Effects of daily listening to 6 Hz binaural beats over one month: an event-related potentials study

Abstract

The aim of the present study was to identify cognitive alterations, as indicated by event-related potentials (ERPs), after one month of daily exposure to theta binaural beats (BBs) for 10 minutes. The recruited healthy subjects (n = 60) were equally divided into experimental and control groups. For a month, the experimental group was required to practice BBs listening daily, while the control group did not. ERPs were assessed at three separate visits over a span of one month, with a two-week interval between each visit. At each visit, ERPs were measured before and after listening. The auditory and visual ERPs significantly increased the auditory and visual P300 amplitudes consistently at each visit. BBs enhanced the auditory N200 amplitude consistently across all visits, but the visual N200 amplitude increased only at the second and third visits. Compared to the healthy controls, daily exposure to BBs for two weeks resulted in increased auditory P300 amplitude. Additionally, four weeks of BBs exposure not only increased auditory P300 amplitude but also reduced P300 latency. These preliminary findings suggest that listening to BBs at 6 Hz for 10 minutes daily may enhance certain aspects of cognitive function. However, further research is needed to confirm these effects and to understand the underlying mechanisms. Identifying the optimal duration and practice of listening to 6 Hz BBs could potentially contribute to cognitive enhancement strategies in healthy individuals.

Introduction

Listening to binaural beats (BBs) refers to dichotic listening to two nearly identical pure tones with different frequencies¹ and it is commonly known as a brainwave entrainment technique that modifies brainwaves to the same frequency as the beat^2–4, which can influence psychomotor performance and emotions⁵. When sinusoidal 250 Hz and 256 Hz pure tones are simultaneously presented to the left and right ears, the brain perceives an amplitude variation with a frequency rate of 6 Hz, which corresponds to theta activity (4–8 Hz). According to previous research, theta activity is associated with the behavioral states of vigilance, attention, working memory, cognitive enhancement, perceptual skills, and emotional regulation^6–9. There is a correlation between heightened theta power in the frontomedial region and the monitoring of task-related activities and cognitive control. These cognitive processes are known to play a role in sustaining attention^10–12. Furthermore, individuals with attention deficit hyperactivity disorder (ADHD) traits exhibit diminished theta activity^13,14, and theta waves are more prevalent in experienced meditators, indicating a state of profound relaxation during meditation^15,16. A previous study has reported that after 10 minutes of listening to 6 Hz BBs, the mid-frequency of theta activity is entrained in all cortical regions; however, exposures lasting longer than 10 minutes do not increase theta activity³. Other research has revealed an important connection between theta brainwave activity and focused attention^7,17,18. These results suggest that theta brainwaves induced by BBs may also be associated with cognitive function. Related studies have used theta stimuli, such as transcranial alternating current stimulation (tACS), to administer electrical stimulation simultaneously at a frequency of 6 Hz to the left prefrontal and parietal cortices, demonstrating that induced frontoparietal theta synchronization leads to a significant improvement in response time (RT) for visual memory-matching tasks¹⁹.

Cognitive function can be evaluated using event-related potentials (ERPs). An ERP is a quantifiable indicator of the electrical activity occurring on the surface of the brain, specifically reflecting a unique stage of cortical information processing. The process of elicitation can be performed by using an experimental oddball paradigm, in which people are shown a series of two different kinds of stimuli. One type of stimulus is presented in a regular manner, while the other is displayed intermittently and can be triggered by auditory, visual, olfactory, or somatosensory stimuli. N200 and P300 are observed when a rare stimulus is presented after 200 ms and 300 ms, respectively, following the presentation of the stimulus. These two ERP components hold significant relevance in the assessment of stimulus evaluation, selective attention, and conscious discrimination in humans^20,21. Higher-education individuals exhibit faster reaction times, greater amplitudes, and shorter latencies of the N200 and P300 ERPs components²². N200 latency is influenced by the discrimination and classification of stimuli²³, and amplitude has a strong correlation with frontal midline theta power²⁴. P300 is a culturally and educationally neutral electrophysiological measure of cognitive activity^25,26, and it is more sensitive to changes in cognition than conventional neuropsychological tests due to its great temporal resolution²⁷. The P300 amplitude is lower in patients with mild cognitive impairment, Alzheimer’s disease, subclinical hypothyroidism, and clinical depression than in healthy individuals^27–31. The P300 decrease in depressed patients is in line with their stated attentional and cognitive problems, which are included in the diagnostic standards for the condition.

