Furthermore, no study to date has fully characterized binaural beats throughout the auditory pathway (from subcortical responses to functional connectivity) and compared their effect to that of a non-binaural rhythmic control (i.e., monaural beats, created by digitally summing each tone before presentation). The reported cognitive modulations, however, appear inconsistent and seem to depend on several mediating factors, such as frequency of stimulation, differing exposure time and stimuli masking ( Garcia-Argibay et al., 2019a). The cognitive effects of binaural beats are attributed to their capacity to drive neural oscillations at the beat frequency through differential hemispheric synchronization frequencies. They also seem to modulate mood ( Wahbeh et al., 2007), pain perception ( Zampi, 2015), and cognitive performance in memory tasks ( Kennerly, 1994). Binaural beats can entrain cortical activity at both the specific frequency of the beat ( Pratt et al., 2010) and cross-frequency modulations, such as θ beats driving interhemispheric α synchronization ( Solcà et al., 2016). This “illusory” third tone is lateralized between the left and right ear of the listener, making binaural beats useful for spatial sound research ( Ross et al., 2014). These beats are thought to originate subcortically in the medial nucleus of the superior olivary complex, the first nucleus in the auditory pathway to receive bilateral input ( Wernick and Starr, 1968 Kuwada et al., 1979). Presenting two tones with a slight frequency mismatch to each ear separately creates a perception of a third tone, a binaural beat, that oscillates at the absolute difference between the tones ( Oster, 1973 Moore, 2012).
The possibility of binaural beats modulating cognitive states without prior training makes them an interesting candidate for cost-effective applications in both healthy and impaired populations. Claims range from entraining the whole brain ( Atwater, 2004 Rhodes, 1993), to altering states of consciousness (I-Doser, accessed May 2018 Atwater, 1997). Binaural beats, an auditory illusion that occurs when presenting two similar pure tones to each ear separately, have been purported to induce mood alterations, contingent on the beat frequency. Be it in social gatherings or late study nights, we use audio stimuli to set the “right mood” and improve our cognitive performance ( Mammarella et al., 2007 Schellenberg et al., 2007 Tarr et al., 2014). Humans use music and rhythm as mood enhancers. Whether binaural beats have an impact on cognitive performance or other mood measurements remains to be seen and can be further investigated within the proposed methodological framework. Our results provide evidence that binaural beats elicit cross frequency connectivity patterns, but weakly entrain the cortex when compared with monaural beat stimuli.
Despite this, we did not find any mood modulation related to our experimental manipulation.
Furthermore, functional connectivity patterns were modulated differentially by both kinds of stimuli, with binaural beats being the only one eliciting cross-frequency activity. Both stimuli elicited standard subcortical responses at the pure tone frequencies of the stimulus, and entrained the cortex at the beat frequency. To do so, we compared the effects of binaural beats with a control beat stimulation (monaural beats, known to entrain brain activity but not mood) across four distinct levels in the human auditory pathway: subcortical and cortical entrainment, scalp-level functional connectivity and self-reports. Here, we sought to address those questions in a robust fashion using a single-blind, active-controlled protocol. Several controversial claims have been attributed to binaural beats regarding their ability to entrain human brain activity and mood, in both the scientific literature and the marketing realm. Binaural beating is a perceptual auditory illusion occurring when presenting two neighboring frequencies to each ear separately.
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