Coupled Computational Fluid Dynamics-Discrete Element Method Model for Investigation of Powder Effects in Nonconventional Laser Powder Bed Fusion Process.

The present study proposes a comprehensive 3D computational fluid dynamics-discrete element method (CFD-DEM) coupled simulation model to investigate the particle dynamics induced by SS316L metal vapor spouting during single-scan-track laser powder bed fusion (L-PBF) processing. The model provides the ability to examine the effects of nonconventional process variables such as the chamber pressure and gravitational force on the suppression of the spatter and denudation phenomena. The simulation results imply that adjusting the gravitational force provides an effective technique for suppressing both spatter formation and powder bed denudation. In addition, the chamber pressure has only a marginal effect on the denudation phenomenon. In particular, under a higher operating pressure, the metal vapor tends to spout in the upward direction, while under a lower pressure, the spouting is more radially distributed. As a result, the simulation results obtained in this study have suggested that the chamber pressure and gravitational force may both provide feasible approaches for suppressing the spattering and denudation phenomena, particularly in the L-PBF processing of light-weight materials.

The Reindeer Circadian Clock Is Rhythmic and Temperature-compensated But Shows Evidence of Weak Coupling Between the Secondary and Core Molecular Clock Loops.

Circadian rhythms synchronize the internal physiology of animals allowing them to anticipate daily changes in their environment. Arctic habitats may diminish the selective advantages of circadian rhythmicity by relaxing daily rhythmic environmental constraints, presenting a valuable opportunity to study the evolution of circadian rhythms. In reindeer, circadian control of locomotor activity and melatonin release is weak or absent, and the molecular clockwork is reportedly non-functional. Here we present new evidence that the circadian clock in cultured reindeer fibroblasts is rhythmic and temperature-compensated. Compared with mouse fibroblasts, however, reindeer fibroblasts have a short free-running period, and temperature cycles have an atypical impact on clock gene regulation. In reindeer cells, Per2 and Bmal1 reporters show rapid responses to temperature cycles, with a disintegration of their normal antiphasic relationship. The antiphasic Per2-Bmal1 relationship re-emerges immediately after release from temperature cycles, but without complete temperature entrainment and with a marked decline in circadian amplitude. Experiments using Bmal1 promoter reporters with mutated RORE sites showed that a reindeer-like response to temperature cycles can be mimicked in mouse or human cell lines by decoupling Bmal1 reporter activity from ROR/REV-ERB-dependent transcriptional regulation. We suggest that weak coupling between core and secondary circadian feedback loops accounts for the observed behavior of reindeer fibroblasts in vitro. Our findings highlight diversity in how the thermal environment affects the temporal organization of mammals living under different thermoenergetic constraints.

Systemic neurophysiological entrainment to behaviorally relevant rhythmic stimuli.

Physiological oscillations, such as those involved in brain activity, heartbeat, and respiration, display inherent rhythmicity across various timescales. However, adaptive behavior arises from the interaction between these intrinsic rhythms and external environmental cues. In this study, we used multimodal neurophysiological recordings, simultaneously capturing signals from the central and autonomic nervous systems (CNS and ANS), to explore the dynamics of brain and body rhythms in response to rhythmic auditory stimulation across three conditions: baseline (no auditory stimulation), passive auditory processing, and active auditory processing (discrimination task). Our findings demonstrate that active engagement with auditory stimulation synchronizes both CNS and ANS rhythms with the external rhythm, unlike passive and baseline conditions, as evidenced by power spectral density (PSD) and coherence analyses. Importantly, phase angle analysis revealed a consistent alignment across participants between their physiological oscillatory phases at stimulus or response onsets. This alignment was associated with reaction times, suggesting that certain phases of physiological oscillations are spontaneously prioritized across individuals due to their adaptive role in sensorimotor behavior. These results highlight the intricate interplay between CNS and ANS rhythms in optimizing sensorimotor responses to environmental demands, suggesting a potential mechanism of embodied predictive processing.

