A natural stimulus for entraining brain oscillations in Alzheimer's disease therapy: Canary song

Abstract

Background The potential therapeutic effects of 40Hz gamma stimulation in Alzheimer's Disease (AD) has recently been under study (Suk et al. Alzheimer’s and Dementia 2020; Adaikkan et al., Trends in Neuroscience 2020; Sedghizadeh et al. Alzheimer’s and Dementia 2020). While measuring the gamma power as a marker for brain entrainment is well established in the literature, some studies have focused on theta‐gamma coupling (TGC) (Etter, Guillaume, et al., Nature Communications 2019; Munia & Aviyente, Scientific Reports 2019) as TGC is known to play a critical role in working/spatial memory tasks. Synthetic 40Hz amplitude‐modulated auditory chirp sounds have been used to entrain gamma oscillations. As a natural alternative, we propose the canary song, which is innate, pleasant, and includes diverse modulating sounds with chirp frequencies up to 20Hz. Since harmonic components are present in entrained response of the brain (Jones et al., Journal of Alzheimer's Disease 2019) albeit at lower powers, entrainment with the 20Hz canary chirp song can be a substitute for the commonly used synthetic 40Hz sounds. Method We observed the entrainment characteristics for the complete course of a canary’s singing as well as for selective 20Hz chirp segments of the song on eight young adults with simultaneous EEG recording. We measured the power spectrum and TGC strength during the stimulus and rest intervals on selective independent components (IC) of the recorded response. Result Canary song’s 20Hz chirp increases the theta band and 20Hz oscillation activity. During the stimuli intervals, ICs were found in the response close to the midbrain area that were entrained by the 20Hz stimuli while also showing high power in the theta band. TGC with high values around 40 Hz was also observed during the 20 Hz chirp intervals. Conclusion Employing natural sounds for AD therapy campaigns offers a more pleasant and serene alternative to artificial sounds. We selected segments of canary’s natural song which can produce entrainment effects similar to those of the synthetic 40Hz auditory tones commonly used for brain entrainment. Other natural sounds such as those of cricket and woodpecker can also be good candidates for entraining the brain in AD therapy.