Hippocampal and amygdala electrophysiology of human mind-wandering versus mindfulness meditation

Introduction: Mind-wandering is a pervasive human state that occupies up to 50% of waking consciousness, and may drive negative emotions such as stress and depression. Mindfulness meditation represents an opposing state to mind-wandering, in which thought is focused on a single stimuli, such as the breath. Evidence from functional magnetic resonance imaging indicates a critical role of the hippocampus and amygdala in both mind-wandering and mindfulness. However, the electrophysiologic nature of these state differences remains unknown.

Methods: Stereoelectroencephalography (sEEG) in the hippocampus and amygdala was recorded in patients undergoing invasive monitoring for epilepsy. To isolate functional differences across conditions, only patients with a normal MRI and with no hippocampal or amygdala epileptiform activity, determined after sEEG, were included. SEEG was recorded during mindfulness meditation and during mind-wandering. Integrated power across canonical frequency bands (theta 4-8Hz; alpha 8-12Hz; beta 12-30Hz; gamma 30-60Hz) was compared between mind-wandering and mindfulness meditation, following fitting one-over-f processing to isolate periodic activity.

Results: Six subjects were included, with 47 amygdalohippocampal contacts, including 28 within the hippocampus and 19 the amygdala. Compared with states of mind-wandering, hippocampal power was significantly lower during mindfulness meditation across alpha (mind-wandering median power = 0.61dB; mindfulness = 0.35dB; p=3.36E-3) and gamma (mind-wandering = 2.21dB; mindfulness = 1.31dB; p=8.35E-4) frequencies. Amygdala power was significantly lower with mindfulness meditation compared with mind-wandering across beta (mind-wandering = 2.14dB; mindfulness = 0.36dB; p=0.033) and gamma (mind-wandering = 1.29dB; mindfulness = 0.00dB; p=0.009) frequencies.

Conclusion : We demonstrate the first human intracranial electrophysiology of the hippocampus and amygdala during mind-wandering versus mindfulness meditation. Increased hippocampal and amygdala alpha (8-12Hz), beta (12-30Hz), and low gamma (30-60Hz) activity was seen with mind-wandering, compared with mindfulness meditation. Further studies with additional patients and electrophysiology across brain regions will elucidate more complete neural mechanisms of mind-wandering and mindfulness.