Most studies support that neural entrainment and the frequency-following response (FFR) process are the main ways in which BBs are perceived, helping the two sides of the brain work together and communicate with each other due to the difficulty in perceiving BBs^2–4. The variations in electroencephalography (EEG) research may be due to studies using various stimulus and control conditions, as well as the different effects of BBs on cognitive processes. Several studies have reported that listening to BBs has a beneficial impact on several cognitive functions. Specifically, it has been found to improve episodic memory³², working memory^33,34, long-term memory³⁵, as well as reducing anxiety and promoting relaxation³⁶. Nevertheless, certain studies have found no discernible effect of BBs exposure on cognitive fluency³⁷ and have even seen a detrimental impact on short-term memory³⁸. Thus, further investigation is required to gain a more comprehensive understanding of the neurological processes that occur within the brain after exposure to BBs for a period of time. According to previous research, theta activity is a sign of concentration, concentrated attention, and a contemplative state. During meditation, there are generally theta rhythms in the frontal midline area^39,40. Because 6 Hz BBs have been observed in the frontal midline theta at 10 minutes after listening³, 6 Hz BBs may increase cognitive function, which can be determined by measuring ERPs. Here, the aim of the present study was to determine the cognitive impact of long-term exposure to 6 Hz BBs, as indicated by ERPs. We hypothesized that 4 weeks of daily listening to 6 Hz BBs would lead to ERP changes, increased cognitive function, and decreased RT to the target, with participants expressing more efficiency relative to the control. The present findings may reveal a novel variable leading to the success of brain entrainment applications.

Results

The present study included 60 participants, with a mean age of $26.22\pm 5.02$ years and 100% right-handedness. Participants were randomly assigned to the experimental or control group. The experimental group consisted of 30 individuals with an average age of $25.23\pm 5.46$ years, and there were 22 females and 8 males. The control group consisted of 30 individuals with an average age of $27.2\pm 4.8$ years, and there were 21 females and 9 males. The ages of the participants in the experimental and control groups did not significantly differ, suggesting that their auditory and visual ERPs may be comparable. The experimental group consisted of 18 individuals (60%) who had completed a bachelor’s degree and 12 individuals (40%) who were currently pursuing a bachelor’s degree. The education level of the control group consisted of 19 individuals (63.33%) with bachelor’s degrees and 11 individuals (36.67%) with undergraduate degrees. All experimental participants confirmed that they listened to the 6 Hz BBs every day, and this was verified through their logbook records. The ERPs were obtained from 60 participants using auditory and visual stimuli. The ERPs of the participants were calculated, and the results are presented as the mean and standard deviation (SD) in the experimental and control groups. In addition, the ERP parameters of the two groups at baseline (first visit and before the session) were compared using a permutation t-test, revealing no significant differences (p > 0.05) (Table 1).

Table 1.

The ERP parameters of the experimental and control groups showed a mean ± standard deviation

