Introduction to Gamma Waves
Gamma (30-100+ Hz) waves are the highest frequency and lowest amplitude waves in the brain. Gamma waves were virtually unheard of prior to the development of digital EEG, as analog EEG was not able to measure frequencies as high as Gamma.
Gamma waves can be hard to measure accurately during neurofeedback. This is because the frequency range of Gamma overlaps with that of electrical signals produced by muscles. Eye and jaw muscle movements create electrical signals in the 50-150 Hz range, which is also the range of Gamma brain waves. For this reason, one must be very still during neurofeedback in order to prevent muscular contamination of the signal.
Subjectively, increases in Gamma are associated with a sharp focus and feelings of insight, creativity, and being energized. Overly high amounts of Gamma can lead to anxiety, stress, and hyperarousal, while Gamma’s suppression is associated with ADHD, depression, and learning disabilities.
Gamma waves are generated throughout the brain, including in cortical and subcortical structures. Gamma that is generated in the thalamus sweeps the cortex from frontal to occipital sites.
Gamma Functions
Gamma waves play multifunctional roles in the brain. They have been implicated in a host of cognitive functions, including attention, conscious awareness, feature integration, movement preparation, memory formation and maintenance, and intelligence (Engel and Fries 2010, Jensen et al. 2007). In addition, the Gamma band has attracted much interest over recent years as a promoter of neuroplasticity and the formation of new neural pathways important for long-term memories.
Gamma activity facilitates the neural mechanisms underlying visual representation. By enabling neural postsynaptic potentials to integrate across disparate regions of the brain, synchronized Gamma directs downstream networks to bind sensory features into a coherent whole (Travis and Shear 2010). For this reason, it has been called the “binding frequency” that solves the binding problem of visual perception.
Gamma Waves in Meditation
Gamma waves are commonly seen in meditation, particularly in those with high levels of expertise. Gamma is more associated with bottom-up attentional processing than are top-down control frequencies such as Beta and Alpha. Meditations that enhance sensory awareness see Gamma increase in the back of the brain where raw sensory perceptions are processed. For instance, body-scanning meditations require lots of posterior Gamma for fine-tuned body awareness.
Conversely, inward meditations that attempt to block out stimulus processing of the outside world see Gamma decrease in the front and back of the brain. TM/Quiet Mind meditators show decreased Gamma across the whole brain. Their brains are not as activated during the practice as other meditations, as the meditators seek to attain a de-excited ground state of the mind.
Long-term Open Monitoring (OM) meditators show increased occipital Gamma power due to their improved sensory awareness. Cahn and colleagues found the largest occipital Gamma power increases in Vipassana meditators with more than ten years of daily practice (Cahn et al. 2010). Similarly, Braboszcz and colleagues found that meditators in three different meditation traditions (Vipassana, Himalayan Yoga, and Isha Shoonya) showed higher parieto-occipital Gamma power (60-110 Hz) than controls as a trait effect. Naturally, the Gamma increases were positively correlated to the meditation experience of the participants (Braboszcz et al. 2017). Advanced Zen practitioners also show higher frontal High-Gamma (100-245 Hz) than control subjects, and this finding was found to correlate strongly with scores on a mindfulness scale (MAAS), which in turn significantly correlates with meditative expertise.
Mindfulness meditators show small increases in whole-brain Gamma power during meditation, with the smallest increases in advanced practitioners due to neuroplastic changes that have turned state effects into trait effects. Highly advanced Mindfulness meditators show decreased Gamma power on the left side of the brain as they achieve minimal levels of self awareness. This is because speech is produced on the left side of the brain and the narrative self (the self that talks to you) begins to subside in these advanced stages.
An Essential Frequency in Loving Kindness
Loving Kindness meditators show the most ubiquitous Gamma band activity, particularly in highly skilled practitioners. Tibetan monks practicing a form of Loving Kindness (non-referential compassion meditation) have been found to produce high-amplitude Gamma waves sourced in frontal and parieto-temporal regions (back of the brain and behind the ears). This synchronized activity in the Low-Gamma range is a well-established correlate of peak levels of concentration and compassion (Lutz et al. 2004). The researchers found a remarkable 30x Gamma increase in monks compared to controls. Intensity in the meditation appeared to correlate strongly with the amount of Gamma produced. The Tibetan monks studied also showed differences in their resting baseline before meditation because of neuroplastic changes that gradually blurred the boundary between daily living and formal practice (Lutz et al. 2004). Compared to controls, Tibetan monks showed significantly higher (2x) baseline relative Gamma power, quantified as the ratio between Gamma and Theta-Alpha (Lutz et al. 2004).
Frontal Gamma Asymmetry
In addition to Alpha asymmetry, Gamma asymmetries in the frontal region can closely track frontal activation patterns. Gamma is an activating frequency, and its asymmetry protocol follows the reverse pattern of Alpha asymmetry (Tarrant and Cope 2018). That is to say, when Gamma increases in the left frontal region, this bolsters left-sided activation. More left-sided activation is associated with positive emotions and approach-related motivation. Frontal Gamma asymmetry may be a better metric of emotional state than Alpha, as Gamma closely tracks glucose metabolism in the front of the brain (Tarrant and Cope 2018).
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