Isochronic tones are regular beats of a single tone that are used alongside monaural beats and binaural beats in the process called brainwave entrainment. At its simplest level, an isochronic tone is a tone that is being turned on and off rapidly. They create sharp, distinctive pulses of sound.
Brainwave entrainment does not have a long-term effect on the patterns of neural impulses. That is, very soon after the external stimulus stops, the brainwaves return to their normal state.
In 2008, clinical neurologist Steven Novella published an article on brainwave entrainment, claiming 'A number of companies and individuals have then extrapolated from the phenomenon of entrainment to claim that altering the brain waves changes the actual functioning of the brain. There is no theoretical or empirical basis for this.' However, Novella is a renowned skeptic who founded The Skeptics' Guide to the Universe in 2005, along with numerous other professional ventures to promote scientific skepticism.
In direct contradiction to Novella's claim, more than twenty-one independent peer-reviewed, placebo-controlled studies have been conducted between 1979 and 2012 which show a range of cognitive-behavioral benefits achieved through the practice of temporarily altering brain waves, including: cognitive enhancement after 6 weeks of gamma brain wave stimulation; improvement in academic achievement after beta brain wave stimulation; increase in alpha brain wave strength measured by EEG during meditation; substantial reduction in anxiety and corresponding increase in relaxation after theta brain wave stimulation; and reduction of headache pain, reduction of anxiety, and improved sleep after delta brain wave stimulation. These temporary benefits may be sustained over the long term by incorporating routine practice of audio-visual entrainment technologies and mindfulness meditation. Audio-visual entrainment (AVE) refers to the use of flashes of lights and pulses of tones to purposefully guide the brain into various states of brain wave activity. By stimulating the brain with flashing LED lights built into special eye glasses and pulsing auditory tones (isochronic tones) transmitted through headphones within a frequency range of about 0.5 to 25 Hertz, it is possible to shift the frequency of the dominant brain waves either higher or lower and thereby change brain function. A 2001 study by Le Scouarnec RP, et al., found 'monaural beats can produce brainwave entrainment inasmuch as they are in beat form before striking the ear drum, which impacts the thalamus, and therefore the cortex. EEG studies of monaural beats have conclusively shown that monaural beats produce a frequency following response in the contralateral hemisphere of the brain, and are therefore quite useful for entrainment.'
Although the AVE mechanism is not fully understood, it is thought that the auditory and visual elements of the stimulation modulate endogenous brain activity by activating retinal cells in the eyes and pressure sensitive cilia within the cochlea of the ears. The evoked electrical potential is then transmitted via neural pathways (audio signals via the medial geniculate; visual signals via the lateral geniculate) to the thalamus where audio and visual sensory information is processed. From the thalamus, the entrained electrical activity is propagated through the cortical thalamic loop to the rest of the limbic system and cerebral cortex.
The use of isochronic tones as the audio component of AVE has been found to assist with relaxation, meditation, stress relief, the management of anxiety, and improved cognition and focus in individuals who have been diagnosed with attention deficit hyperactivity disorder (ADHD), panic attacks, post traumatic stress disorder (PTSD), bipolar disorder and schizophrenia.
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