Entrainment and multi-stability of the p53 oscillator in human cells.

The tumor suppressor p53 responds to cellular stress and activates transcription programs critical for regulating cell fate. DNA damage triggers oscillations in p53 levels with a robust period. Guided by the theory of synchronization and entrainment, we developed a mathematical model and experimental system to test the ability of the p53 oscillator to entrain to external drug pulses of various periods and strengths. We found that the p53 oscillator can be locked and entrained to a wide range of entrainment modes. External periods far from p53's natural oscillations increased the heterogeneity between individual cells whereas stronger inputs reduced it. Single-cell measurements allowed deriving the phase response curves (PRCs) and multiple Arnold tongues of p53. In addition, multi-stability and non-linear behaviors were mathematically predicted and experimentally detected, including mode hopping, period doubling, and chaos. Our work revealed critical dynamical properties of the p53 oscillator and provided insights into understanding and controlling it. A record of this paper's transparent peer review process is included in the supplemental information.

Environmental Light Controls the Daily Organization of Breathing by Activating Brn3b-expressing Intrinsically Photosensitive Retinal Ganglion Cells in Mice.

Rhythmic, daily fluctuations in minute ventilation are controlled by the endogenous circadian clock located in the suprachiasmatic nucleus (SCN). While light serves as a potent synchronizer for the SCN, it also influences physiology and behavior by activating Brn3b-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs). It is currently unclear the extent to which the external light environment shapes daily ventilatory patterns independent of the SCN. To determine the relative influence of environmental light versus circadian timing on the organization of daily rhythms in minute ventilation, we used whole-body plethysmography to measure the breathing of mice housed on a non-entraining T28 cycle (14 h light:14 h dark). Using this protocol, we found that minute ventilation exhibits a ~28-h rhythm with a peak at dark onset that coincides with the light:dark cycle and the animals' locomotor activity. To determine if this 28-h rhythm in minute ventilation was mediated by Brn3b-expressing ipRGCs, we measured the breathing of Brn3bDTA mice housed under the T28 cycle. Brn3bDTA mice lack the Brn3b-expressing ipRGCs that project to many non-SCN brain regions. We found that despite rhythmic light cues occurring on a 28-h basis, Brn3bDTA mice exhibited 24-h rhythms in minute ventilation, locomotor activity, and core body temperature consistent with organization by the SCN. The 24-h minute ventilation rhythm of Brn3bDTA mice was found to be driven predominantly by tidal volume rather than respiratory rate. These data indicate that the external light:dark cycle can directly drive daily patterns in minute ventilation by way of Brn3b-expressing ipRGCs. In addition, these data strongly suggest that the activation of Brn3b-expressing ipRGCs principally organizes daily patterns in breathing and locomotor activity when light:dark cues are presented in opposition to endogenous clock timing.

Association of Fear and Anxiety Scales in Pediatric Dental Patients Using Brainwave Entrainment: A Randomized Controlled Trial.

Background Dental fear and anxiety are significant issues among pediatric patients, often complicating dental treatments. Various tools measure these emotional responses, including subjective scales such as the Visual Facial Anxiety Scale (VFAS) and Children Fear Scale (CFS), and objective scales such as Venham's Anxiety Scale (VAS) and Frankl Behavior Rating Scale (FBRS). This study explores the association between these measures in children subjected to brainwave entrainment (BWE) therapy. This study aimed to evaluate the association between subjective and objective fear and anxiety measures in pediatric dental patients within both the brainwave entrainment (BWE) intervention group and control group. Methods This randomized controlled trial included pediatric participants aged seven to 12 years reporting to the department for dental treatment. Participants were randomized into two following groups: an experimental group receiving BWE therapy and a control group receiving traditional behavioral management. Fear and anxiety levels were measured using subjective and objective scales before and after the intervention. Data were analyzed using Spearman's correlation to examine the associations between these scales, with statistical significance set at p<0.05. Results Post-intervention analysis revealed significant correlations between subjective and objective measures of fear and anxiety in both groups. In the BWE group (N=126), there was a moderate positive correlation between the VFAS and VAS (rho=0.540, p<0.001) and a strong negative correlation between the CFS and FBRS (rho=-0.666, p<0.001). The control group (N=126) showed stronger correlations, rho=0.778 for anxiety scales and rho=-0.817 for fear and behavior scales (p<0.001). Combined data analysis from both groups (N=252) confirmed strong correlations. Conclusion This study found a significant association between subjective and objective measures of fear and anxiety in pediatric dental patients within both the brainwave entrainment (BWE) intervention group and control group. Thereby proving that self-reporting behavioral scales are useful for quickly assessing anxiety in pediatric dental settings.

