Divergent roles of early visual cortex and inferior frontal junction in visual working memory.

BACKGROUND: Recent studies indicate that both prefrontal and visual regions play critical roles in visual working memory (VWM), with prefrontal regions mainly associated with executive functions, and visual cortices linked to representations of memory contents. VWM involves the selective filtering of irrelevant information, yet the specific contributions of the prefrontal regions and visual cortex in this process remain unclear. OBJECTIVE: To understand the dynamic causal roles of prefrontal and visual regions in VWM. METHODS: The differentiation of VWM components was achieved using a computational model that incorporated a swap rate for non-target stimuli. Single-pulse magnetic transcranial stimulation (spTMS) was delivered to the early visual cortex (EVC) and the inferior frontal junction (IFJ) across different phases of an orientation recall task that with or without distractors. RESULTS: Our results indicate that spTMS over the EVC and IFJ influences VWM particularly when distractors are present. VWM precision can be impacted by spTMS applied to either region during the early retention, while spTMS effect is especially prominent when EVC is stimulated during the late retention phase and when directed at the ipsilateral EVC. Conversely, the probability of accurately recalling the target exhibited comparable patterns when spTMS was administered to either the EVC or IFJ. CONCLUSIONS: We highlight the "sensory recruitment" of VWM characterized by critical involvement of EVC particularly in the information-filtering process within VWM. The maintenance of memory content representations necessitates ongoing communication between the EVC and IFJ throughout the entirety of the VWM process in a dynamic pattern.

Alpha neurofeedback training improves visual working memory in healthy individuals.

Neurofeedback (NF) training is a closed-loop brain training in which participants learn to regulate their neural activation. NF training of alpha (8-12 Hz) activity has been reported to enhance working memory capacity, but whether it affects the precision in working memory has not yet been explored. Moreover, whether NF training distinctively influences performance in different types of working memory tasks remains unclear. Therefore, the present study conducted a randomized, single-blind, sham-controlled experiment to investigate how alpha NF training affected the capacity and precision of working memory, as well as the related neural change. Forty participants were randomly and equally assigned to the NF group and the sham control group. Both groups received NF training (about 30 min daily) for five consecutive days. The NF group received alpha (8-12 Hz) training, while the sham control group received sham NF training. We found a significant alpha increase within sessions but no significant difference across sessions. However, the behavioral performance and neural activity in the modified Sternberg task did not show significant change after alpha NF training. On the contrary, the alpha NF training group significantly increased visual working memory capacity measured by the Corsi-block tapping task and improved visual working memory precision in the interference condition in a color-recall task. These results suggest that alpha NF training influences performance in working memory tasks involved in the visuospatial sketchpad. Notably, we demonstrated that alpha NF training improves the quantity and quality of visual working memory.

Long-term abacus training gains in children are predicted by medial temporal lobe anatomy and circuitry.

Abacus-based mental calculation (AMC) is a widely used educational tool for enhancing math learning, offering an accessible and cost-effective method for classroom implementation. Despite its universal appeal, the neurocognitive mechanisms that drive the efficacy of AMC training remain poorly understood. Notably, although abacus training relies heavily on the rapid recall of number positions and sequences, the role of memory systems in driving long-term AMC learning remains unknown. Here, we sought to address this gap by investigating the role of the medial temporal lobe (MTL) memory system in predicting long-term AMC training gains in second-grade children, who were longitudinally assessed up to fifth grade. Leveraging multimodal neuroimaging data, we tested the hypothesis that MTL systems, known for their involvement in associative memory, are instrumental in facilitating AMC-induced improvements in math skills. We found that gray matter volume in bilateral MTL, along with functional connectivity between the MTL and frontal and ventral temporal-occipital cortices, significantly predicted learning gains. Intriguingly, greater gray matter volume but weaker connectivity of the posterior parietal cortex predicted better learning outcomes, offering a more nuanced view of brain systems at play in AMC training. Our findings not only underscore the critical role of the MTL memory system in AMC training but also illuminate the neurobiological factors contributing to individual differences in cognitive skill acquisition. A video abstract of this article can be viewed at https://youtu.be/StVooNRc7T8. RESEARCH HIGHLIGHTS: We investigated the role of medial temporal lobe (MTL) memory system in driving children's math learning following abacus-based mental calculation (AMC) training. AMC training improved math skills in elementary school children across their second and fifth grade. MTL structural integrity and functional connectivity with prefrontal and ventral temporal-occipital cortices predicted long-term AMC training-related gains.

