythmic stimuli, are selected because rhythmic neural activity plays a critical role in sensory and cognitive processes, with evidence suggesting that reinforcing these oscillations can improve neural performance. By exploring the interaction between these two signals, we demonstrate that response coupling significantly improves the detection accuracy of ErrPs, especially in the parietal and occipital regions. This method introduces a new paradigm for enhancing BCI performance, where the interaction between a primary and an auxiliary signal is harnessed to enhance the detection performance. Additionally, the phase-locking properties of SSVEPs allow for unsupervised rejection of suboptimal data, further increasing BCI reliability.

Context familiarity is a third kind of episodic memory distinct from item familiarity and recollection

Episodic memory is accounted for with two processes: "familiarity" when generally recognizing an item and "recollection" when retrieving the full contextual details bound with the item. We tested a combination of item recognition confidence and source memory, focusing upon three conditions: "item-only hits with source unknown" ('item familiarity'), "low-confidence hits with correct source memory" ('context familiarity'), and "high-confidence hits with correct source memory" ('recollection'). Behaviorally, context familiarity was slower than the others during item recognition, but faster during source memory. Electrophysiologically, a triple dissociation was evident in event-related potentials (ERPs), which was independently replicated. Context familiarity exhibited a negative effect from 800 to 1200 ms, differentiated from positive ERPs for item-familiarity (400-600 ms) and recollection (600-900 ms). These three conditions thus reflect mutually exclusive, fundamentally different processes of episodic memory, and we offer a new, tri-component model of memory. Context familiarity is a third distinct process of episodic memory.

Sensory stimulation enhances visual working memory capacity

Visual working memory (vWM) plays a crucial role in visual information processing and higher cognitive functions; however, it has a very limited capacity. Recently, several studies have successfully modulated vWM capacity in humans using entrainment with transcranial alternate current stimulation (tACS) by targeting parietal theta in a frequency-specific manner. In the current study, we aim to expand upon these findings by utilizing sensory instead of electrical stimulation. Across six behavioral experiments (combined N = 209), we applied rhythmic visual and auditory sensory stimulation at 4 Hz and 7 Hz, aiming to modulate vWM capacity. Collectively, the results showed an overall robust improvement with sensory stimulation at either frequency, compared to baseline. However, contrary to our prediction, 7 Hz stimulation tended to slightly outperform 4 Hz stimulation. Importantly, the observed facilitatory effect was mainly driven by the low-capacity sub-group of participants. Follow-up experiments using the Attention Network Test (ANT) and pupillometry measures did not find evidence that this effect could be directly attributed to modulation of phasic or tonic arousal. We speculate that our results differed from those obtained with tACS due to targeting functionally different theta oscillations, or the modulation of participants' temporal expectations.

A third kind of episodic memory: Context familiarity is distinct from item familiarity and recollection

Episodic memory is accounted for with two processes: 'familiarity' when generally recognizing an item and 'recollection' when retrieving the full contextual details bound with the item. Paradoxically, people sometimes report contextual information as familiar but without recollecting details, which is not easily accounted for by existing theories. We tested a combination of item recognition confidence and source memory, focusing upon 'item-only hits with source unknown' ('item familiarity'), 'low-confidence hits with correct source memory' ('context familiarity'), and 'high-confidence hits with correct source memory' ('recollection'). Results across multiple within-subjects (trial-wise) and between subjects (individual variability) levels indicated these were behaviorally and physiologically distinct. Behaviorally, a crossover interaction was evident in response times, with context familiarity being slower than each condition during item recognition, but faster during source memory. Electrophysiologically, a Condition x Time x Location triple dissociation was evident in event-related potentials (ERPs), which was then independently replicated. Context familiarity exhibited an independent negative central effect from 800-1200 ms, differentiated from positive ERPs for item-familiarity (400 to 600 ms) and recollection (600 to 900 ms). These three conditions thus reflect mutually exclusive, fundamentally different processes of episodic memory. Context familiarity is a third distinct process of episodic memory.

Summary

Memory for past events is widely believed to operate through two different processes: one called 'recollection' when retrieving confident, specific details of a memory, and another called 'familiarity' when only having an unsure but conscious awareness that an item was experienced before. When people successfully retrieve details such as the source or context of a prior event, it has been assumed to reflect recollection. We demonstrate that familiarity of context is functionally distinct from familiarity of items and recollection and offer a new, tri-component model of memory. The three memory responses were differentiated across multiple behavioral and brain wave measures. What has traditionally been thought to be two kinds of memory processes are actually three, becoming evident when using sensitive enough multi-measures. Results are independently replicated across studies from different labs. These data reveal that context familiarity is a third process of human episodic memory.

Orienting of attention and spatial cognition

Humans orient to their sensory world through foveation of target location or through covert shifts of attention. Orienting provides primacy to the selected location and in humans improves the precision of discrimination. Covert orienting appears to arise separately from the mechanisms involved in saccadic eye movements. Covert orienting can serve to prioritize processing the target even increasing its subjective intensity and its acuity. However, this network does not appear to be involved in the operations related to binding and segmentation. Cells exist in the early visual cortex that are activated by both color and form features without attention, however, color and form appear to remain independent even when oriented to the target that is required to be reported. An understanding of the pathways that connect attention networks to memory networks may allow us to understand more complex aspects of spatial cognition and enhance orienting and thus improve spatial cognition.

Role of visual brainwave entrainment on the resting state brainwaves of children with and without attention-deficit/hyperactivity disorder

The relationship between brainwave oscillations and Attention-Deficit/Hyperactivity Disorder (ADHD)-related cognitive challenges is a trending proposition in the field of Cognitive Neuroscience. Studies suggest the role of brainwave oscillations in the symptom expressions of ADHD-diagnosed children. Intervention studies have further suggested the scope of brain stimulation techniques in improving cognition. The current manuscript explored the effect of changes in the brainwaves post-sensory entrainment on cognitive performance of children. We calculated each participant's brainwave difference and ratios of theta, alpha, and beta power after the entrainment sessions. Further, we explored possible correlations between these values and the psychometric scores. The beta resting state showed the strongest association with selective attention performance of all participants. Theta-beta ratio (TBR) showed an inverse correlation with selective attention and working memory performances. The theta frequency was associated with decreased working performance in children without ADHD. Our findings also suggest a predominant role of TBR than the theta-alpha ratio in determining the cognitive performance of children with ADHD. The individual differences in the entrainment reception were attributed to the participant's age, IQ, and their innate baseline frequencies. The implications of our findings can initiate substantiating brainwave-based entrainment sessions as a therapeutic modality to improve cognition among children.