Determining the debris flow yield strength of weathered soils: a case study of the Miryang debris flow in the Republic of Korea.

Debris flow hazards are often interpreted through back-calculated simulation analysis or empirical methods. The mobility of a debris flow is greatly influenced by mechanical and hydrological parameters. The strength parameters play important roles in the debris flow initiation and flow stages. In particular, the rheological parameters of yield strength and plastic viscosity directly affect the debris flow runout distance and velocity. One of the most important parameters to consider when evaluating debris flow hazards is the shear strength. This strength is called the residual shear strength in the failure stage and the yield strength in the post-failure stage. The residual shear strength obtained from ring shear tests can be related to the initiation of mass movements; the yield strength obtained from rheological tests can be related to the mobilization of debris flows. The residual shear stresses obtained from ring shear tests of weathered soils typically range between 10 and 100 kPa and strongly depend on the normal stress and shear velocity. When progressive slope failure (i.e., strain-softening behavior) occurs at a relatively shallow slope depth (e.g., < 1 m), the soil strength ranges from approximately 5-10 kPa. If the liquid limit state (i.e., solid‒liquid transition) is reached, the shear strength of the soil is approximately 2 kPa. Once the soil fails and mixes with ambient water along the slip surface, the yield strength decreases dramatically, resulting in high mobilization. A suggestion on how strength parameters can be applied to estimate debris flow mobility is presented by considering the 2011 Miryang debris flow, which occurred in weathered soil deposits in Miryang city, Republic of Korea. The best approach for debris flow yield strength estimation would be to consider the residual shear strength in the initiation stage, the yield strength in the flow stage, and the reduction in yield strength with the entrainment effect of the flow in the rapid fluidization stage.

The positive F wave in lead V1 of typical atrial flutter is caused by activation of the right atrial appendage: Insight from mapping during entrainment from the right atrial appendage.

INTRODUCTION: Typical atrial flutter (AFL) is a macroreentrant tachycardia in which intracardiac conduction rotates counterclockwise around the tricuspid annulus. Typical AFL has specific electrocardiographic characteristics, including a negative sawtooth-like wave in the inferior lead and a positive F wave in lead V1. This study aimed to analyze the origin of the positive F wave in lead V1, which has not been completely understood. METHODS: This study enrolled 10 patients who underwent radiofrequency catheter ablation for a typical AFL. Electroanatomical mapping was performed both during typical AFL and entrainment from the right atrial appendage (RAA). The 12-lead electrocardiogram (ECG) and three-dimensional (3D) electroanatomical maps were analyzed. RESULTS: The positive F wave in lead V1 changed during entrainment from the RAA in all the cases. The 3D map during entrainment from the RAA revealed an area of antidromic capture around the RAA, which collided with the orthodromic wave in the anterior right atrium. This area of antidromic capture around the RAA was the only difference from the 3D electroanatomical map of AFL and is considered the cause of the change in the F wave in lead V1 during entrainment. CONCLUSION: The analysis of the differences in the 12-lead ECG and 3D maps between tachycardia and entrainment from the RAA clearly demonstrated that activation around the RAA is responsible for the generation of the positive F wave in lead V1 of typical AFL.