Crossmodal Associations and Working Memory in the Brain.

Crossmodal associations between stimuli from different sensory modalities could emerge in non-synesthetic people and be stored in working memory to guide goal-directed behaviors. This chapter reviews a plethora of studies in this field to summarize where, when, and how crossmodal associations and working memory are processed. It has been found that in those brain regions that are traditionally considered as unimodal primary sensory areas, neural activity could be influenced by crossmodal sensory signals at temporally very early stage of information processing. This phenomenon could not be due to feedback projections from higher level associative areas. Sequentially, neural processes would then occur in associative cortical areas including the posterior parietal cortex and prefrontal cortex. Neural oscillations in multiple frequency bands may reflect brain activity in crossmodal associations, and it is likely that neural synchrony is related to potential neural mechanisms underlying these processes. Primary sensory areas and associative areas coordinate together through neural synchrony to fulfil crossmodal associations and to guide working memory performance.

Bridging the gap between EEG and DCNNs reveals a fatigue mechanism of facial repetition suppression.

Facial repetition suppression, a well-studied phenomenon characterized by decreased neural responses to repeated faces in visual cortices, remains a subject of ongoing debate regarding its underlying neural mechanisms. Our research harnesses advanced multivariate analysis techniques and the prowess of deep convolutional neural networks (DCNNs) in face recognition to bridge the gap between human electroencephalogram (EEG) data and DCNNs, especially in the context of facial repetition suppression. Our innovative reverse engineering approach, manipulating the neuronal activity in DCNNs and conducted representational comparisons between brain activations derived from human EEG and manipulated DCNN activations, provided insights into the underlying facial repetition suppression. Significantly, our findings advocate the fatigue mechanism as the dominant force behind the facial repetition suppression effect. Broadly, this integrative framework, bridging the human brain and DCNNs, offers a promising tool for simulating brain activity and making inferences regarding the neural mechanisms underpinning complex human behaviors.

Reduced interocular suppression after inverse patching in anisometropic amblyopia.

Purpose: Recent investigations observed substantial enhancements in binocular balance, visual acuity, and stereovision among older children and adults with amblyopia by patching the amblyopic eye (i.e., inverse patching) for 2 h daily over 2 months. Despite these promising findings, the precise neural mechanisms underlying inverse patching remain elusive. This study endeavors to delve deeper into the neural alterations induced by inverse patching, focusing on steady-state visual evoked potentials (SSVEPs). We specifically investigate the changes in SSVEPs following monocular deprivation of either the fellow eye or the amblyopic eye in older amblyopic children and adults. Method: Ten participants (17.60 ± 2.03 years old; mean ± SEM), clinically diagnosed with anisometropic amblyopia, were recruited for this study. Each participant underwent a 120 min patching session on their fellow eye on the first day, followed by a similar session on their amblyopic eye on the second day. Baseline steady-state visual evoked potentials (SSVEPs) measurements were collected each day prior to patching, with post-patching SSVEPs measurements obtained immediately after the patching session. The experimental design incorporated a binocular rivalry paradigm, utilizing SSVEPs measurements. Results: The results revealed that inverse patching induced a heightened influence on neural plasticity, manifesting in a reduction of interocular suppression from the fellow eye to the amblyopic eye. In contrast, patching the fellow eye demonstrated negligible effects on the visual cortex. Furthermore, alterations in interocular suppression subsequent to inverse patching exhibited a correlation with the visual acuity of the amblyopic eye. Conclusion: Inverse patching emerges as a promising therapeutic avenue for adolescents and adults grappling with severe anisometropic amblyopia that proves refractory to conventional interventions. This innovative approach exhibits the potential to induce more robust neural plasticity within the visual cortex, thereby modulating neural interactions more effectively than traditional amblyopia treatments.

Early top-down control of internal selection induced by retrospective cues in visual working memory: advantage of peripheral over central cues.