Visit	ERP results		Before 10 minutes				After 10 minutes
			Experimental group	Control group	t	p	Experimental group	Control group	t	p
1st	Auditory stimuli
	N200	Latency (ms)	198.21 ± 43.68	194.51 ± 39.14	0.346	0.731	201.43 ± 39.82	193.61 ± 45.78	0.706	0.483
		Amplitude ($\mu$V)	6.86 ± 2.36	8.0 ± 3.16	$-$1.588	0.118	8.77 ± 3.58	7.95 ± 2.63	1.024	0.31
	P300	Latency (ms)	375.05 ± 62.38	389.85 ± 34.36	$-$1.139	0.259	368.76 ± 59.34	380.06 ± 36.67	$-$0.888	0.378
		Amplitude ($\mu$V)	12.82 ± 4.06	14.64 ± 5.6	$-$1.435	0.157	14.99 ± 5.12	14.65 ± 4.7	0.267	0.79
	Visual stimuli
	N200	Latency (ms)	267.48 ± 61.09	255.41 ± 64.74	0.743	0.461	265.49 ± 47.14	273.29 ± 55.36	$-$0.588	0.559
		Amplitude ($\mu$V)	5.18 ± 2.27	6.04 ± 3.18	$-$1.203	0.234	5.72 ± 2.74	6.75 ± 3.36	$-$ 1.304	0.197
	P300	Latency (ms)	408.2 ± 28.77	409.79 ± 32.52	$-$0.2	0.842	410.03 ± 26.7	403.06 ± 37.76	0.825	0.413
		Amplitude ($\mu$V)	11.67 ± 3.79	14.32 ± 6.27	$-$ 1.982	0.052	13.48 ± 4.06	14.95 ± 7.06	$-$0.988	0.327
2 nd	Auditory stimuli
	N200	Latency (ms)	208.04 ± 51.57	190.56 ± 52.61	1.3	0.199	188.29 ± 27.39	197.14 ± 59.74	$-$0.737	0.464
		Amplitude ($\mu$V)	7.2 ± 2.04	7.19 ± 2.43	0.014	0.989	8.7 ± 2.49	7.77 ± 2.95	1.323	0.191
	P300	Latency (ms)	389.99 ± 39.81	392.73 ± 32.72	$-$0.292	0.771	384.73 ± 37.62	398.18 ± 41.25	$-$ 1.319	0.192
		Amplitude ($\mu$V)	13.35 ± 4.1	12.65 ± 5.08	0.587	0.56	16.49 ± 4.34	13.57 ± 5.1	2.389	0.02*
	Visual stimuli
	N200	Latency (ms)	277.4 ± 57.21	255.36 ± 60.37	1.452	0.152	254.69 ± 62.21	263.63 ± 65.5	$-$0.542	0.59
		Amplitude ($\mu$V)	5.26 ± 2.34	6.32 ± 2.66	$-$1.629	0.109	6.79 ± 2.55	5.59 ± 3.11	1.634	0.108
	P300	Latency (ms)	420.08 ± 41.51	400.82 ± 35.19	1.938	0.058	417.24 ± 32.86	412.53 ± 27.02	0.607	0.546
		Amplitude ($\mu$V)	12.35 ± 4.07	14.23 ± 3.33	$-$ 1.96	0.055	14.9 ± 4.39	13.01 ± 4.29	1.682	0.098
3 rd	Auditory stimuli
	N200	Latency (ms)	203.65 ± 38.96	190.62 ± 48.38	1.148	0.256	196.35 ± 37.06	190.36 ± 51.42	0.518	0.607
		Amplitude ($\mu$V)	7.35 ± 2.92	7.86 ± 2.65	$-$ 0.708	0.482	8.82 ± 3.41	7.5 ± 2.55	1.7	0.095
	P300	Latency (ms)	377.12 ± 35.32	390.62 ± 44.83	$-$1.296	0.2	364.32 ± 50.99	394.27 ± 45.76	$-$2.394	0.02*
		Amplitude ($\mu$V)	14.49 ± 5.61	14.18 ± 4.24	0.242	0.81	16.68 ± 5.32	13.68 ± 5.18	2.216	0.031*
	Visual stimuli
	N200	Latency (ms)	276.17 ± 51.68	276.43 ± 59.44	$-$ 0.018	0.986	262.89 ± 54.43	264.06 ± 64.44	$-$0.076	0.94
		Amplitude ($\mu$V)	6.02 ± 2.24	6.18 ± 3.06	-0.23	0.819	7.74 ± 3.02	7.15 ± 3.21	0.731	0.468
	P300	Latency (ms)	415.36 ± 35.56	401.69 ± 45.87	1.29	0.202	413.41 ± 30.05	402.86 ± 40.73	1.141	0.258
		Amplitude ($\mu$V)	13.23 ± 4.63	13.73 ± 6.01	$-$ 0.361	0.72	16.59 ± 5.64	14.82 ± 5.93	1.188	0.24

The results were compared using a permutation-based t-test and showed significant differences between the two groups labelled “*” ($p<0.05$)

Comparison of auditory ERPs before and after listening to a 6 Hz BB stimulus

For comparison of auditory ERPs, the experimental group listened to 10 minutes of BBs, and the control group rested. The results were collected before and after 10 minutes, and the data are presented as the means and standard deviations in the graphs in Fig. 1. N200 and P300 latency and amplitude were compared before and after each group. In the experimental group, after each auditory ERP measurement, the amplitudes of N200 and P300 significantly increased. Specifically, the latency of N200 significantly decreased only at the second visit, while there was a decreasing trend in the latencies of both N200 and P300 at the third visit, but it was not statistically significant. In the control group, the N200 and P300 amplitudes did not significantly differ between baseline and after 10 minutes.