Sensorimotor Synchronization and Neural Entrainment to Imagined Rhythms in Individuals With Proficient Imagery Ability.

Sensorimotor synchronization (SMS) is the temporal coordination of motor movements with external or imagined stimuli. Finger-tapping studies indicate better SMS performance with auditory or tactile stimuli compared to visual. However, SMS with a visual rhythm can be improved by enriching stimulus properties (e.g., spatiotemporal content) or individual differences (e.g., one's vividness of auditory imagery). We previously showed that higher self-reported vividness of auditory imagery led to more consistent synchronization-continuation performance when participants continued without a guiding visual rhythm. Here, we examined the contribution of imagery to the SMS performance of proficient imagers, including an auditory or visual distractor task during the continuation phase. While the visual distractor task had minimal effect, SMS consistency was significantly worse when the auditory distractor task was present. Our electroencephalography analysis revealed beat-related neural entrainment, only when the visual or auditory distractor tasks were present. During continuation with the auditory distractor task, the neural entrainment showed an occipital electrode distribution, suggesting the involvement of visual imagery. Unique to SMS continuation with the auditory distractor task, we found neural and sub-vocal (measured with electromyography) entrainment at the three-beat pattern frequency. In this most difficult condition, proficient imagers employed both beat- and pattern-related imagery strategies. However, this combination was insufficient to restore SMS consistency to that observed with visual or no distractor task. Our results suggest that proficient imagers effectively utilized beat-related imagery in one modality when imagery in another modality was limited.

Dance of two brains: Interval subdivision in alternated condition enhances resistance to interference by others.

The accomplishment of interpersonal sensorimotor synchronization is a challenging endeavor because it requires the achievement of a balance between accurate temporal control within individuals and smooth communication between them. This raises a critical question: How does the brain comprehend and process the perceptual information of others to guarantee accurate temporal control of action goals in a social context? A joint synchronization - continuation tapping task was conducted together with varying relative phases (0°/180°) and intervals of tempos (400 ms/800 ms/1600 ms) while neural data was collected using fNIRS (functional near-infrared spectroscopy). Individuals showed better behavioral performance and greater interpersonal brain synchronization(IBS) in the left dorsolateral prefrontal cortex at alternated condition (180° relative phase) compared to symmetric condition (0° relative phase), suggesting that the individual can better maintain behavioral performance and show improved IBS when the partner taps between the individual's gaps. Meanwhile, in most levels of alternated condition, IBS is inversely proportional to interference from partner, implying the counteraction of IBS against interference from others. In addition, when the interval of tempo was 1600 ms, behavioral performance showed a sharp decline, accompanied by a decrease in IBS, reflecting that IBS in SMS reflects effective information exchange between individuals rather than ineffective interference with each other. This study provides insight into the mechanisms underlying sensorimotor synchronization between individuals.

Entrainment echoes in the cerebellum.

Evidence accumulates that the cerebellum's role in the brain is not restricted to motor functions. Rather, cerebellar activity seems to be crucial for a variety of tasks that rely on precise event timing and prediction. Due to its complex structure and importance in communication, human speech requires a particularly precise and predictive coordination of neural processes to be successfully comprehended. Recent studies proposed that the cerebellum is indeed a major contributor to speech processing, but how this contribution is achieved mechanistically remains poorly understood. The current study aimed to reveal a mechanism underlying cortico-cerebellar coordination and demonstrate its speech-specificity. In a reanalysis of magnetoencephalography data, we found that activity in the cerebellum aligned to rhythmic sequences of noise-vocoded speech, irrespective of its intelligibility. We then tested whether these "entrained" responses persist, and how they interact with other brain regions, when a rhythmic stimulus stopped and temporal predictions had to be updated. We found that only intelligible speech produced sustained rhythmic responses in the cerebellum. During this "entrainment echo," but not during rhythmic speech itself, cerebellar activity was coupled with that in the left inferior frontal gyrus, and specifically at rates corresponding to the preceding stimulus rhythm. This finding represents evidence for specific cerebellum-driven temporal predictions in speech processing and their relay to cortical regions.

