Introduction

This article describes how binaural beats can be an effective and non-invasive technique for controlling anxiety and promoting memory. The article being reviewed is titled Auditory Beat Stimulation Modulates Memory-Related Single-Neuron Activity in the Human Medial Temporal Lobe. The researchers who performed this study discuss two different beat patterns, monaural and binaural. Monaural beats are when the same frequency enters both ears simultaneously, while binaural beats are a slightly different frequency in each ear (Chaieb, et al., 2017). In different ways, these two beat patterns will stimulate the neurons in the superior olivary complex, which is a structure in the brain stem that processes the frequency of sound waves that enter the ears (Garcia-Argibay et al., 2019). In this study, the researchers investigated the effects of monaural and binaural (5Hz difference between ears) beat stimulation on neural activity and memory performance in patients who were undergoing neurosurgery. The researchers observed a significant effect of binaural beat stimulation on firing rates in a number of neurons within the medial temporal lobe. The conclusion of this finding is that beat stimulation is linked to memory performance by shifting baseline firing levels, as seen in the patient’s improvement in recall tasks (Derner et al., 2021). This finding is consistent with other studies, along with findings of improvement in cognitive function, anxiety, and mood (Sharpe et al., 2020). However, it is not fully understood how auditory beat stimulation is able to cause such a shift in mood and cognitive function. 

Background

While the process of hearing starts outside the brain, the mechanism being targeted by auditory beat stimulation takes place in the medulla oblongata, which is the lowest part of the brain stem (Olivary Body, 2019). This is where the sound intensity and localization is processed by a brain structure called the superior olivary complex, composed of the lateral superior olive and the medial superior olive (Glackin et al., 2010) The sound waves enter the cochlea and are organized by frequency, sent to the cochlear nucleus via the auditory nerve. In the medulla, the lateral superior olive detects the differences in amplitude and the medial superior olive detects timing differences between ears. This process can happen very quickly because of specialized synapses in the medial nucleus of the trapezoid body. This information gets sent to the upper part of the brainstem called the inferior colliculus and then to the medial geniculate nucleus of the thalamus. For cognitive processing, the information is transmitted to the primary auditory cortex in the temporal lobe (Dumper, et al., n.d.) It is the understanding of this mechanism that allows researchers and manufacturers to make auditory devices such as 3D headphones and speakers that give the illusion of monaural and binaural beats to the listener (Milind, K., 2021).
 

Methods

The participants of this study were 15 humans, 5 of which were undergoing neurosurgery already for seizures. The patients who were already undergoing surgery had microwires implanted in the amygdala, hippocampus, entorhinal cortex and parahippocampal cortex. These wires measure action potentials, which are small changes in electrical current inside the cells (Henley, 2021). The researchers were able to track neuronal activity through these wires while the patients were asked to perform a memory task. This task including an encoding (making new memories) phase where they were given 50 German nouns presented with a colored patch or image of nature. They were to indicate if the noun and image presented were plausible as a unit. For the retrieval (usage of already formed memories) phase, the same 50 nouns were presented with 25 new nouns. The patient was to indicate if a word was a new or old word. Across the six experimental runs of each phase, the auditory beat stimuli or control tones were presented to the patients. The stimulation conditions were binaural beats at 217.5 Hz in one ear and 222.5 Hz in the other, monaural beats with the combination of both frequencies in both ears simultaneously, and a control tone of 220 Hz, no beats (Derner et al., 2021).

Results

The results of this study were that binaural and monaural beat stimulation had opposite effects on memory performance. The binaural beats enhanced the patient’s ability to recall memories, while the monaural beats impaired the same ability. In this study, the only significant findings were in the retrieval phase of the study, not the encoding phase. In the retrieval phase the researchers observed a significant stimulation on the firing rates the neurons of the medial temporal lobe, a part of the brain that receives auditory information for processing. A larger portion of neurons responded to the stimulation of monaural and binaural beats in the left side of the brain, which was also found to be the case in a similar study (Jirakittayakorn et al., 2017) In the neurons that were responsive to the beat stimulation, a significant correlation between firing rate differences and memory retrieval were noted. The conclusion of the study was that beat stimulation is linked to memory performance by shifting the baseline firing levels in the neurons, not necessarily introducing memory-related firing rate changes. 

Conclusion

The importance of studies such as this one come from the premise that non-invasive interventions for conditions such as anxiety and ADHD are effective options for patients (Claesdotter-Hybbinette et al., 2016) Additionally, studies such as this one help further understanding of the processes in fine neuroanatomy, which could assist in accurate diagnosis of hearing related problems. Other studies have shown that binaural temporal processing is impacted by age and negatively impacts the neural encoding and perception of these binaural temporal cues even in individuals with clinically normal hearing sensitivity (Koerner et al., 2020). The potential for non-invasive treatment and more accurate diagnosis of debilitating conditions is enough reason to pursue future research of the benefits and uses of auditory beat stimulation.

[+] References

[+] Other Work By Abigail O'Niel