Therapeutic potential of gamma entrainment using sensory stimulation for cognitive symptoms associated with schizophrenia

Schizophrenia is a complex neuropsychiatric disorder with significant morbidity. Treatment options that address the spectrum of symptoms are limited, highlighting the need for innovative therapeutic approaches. Gamma Entrainment Using Sensory Stimulation (GENUS) is an emerging treatment for neuropsychiatric disorders that uses sensory stimulation to entrain impaired oscillatory network activity and restore brain function. Aberrant oscillatory activity often underlies the symptoms experienced by patients with schizophrenia. We propose that GENUS has therapeutic potential for schizophrenia. This paper reviews the current status of schizophrenia treatment and explores the use of sensory stimulation as an adjunctive treatment, specifically through gamma entrainment. Impaired gamma frequency entrainment is observed in patients, particularly in response to auditory and visual stimuli. Thus, sensory stimulation, such as music listening, may have therapeutic potential for individuals with schizophrenia. GENUS holds novel therapeutic potential to improve the lives of individuals with schizophrenia, but further research is required to determine the efficacy of GENUS, optimize its delivery and therapeutic window, and develop strategies for its implementation in specific patient populations.

Effects of continuous versus intermittent theta-burst TMS on fMRI connectivity

Transcranial magnetic stimulation is a noninvasive technique that can be used to evoke distributed network-level effects. Previous work demonstrated that the Hippocampal-Cortical Network responds preferably (i.e., greater memory improvement and increases in hippocampal-network connectivity) to continuous theta-burst stimulation protocol relative to intermittent theta-burst and to 20-Hz rTMS. Here, these data were further analyzed to characterize effects of continuous versus intermittent theta-burst stimulation on network-level connectivity measures - as well as local connectedness - via resting-state fMRI. In contrast to theories that propose continuous and intermittent theta-burst cause local inhibitory versus excitatory effects, respectively, both protocols caused local decreases in fMRI connectivity around the stimulated parietal site. While iTBS caused decreases in connectivity across the hippocampal-cortical network, cTBS caused increases and decreases in connectivity across the network. cTBS had no effect on the parietal-cortical network, whereas iTBS caused decreases in the right parietal cortex (contralateral hemisphere to the stimulation target). These findings suggest that continuous theta-burst may have entrained the endogenous hippocampal-cortical network, whereas the intermittent train was unable to maintain entrainment that may have yielded the long-lasting effects measured in this study (i.e., within 20-min post-stimulation). Furthermore, these effects were specific to the hippocampal-cortical network, which has a putative endogenous functionally-relevant theta rhythm, and not to the parietal network. These results add to the growing body of evidence that suggests effects of theta-burst stimulation are not fully characterized by excitatory/inhibitory theories. Further work is required to understand local and network-level effects of noninvasive stimulation.

The Effect of Rhythmic Audio-Visual Stimulation on Inhibitory Control: An ERP Study

Inhibitory control, as an essential cognitive ability, affects the development of higher cognitive functions. Rhythmic perceptual stimulation has been used to improve cognitive abilities. It is unclear, however, whether it can be used to improve inhibitory control. This study used the Go/NoGo task and the Stroop task to assess various levels of inhibitory control using rhythmic audio-visual stimuli as the stimulus mode. Sixty subjects were randomly divided into three groups to receive 6 Hz, 10 Hz, and white noise stimulation for 30 min. Two tasks were completed by each subject both before and after the stimulus. Before and after the task, closed-eye resting EEG data were collected. The results showed no differences in behavioral and EEG measures of the Go/NoGo task among the three groups. While both 6 Hz and 10 Hz audio-visual stimulation reduced the conflict effect in the Stroop task, only 6 Hz audio-visual stimulation improved the amplitude of the N2 component and decreased the conflict score. Although rhythmic audio-visual stimulation did not enhance response inhibition, it improved conflict inhibition.

Multisensory flicker modulates widespread brain networks and reduces interictal epileptiform discharges

Modulating brain oscillations has strong therapeutic potential. Interventions that both non-invasively modulate deep brain structures and are practical for chronic daily home use are desirable for a variety of therapeutic applications. Repetitive audio-visual stimulation, or sensory flicker, is an accessible approach that modulates hippocampus in mice, but its effects in humans are poorly defined. We therefore quantified the neurophysiological effects of flicker with high spatiotemporal resolution in patients with focal epilepsy who underwent intracranial seizure monitoring. In this interventional trial (NCT04188834) with a cross-over design, subjects underwent different frequencies of flicker stimulation in the same recording session with the effect of sensory flicker exposure on local field potential (LFP) power and interictal epileptiform discharges (IEDs) as primary and secondary outcomes, respectively. Flicker focally modulated local field potentials in expected canonical sensory cortices but also in the medial temporal lobe and prefrontal cortex, likely via resonance of stimulated long-range circuits. Moreover, flicker decreased interictal epileptiform discharges, a pathological biomarker of epilepsy and degenerative diseases, most strongly in regions where potentials were flicker-modulated, especially the visual cortex and medial temporal lobe. This trial met the scientific goal and is now closed. Our findings reveal how multi-sensory stimulation may modulate cortical structures to mitigate pathological activity in humans.

Integrative neuro-cardiovascular dynamics in response to test anxiety: A brain-heart axis study

Test anxiety (TA), a recognized form of social anxiety, is the most prominent cause of anxiety among students and, if left unmanaged, can escalate to psychiatric disorders. TA profoundly impacts both central and autonomic nervous systems, presenting as a dual manifestation of cognitive and autonomic components. While limited studies have explored the physiological underpinnings of TA, none have directly investigated the intricate interplay between the CNS and ANS in this context. In this study, we introduce a non-invasive, integrated neuro-cardiovascular approach to comprehensively characterize the physiological responses of 27 healthy subjects subjected to test anxiety induced via a simulated exam scenario. Our experimental findings highlight that an isolated analysis of electroencephalographic and heart rate variability data fails to capture the intricate information provided by a brain-heart axis assessment, which incorporates an analysis of the dynamic interaction between the brain and heart. With respect to resting state, the simulated examination induced a decrease in the neural control onto heartbeat dynamics at all frequencies, while the studying condition induced a decrease in the ascending heart-to-brain interplay at EEG oscillations up to 12Hz. This underscores the significance of adopting a multisystem perspective in understanding the complex and especially functional directional mechanisms underlying test anxiety.