Figure 1.

Changes in latency and amplitude of auditory ERPs (P300 and N200) shown as means and 95% confidence intervals before and after 10 minutes of listening to 6 Hz BBs. The P300 and N200 latency and amplitude parameters are presented for both the experimental and control groups. Changes in amplitude from the baseline ERPs in the experimental group were determined using paired t-tests (* indicates $p<0.05$). Comparisons of ERP parameters between groups were made using permutation-based t-tests (** indicates $p<0.05$).

Comparison of visual ERPs before and after listening to a 6 Hz BB stimulus

For comparison of visual ERPs, the experimental group listened to 10 minutes of BBs, and the control group rested. The results were collected before and after 10 minutes, and the data are presented as the means and standard deviations in the graphs in Fig. 2. Following each visual ERP measurement, the P300 amplitudes increased significantly in the experimental group, and the N200 amplitude increased in the second and third sessions in the experimental group. However, there was no significant difference in the N200 or P300 latencies between baseline and after 10 minutes of response in the experimental group. In the control group, the N200 and P300 amplitudes did not significantly differ between baseline and after 10 minutes.

Figure 2.

Changes in latency and amplitude of visual ERPs (P300 and N200) shown as means and 95% confidence intervals before and after 10 minutes of listening to 6 Hz BBs. The P300 and N200 latency and amplitude parameters are presented for both the experimental and control groups. Changes in amplitude from the baseline ERPs in the experimental group were determined using paired t-tests (* indicates $p<0.05$). No significant differences in ERP parameters between groups were found using permutation-based t-tests.

Comparison of auditory and visual ERPs between the experimental and control groups

Between the two groups, there was no significant difference in the latency or amplitude of the auditory P300 component before testing at any visit. After the 10-minute test, there was a significant difference between the two groups in the amplitude of the P300 component at the second and third visits. At the third visit, there was a significant difference only in the P300 latency between groups, with a shorter latency in the experimental group ($p<0.05$), as depicted in Table 1. For the visual P300 component, there was no significant difference when comparing latency and amplitude before testing at each visit and after the same response as before ($p>0.05$), as depicted in Table 1. For the N200 component, there was no significant difference between groups for either auditory or visual stimuli.

Response time and accuracy in Auditory and Visual stimuli

For the experimental group, the baseline RTs were 0.398 ± 0.057 s for auditory stimuli and 0.417 ± 0.029 s for visual stimuli, as shown in Tables 2 and 3, respectively. The RTs tended to decrease, and there was a significant decrease after listening to the 6 Hz BB stimulus only at the last visit for both the auditory and visual ERPs. In the control group, the baseline RTs were 0.382 ± 0.038 and 0.399 ± 0.0031 s for auditory and visual stimuli, respectively, as shown in Tables 2 and 3. The results did not show a significant difference before and after resting for 10 minutes in either the auditory or visual ERPs. The RT was compared between the experimental group and the control group. After 10 minutes, the RT in to auditory stimuli in the experimental group was significantly lower than that of the control group at the second and third visits. There were no significant changes in visual stimuli.

Table 2.

Response time to auditory stimuli

Groups		Experimental		Control
Values		Response time (s)	Response accuracy (%)	Response time (s)	Response accuracy (%)
1st visit	Before	0.398 ± 0.057	99.5 ± 1.526	0.382 ± 0.038	99.286 ± 2.955
	After	0.386 ± 0.053	99.667 ± 1.269	0.381 ± 0.036	99.286 ± 2.242
2nd visit	Before	0.366 ± 0.043	99.833 ± 0.913	0.387 ± 0.049	98.929 ± 2.841
	After	0.369 ± 0.045**	100.0 ± 0.0	0.397 ± 0.055	99.821 ± 0.945
3rd visit	Before	0.373 ± 0.036	100.0 ± 0.0	0.384 ± 0.061	99.464 ± 1.575
	After	0.361 ± 0.031*,**	100.0 ± 0.0	0.394 ± 0.071	99.464 ± 1.575

The asterisk “*” in the table indicates a significant difference before and after 10 minutes. The response times of the experimental and control groups in each visit were compared using a permutation-based t-test and showed significant differences between the two groups labeled “**” ($p<0.05$).

Table 3.

Response time to visual stimuli.