Attention can be deployed among external sensory stimuli or internal working memory (WM) representations, and recent primate studies have revealed that these external and internal selections share a common neural basis in the prefrontal cortex (PFC). However, it remains to be elucidated how PFC implements these selections, especially in humans. The present study aimed to further investigate whether PFC responded differentially to the peripheral and central retrospective cues (retro-cues) that induced attention selection among WM representations. To achieve this, we combined magnetoencephalography (MEG, Experiment 1) and transcranial magnetic stimulation (TMS, Experiment 2) with an orientation-recall paradigm. Experiment 1 found that a peripheral retro-cue with 100% reliability had a greater benefit on WM performance than a central retro-cue, while this advantage of peripheral over central cues vanished when the cue reliability dropped to 50% (non-informative). MEG source analysis indicated that the 100% peripheral retro-cue elicited earlier (∼125 ms) PFC responses than the central retro-cue (∼275 ms). Meanwhile, Granger causality analysis showed that PFC had earlier (0-200 ms) top-down signals projecting to the superior parietal lobule (SPL) and the lateral occipital cortex (LOC) after the onset of peripheral retro-cues, while these top-down signals appeared later (300-500 ms) after the onset of central retro-cues. Importantly, PFC activity within this period of 300-500 ms correlated with the peripheral advantage in behavior. Moreover, Experiment 2 applied TMS at different time points to test the causal influence of brain activity on behavior and found that stimulating PFC at 100 ms abolished the behavioral benefit of the peripheral retro-cue, as well as its advantage over the central retro-cue. Taken together, our results suggested that the advantage of peripheral over central retro-cues in the mnemonic domain is realized through faster top-down control from PFC, which challenged traditional opinions that the top-down control of attention on WM required at least 300 ms to appear. The present study highlighted that in addition to the causal role of PFC in attention selection of WM representations, timing was critical as well and faster was better.

Successful alpha neurofeedback training enhances working memory updating and event-related potential activity.

Neurofeedback (NF) is a promising method to self-regulate human brain activity for cognition enhancement. Due to the unclear results of alpha NF training on working memory updating as well as the impact of feedback modality on NF learning, this study aimed to understand further the underlying neural mechanism of alpha NF training effects on working memory updating, where the NF learning was also compared between visual and auditory feedback modalities. A total of 30 participants were assigned to Visual NF, Auditory NF, and Control groups. Working memory updating was evaluated by n-back (n =2,3) tasks before and after five alpha upregulation NF sessions. The result showed no significant difference in NF learning performance between the Visual and Auditory groups, indicating that the difference in feedback modality did not affect NF learning. In addition, compared to the control group, the participants who achieved successful NF learning showed a significant increase in n-back behavioral performance and P3a amplitude in 2-back and a significant decrease in P3a latency in 3-back. Our results in n-back further suggested that successful alpha NF training might improve updating performance in terms of the behavioral and related event-related potential (ERP) measures. These findings contribute to the understanding of the effect of alpha training on memory updating and the design of NF experimental protocol in terms of feedback modality selection.

Mnemonic-trained brain tuning to a regular odd-even pattern subserves digit memory in children.

It is said that our species use mnemonics - that "magic of memorization" - to engrave an enormous amount of information in the brain. Yet, it is unclear how mnemonics affect memory and what the neural underpinnings are. In this electroencephalography study, we examined the hypotheses whether mnemonic training improved processing-efficiency and/or altered encoding-pattern to support memory enhancement. By 22-day training of a digit-image mnemonic (a custom memory technique used by world-class mnemonists), a group of children showed increased short-term memory after training, but with limited gain generalization. This training resulted in regular odd-even neural patterns (i.e., enhanced P200 and theta power during the encoding of digits at even- versus odd- positions in a sequence). Critically, the P200 and theta power effects predicted the training-induced memory improvement. These findings provide evidence of how mnemonics alter encoding pattern, as reflected in functional brain organization, to support memory enhancement.

Decoding emotion from high-frequency steady state visual evoked potential (SSVEP).