The Feeling of Time Passing Is Associated with Recurrent Sustained Activity and Theta Rhythms Across the Cortex

Introduction: We are constantly estimating how much time has passed, and yet know little about the brain mechanisms through which this process occurs. In this pilot study, we evaluated so-called subjective time estimation with the temporal bisection task, while recording brain activity from electroencephalography (EEG). Methods: Nine adult participants were trained to distinguish between two durations of visual stimuli as either "short" (400 msec) or "long" (1600 msec). They were then presented with stimulus durations in between the long and short stimuli. EEG data from 128 electrodes were examined with a novel analytical method that identifies segments of sustained cortical activity during the task. Results: Participants tended to categorize intermediate durations as "long" more frequently than "short" and were thus experiencing time as moving faster while overestimating the amount of time passing. Their mean bisection point (during which frequency of selecting short vs. long is equal) was closer to the geometric mean of task stimuli (800 msec) rather than the arithmetic mean (1000 msec). In contrast, sustained brain activity occurred closer to the arithmetic mean. The recurrence rate of this activity was highly related to the bisection point, especially when analyzed within naturally occurring theta oscillations (4-8 Hz) (r = -0.90). Discussion: Sustained activity across the cortex within the theta range may reflect temporal durations, whereas its repeated appearance relates to the subjective feeling of time passing.

Network connectivity underlying episodic memory in children: Application of a pediatric brain tumor survivor injury model

Episodic memory involves personal experiences paired with their context. The Medial Temporal, Posterior Medial, Anterior Temporal, and Medial Prefrontal networks have been found to support the hippocampus in episodic memory in adults. However, there lacks a model that captures how the structural and functional connections of these networks interact to support episodic memory processing in children. Using diffusion-weighted imaging, magnetoencephalography, and memory tests, we quantified differences in white matter microstructure, neural communication, and episodic memory performance, respectively, of healthy children (n = 23) and children with reduced memory performance. Pediatric brain tumor survivors (PBTS; n = 24) were used as a model, as they exhibit reduced episodic memory and perturbations in white matter and neural communication. We observed that PBTS, compared to healthy controls, showed significantly (p < 0.05) (1) disrupted white matter microstructure between these episodic memory networks through lower fractional anisotropy and higher mean and axial diffusivity, (2) perturbed theta band (4-7 Hz) oscillatory synchronization in these same networks through higher weighted phase lag indices (wPLI), and (3) lower episodic memory performance in the Transverse Patterning and Children's Memory Scale (CMS) tasks. Using partial-least squares path modeling, we found that brain tumor treatment predicted network white matter damage, which predicted inter-network theta hypersynchrony and lower verbal learning (directly) and lower verbal recall (indirectly via theta hypersynchrony). Novel to the literature, our findings suggest that white matter modulates episodic memory through effect on oscillatory synchronization within relevant brain networks. RESEARCH HIGHLIGHTS: Investigates the relationship between structural and functional connectivity of episodic memory networks in healthy children and pediatric brain tumor survivors Pediatric brain tumor survivors demonstrate disrupted episodic memory, white matter microstructure and theta oscillatory synchronization compared to healthy children Findings suggest white matter microstructure modulates episodic memory through effects on oscillatory synchronization within relevant episodic memory networks.

On natural attunement: Shared rhythms between the brain and the environment

Rhythms exist both in the embodied brain and the built environment. Becoming attuned to the rhythms of the environment, such as repetitive columns, can greatly affect perception. Here, we explore how the built environment affects human cognition and behavior through the concept of natural attunement, often resulting from the coordination of a person's sensory and motor systems with the rhythmic elements of the environment. We argue that the built environment should not be reduced to mere states, representations, and single variables but instead be considered a bundle of highly related continuous signals with which we can resonate. Resonance and entrainment are dynamic processes observed when intrinsic frequencies of the oscillatory brain are influenced by the oscillations of an external signal. This allows visual rhythmic stimulations of the environment to affect the brain and body through neural entrainment, cross-frequency coupling, and phase resetting. We review how real-world architectural settings can affect neural dynamics, cognitive processes, and behavior in people, suggesting the crucial role of everyday rhythms in the brain-body-environment relationship.

Neurophysiological mechanisms of cognition in the developing brain: Insights from intracranial EEG studies

The quest to understand how the development of the brain supports the development of complex cognitive functions is fueled by advances in cognitive neuroscience methods. Intracranial EEG (iEEG) recorded directly from the developing human brain provides unprecedented spatial and temporal resolution for mapping the neurophysiological mechanisms supporting cognitive development. In this paper, we focus on episodic memory, the ability to remember detailed information about past experiences, which improves from childhood into adulthood. We review memory effects based on broadband spectral power and emphasize the importance of isolating narrowband oscillations from broadband activity to determine mechanisms of neural coordination within and between brain regions. We then review evidence of developmental variability in neural oscillations and present emerging evidence linking the development of neural oscillations to the development of memory. We conclude by proposing that the development of oscillations increases the precision of neural coordination and may be an essential factor underlying memory development. More broadly, we demonstrate how recording neural activity directly from the developing brain holds immense potential to advance our understanding of cognitive development.

Theta EEG neurofeedback promotes early consolidation of real life-like episodic memory

Theta oscillations are believed to coordinate neuronal activity related to human cognition, especially for memory functions. Theta power during learning and retrieval has been found to correlate with memory performance success. Additionally, up-regulating theta oscillations during a post-encoding epoch crucial for memory consolidation was previously shown to benefit long-term memory for acquired motor sequences, pictures, and object-location associations. However, it remains to be determined whether such effects would be found for more ecological aspects of long-term episodic memory. Therefore, the current study assessed neurofeedback-based theta upregulation effects on movie memory. After viewing a 15-minute silent, narrative movie, participants engaged in neurofeedback-based theta/beta up-regulation, neurofeedback beta/theta up-regulation as an active control condition, or an unrelated passive control task. Memory was tested three times: once immediately after watching the movie (as baseline); 24 hours thereafter; and once again 1 week later. Memory performance 1 week after encoding was significantly enhanced in the theta/beta up-regulation group compared with the other groups. Additionally, changes in neurofeedback theta/beta ratio from baseline EEG recordings correlated with long-term memory gains in retrieving the movie's content. These findings highlight the relationship between post-learning theta oscillations and the consolidation of episodic memory for a naturalistic event.

