BALTIMORE – Disruption of slow-wave activity may potentially explain the positive influence that sleep deprivation may have on major depressive disorder, according to results of a study presented at the annual meeting of the Associated Professional Sleep Societies.
Jennifer Goldschmied, PhD, of the University of Pennsylvania, Philadelphia, reported preliminary results of a study of slow-wave activity (SWA) disruption in 26 subjects – 12 healthy controls and 14 people diagnosed with major depressive disorder – that found a significant decrease of about 20% in waking theta activity, as measured with EEG, in the MDD group. In the 3-night sleep study, conducted at the University of Michigan, Ann Arbor, an adaptation night was followed by baseline and SWA disruption nights with EEGs performed each night. After the baseline night, patients also had a morning and afternoon EEG.
Across the baseline day, patients with depression showed “no modulation of theta activity whatsoever,” Dr. Goldschmied said. “And then we see, following slow-wave disruption, a significant decrease in theta activity,” whereas, healthy controls showed no change in waking theta following slow-wave disruption. “So 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 MDD patients, the decline in theta power following slow-wave disruption was from around 5.4 to 4.3.
Dr. Goldschmied noted that this finding somewhat supports what is known as the synaptic homeostasis hypothesis that University of Wisconsin researchers Giulio Tononi, MD, PhD, and Chiara Cirelli, MD, PhD, reported (Brain Res Bull. 2003;62:143-50). 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.
Dr. Goldschmied noted other research that has found SWA disruption improves mood (Psychiatry Res. 2015;228:715-8; J Psychiatr Res. 2011;45:1019-26), but the study she reported on 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, Dr. Goldschmied said. She noted that 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.
Dr. Goldschmied reported having no financial relationships.
SOURCE: Goldschmied J et al. Sleep 2018, Abstract 0245.