Groups		Experimental		Control
Values		Response time (s)	Response accuracy (%)	Response time (s)	Response accuracy (%)
1st visit	Before	0.417 ± 0.029	99.0 ± 4.026	0.399 ± 0.031	99.833 ± 0.913
	After	0.42 ± 0.035	100.0 ± 0.0	0.405 ± 0.04	100.0 ± 0.0
2nd visit	Before	0.412 ± 0.033	99.0 ± 4.026	0.406 ± 0.043	99.667 ± 1.269
	After	0.405 ± 0.031	99.833 ± 0.913	0.412 ± 0.041	99.5 ± 1.526
3rd visit	Before	0.412 ± 0.034	99.167 ± 2.306	0.403 ± 0.045	100.0 ± 0.0
	After	0.4 ± 0.033*	99.833 ± 0.913	0.396 ± 0.05	99.167 ± 3.733

The asterisk "*" in the table indicates a significant difference before and after 10 minutes (p < 0.05).

Discussion

The present study demonstrated that the effect of listening to a 6 Hz BB stimulus before the task increased the auditory and visual P300 amplitudes at every visit. Listening to the BBs also increased the auditory N200 amplitude at all visits, but the visual N200 amplitude increased only at the second and third visits. There was no statistically significant difference in latency after listening to the BBs. The results also suggested that daily practice listening to BBs for 2 and 4 weeks enhanced the auditory P300 amplitude compared to that of healthy controls. However, only 4 weeks of listening to the BBs shortened the P300 latency.

Short- and long-term listening to a 6 Hz BB stimulus may differentially alter cognitive function in the brain. A previous study has revealed that listening to a short 10 minutes of 6 Hz BBs entrains the brain to produce frontal midline theta oscillations³. This theta brainwave, a sign of concentration and attention during the contemplative state^39,40, is highly correlated with N200 and P300 amplitudes in the same region of the brain^24,41. Based on the present findings and previous evidence, listening to 6 Hz BBs within a short period of time may increase concentration and attention during cognitive performance, resulting in increased N200 and P300 amplitudes. The neural source of these signals is generated by the anterior cingulate cortex⁴², which is also used to track the level of difficulty in the task, reflecting cognitive effort^43,44. Hence, short-term listening to 6 Hz BBs before performing a task may help increase attention and concentration levels.

After long-term exposure to 6 Hz BBs, the results showed a shorter auditory P300 latency compared to the control group after listening. The delay in P300 latency is associated with potential impairment in cognitive processing, as the activation of this response involves cortical regions responsible for auditory memory, attention, perception, and cognitive mechanisms^31,45. Thus, the results showed a shorter auditory P300 latency after one month of exposure to BBs, indicating that consistent practice in listening is important to receive the full benefits of BBs.

RT is the time required for an individual to respond to auditory or visual stimuli, and the RT in the present study was calculated as the time required to press a keyboard after receiving a stimulus. Motor and cognitive processing speeds, as well as movement time, response accuracy, and impulsivity, can influence the RT⁴⁶. A previous study has suggested that a respondent’s delayed response may indicate either sluggish processing speed or meticulousness. A respondent may react promptly and accurately due to a fortunate guess or take more time to answer accurately, but the respondent may respond rapidly with the right motivation. Incorrect responses may result from a lack of knowledge, insufficient time for information processing, or confusion leading to the abandonment of the answer⁴⁶. Listening to BBs also affects RT discrepancies. A previous study has compared the effects of listening to 10, 16, and 40 Hz BBs for 8 minutes on RT, revealing that low-frequency BB listening, especially at 10 Hz, significantly decreases RT (faster response) compared to the prelistening condition and other BB frequencies⁴⁷. Consistently, the present study demonstrated that the RTs to auditory and visual stimulation decreased significantly in the experimental group after the participants listened daily to the 6 Hz BB stimulus for 1 month, and the RTs were significantly faster in the experimental group than in the control group. In addition to a 6 Hz BB stimulus improving cognitive performance, the present findings suggested that a 6 Hz BB stimulus also increases cognitive processing speed, resulting in a shorter RT.