An ERP measure of non-conscious memory reveals dissociable implicit processes in human recognition using an open-source automated analytic pipeline

Non-conscious processing of human memory has traditionally been difficult to objectively measure and thus understand. A prior study on a group of hippocampal amnesia (N = 3) patients and healthy controls (N = 6) used a novel procedure for capturing neural correlates of implicit memory using event-related potentials (ERPs): old and new items were equated for varying levels of memory awareness, with ERP differences observed from 400 to 800 ms in bilateral parietal regions that were hippocampal-dependent. The current investigation sought to address the limitations of that study by increasing the sample of healthy subjects (N = 54), applying new controls for construct validity, and developing an improved, open-source tool for automated analysis of the procedure used for equating levels of memory awareness. Results faithfully reproduced prior ERP findings of parietal effects that a series of systematic control analyses validated were not contributed to nor contaminated by explicit memory. Implicit memory effects extended from 600 to 1000 ms, localized to right parietal sites. These ERP effects were found to be behaviorally relevant and specific in predicting implicit memory response times, and were topographically dissociable from other traditional ERP measures of implicit memory (miss vs. correct rejections) that instead occurred in left parietal regions. Results suggest first that equating for reported awareness of memory strength is a valid, powerful new method for revealing neural correlates of non-conscious human memory, and second, behavioral correlations suggest that these implicit effects reflect a pure form of priming, whereas misses represent fluency leading to the subjective experience of familiarity.

Promising neurostimulation routes for targeting the hippocampus to improve episodic memory: A review

This review aims to highlight modern neurostimulation approaches that are effectively activating the hippocampus and enhancing episodic memory performance. The hippocampus is a brain region known to play an essential role in episodic memory processes. However, as it is nestled deep within the brain, it has been a challenging target for traditional neurostimulation approaches, with studies reporting inconsistent memory effects. Recent studies suggest more than half of the electrical current from non-invasive transcranial electrical stimulation (tES) methods may be attenuated by the human scalp, skull, and cerebral spinal fluid. Thus, this review aims to highlight novel neurostimulation approaches that are showing promise as alternative routes for activating hippocampal circuitry. Early evidence suggests temporal interference, closed-loop and individualized protocols, sensory stimulation and peripheral nerve-targeted tES protocols warrant further investigation. These approaches each provide promising routes for activating the hippocampus by a) increasing its functional connectiveness to key brain regions, b) strengthening synaptic plasticity mechanisms, or c) enhancing neural entrainment specifically within and between theta and gamma frequencies in these regions. Importantly, these three functional mechanisms and the hippocampus' structural integrity are negatively impacted throughout the progression of Alzheimer's Disease, with episodic memory deficits likewise evident in early stages. Consequently, depending on further validation of the approaches reviewed here, these techniques could offer significant applied therapeutic value for patients suffering from memory deficits or neurodegenerative diseases including amnestic Mild Cognitive Impairment or Alzheimer's disease.

Potential of binaural beats intervention for improving memory and attention: insights from meta-analysis and systematic review

Binaural beats (BB) entrainment is an auditory perceptual occurrence that exists when two tones of separate frequencies are simultaneously presented to each ear. Research on BB entrainment has gained attention due to its ability to treat various conditions like anxiety, attention-deficit/hyperactivity (ADHD), etc. Even though research on BB entrainment suggests its efficiency in improving cognition among individuals, existing literature indicates mixed results in the cognitive domains of attention and memory. Thus, we conducted meta-analysis to examine the effect of BB intervention on memory and attention, respectively, in the current paper. We further performed a systematic review on the selected studies to report their variables, demographic characteristics of the participants, and outcomes to comprehensively position the research on BB intervention exclusively in the areas of memory and attention. Fifteen studies met our inclusion criteria. Based on 31 effect sizes, the results indicated an overall medium and significant effect size (g = 0.40). Findings from systematic review reveal conflicting results, especially concerning theta and beta's efficacy on memory (recall and recognition tasks) and attention-related tasks. The findings of the current paper add to the growing evidence that BB intervention improves attention and memory in humans. Since the findings suggest a near-moderate effect of BB interventions and mixed results in the systematic review, more research with robust study designs must explore its guiding principle and the expanding role of brainwaves in improving memory and attention in individuals. Such an intervention has important implications in both clinical and non-clinical settings.

Multi-band oscillations emerge from a simple spiking network

In the brain, coherent neuronal activities often appear simultaneously in multiple frequency bands, e.g., as combinations of alpha (8-12 Hz), beta (12.5-30 Hz), and gamma (30-120 Hz) oscillations, among others. These rhythms are believed to underlie information processing and cognitive functions and have been subjected to intense experimental and theoretical scrutiny. Computational modeling has provided a framework for the emergence of network-level oscillatory behavior from the interaction of spiking neurons. However, due to the strong nonlinear interactions between highly recurrent spiking populations, the interplay between cortical rhythms in multiple frequency bands has rarely been theoretically investigated. Many studies invoke multiple physiological timescales (e.g., various ion channels or multiple types of inhibitory neurons) or oscillatory inputs to produce rhythms in multi-bands. Here, we demonstrate the emergence of multi-band oscillations in a simple network consisting of one excitatory and one inhibitory neuronal population driven by constant input. First, we construct a data-driven, Poincaré section theory for robust numerical observations of single-frequency oscillations bifurcating into multiple bands. Then, we develop model reductions of the stochastic, nonlinear, high-dimensional neuronal network to capture the appearance of multi-band dynamics and the underlying bifurcations theoretically. Furthermore, when viewed within the reduced state space, our analysis reveals conserved geometrical features of the bifurcations on low-dimensional dynamical manifolds. These results suggest a simple geometric mechanism behind the emergence of multi-band oscillations without appealing to oscillatory inputs or multiple synaptic or neuronal timescales. Thus, our work points to unexplored regimes of stochastic competition between excitation and inhibition behind the generation of dynamic, patterned neuronal activities.