Echoes from Sensory Entrainment in Auditory Working Memory for Pitch.

Ongoing neural oscillations reflect cycles of excitation and inhibition in local neural populations, with individual neurons being more or less likely to fire depending upon the oscillatory phase. As a result, the oscillations could determine whether or not a sound is perceived and/or whether its neural representation enters into later processing stages. While empirical support for this idea has come from sound detection studies, large gaps in knowledge still exist regarding memory for sound events. In the current study, it was investigated how sensory entrainment impacts the fidelity of working memory representations for pitch. In two separate experiments, an 8 Hz amplitude modulated (AM) entraining stimulus was presented prior to a multitone complex having an f0 between 270 and 715 Hz. This "target" sound could be presented at phases from 0 to 2π radians in relation to the previous AM. After a retention interval of 4 s (Experiment 1; n = 26) or 2 s (Experiment 2; n = 28), listeners were tasked to reproduce the target sound's pitch by moving their finger along the horizontal axis of a response pad. It was hypothesized that if entrainment modulates auditory working memory fidelity, reproductions of a target's pitch would be more accurate and precise when targets were presented in phase with the entrainment. Cosine fits of the average data for both experiments showed a significant entrainment "echo" in the accuracy of pitch matches. There was no apparent echo in the matching precision. Fitting of the individual data accuracy showed that the optimal phase was consistent across individuals, aligning near the next AM peak had the AM continued. The results show that sensory entrainment modulates auditory working memory in addition to stimulus detection, consistent with the proposal that ongoing neural oscillatory activity modulates higher-order auditory processes.

Rethinking fish-friendliness of pumps by shifting focus to both safe and timely fish passage for effective conservation.

Globally, catadromous freshwater eels of the genus Anguilla are of conservation concern, including critically endangered European eel (Anguilla anguilla). Pumping stations that move river water to a higher elevation severely impact eels during their seaward spawning migration. Fish-friendly pumps can mitigate fish injury and mortality but here we uniquely rethink a fish-friendly pump as a fish passage solution. In this pluriannual study, the seasonal timing of pump operation was misaligned with the typical silver eel migration period. Eels were almost exclusively nocturnal but night-time pumping represented as little as 5.6% a year. Night-time eel approaches were primarily influenced by pump duration and temperature, but did not align with lunar phase, unlike in unregulated rivers. After reaching the pumping station, eel passage was influenced by weedscreen aperture and increased when the aperture was increased. Passive sensor collision suggested non-pump infrastructure could cause injury and mortality to eels. It is therefore recommended pump operation should align with the timing of silver eel migration, weedscreen and pump entrance efficiencies should be maximised, and non-pump infrastructure must have low fish injury risk. Ultimately, considering the entire structure a fish passage solution will help ensure fish-friendly pumps have high conservation value for anguillid eels globally.

Frequency-Selective Suppression of Essential Tremor via Transcutaneous Spinal Cord Stimulation.

BACKGROUND: Essential tremor (ET) is a common debilitating condition, yet current treatments often fail to provide satisfactory relief. Transcutaneous spinal cord electrical stimulation (tSCS) has emerged as a potential noninvasive neuromodulation technique capable of disrupting the oscillatory activity underlying tremors. OBJECTIVE: This study aimed to investigate the potential of tSCS to disrupt tremor in a frequency-dependent manner in a cohort of patients with ET. METHODS: Eighteen patients with ET completed the study. The experiment consisted of 60-s postural tremor recording, during tSCS at tremor frequency, at 1 Hz, at 21 Hz, no stimulation, and trapezius stimulation. Tremor frequency and amplitude were analyzed and compared across the conditions. RESULTS: We found tremor amplitude reduction at tremor frequency stimulation significant only during the second half of the stimulation. The same stimulation resulted in the highest number of responders. tSCS at 1 Hz showed a trend toward decreased tremor amplitude in the latter half of stimulation. tSCS at 21 Hz did not produce any significant alterations in tremor, whereas trapezius stimulation exacerbated it. Notably, during tremor frequency stimulation, a subgroup of responders exhibited consistent synchronization between tremor phase and delivered stimulation, indicating tremor entrainment. CONCLUSIONS: Cervical tSCS holds promise for alleviating postural tremor in patients with ET when delivered at the subject's tremor frequency. The observed changes in tremor amplitude likely result from the modulation of spinal cord circuits by tSCS, which disrupts the oscillatory drive to muscles by affecting afferent pathways or spinal reflexes. However, the possibility of an interplay between spinal and supraspinal centers cannot be discounted. © 2024 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Readjustment of circadian clocks by exercise intervention is a potential therapeutic target for sleep disorders: a narrative review.