BACKGROUND: Steady-state visual evoked potential (SSVEP) by flickering sensory stimuli has been widely applied in the brain-machine interface (BMI). Yet, it remains largely unexplored whether affective information could be decoded from the signal of SSVEP, especially from the frequencies higher than the critical flicker frequency (an upper-frequency limit one can see the flicker). NEW METHOD: Participants fixated on visual stimuli presented at 60 Hz above the critical flicker frequency. The stimuli were pictures with different affective valance (positive, neutral, negative) in distinctive semantic categories (human, animal, scene). SSVEP entrainment in the brain evoked by the flickering stimuli at 60 Hz was used to decode the affective and semantic information. RESULTS: During the presentation of stimuli (1 s), the affective valance could be decoded from the SSVEP signals at 60 Hz, while the semantic categories could not. In contrast, neither affective nor semantic information could be decoded from the brain signal one second before the onset of stimuli. COMPARISON WITH EXISTING METHOD(S): Previous studies focused mainly on EEG activity tagged at frequencies lower than the critical flickering frequency and investigated whether the affective valence of stimuli drew participants' attention. The current study was the first to use SSVEP signals from high-frequency (60 Hz) above the critical flickering frequency to decode affective information from stimuli. The high-frequency flickering was invisible and thus substantially reduced the fatigue of participants. CONCLUSIONS: We found that affective information could be decoded from high-frequency SSVEP and the current finding could be added to designing affective BMI in the future.

Intermittent theta burst stimulation to the left dorsolateral prefrontal cortex improves working memory of subjects with methamphetamine use disorder.

BACKGROUND: Repetitive transcranial magnetic stimulation has been employed to treat drug dependence, reduce drug use and improve cognition. The aim of the study was to analyze the effectiveness of intermittent theta-burst stimulation (iTBS) on cognition in individuals with methamphetamine use disorder (MUD). METHODS: This was a secondary analysis of 40 MUD subjects receiving left dorsolateral prefrontal cortex (L-DLPFC) iTBS or sham iTBS for 20 times over 10 days (twice-daily). Changes in working memory (WM) accuracy, reaction time, and sensitivity index were analyzed before and after active and sham rTMS treatment. Resting-state EEG was also acquired to identify potential biological changes that may relate to any cognitive improvement. RESULTS: The results showed that iTBS increased WM accuracy and discrimination ability, and improved reaction time relative to sham iTBS. iTBS also reduced resting-state delta power over the left prefrontal region. This reduction in resting-state delta power correlated with the changes in WM. CONCLUSIONS: Prefrontal iTBS may enhance WM performance in MUD subjects. iTBS induced resting EEG changes raising the possibility that such findings may represent a biological target of iTBS treatment response.

Reward advantage over punishment for incentivizing visual working memory.

The prospects of gaining reward and avoiding punishment widely influence human behavior. Despite of numerous attempts to investigate the influence of motivational signals on working memory (WM), whether the valence and the magnitude of motivational signals interactively influence WM performance remains unclear. To investigate this, the present study used a free-recall working memory task with EEG recording to compare the effect of incentive valence (reward or punishment), as well as the magnitude of incentives on visual WM. Behavioral results revealed that the presence of incentive signals improved WM precision when compared with no-incentive condition, and compared with punishing cues, rewarding cues led to greater facilitation in WM precision, as well as confidence ratings afterward. Moreover, event related potential (ERP) results suggested that compared with punishment, reward led to an earlier latency of late positive component (LPC), a larger amplitude of contingent negative variation (CNV) during the expectation period, and a larger P300 amplitude during the sample and delay periods. Furthermore, reward advantage over punishment in behavioral and neural results were correlated, such that individuals with larger CNV difference between reward and punishment conditions also report greater distinction in confidence ratings between the two conditions. In sum, our results demonstrate what and how rewarding cues cause more beneficial effects than punishing cues when incentivizing visual WM.

Decoding semantics from intermodulation responses in frequency-tagged stereotactic EEG.