Multisensory Flicker Modulates Widespread Brain Networks and Reduces Interictal Epileptiform Discharges in Humans

Modulating brain oscillations has strong therapeutic potential. However, commonly used non-invasive interventions such as transcranial magnetic or direct current stimulation have limited effects on deeper cortical structures like the medial temporal lobe. Repetitive audio-visual stimulation, or sensory flicker, modulates such structures in mice but little is known about its effects in humans. Using high spatiotemporal resolution, we mapped and quantified the neurophysiological effects of sensory flicker in human subjects undergoing presurgical intracranial seizure monitoring. We found that flicker modulates both local field potential and single neurons in higher cognitive regions, including the medial temporal lobe and prefrontal cortex, and that local field potential modulation is likely mediated via resonance of involved circuits. We then assessed how flicker affects pathological neural activity, specifically interictal epileptiform discharges, a biomarker of epilepsy also implicated in Alzheimer's and other diseases. In our patient population with focal seizure onsets, sensory flicker decreased the rate interictal epileptiform discharges. Our findings support the use of sensory flicker to modulate deeper cortical structures and mitigate pathological activity in humans.

Habitual night waking associates with dynamics of waking cortical theta power in infancy

The implications of the substantial individual differences in infant sleep for early brain development remain unclear. Here, we examined whether night sleep quality relates to daytime brain activity, operationalized through measures of EEG theta power and its dynamic modulation, which have been previously linked to later cognitive development. For this longitudinal study, 76 typically developing infants were studied (age: 4-14 months, 166 individual study visits) over the course of 6 months with one, two, three, or four lab visits. Habitual sleep was measured with a 7-day sleep diary and actigraphy, and the Brief Infant Sleep Questionnaire. Twenty-channel EEG was recorded while infants watched multiple rounds of videos of women singing nursery rhymes; oscillatory power in the theta band was extracted. Key metrics were average theta across stimuli and the slope of change in theta within the first novel movie. Both objective and subjective sleep assessment methods showed a relationship between more night waking and higher overall theta power and reduced dynamic modulation of theta over the course of the novel video stimuli. These results may indicate altered learning and consolidation in infants with more disrupted night sleep, which may have implications for cognitive development.

The hearing hippocampus

The hippocampus has a well-established role in spatial and episodic memory but a broader function has been proposed including aspects of perception and relational processing. Neural bases of sound analysis have been described in the pathway to auditory cortex, but wider networks supporting auditory cognition are still being established. We review what is known about the role of the hippocampus in processing auditory information, and how the hippocampus itself is shaped by sound. In examining imaging, recording, and lesion studies in species from rodents to humans, we uncover a hierarchy of hippocampal responses to sound including during passive exposure, active listening, and the learning of associations between sounds and other stimuli. We describe how the hippocampus' connectivity and computational architecture allow it to track and manipulate auditory information - whether in the form of speech, music, or environmental, emotional, or phantom sounds. Functional and structural correlates of auditory experience are also identified. The extent of auditory-hippocampal interactions is consistent with the view that the hippocampus makes broad contributions to perception and cognition, beyond spatial and episodic memory. More deeply understanding these interactions may unlock applications including entraining hippocampal rhythms to support cognition, and intervening in links between hearing loss and dementia.

The influence of temporal unpredictability on the electrophysiological mechanisms of neural entrainment

Neural entrainment, or the synchronization of endogenous oscillations to exogenous rhythmic events, has been postulated as a powerful mechanism underlying stimulus prediction. Nevertheless, studies that have explored the benefits of neural entrainment on attention, perception, and other cognitive functions have received criticism, which could compromise their theoretical and clinical value. Therefore, the aim of the present study was [1] to confirm the presence of entrainment using a set of pre-established criteria and [2] to establish whether the reported behavioral benefits of entrainment remain when temporal predictability related to target appearance is reduced. To address these points, we adapted a previous neural entrainment paradigm to include: a variable entrainer length and increased target-absent trials, and instructing participants to respond only if they had detected a target, to avoid guessing. Thirty-six right-handed women took part in this study. Our results indicated a significant alignment of neural activity to the external periodicity as well as a persistence of phase alignment beyond the offset of the driving signal. This would appear to indicate that neural entrainment triggers preexisting endogenous oscillations, which cannot simply be explained as a succession of event-related potentials associated with the stimuli, expectation and/or motor response. However, we found no behavioral benefit for targets in-phase with entrainers, which would suggest that the effect of neural entrainment on overt behavior may be more limited than expected. These results help to clarify the mechanistic processes underlying neural entrainment and provide new insights on its applications.

Beyond Infant's Looking: The Neural Basis for Infant Prediction Errors

Contemporary conceptualizations on infant cognitive development focus on predictive processes; the basic idea is that the brain continuously creates predictions about what is expected and that the divergence between predicted and actual perceived data yields a prediction error. This prediction error updates the model from which the predictions are generated and therefore is a basic mechanism for learning and adaptation to the dynamics of the ever-changing environment. In this article, we review the types of available empirical evidence supporting the idea that predictive processes can be found in infancy, especially emphasizing the contribution of electrophysiology as a potential method for testing the similarity of the brain mechanisms for processing prediction errors in infants to those of adults. In infants, as with older children, adolescents, and adults, predictions involve synchronization bursts of middle-central theta reflecting brain activity in the anterior cingulate cortex. We discuss how early in development such brain mechanisms develop and open questions that still remain to be empirically investigated.

Theta oscillations support active exploration in human spatial navigation

Active navigation seems to yield better spatial knowledge than passive navigation, but it is unclear how active decision-making influences learning and memory. Here, we examined the contributions of theta oscillations to memory-related exploration while testing theories about how they contribute to active learning. Using electroencephalography (EEG), we tested individuals on a maze-learning task in which they made discrete decisions about where to explore at each choice point in the maze. Half the participants were free to make active decisions at each choice point, and the other half passively explored by selecting a marked choice (matched to active exploration) at each intersection. Critically, all decisions were made when stationary, decoupling the active decision-making process from movement and speed factors, which is another prominent potential role for theta oscillations. Participants were then tested on their knowledge of the maze by traveling from object A to object B within the maze. Results show an advantage for active decision-making during learning and indicate that the active group had greater theta power during choice points in exploration, particularly in midfrontal channels. These findings demonstrate that active exploration is associated with theta oscillations during human spatial navigation, and that these oscillations are not exclusively related to movement or speed. Results demonstrating increased theta oscillations in prefrontal regions suggest communication with the hippocampus and integration of new information into memory. We also found evidence for alpha oscillations during active navigation, suggesting a role for attention as well. This study finds support for a general mnemonic role for theta oscillations during navigational learning.

