What is Delta?
Delta (1-4 Hz) is the slowest frequency and highest amplitude brain wave of the five major brain wave categories. It is known as a global processing mode that synchronizes activity across far away brain areas. This is in contrast to the short local calculations offered by higher frequencies such as Beta or Gamma.
Evolutionarily, Delta is the oldest frequency band. It occurs in all mammals, and is the dominant frequency in awake reptiles. In humans, Delta is the dominant brain wave in early developmental stages, including in babies and young infants up to a year old. Delta wave production tends to decrease as we age, and by age seventy-five Delta waves may be entirely absent.
Delta waves are generated in the front of the brain (medial frontal cortex) and in deeper subcortical structures that make up the brain reward system (nucleus accumbens, tegmental brainstem area). Delta that originates in the frontal cortex can modulate activity in regions that are distant from the front of the brain (Harmony 2013). Delta originating from the brain reward system supports motivational processes (Knyazev 2007).
Delta Functions
In adult humans, Delta waves occur during deep, dreamless sleep. They play a crucial role in rest, regeneration, and repair. You can begin to see Delta waves in stage 3 of slow wave sleep (SWS), and by stage 4 they almost entirely dominate the EEG. High whole-brain Delta is a signal for the body to urgently rest and rejuvenate. By the time Delta waves generated in the front propagate to the back of the brain, the brain is going to sleep.
High Delta activity may also be seen in brain regions that may be damaged in some way. It is the brain’s way of taking areas offline for repair and rejuvenation.
Delta in the Waking Brain
According to many cognitive neuroscientists, Delta waves play an important role in cognitive processing in the awake brain, particularly in regards to mental tasks demanding attention (Harmony 2013, Knyazev 2007). Delta is an inhibitory oscillation that acts to selectively suppress non-relevant sensory input that interferes with internal concentration on mental tasks (Harmony 2013).
Delta waves have also been proposed to play a key role in primitive motivational and homeostatic drives. Primitive functions subserved by delta include hunger, sexual arousal, fatigue, pain, and threat response (Knyazev 2007). Delta increases when these basic survival functions are dysregulated and decreases when they are brought back into homeostasis. Delta’s role in cognitive processing may therefore be connected to motivation as cognitive performance improves when motivation is high.
Delta is the main gateway to the collective unconscious (Wise 2002). That is to say, we access unconscious information through Delta that transcends the individual level of consciousness. Psychics, energy healers, and those in helping professions generally generate high amounts of Delta during experiences of empathy and intuition. People with trauma histories also show high Delta, which may manifest as hypervigilance in adulthood wherein one is constantly scanning the emotional environment for threats (Wise 2002).
Delta During Meditation
Delta has been found to increase in desire-based meditations such as Loving Kindness (Faber 2016, Kakumanu et al. 2018), and decrease in desireless meditations such as Vipassana (Cahn 2010, Amihai & Kozhevinkov 2014, Braboszcz & Delorme 2010, Hinterberger 2014).
Loving Kindness meditators show increased Delta in the right frontal region. Being an inhibitory frequency, increased Delta on the right signals more left-sided activation. According to the left/right frontal asymmetry literature, more left-sided frontal activation is associated with increased positive emotions (Faber 2016).
On the other hand, Vipassana meditators show Delta power decreases in the front of the brain during their meditations. Decreased frontal Delta correlates with increased frontal activation associated with the detection and integration of internal and external sensory information (Cahn 2010). Beginning Vipassana meditators show higher Delta readings than advanced meditators as their meditations are generally more sleepy and require a higher degree of effort (Kakumanu et al 2018).
When delta arises in beginning and novice meditators, we usually decrease the meditation depth score. This is because high Delta has been associated with mind wandering and drowsiness (Braboszcz & Delorme 2010). More advanced protocols reward lower Delta in the back of the brain to keep a clear mind that is free of sleepiness.
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