Binaural beats may influence functions of the brain in ways besides those related to hearing. A study of aphasic subjects who had a severe stroke versus normal subjects showed that the aphasic subject could not hear the binaural beats whereas the normal subjects could. Tracking temporal modulations additionally activated predominantly right prefrontal, anterior cingulate, and intraparietal regions as well as posterior cerebellar hemispheres. Within the cerebellum, vermal regions and anterior hemispheres ipsilateral to the movement became significantly activated. Activated regions include primary sensorimotor and cingulate areas bilateral opercular premotor areas bilateral SII ventral prefrontal cortex and, subcortically, anterior insula, putamen, and thalamus. Regarding entrainment, the study of rhythmicity provides insights into the understanding of temporal information processing in the human brain - auditory rhythms rapidly entrain motor responses into stable steady synchronisation states, both below and above conscious perception thresholds. The sensation of binaural beats is believed to originate in the superior olivary nucleus, a part of the brainstem and appear to be related to the brain's ability to locate the sources of sounds in three dimensions and to track moving sounds, which also involves inferior colliculus (IC) neurons. The binaural beat is perceived as a fluctuating rhythm at the frequency of the difference between the two auditory inputs. The difference between the signals waxes and wanes as the two stereo sounds mesh in and out of phase. A ‘perceptual integration’ of the two signals is perceived in the brain, producing the sensation of a third ‘beat’ – at the desired frequency for a particular form of brainwave entrainment. The brain processes this anomalous information differently when these phase differences are heard with stereo headphones or speakers. Simply put then, when signals of two different frequencies (sounds) are presented, one to each ear, the brain detects phase differences between these signals. The difference between the two frequencies must be small (less than or equal to 30 Hz) for the effect to occur - otherwise, the two tones will be heard separately and no beat will be perceived by the listener. The frequencies of the tones must be below 1,000 hertz for the beating to be noticeable. A beating tone will be perceived, as if the two tones mixed naturally, out of the brain. The brain produces a phenomenon resulting in low-frequency pulsations in the amplitude and sound localisation of a perceived sound when two tones at slightly different frequencies are presented separately - one to each of a subject's ears - using stereo headphones. The effect on the brainwaves depends on the difference in frequencies of each tone, for example, if 300 Hz was played in one ear and 310 in the other, then the binaural beat would have a frequency of 10 Hz. This effect was discovered in 1839 by Prussian physicist and meteorologist, Heinrich Wilhelm Dove, and garnered greater public awareness in the late 20th century based on claims that binaural beats may help induce relaxation, meditation, creativity and other desirable mental states. Binaural beats or binaural tones are auditory processing artifacts (or apparent sounds), the perception of which arises in the brain for specific physical stimuli.
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