5-Min Science: The Autonomic Effects of Infraslow Frequency Neurofeedback

Balt and colleagues (2020) investigated the effects of infraslow frequency (ISF) neurofeedback on autonomic nervous system (ANS) regulation in adults with anxiety. Infraslow frequency (ISF) neurofeedback is a neurofeedback technique that targets extremely low brainwave frequencies, typically below 0.1 Hz, to influence autonomic nervous system (ANS) regulation and promote mental and physical calm. ISF neurofeedback uses real-time feedback on infraslow oscillations to help clients achieve states of relaxation and emotional regulation by gradually guiding them toward these low-frequency brainwave states.

Infraslow Frequency Neurofeedback

Their hypothesis was that ISF neurofeedback could influence ANS function, as measured by various peripheral biofeedback metrics, including heart rate variability (HRV), electromyography (EMG), skin conductance, skin temperature, blood pressure, and respiration rate. These physiological markers were selected for their roles in reflecting changes in ANS activity, specifically within the sympathetic and parasympathetic nervous systems.

Participants

The study involved 30 adults aged 18–55 with reported symptoms of anxiety, memory and concentration issues, sleep difficulties, and challenges in emotional regulation. Anxiety was the primary symptom among participants, making them suitable candidates to test ISF neurofeedback's effects on ANS function. The inclusion criteria required participants to have high anxiety levels and the ability to attend at least ten sessions over a 5-week period. Exclusion criteria included the use of benzodiazepines, recreational drugs, or any new medication that might affect physiological metrics.

Method

The participants were randomized into an experimental group (20 participants) receiving ISF neurofeedback and a control group (9 participants) receiving sensorimotor rhythm (SMR) neurofeedback. ISF neurofeedback targets very low brainwave frequencies (below 0.1 Hz), which are hypothesized to help regulate ANS functions such as blood pressure, heart rate, and the stress response. In contrast, SMR neurofeedback focuses on higher frequency brainwaves associated with calm focus.

Both groups participated in ten 30-minute neurofeedback sessions. The ISF group underwent neurofeedback sessions guided by real-time feedback on infraslow brainwave frequencies, with adjustments made to optimize relaxation and focus. During these sessions, physiological metrics were continuously monitored with the ProComp Infiniti biofeedback system, a device capable of recording and displaying real-time biofeedback on multiple channels (including muscle activity, skin temperature, and heart rate variability) without participants' conscious awareness of these measurements.

The authors monitored blood pressure, electromyography (EMG), heart rate variability (very-low-frequency and low-frequency percentage power, respiration rate, skin conductance, and skin temperature.

The ISF group's neurofeedback protocol used visual and auditory cues to guide participants toward optimized infraslow brainwave states, hypothesized to reduce anxiety by promoting parasympathetic dominance. The control group received SMR training, focusing on different brainwave frequencies to serve as a comparison without targeting infraslow frequencies.

Results

The ISF group showed significant improvements in several biofeedback measures compared to the control group. Systolic blood pressure significantly decreased (p = .049), and diastolic blood pressure approached significance (p = .083). EMG decreased (p = 0.01). Low-frequency power increased (p = .004), which the decrease in very-low-frequency power approached significance (p = .05). Skin conductance decreased (p < .0001).

Implications

The study's findings suggest that ISF neurofeedback can influence autonomic nervous system activity, helping individuals with anxiety reduce physiological arousal and improve autonomic regulation. These results imply that ISF neurofeedback may be a valuable intervention for anxiety management, offering a non-pharmacological option that directly targets the ANS. Future studies with larger sample sizes and blinded designs could further validate ISF neurofeedback’s potential to modulate autonomic functions and aid in anxiety reduction.

Perspective

The Balt and colleagues study addressed an important question: Does their ISF protocol reduce sympathetic arousal in patients diagnosed with anxiety. They deserve credit for their extensive psychophysiological monitoring. A critical analysis raises cautions regarding the absence of a manipulation check, failure to report effect sizes, failure to report controls for violating statistical assumptions, and their statistical conclusions.

Manipulation Check

The authors did not demonstrate that the ISF and SMR protocols produced the intended EEG changes. Assigning participants to training sessions does not ensure that they learned to self-regulate. The authors should have compared prebaseline with postbaseline EEG values. Since the authors did not demonstrate that their SMR protocol increased SMR amplitude, they cannot draw conclusions about SMR training's autonomic effects.

Effect Sizes

We cannot evaluate the real-world meaning of their findings using p-values alone. Statistical significance is the lowest bar in inferential statistics because it only means a rare event has occurred.

Caption: “If all else fails, use ‘significant at p > 0.05 level’ and hope no one notices.” (http://xkcd.com/1478/, Randall Munroe, Creative Commons Attribution-NonCommercial 2.5 License).