BACKGROUND: Humans perform object recognition using holistic processing, which is different from computers. Intermodulation responses in the steady-state visual evoked potential (SSVEP) of scalp electroencephalography (EEG) have recently been used as an objective label for holistic processing. NEW METHOD: Using stereotactic EEG (sEEG) to record SSVEP directly from inside of the brain, we aimed to decode Chinese characters from non-characters with activation from multiple brain areas including occipital, parietal, temporal, and frontal cortices. RESULTS: Semantic categories could be decoded from responses at the intermodulation frequency with high accuracy (80%-90%), but not the base frequency. Moreover, semantic categories could be decoded with activation from multiple areas including temporal, parietal, and frontal areas. COMPARISON WITH EXISTING METHOD(S): Previous studies investigated holistic processing in faces and words with frequency-tagged scalp EEGs. The current study extended the results to stereotactic EEG signals directly recorded from the brain. CONCLUSIONS: The human brain applies holistic processing in recognizing objects like Chinese characters. Our findings could be extended to an add-on feature in the existing SSVEP BCI speller.

Intermittent Theta-Burst Stimulation Increases the Working Memory Capacity of Methamphetamine Addicts.

The present study aimed to explore the effect of intermittent theta-burst stimulation (iTBS) on visual working memory for people suffering from methamphetamine use disorder (MUD). Five sessions of iTBS were carried over the left dorsolateral prefrontal cortex (DLPFC) or the vertex as a sham control, with each session in one day. Orientation free-recall tasks were conducted before the iTBS stimulation, after the first and fifth sessions of stimulation. Results showed that when compared with the sham group, a single session of iTBS over the left DLPFC improved participants' working memory performance. Specifically, iTBS over the left DLPFC increased the working memory capacity and such effects enlarged with multiple sessions. The present finding suggested that iTBS over DLPFC could be a promising intervention method to enhance the cognitive function of addicts with MUD.

Music-based casual video game training alleviates symptoms of subthreshold depression.

Objectives: In this preregistered study, we investigated the beneficial effects of music-based casual video game training on the depression, anxiety and stress symptoms in a cohort of young individuals with subthreshold depression and the underlying mechanisms. Methods: The study included 56 young individuals (18-26 years of age) with subthreshold or mild depression based on the Beck Depression Inventory-II (BDI-II) scores between 14 and 19. They were randomly assigned into the experimental group (n = 28) or the control group (n = 28). The experimental group underwent music-based casual video game training for 4 weeks. During the same time, the control group participants conducted daily life activities without any intervention. The study participants in the two groups were analyzed using the Depression Anxiety and Stress Scale (DASS-21) during the baseline before the intervention, as well as DASS-21, Positive and negative Affect Scale (PANAS), General Self-efficacy Scale (GSES), and the Emotional Regulation Questionnaire (ERQ) twice a week during the 4 weeks of intervention. Results: The depression, anxiety, and stress symptoms were significantly reduced in the experimental group participants after 4 weeks of music-based video game training compared with the control group. The DAS scores in the experimental group were alleviated in the third and fourth weeks of training compared with the control group. Moreover, analysis using the general linear model demonstrated that the number of training weeks and self-efficacy were associated with significant reduction in depression, anxiety and stress. Furthermore, our results demonstrated that self-efficacy was correlated with positive emotion and emotional regulation. Conclusion: Our study showed that music-based casual video game training significantly decreased depression, anxiety, and stress in the young individuals with subthreshold depression by enhancing self-efficacy.

Mnemonic attention in analogy to perceptual attention: harmony but not uniformity.

It has been found that a spatial cue in perception causes benefits through target facilitation at low external noise but noise reduction at high external noise. Assuming that mnemonic attention is similar to perceptual attention, we propose that how a spatial retro-cue is used depends on internal noise. To test this hypothesis, we manipulated internal noise with memory load. We focused on questioning whether/why there was a difference between peripheral and central retro-cues at low or high internal noise. In Experiments 1 and 2, we consistently found that peripheral retro-cues were more effective than central retro-cues at low internal noise. Results from Experiments 3-5 showed that this difference was due to a voluntary process of target facilitation, which happened much earlier on peripheral than central retro-cue trials. These findings are consistent with the hypothesis and indicated that mnemonic attention and perceptual attention could be incorporated into one framework. Nevertheless, spatial retro-cues, including peripheral ones, relied on voluntary control to become effective, different from peripheral cues in perception. To conclude, our findings suggest that the effects of spatial cues on memory and perception are similar but not identical.