PURPOSE: Circadian clocks are evolved endogenous biological systems that communicate with environmental cues to optimize physiological processes, such as the sleep-wake cycle, which is nearly related to quality of life. Sleep disorders can be treated using pharmacological strategies targeting melatonin, orexin, or core clock genes. Exercise has been widely explored as a behavioral treatment because it challenges homeostasis in the human body and affects the regulation of core clock genes. Exercise intervention at the appropriate time of the day can induce a phase shift in internal clocks. Although exercise is a strong external time cue for resetting the circadian clock, exercise therapy for sleep disorders remains poorly understood. METHODS: This review focused on exercise as a potential treatment for sleep disorders by tuning the internal circadian clock. We used scientific paper depositories, including Google Scholar, PubMed, and the Cochrane Library, to identify previous studies that investigated the effects of exercise on circadian clocks and sleep disorders. RESULTS: The exercise-induced adjustment of the circadian clock phase depended on exercise timing and individual chronotypes. Adjustment of circadian clocks through scheduled morning exercises can be appropriately prescribed for individuals with delayed sleep phase disorders. Individuals with advanced sleep phase disorders can synchronize their internal clocks with their living environment by performing evening exercises. Exercise-induced physiological responses are affected by age, sex, and current fitness conditions. CONCLUSION: Personalized approaches are necessary when implementing exercise interventions for sleep disorders.

Effects of External Pacing Type on the Cross-Education of Motor Skill.

Cross-education (CE) is a phenomenon whereby motor training of one limb leads to improved performance in the opposite untrained limb. External pacing of a motor task can enhance CE; however, the influence of different pacing methods is poorly understood. This study explored how motor training with auditory (AP) and visual pacing (VP) impacts CE with a visuomotor force target task. Sixty-one participants performed a unimanual motor task. Participants were randomized into a visual (n = 31) or auditory (n = 30) pacing stimuli condition. The primary outcome was cumulative error scores for each hand, before and after visuomotor training. Pacing type did not yield different magnitudes of CE. However, after adjusting for baseline differences, a significant hand (trained vs. untrained) × practice side (dominant or non-dominant) interaction (p = .013, ηp2 = .106) and a group main effect (p = .036, ηp2 = .165) were observed. Visual pacing resulted in greater improvements in task performance compared to auditory pacing regardless of hand or practice side, while training the dominant limb resulting in a greater interlimb asymmetry regardless of pacing stimulus. These findings have implications for applying pacing strategies during rehabilitation from unilateral injury or neurological impairment.

One-HIIT wonder: Can music make high-intensity interval training more pleasant?

