Slow-Wave Activity May Affect Depression

BALTIMORE—Disruption of slow-wave activity (SWA) may explain the positive influence that sleep deprivation appears to have on major depressive disorder, according to results of a study presented at the 32nd Annual Meeting of the Associated Professional Sleep Societies.

Jennifer Goldschmied, PhD, a postdoctoral fellow at the University of Pennsylvania in Philadelphia, reported preliminary results of a study of SWA disruption in 26 subjects (12 healthy controls and 14 people with major depressive disorder) that found a significant decrease of about 20% in waking theta activity, as measured with EEG, among patients with depression. In the three-night sleep study, conducted at the University of Michigan in Ann Arbor, an adaptation night was followed by baseline and SWA disruption nights. Investigators performed EEGs each night. After the baseline night, patients also had a morning and afternoon EEG.

Jennifer Goldschmied, PhD

Across the baseline day, patients with depression showed “no modulation of theta activity whatsoever,” said Dr. Goldschmied. “Then we see, following slow-wave disruption, a significant decrease in theta activity,” whereas healthy controls showed no change in waking theta following SWA disruption. “What this means is that the presence of SWA may actually be facilitating the reduction of theta or sleep propensity during typical sleep in healthy individuals,” she added. In patients with depression, theta power declined from around 5.4 Hz to 4.3 Hz following SWA disruption.

This finding supports the synaptic homeostasis hypothesis proposed by Giulio Tononi, MD, PhD, and Chiara Cirelli, MD, PhD, of the University of Wisconsin, said Dr. Goldschmied. This hypothesis holds that SWA is a marker of synaptic strength and promotes the downscaling of synaptic strength during sleep. No method for measuring synaptic strength in humans exists, Dr. Goldschmied added, but waking theta can be considered a proxy for net synaptic strength across the cortex.

Other research that has found SWA disruption improves mood, but Dr. Goldschmied and colleagues found no role of decreased theta activity in that change. “To go even further,” she said, “we looked at the entire data set and found no relationship between the decrease in theta and any of the measures of sleep architecture, so there’s really no way to predict this decrease in our sample of people with depression.”

SWA plays a significant role in depression and merits more study, said Dr. Goldschmied. Future research should examine the effects of SWA disruption in a larger sample, investigate theta findings with other proxy measures of synaptic strength such as brain-derived neurotrophic factor and transcranial magnetic stimulation, explore differences in SWA between sexes, and explore how SWA enhancement influences mood and theta activity, she concluded.

—Richard Mark Kirkner

Suggested Reading

Cheng P, Goldschmied J, Casement M, et al. Reduction in delta activity predicted improved negative affect in major depressive disorder. Psychiatry Res. 2015;228(3):715-718.

Tononi G, Cirelli C. Sleep and synaptic homeostasis: a hypothesis. Brain Res Bull. 2003;62(2):143-150.