Sensory Recruitment Revisited: Ipsilateral V1 Involved in Visual Working Memory.

The "sensory recruitment hypothesis" posits an essential role of sensory cortices in working memory, beyond the well-accepted frontoparietal areas. Yet, this hypothesis has recently been challenged. In the present study, participants performed a delayed orientation recall task while high-spatial-resolution 3 T functional magnetic resonance imaging (fMRI) signals were measured in posterior cortices. A multivariate inverted encoding model approach was used to decode remembered orientations based on blood oxygen level-dependent fMRI signals from visual cortices during the delay period. We found that not only did activity in the contralateral primary visual cortex (V1) retain high-fidelity representations of the visual stimuli, but activity in the ipsilateral V1 also contained such orientation tuning. Moreover, although the encoded tuning was faded in the contralateral V1 during the late delay period, tuning information in the ipsilateral V1 remained sustained. Furthermore, the ipsilateral representation was presented in secondary visual cortex (V2) as well, but not in other higher-level visual areas. These results thus supported the sensory recruitment hypothesis and extended it to the ipsilateral sensory areas, which indicated the distributed involvement of visual areas in visual working memory.

Atypically larger variability of resource allocation accounts for visual working memory deficits in schizophrenia.

Working memory (WM) deficits have been widely documented in schizophrenia (SZ), and almost all existing studies attributed the deficits to decreased capacity as compared to healthy control (HC) subjects. Recent developments in WM research suggest that other components, such as precision, also mediate behavioral performance. It remains unclear how different WM components jointly contribute to deficits in schizophrenia. We measured the performance of 60 SZ (31 females) and 61 HC (29 females) in a classical delay-estimation visual working memory (VWM) task and evaluated several influential computational models proposed in basic science of VWM to disentangle the effect of various memory components. We show that the model assuming variable precision (VP) across items and trials is the best model to explain the performance of both groups. According to the VP model, SZ exhibited abnormally larger variability of allocating memory resources rather than resources or capacity per se. Finally, individual differences in the resource allocation variability predicted variation of symptom severity in SZ, highlighting its functional relevance to schizophrenic pathology. This finding was further verified using distinct visual features and subject cohorts. These results provide an alternative view instead of the widely accepted decreased-capacity theory and highlight the key role of elevated resource allocation variability in generating atypical VWM behavior in schizophrenia. Our findings also shed new light on the utility of Bayesian observer models to characterize mechanisms of mental deficits in clinical neuroscience.

Cognitive Enhancement of Repetitive Transcranial Magnetic Stimulation in Patients With Mild Cognitive Impairment and Early Alzheimer's Disease: A Systematic Review and Meta-Analysis.

Repetitive transcranial magnetic stimulation (rTMS), a non-invasive brain stimulation technique, has been considered as a potentially effective treatment for the cognitive impairment in patients with mild cognitive impairment (MCI) and Alzheimer's Disease (AD). However, the effectiveness of this therapy is still under debate due to the variety of rTMS parameters and individual differences including distinctive stages of AD in the previous studies. The current meta-analysis is aiming to assess the cognitive enhancement of rTMS treatment on patients of MCI and early AD. Three datasets (PubMed, Web of Science and CKNI) were searched with relative terms and finally twelve studies with 438 participants (231 in the rTMS group and 207 in the control group) in thirteen randomized, double-blind and controlled trials were included. Random effects analysis revealed that rTMS stimulation significantly introduced cognitive benefits in patients of MCI and early AD compared with the control group (mean effect size, 1.17; 95% CI, 0.76 - 1.57). Most settings of rTMS parameters (frequency, session number, stimulation site number) significantly enhanced global cognitive function, and the results revealed that protocols with 10 Hz repetition frequency and DLPFC as the stimulation site for 20 sessions can already be able to produce cognitive improvement. The cognitive enhancement of rTMS could last for one month after the end of treatment and patients with MCI were likely to benefit more from the rTMS stimulation. Our meta-analysis added important evidence to the cognitive enhancement of rTMS in patients with MCI and early AD and discussed potential underlying mechanisms about the effect induced by rTMS.