The use of music as an aid to recovery during and after exercise is an area of growing scientific interest. We investigated the effects of in-task, asynchronous music and respite-active music (i.e., music used for active recovery in between high-intensity exercise bouts) on a range of psychological, psychophysical and psychophysiological outcomes. Participants (N = 28; 14 females) made five laboratory visits for: (a) pre-test/familiarisation; (b) fast-tempo music during supramaximal exercise bouts and medium-tempo music during active-recovery periods; (c) fast-tempo music during exercise and no music during recovery; (d) no music during exercise and medium-tempo music during recovery; and (e) a no-music (throughout) control. A cycle ergometer-based HIIT protocol comprising 6 × 60-s bouts at 100% Wmax with 75-s active recovery was administered. Measures were taken at the end of supramaximal bouts and active recovery periods (RPE, state attention, core affect, state motivation), then upon cessation of the protocol (remembered pleasure and exercise enjoyment). Heart rate and heart rate variability (HRV) measures were taken throughout. The music manipulations only had an effect on state motivation, which was higher (p = 0.036) in the fast tempo-medium tempo condition compared to no-music control (Cohen's d = 0.49), and the SDNN component of HRV, which was lower (p = 0.007) in the fast-tempo-no-music condition compared to control (Cohen's d = 0.32). Collectively, the present findings do not support any of the study hypotheses regarding the music-related manipulations, and do not concur with the findings of related studies (e.g., Karageorghis et al., 2021). The unexpected results are discussed with reference to extant theory, and recommendations are offered in regard to music-related applications.

Development of full-body rhythmic synchronization in middle childhood.

Rhythmic entrainment is a fundamental aspect of musical behavior, but the skills required to accurately synchronize movement to the beat seem to develop over many years. Motion capture studies of corporeal synchronization have shown immature abilities to lock in to the beat in children before age 5, and reliable synchronization ability in adults without musical training; yet there is a lack of data on full-body synchronization skills between early childhood and adulthood. To document typical rhythmic synchronization during middle childhood, we used a wireless motion capture device to measure period- and phase-locking of full body movement to rhythm and metronome stimuli in 6 to 11 year-old children in comparison with adult data. Results show a gradual improvement with age; however children's performance did not reach adult levels by age 12, suggesting that these skills continue to develop during adolescence. Our results suggest that in the absence of specific music training, full-body rhythmic entrainment skills improve gradually during middle childhood, and provide metrics for examining the continued maturation of these skills during adolescence.

Optimal gamma-band entrainment of visual cortex.

Visual entrainment is a powerful and widely used research tool to study visual information processing in the brain. While many entrainment studies have focused on frequencies around 14-16 Hz, there is renewed interest in understanding visual entrainment at higher frequencies (e.g., gamma-band entrainment). Notably, recent groundbreaking studies have demonstrated that gamma-band visual entrainment at 40 Hz may have therapeutic effects in the context of Alzheimer's disease (AD) by stimulating specific neural ensembles, which utilize GABAergic signaling. Despite such promising findings, few studies have investigated the optimal parameters for gamma-band visual entrainment. Herein, we examined whether visual stimulation at 32, 40, or 48 Hz produces optimal visual entrainment responses using high-density magnetoencephalography (MEG). Our results indicated strong entrainment responses localizing to the primary visual cortex in each condition. Entrainment responses were stronger for 32 and 40 Hz relative to 48 Hz, indicating more robust synchronization of neural ensembles at these lower gamma-band frequencies. In addition, 32 and 40 Hz entrainment responses showed typical patterns of habituation across trials, but this effect was absent for 48 Hz. Finally, connectivity between visual cortex and parietal and prefrontal cortices tended to be strongest for 40 relative to 32 and 48 Hz entrainment. These results suggest that neural ensembles in the visual cortex may resonate at around 32 and 40 Hz and thus entrain more readily to photic stimulation at these frequencies. Emerging AD therapies, which have focused on 40 Hz entrainment to date, may be more effective at lower relative to higher gamma frequencies, although additional work in clinical populations is needed to confirm these findings. PRACTITIONER POINTS: Gamma-band visual entrainment has emerged as a therapeutic approach for eliminating amyloid in Alzheimer's disease, but its optimal parameters are unknown. We found stronger entrainment at 32 and 40 Hz compared to 48 Hz, suggesting neural ensembles prefer to resonate around these relatively lower gamma-band frequencies. These findings may inform the development and refinement of innovative AD therapies and the study of GABAergic visual cortical functions.