Non-REM sleep in major depressive disorder

Disturbed sleep is a key symptom in major depressive disorder (MDD). REM sleep alterations are well described in the current literature, but little is known about non-REM sleep alterations. Additionally, sleep disturbances relate to a variety of cognitive symptoms in MDD, but which features of non-REM sleep EEG contribute to this, remains unknown. We comprehensively analyzed non-REM sleep EEG features in two central channels in three independently collected datasets (N = 284 recordings of 216 participants). This exploratory and descriptive study included MDD patients with a broad age range, varying duration and severity of depression, unmedicated or medicated, age- and gender-matched to healthy controls. We explored changes in sleep architecture including sleep stages and cycles, spectral power, sleep spindles, slow waves (SW), and SW-spindle coupling. Next, we analyzed the association of these sleep features with acute measures of depression severity and overnight consolidation of procedural memory. Overall, no major systematic alterations in non-REM sleep architecture were found in patients compared to controls. For the microstructure of non-REM sleep, we observed a higher spindle amplitude in unmedicated patients compared to controls, and after the start of antidepressant medication longer SWs with lower amplitude and a more dispersed SW-spindle coupling. In addition, long-term, but not short-term medication seemed to lower spindle density. Overnight procedural memory consolidation was impaired in medicated patients and associated with lower sleep spindle density. Our results suggest that alterations of non-REM sleep EEG in MDD might be more subtle than previously reported. We discuss these findings in the context of antidepressant medication intake and age.

The consolidation of a motor skill in young adults with ADHD: Shorter practice can be better

Practice on a given sequence of movements can lead to robust procedural memory (skill). In young adults, in addition to gains in performance accrued during practice, speed and accuracy can further improve overnight; the latter, delayed, 'offline', gains are thought to emerge when procedural memory consolidation processes are completed. A recent study suggested that female college students with ADHD show an atypical procedural memory consolidation phase, specifically, gaining speed but losing accuracy, overnight. Here, to test if this accuracy loss reflected a cost of overlong training in adults with ADHD, we compared the performance of female college students with (N=16) and without (N=16) ADHD, both groups given a shorter training protocol (80 rather than the standard 160 task repetitions). Speed and accuracy were recorded before training, immediately after, and at 24-h and 2 weeks post-training. The shortened practice session resulted in as robust within-session gains and additional overnight gains in speed at no costs in accuracy, in both groups. Moreover, individuals with ADHD showed as robust speed gains and retention as in the longer training session, but the costs in accuracy incurred in the latter were eliminated. The shortening of practice sessions may benefit motor skill acquisition in ADHD.

Medial prefrontal-hippocampal connectivity and motor memory consolidation in depression and schizophrenia

BACKGROUND

Overnight memory consolidation is disturbed in both depression and schizophrenia, creating an ideal situation to investigate the mechanisms underlying sleep-related consolidation and to distinguish disease-specific processes from common elements in their pathophysiology.

METHODS

We investigated patients with depression and schizophrenia, as well as healthy control subjects (each n = 16), under a motor memory consolidation protocol with functional magnetic resonance imaging and polysomnography.

RESULTS

In a sequential finger-tapping task associated with the degree of hippocampal-prefrontal cortex functional connectivity during the task, significantly less overnight improvement was identified as a common deficit in both patient groups. A task-related overnight decrease in activation of the basal ganglia was observed in control subjects and schizophrenia patients; in contrast, patients with depression showed an increase. During the task, schizophrenia patients, in comparison with control subjects, additionally recruited adjacent cortical areas, which showed a decrease in functional magnetic resonance imaging activation overnight and were related to disease severity. Effective connectivity analyses revealed that the hippocampus was functionally connected to the motor task network, and the cerebellum decoupled from this network overnight.

CONCLUSIONS

While both patient groups showed similar deficits in consolidation associated with hippocampal-prefrontal cortex connectivity, other activity patterns more specific for disease pathology differed.