Brain electrophysiological responses associated with the retrieval of temporal and spatial contexts in episodic memory

Episodic memory allows us to remember three main elements regarding an event: what (it is), where (it is in space), and when (it appears). The brain's electrical activity signaling the occurrence of these processes has been studied separately, revealing different patterns of ERP components and changes in the EEG theta band amplitude. However, how these patterns signal the retrieval of the temporal and spatial contexts of the same episode is unknown. The objective of this study was to evaluate the ERP components and the EEG theta band in association to the retrieval of the what, where, and when of the same episode through a source memory task. Three types of trials were identified here: total retrieval (what, where, and when), spatial retrieval (what and where), and correct rejections (correctly identified as new items). Attentional components, N200 and P300, and theta band were sensitive to the amount of information retrieved from episodic memory. Total retrieval and spatial trials elicited higher mean amplitude of FN400 and LPC, familiarity and recollection markers, respectively, than correct rejections. Our results suggest that early attention mechanisms can discern the strength of retrieval; in turn, familiarity and recollection mechanisms participate in the retrieval of the main contexts of episodic memory, but not in a cumulative way.

Integrating music-based interventions with Gamma-frequency stimulation: Implications for healthy ageing

In recent years, music-based interventions (MBIs) have risen in popularity as a non-invasive, sustainable form of care for treating dementia-related disorders, such as Mild Cognitive Impairment (MCI) and Alzheimer's disease (AD). Despite their clinical potential, evidence regarding the efficacy of MBIs on patient outcomes is mixed. Recently, a line of related research has begun to investigate the clinical impact of non-invasive Gamma-frequency (e.g., 40 Hz) sensory stimulation on dementia. Current work, using non-human-animal models of AD, suggests that non-invasive Gamma-frequency stimulation can remediate multiple pathophysiologies of dementia at the molecular, cellular and neural-systems scales, and, importantly, improve cognitive functioning. These findings suggest that the efficacy of MBIs could, in theory, be enhanced by incorporating Gamma-frequency stimulation into current MBI protocols. In the current review, we propose a novel clinical framework for non-invasively treating dementia-related disorders that combines previous MBIs with current approaches employing Gamma-frequency sensory stimulation. We theorize that combining MBIs with Gamma-frequency stimulation could increase the therapeutic power of MBIs by simultaneously targeting multiple biomarkers of dementia, restoring neural activity that underlies learning and memory (e.g., Gamma-frequency neural activity, Theta-Gamma coupling), and actively engaging auditory and reward networks in the brain to promote behavioural change.

Working-Memory, Alpha-Theta Oscillations and Musical Training in Older Age: Research Perspectives for Speech-on-speech Perception

During the normal course of aging, perception of speech-on-speech or “cocktail party” speech and use of working memory (WM) abilities change. Musical training, which is a complex activity that integrates multiple sensory modalities and higher-order cognitive functions, reportedly benefits both WM performance and speech-on-speech perception in older adults. This mini-review explores the relationship between musical training, WM and speech-on-speech perception in older age (> 65 years) through the lens of the Ease of Language Understanding (ELU) model. Linking neural-oscillation literature associating speech-on-speech perception and WM with alpha-theta oscillatory activity, we propose that two stages of speech-on-speech processing in the ELU are underpinned by WM-related alpha-theta oscillatory activity, and that effects of musical training on speech-on-speech perception may be reflected in these frequency bands among older adults.

Decision Making as a Learned Skill in Mice and Humans

Attention is a necessary component in many forms of human and animal learning. Numerous studies have described how attention and memory interact when confronted with a choice point during skill learning. In both animal and human studies, pathways have been found that connect the executive and orienting networks of attention to the hippocampus. The anterior cingulate cortex, part of the executive attention network, is linked to the hippocampus via the nucleus reuniens of the thalamus. The parietal cortex, part of the orienting attention network, accesses the hippocampus via the entorhinal cortex. These studies have led to specific predictions concerning the functional role of each pathway in connecting the cortex to the hippocampus. Here, we review some of the predictions arising from these studies. We then discuss potential methods for manipulating the two pathways and assessing the directionality of their functional connection using viral expression techniques in mice. New studies may allow testing of a behavioral model specifying how the two pathways work together during skill learning.

Evidence from theta-burst stimulation that age-related de-differentiation of the hippocampal network is functional for episodic memory

Episodic memory is supported by hippocampal interactions with a distributed network. Aging is associated with memory decline and network de-differentiation. However, the role of de-differentiation in memory decline has not been directly tested. We reasoned that hippocampal network-targeted stimulation could test these theories, as age-related changes in the network response to stimulation would indicate network reorganization, and corresponding changes in memory would suggest that this reorganization is functional. We compared effects of stimulation on fMRI connectivity and memory in younger versus older adults. Theta-burst network-targeted stimulation of left lateral parietal cortex selectively increased hippocampal network connectivity and modulated memory in younger adults. In contrast, stimulation in older adults increased connectivity throughout the brain, without network selectivity, and did not influence memory. These findings provide evidence that network responses to stimulation are de-differentiated in aging and suggest that age-related de-differentiation is relevant for memory. This manuscript is part of the Special Issue entitled "Cognitive Neuroscience of Healthy and Pathological Aging" edited by Drs. M. N. Rajah, S. Belleville, and R. Cabeza. This article is part of the Virtual Special Issue titled COGNITIVE NEUROSCIENCE OF HEALTHY AND PATHOLOGICAL AGING. The full issue can be found on ScienceDirect at https://www.sciencedirect.com/journal/neurobiology-of-aging/special-issue/105379XPWJP.