Although p-values can identify outcomes that are unlikely, they convey nothing about their importance. Statistics like Cohen's d express the treatment effect in standard deviation units.

Controls for Violating Statistical Assumptions

A t-test for independent groups assumes that the variances for the ISF and SMR groups were equal. The unequal sample sizes, 20 and 9, violated this assumption and required statistical correction to reduce the risk of false positives. The authors did not acknowledge this problem or explain how they addressed it.

Statistical Conclusions

The replication crisis literature showed that studies with p-values between .025 and .05 were not replicated. Their findings of a reduction in very-low-frequency power (p = .05) and systolic blood pressure (p < .049) are too statistically likely to be replicated. Their claim of diastolic blood pressure trend (p <.083) suspends the rules and asks the reader to believe that this reduction would have achieved significance with more participants. The term "trend toward significance" lacks a clear statistical definition, making it a subjective judgment that may imply an effect when none is definitively observed. It can lead readers to interpret results as meaningful when they may be due to random variation. Reporting a trend toward significance can create misleading implications about the robustness and reliability of the findings. It is generally more appropriate to report results as they are (i.e., not statistically significant) and avoid implying an effect without sufficient statistical support.

Conclusion

Balt et al. (2020) explored the effects of infraslow frequency (ISF) neurofeedback on autonomic nervous system (ANS) regulation in adults with anxiety, aiming to improve physiological markers like heart rate variability, muscle tension, skin conductance, and blood pressure associated with sympathetic and parasympathetic function. Thirty participants were randomized into ISF neurofeedback and control (sensorimotor rhythm) groups, completing ten sessions each while various ANS markers were monitored. The ISF group showed significant improvements, including reduced systolic blood pressure, muscle tension, and skin conductance, suggesting lower arousal levels and increased parasympathetic activity. While the findings support ISF neurofeedback's potential for anxiety management, limitations in methodological rigor—such as the lack of a manipulation check, effect size reporting, and statistical controls—caution against definitive conclusions.

Glossary

autonomic nervous system (ANS): peripheral nervous system division that controls involuntary physiological functions, split into sympathetic and parasympathetic branches.

electromyography (EMG): measures electrical activity in muscles, where higher readings indicate more muscle action potentials.

galvanic skin response (GSR): a measure of skin electrical conductivity, which changes in response to sweat gland activity. Because sweat secretion is influenced by the autonomic nervous system, specifically the sympathetic branch (which is activated during stress or arousal), GSR provides a useful indicator of emotional and physiological arousal.

heart rate variability (HRV): the variability in heartbeats over time, with different frequency components reflecting baroreceptor, sympathetic, and parasympathetic influences.

infraslow frequency (ISF): EEG frequencies below 0.1 Hz, associated with foundational autonomic processes.

low-frequency (LF) power: an HRV component that reflects baroreceptor and parasympathetic input.

sensorimotor rhythm (SMR): an EEG frequency (12–15 Hz) associated with calm, alert mental states.

skin conductance: the skin’s ability to conduct electricity, influenced by sweating and used as a marker of emotional arousal.

sympathetic arousal: the activation of the sympathetic nervous system (SNS), a part of the autonomic nervous system that prepares the body for rapid, intense physical activity in response to perceived threats or stress, commonly known as the "fight or flight" response. This arousal triggers physiological changes such as an increased heart rate, elevated blood pressure, faster breathing, dilated pupils, and reduced digestive activity.

very-low-frequency (VLF) power: an HRV component believed to reflect vagal withdrawal.

Open Access Article

Balt, K., Du Toit, P., Smith, M., & van Rensburg, C. J. (2020). The effect of infraslow frequency neurofeedback on autonomic nervous system function in adults with anxiety and related diseases. NeuroRegulation, 7(2), 64–74. https://doi.org/10.15540/nr.7.2.64

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Dr. Inna Khazan's BCIA Introduction to biofeedback workshop will be offered in two parts this year.

​Part 1 is entirely virtual, consisting of 20 hours (over 5 days) of live online instruction, home-study materials distributed prior to the live workshop, and written instructions for practical lab work to be completed during the week of the workshop or after its completion. Part 1 fulfills BCIA requirements for introduction to biofeedback didactic. Part 1 will take place on Zoom, November 4 - 8, 2024, 12 - 4pm EDT. Tuition is $1395.

​​Part 2 is optional, and consists of 14 hours (over 2 days) of in-person hands-on practical training using state-of-the-art equipment, designed to help participants be better prepared to start working with clients. Part 2 will take place in Boston on November 11 & 12, 2024, 9am-5pm EDT. Tuition is $395. (Please note that an Introduction to Biofeedback didactic (taken at any previous time, anywhere) is a pre-requisite to the hands-on training).