The effect of listening to 6 Hz BBs can change after practicing for a period of time. A previous study has revealed that daily listening to BBs for 1 month significantly improves HRV compared to listening for 10 minutes for the first time and even daily listening for 2 weeks³⁶. Listening to BBs can achieve better effects after practicing, and meditation in the short- and long-term can alter cognitive function differently^48,49. Based on the present findings, daily listening to a 6 Hz BB stimulus for 1 month amplifies the effect of 10 minutes of listening, as indicated by the increased visual and auditory P300 and N200 amplitudes. In addition, the latency of the experimental group was shorter than that of the control group at the third visit, suggesting that long-term BB listening increases the motor response to auditory stimuli in the oddball paradigm. Therefore, these findings suggested that 1 month of daily practice listening to BBs may further amplify the brain entrainment capability of short-term listening to 10 minutes of BBs.

Although the visual and auditory components of the ERPs have similarities in terms of cognitive processes, they have significant differences in generating sensory modalities. The findings from the first visit indicated a difference between auditory and visual N200 amplitudes. The auditory N200 amplitude increased due to listening to 6 Hz BBs, but no significant difference was detected in the visual N200 amplitude. Because 6 Hz BBs entrain the brain via the sensory modality, less impact on the visual response can be expected. As a result of the effect of long-term listening, the second and third visits of the present experiment showed a significant increase in both auditory and visual N200 amplitudes. These findings may explain the effects of long-term 6 Hz BB listening on cognitive function improvement.

The present study explored the potential connections among 6 Hz BBs and cognitive reactions in healthy subjects. Initial findings suggest that inexperienced listeners might experience enhanced cognitive performance after their first exposure to the stimuli. Additionally, the impact of 6 Hz BBs during stimulus exposure appears to improve with daily practice over a period of 2–4 weeks. This observation provides preliminary insights into the time frame required to potentially experience the beneficial effects of listening to a 6 Hz BB stimulus. Initially, the impact of the 6 Hz BB stimulus on the auditory ERPs did not differ significantly from that in the control group during the initial listening session. However, after 2 weeks of daily listening, some improvement was observed, with further enhancements being significant after 4 weeks, as indicated by a decrease in RT. These results tentatively suggest that daily exposure to 6 Hz BBs for 4 weeks may lead to quicker reactions, implying a potential enhancement in cognitive function.

Limitations and future directions

The limitations of this study should be acknowledged. Despite our efforts to emphasize the importance of daily listening to the 6 Hz BB stimulus for at least 10 minutes and verifying their logbooks, we lacked a direct method to monitor or enforce compliance outside the laboratory. Future studies could benefit from using digital monitoring tools, such as mobile apps, to track listening duration and frequency, ensuring adherence to the at-home stimulation protocol. To better understand the combined effects of at-home listening and ERP sessions, future research should consider including an additional control group that only receives 10-minute BBs listening during each ERP session to clarify the short-term effects of BBs on cognitive function. Additionally, studies should investigate the impact of other EEG activities on the frontal and occipital areas. While this study focused on comparing theta BBs to a no-stimulation condition, future research could build on these findings by including additional control groups that receive placebo auditory stimulation. This would help refine our understanding of how specific frequencies and types of auditory stimuli impact brain activity and cognitive function. These steps would provide a more comprehensive understanding of the specific cognitive and neural mechanisms influenced by BB exposures, as well as the temporal dynamics of these effects.

Methods

Participants

Participants were recruited through campuses and online advertisements at a local college. All participants were required to submit a written agreement and informed consent prior to trial participation. Participants were between the ages of 18 and 40, free of oropharyngeal infection, and devoid of any somatic, neurological, or mental illness. In addition, the volunteers did not consume psychoactive medicines, such as antidepressants or anticonvulsants. Over the duration of the study, all participants were fully conscious, able to speak effectively, and able to comprehend any relevant surveys. Since the beginning of the study, participants were provided with an explanation of the study’s objective and procedures. Participants were randomly allocated to either the experimental or control group. The experimental group’s participants received instructions to listen to the BB stimulus at home for a minimum of 10 minutes every day, with self-records in their logbook. Compliance with the logbook procedure was verified during the second and third visits. The study excluded participants whose documented listening sessions did not meet the daily requirement. The control group’s participants did not receive any specific instructions or auditory stimulation, establishing a baseline for comparison with the experimental group exposed to BBs. This design was chosen to isolate the specific effects of the BBs from any potential placebo effects or general auditory stimulation effects. Additionally, an ethical consideration underpinned this decision: providing placebo auditory stimulation for a month was not feasible without a clear understanding of its potential disadvantages to participants.