Improving autobiographical memory in Alzheimer's disease by transcranial alternating current stimulation

We review the latest evidence from animal models, studies in humans using electrophysiology, experimental memory paradigms, and non-invasive brain stimulation (NIBS), in the form of transcranial alternating current stimulation (tACS), suggesting that the altered activity in networks that contribute to the autobiographical memory (ABM) deficits may be modifiable. ABM involves a specific brain network of interacting regions that store and retrieve life experiences. Deficits in ABM are early symptoms in patients with Alzheimer's disease (AD), and serve as relevant predictors of disease progression. The possibility to modify the neural substrates of ABM opens exciting avenues for the development of therapeutic approaches. Beyond a summary of the causal role of brain oscillations in ABM, we propose a new approach of modulating brain oscillations using personalized tACS with the possibility of reducing ABM deficits. We suggest that human experimental studies using cognitive tasks, EEG, and tACS can have future translational clinical implications.

Patient-Tailored, Home-Based Non-invasive Brain Stimulation for Memory Deficits in Dementia Due to Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible, progressive brain disorder that can cause dementia (Alzheimer's disease-related dementia, ADRD) with growing cognitive disability and vast physical, emotional, and financial pressures not only on the patients but also on caregivers and families. Loss of memory is an early and very debilitating symptom in AD patients and a relevant predictor of disease progression. Data from rodents, as well as human studies, suggest that dysregulation of specific brain oscillations, particularly in the hippocampus, is linked to memory deficits. Animal and human studies demonstrate that non-invasive brain stimulation (NIBS) in the form of transcranial alternating current stimulation (tACS) allows to reliably and safely interact with ongoing oscillatory patterns in the brain in specific frequencies. We developed a protocol for patient-tailored home-based tACS with an instruction program to train a caregiver to deliver daily sessions of tACS that can be remotely monitored by the study team. We provide a discussion of the neurobiological rationale to modulate oscillations and a description of the study protocol. Data of two patients with ADRD who have completed this protocol illustrate the feasibility of the approach and provide pilot evidence on the safety of the remotely-monitored, caregiver-administered, home-based tACS intervention. These findings encourage the pursuit of a large, adequately powered, randomized controlled trial of home-based tACS for memory dysfunction in ADRD.

Improved Cognitive Promotion through Accelerated Magnetic Stimulation

Noninvasive brain stimulation to enhance cognition is an area of increasing research interest. Theta burst stimulation (TBS) is a novel accelerated form of stimulation, which more closely mimics the brain's natural firing patterns and may have greater effects on cognitive performance. We report here the comparative assessment of the effect of conventional high-frequency repetitive transcranial magnetic stimulation (HF-rTMS) protocols and TBS protocols on cognition enhancement in healthy controls. Sixty healthy adults (34 males and 26 females) were randomized and counterbalanced and assigned to HF-rTMS (n = 20), TBS (n = 20), or sham (n = 20) groups. The promotion effects of different parameters of prefrontal stimulation on working memory and executive function were compared, as assessed by performance in N-back tasks and the Wisconsin Card Sorting Test (WCST). Both HF-rTMS and intermittent TBS (iTBS) groups displayed a significant improvement in N-back tasks, with an effect size of 0.79 and 1.50, respectively. Furthermore, the iTBS group displayed a significant improvement in the WCST, with an effect size of 0.84. The iTBS group demonstrated higher effect sizes than the HF-rTMS group (t = 2.68, p = 0.011), with an effect size of 0.85. However, no improvement in other tasks was observed (p > 0.05). Intermittent TBS has a stronger cognitive promoting effect than conventional rTMS. In summary, our findings provide direct evidence that iTBS may be a superior protocol for cognitive promotion.

Increasing the amplitude of intrinsic theta in the human brain

In a mouse study we found increased myelination of pathways surrounding the anterior cingulate cortex (ACC) following stimulation near the theta rhythm (4-8 Hz), and evidence that this change in connectivity reduced behavioral anxiety. We cannot use the optogenetic methods with humans that were used in our mouse studies. This paper examines whether it is possible to enhance intrinsic theta amplitudes in humans using less invasive methods. The first experiment compares electrical, auditory and biofeedback as methods for increasing intrinsic theta rhythm amplitudes in the Anterior Cingulate Cortex (ACC). These methods are used alone or in conjunction with a task designed to activate the same area. The results favor using electrical stimulation in conjunction with a task targeting this region. Stimulating the ACC increases intrinsic theta more in this area than in a control area distant from the site of stimulation, suggesting some degree of localization of the stimulation. In Experiment 2, we employed electrical stimulation with the electrodes common to each person, or with electrodes selected from an individual head model. We targeted the ACC or Motor Cortex (PMC). At baseline, intrinsic theta is higher in the ACC than the PMC. In both areas, theta can be increased in amplitude by electrical stimulation plus task. In the PMC, theta levels during stimulation plus task are not significantly higher than during task alone. There is no significant difference between generic and individual electrodes. We discuss steps needed to determine whether we can use the electrical stimulation + task to improve the connectivity of white matter in different brain areas.

The rhythm of learning: Theta oscillations as an index of active learning in infancy

Active learning is a critical component of human development, however, the mechanisms supporting it are not fully understood. Given that early learning experiences may affect both infants' immediate learning success, as well as their motivation to learn, it is particularly important to investigate the mechanisms of active learning in this period, when the foundations of learning habits and curiosity are built. Traditional behavioural approaches of studying infant learning face challenges that emerging tools from neuroscience may help relieve. We introduce one such tool, EEG theta oscillations, and propose this neural marker has great potential for offering novel insights into active learning. Theta activity, recorded prior to or during learning, has been shown to be predictive of learning success. We argue that this involvement in memory formation, combined with theta activity's tight association with reward processing, makes theta oscillations a uniquely suited tool for the investigation of motivational mechanisms underlying active learning. We outline research questions as well as methodological approaches pertinent to infant learning and suggest how and why theta oscillations may offer complementary insights. As such, we aim to bridge the gap between cognitive and neural approaches, and advance our knowledge of active learning in development more broadly.

