Thinking about a good night's sleep

Even a single night where a person suffers partial sleep deprivation (PSD) is enough to have a negative impact on thinking. A functional magnetic resonance imaging (fMRI) study suggests that as cognition and affective processing are disrupted, sleep pressure must represent a basic physiological constraint of brain function.

Philipp Sämann, Carolin Tully, Victor Spoormaker, Thomas Wetter, Florian Holsboer, Renate Wehrle, and Michael Czisch, of the Max Planck Institute of Psychiatry, Neuroimaging Research Group, in Munich, Germany, explain that in humans, that fMRI studies in volunteers deprived of sleep reveal altered activation patterns in neural networks in the brain. Among the resting states of these networks that spontaneously fluctuate, the default mode network (DMN) and its anticorrelated network (ACN) are the two that play key roles in separating internally and externally directed awareness.

The team explains that (partial) sleep deprivation is known to affect brain function, altering mood and cognition as well as cardiovascular events and metabolic parameters. Understanding the effects of even small disturbances in sleep patterns is important clinically for understanding long-term patient wellbeing.

To validate their hypothesis that effects of PSD in these intrinsically coupled networks can be detected by resting state fMRI, the team obtained six-minute echoplanar imaging time series (on a 1.5 Tesla machine) while 16 healthy volunteers had eyes-closed or were simply in a wakeful but resting state both after normal sleep and after PSD. "We ask the subjects rest quietly inside the scanner with eyes closed and not to think of anything in particular," Czisch told SpectroscopyNOW. They then applied independent component and cross-correlation analysis to determine whether there were any functional connectivity in the DMN and ACN.

The team explains that coherent neural oscillations occur at many frequencies in the brain, across different distances in the brain, and are a well-known phenomenon. Researchers think that this neural synchrony is involved in coordination and organization of information processing in the brain. Blood-oxygen levels as measured by fMRI can indirectly reflect the activity of collections of neurons behaving in a coherent way, they say. "There is now substantial evidence that [these] low frequency BOLD fluctuations indeed reflect neuronal activity rather than vascular rhythms, thermal noise, scanner instability or other extraneural physiological oscillations," the team explains. This makes fMRI and BOLD revelations the primary tool used in investigations of such functional networks in the human brain.

Their study revealed that volunteers who had suffered partial sleep deprivation demonstrated focal reductions of auto-correlation strength in the posterior and anterior midline node of the DMN and in the lateral parietal and insular nodes of the ACN. "Cross-correlation analysis confirmed reduced cortico-cortical connectivity within and between the DMN and ACN," the team says. This, the team says, has implications for our understanding of perceptual and cognitive changes after sleep deprivation. Such insights will be relevant to clinical studies on conditions, such as insomnia and other conditions.

"The fact that effects of a mild PSD protocol are detected by resting state fc analysis renders the methodology a sensitive tool to study sleep homeostasis," the team says. fMRI/EEG studies are now needed to demonstrate which exact particular causes of partial sleep deprivation lead to the neural networks losing focus and so giving rise to the effects on mood change and cognition.

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