The binaural beat stimulus

The BB stimulus was created specifically for the experiment by playing two similar tones at slightly different frequencies. The left ear hears the carrier tone at 250 Hz, while the right ear hears a slightly different tone at 256 Hz. On each laboratory visit, the BB stimulus was generated using the MATLAB R2021a application⁵⁰. The loudness was set to 65 dB SPL, and earphones were used for measurement. Participants in the experimental group were given 6 Hz BB files and were instructed to listen to them for at least 10 minutes per day on their mobile devices, using earbuds or headphones, at their comfort level.

ERP recording

ERPs were acquired using the Brain Master Discovery 24E amplifier at a sampling rate of 256 Hz and a 24-bit accuracy with disposable Ag–AgCl electrodes aligned in the vertex (Cz, Vin+) and earlobe (A1, A2, Vin-) and recorded by OpenViBE software⁵¹. In the auditory condition, participants performed the exercise with their eyes closed while wearing earphones and sitting on a comfortable chair in a dimly lit, quiet room. An “oddball” audio paradigm was utilized to elicit ERP components. Standard and target stimulation frequencies corresponded to 1,000 Hz and 2,000 Hz tone bursts, respectively, with 50 and 100 rise and decay times at 60 dB SPL. In the target (oddball) paradigm, stimuli were presented with probabilities of 20%. The frequency of the pulses was 1 Hz, and the number of stimuli was 200⁴⁸. Participants were instructed to close their eyes, not move their eyes, and respond to the target as rapidly as possible by pressing the space bar button with their right index finger. The trial training provided participants with cues to ensure that they understood the task. In the visual condition, ERPs were induced by a center-field presentation (15 mm in height and 20 mm in breadth) of ’X’ (target) and ’O’ (standard), observed from a distance of 130 cm, and lasting 70 ms⁵². The participants were required to respond when they observed the target by pressing a space bar button with their right index finger.

Procedures

The trial protocols involving participants in the present study were approved by the Institutional Review Board of Mahidol University with certificate of approval (COA) number 2023/002.0601. We confirm that all research was performed in accordance with the Declaration of Helsinki. Informed consents were obtained from all participants. This investigation aimed to assess cognitive changes over a duration of one month. In accordance with the design, three evaluation visits were planned. The initial visit served as a baseline response. After 2 weeks of daily exposure to the BB stimulus, the second visit occurred. The third visit occurred 4 weeks after the initial visit. Three visits were evaluated with the same methodology. The trial was conducted in a soundproof room with white walls. The temperature of the room was maintained at 25 degrees Celsius, and there was sufficient light to see clearly (300 lux). The theta BB stimulus (6 Hz, 250 Hz carrier frequency) was the condition for the experimental group, while silence served as the condition for the control group. On the first visit, after the research methodology was explained, the auditory and visual ERPs were trained to respond before the test to ensure that the participants understood the task. Then, at each research visit, auditory and visual ERPs were measured before and after the listening session. In this period, the experimental group listens to 6 Hz BBs for 10 minutes by using earphones, and the control group wears silent earphones for 10 minutes. To begin the session, the participants were asked to sit in an ergonomic chair in the most relaxed position possible. After applying a gel skin preparation to improve conductance, gold cup electrodes filled with conductive paste were attached to the vertical (Cz positive electrode) and earlobe (A1, A2 negative electrode) to record the ERPs.

The signal was averaged during the recording process. The cerebral activity signal mean was calculated independently for target and nontarget stimuli. P300 was defined as the largest positive peak between 250 and 450 ms, and N200 was defined as the negative peak between 180 and 325 ms occurring before the P300. Additionally, the response time (RT), the time required for a participant to respond to the auditory or visual stimuli, was recorded.

Statistical analysis

For descriptive and inferential statistics, the Python SciPy statistics library⁵³ was utilized. The mean and standard deviation were used to represent the data, and paired t-test were used to determine statistical significance. These independent comparisons between each group were conducted using the permutation-based t-test⁵⁴ because it is more reliable than its parametric counterparts. Statistical significance was defined as a p value of 0.05.

Author contributions

M.C., T.J., K.L., and Y.W. contributed to the conception and design of the study. M.C., T.J. and Y.W. performed the experiment and statistical analysis. M.C. and Y.W. also wrote the first draft of the manuscript. All authors contributed to manuscript revision and read and approved the submitted version.

Data availibility

The datasets used and analysed during the current study available from the corresponding author on reasonable request.

Competing interests

The authors declare no competing interests.