Neural correlates of the Dunning-Kruger effect

The Dunning-Kruger effect (DKE) is a metacognitive phenomenon of illusory superiority in which individuals who perform poorly on a task believe they performed better than others, yet individuals who performed very well believe they under-performed compared to others. This phenomenon has yet to be directly explored in episodic memory, nor explored for physiological correlates or reaction times. We designed a novel method to elicit the DKE via a test of item recognition while electroencephalography (EEG) was recorded. Throughout the task, participants were asked to estimate the percentile in which they performed compared to others. Results revealed participants in the bottom 25th percentile over-estimated their percentile, while participants in the top 75th percentile under-estimated their percentile, exhibiting the classic DKE. Reaction time measures revealed a condition-by-group interaction whereby over-estimators responded faster than under-estimators when estimating being in the top percentile and responded slower when estimating being in the bottom percentile. Between-group EEG differences were evident between over-estimators and under-estimators during Dunning-Kruger responses, which revealed FN400-like effects of familiarity supporting differences for over-estimators, whereas "old-new" memory event-related potential effects revealed a late parietal component associated with recollection-based processing for under-estimators that was not evident for over-estimators. Findings suggest over- and under-estimators use differing cognitive processes when assessing their performance, such that under-estimators may rely on recollection during memory while over-estimators may draw upon excess familiarity when over-estimating their performance. Episodic memory thus appears to play a contributory role in metacognitive judgements of illusory superiority.

Assessing Rhythmic Visual Entrainment and Reinstatement of Brain Oscillations to Modulate Memory Performance

The human brain’s ability to store information and remember past events is thought to be orchestrated by the synchronization of neuronal oscillations in various frequency bands. A vast amount of research has found that neural oscillations in the theta (∼4–7 Hz) and alpha (∼8–12 Hz) bands play an important role in memory formation. More specifically, it has been suggested that memory performance benefits if the same oscillatory pattern is present during encoding and retrieval. However, the causal relevance of these oscillations is not well understood. Rhythmic sensory stimulation is thought to entrain ongoing brain oscillations and modulate associated functions (e.g., memory formation). In the present study, we used rhythmic visual stimulation at 6 and 10 Hz to experimentally modulate the memory encoding process in a recognition memory task. In addition, we reinstated oscillatory activity from the encoding episode during retrieval, which has been hypothesized to result in memory performance improvements compared to non-reinstated conditions and incongruent reinstatement. Contrary to our hypothesis, we find no effect of neural entrainment during encoding on subsequent memory performance. Likewise, memory retrieval does not benefit from neural reinstatement. The results are discussed with respect to methodological challenges of rhythmic sensory stimulation as a means to alter cognitive processes and induce context-dependent memory effects.

A New Unifying Account of the Roles of Neuronal Entrainment

Rhythms are a fundamental and defining feature of neuronal activity in animals including humans. This rhythmic brain activity interacts in complex ways with rhythms in the internal and external environment through the phenomenon of 'neuronal entrainment', which is attracting increasing attention due to its suggested role in a multitude of sensory and cognitive processes. Some senses, such as touch and vision, sample the environment rhythmically, while others, like audition, are faced with mostly rhythmic inputs. Entrainment couples rhythmic brain activity to external and internal rhythmic events, serving fine-grained routing and modulation of external and internal signals across multiple spatial and temporal hierarchies. This interaction between a brain and its environment can be experimentally investigated and even modified by rhythmic sensory stimuli or invasive and non-invasive neuromodulation techniques. We provide a comprehensive overview of the topic and propose a theoretical framework of how neuronal entrainment dynamically structures information from incoming neuronal, bodily and environmental sources. We discuss the different types of neuronal entrainment, the conceptual advances in the field, and converging evidence for general principles.

Pure-list production improves item recognition and sometimes also improves source memory

Relative to reading silently, reading words aloud (a type of "production") typically enhances item recognition, even when production is manipulated between groups using pure lists. We investigated whether pure-list production also enhances memory for various item details (i.e., source memory). Screen side (Experiment 1), font size (Experiment 2), or reading versus generating from anagrams (Experiments 3-4) were the sources varied within-subject, and aloud versus silent reading was varied across groups. Thus, the manipulation of source was apparent to participants, whereas the manipulation of production was not. Traditional measures and multinomial modeling established that the aloud groups generally showed improved item recognition-and showed improved source memory when steps were taken to enhance the salience of the source manipulation (Experiment 4). In summary, reading an entire list of items improves item recognition and can also improve memory for some types of source details.

Site-Specific Effects of Online rTMS during a Working Memory Task in Healthy Older Adults

The process of manipulating information within working memory is central to many cognitive functions, but also declines rapidly in old age. Improving this process could markedly enhance the health-span in older adults. The current pre-registered, randomized and placebo-controlled study tested the potential of online repetitive transcranial magnetic stimulation (rTMS) applied at 5 Hz over the left lateral parietal cortex to enhance working memory manipulation in healthy elderly adults. rTMS was applied, while participants performed a delayed-response alphabetization task with two individually titrated levels of difficulty. Coil placement and stimulation amplitude were calculated from fMRI activation maps combined with electric field modeling on an individual-subject basis in order to standardize dosing at the targeted cortical location. Contrary to the a priori hypothesis, active rTMS significantly decreased accuracy relative to sham, and only in the hardest difficulty level. When compared to the results from our previous study, in which rTMS was applied over the left prefrontal cortex, we found equivalent effect sizes but opposite directionality suggesting a site-specific effect of rTMS. These results demonstrate engagement of cortical working memory processing using a novel TMS targeting approach, while also providing prescriptions for future studies seeking to enhance memory through rTMS.

Temporal predictions provided by musical rhythm influence visual memory encoding

Selective attention plays a key role in determining what aspects of our environment are encoded into long-term memory. Auditory rhythms with a regular beat provide temporal expectations that entrain attention and facilitate perception of visual stimuli aligned with the beat. The current study investigated whether entrainment to background auditory rhythms also facilitates higher-level cognitive functions such as episodic memory. In a series of experiments, we manipulated temporal attention through the use of rhythmic, instrumental music. In Experiment 1A and 1B, we found that background musical rhythm influenced the encoding of visual targets into memory, evident in enhanced subsequent memory for targets that appeared in-synchrony compared to out-of-synchrony with the background beat. Response times at encoding did not differ for in-synchrony compared to out-of-synchrony stimuli, suggesting that the rhythmic modulation of memory does not simply reflect rhythmic effects on perception and action. Experiment 2 investigated whether rhythmic effects on response times emerge when task procedures more closely match prior studies that have demonstrated significant auditory entrainment effects. Responses were faster for in-synchrony compared to out-of-synchrony stimuli when participants performed a more perceptually-oriented task that did not contain intervening recognition memory tests, suggesting that rhythmic effects on perception and action depend on the nature of the task demands. Together, these results support the hypothesis that rhythmic temporal regularities provided by background music can entrain attention and influence the encoding of visual stimuli into memory.