PLoS One. 2016 Nov 28;11(11):e0166630. doi: 10.1371/journal.pone.0166630.

The Effect of Binaural Beats on Visuospatial Working Memory and Cortical Connectivity.

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Supplementary Information

Figure 1: The frontoparietal network

Various complex cognitive processes, such as memory, rely on simultaneous activation of multiple brain regions. However, these large-scale interactions between behavior and brain activity can be difficult to quantify. As a result, it is essential to understand the properties of the connectivity network linking areas of the brain together. In this work, we focus on working memory which is the system in control of temporary retention and online organization of thoughts for successful goal directed behavior [1]. Individuals typically exhibit a small capacity limit on the number of items that can be simultaneously retained in working memory.  Specifically, we target visuospatial working memory which maintains what and where an object is. Increased communication, or neural synchrony, in the frontoparietal network, shown in Figure 1, is particularly important for boosting performance on a task. To modify network connections and thereby augment working memory capacity, a non-invasive brain stimulation technique called binaural beats can be used. Binaural beats take advantage of the brain’s response to two pure tones, delivered independently to each ear, when those tones have a small frequency mismatch. The mismatch between the tones is interpreted as a beat frequency, which may act to synchronize cortical oscillations at salient frequencies.

 

 

This research seeks to answer the question of whether binaural beats can be used to successfully augment working memory. Before this research, only a few studies had investigated the effects of binaural beats on working memory and no studies had evaluated the effects of binaural beats on brain connectivity during working memory tasks. In this study, we determined the effects of different acoustic stimulation conditions on participant response accuracy and brain connectivity, as measured by electroencephalography (EEG) recordings, during a delayed-match-to-sample visuospatial working memory task. Three acoustic stimulation control conditions and three binaural beats stimulation conditions were used: None, Pure Tone, Classical Music, 5Hz binaural beats, 10Hz binaural beats, and 15Hz binaural beats. Each condition was played for 5 minutes and during that time the participants responded to the task 40 times.

 

To assess the behavioral changes, the change in accuracy (Δ Accuracy), over the 5 minutes was computed. A 3% increase in Δ Accuracy was found in participants who listened to the 15Hz binaural beats. During all other conditions (None, Pure Tone, Classical, 5Hz binaural beats, and 10Hz binaural beats), the Δ Accuracy decreased by 1% – 3%. This increase in performance of the working memory task can be potentially explained by noting that 15Hz binaural beats falls within the beta band which is typically associated with active concentration.

 

To assess the changes in brain connectivity, we used graph theory approaches to compare properties of connectivity networks built with EEG. The graphical networks are comprised of nodes, the EEG channels, and edge weights, computed as Phase Locking Value (PLV) between pairs of EEG channels [2]. PLV measures the phase coherence between two signals. Figure 2 shows three examples of how PLV can change with increasing frequency difference between the two signals.

 

The overarching goal was to link the changes observed in the networks to the changes in the behavior. During the 15Hz binaural beats condition, the overall network connection strengths were stronger than the other conditions. This consistent network strength likely reflects the participants’ ability to remember and compare the visuospatial patterns. In addition, to understand the overall interactions between regions, average connections were computed for clusters of electrodes. Figure 3 shows the regional connections strengths for each condition when normalized with respect to the None condition. Again, the 15Hz binaural beats produced the network with the only increase in connection strength between the frontal (F) and parietal (P) regions. Even though other conditions produced increased strength between other regions, the literature tells us that the primary indication of working memory performance is the frontal to parietal connection. Therefore, a 15Hz binaural beats can be used to successfully augment working memory performance and cortical connectivity.

 

 

Figure 2: PLV values for four examples of sinusoidal oscillators

 

 

Figure 3: Regional connections strengths thresholded against the None condition. Red indicates an increase in connection strength while blue represents a weaker connection. The width of the lines indicates the strength of the change. The regions are denoted Frontal (F), Temporal (T), Parietal (P) and Occipital (O).

 

 

References

[1] A. D. Baddeley and G. J. Hitch, “Working memory,” The Psychology of Learning and Motivation, vol. 8, pp. 47–89, 1974.
[2] J.-P. Lachaux, E. Rodriguez, J. Martinerie, F. J. Varela, et al., “Measuring phase synchrony in brain signals,” Human Brain Mapping, vol. 8, no. 4, pp. 194–208, 1999.