MRI Measurement of Brain Metabolism Across the Sleep-Wake Cycle

Objective. The objective of the proposed study is to investigate the spatio-temporal characteristics of brain activity during sleep. A number of recent fMRI (Ogawa, Lee et al. 1990) studies have shown that in absence of external stimuli, the brain continues to show spatial patterns of activity that resemble the networks that activate during sensory and cognitive tasks. This phenomenon greatly affects the interpretation of neuroimaging studies based on PET and fMRI, since these rely on differential imaging in which activity during a task is contrasted against activity during rest. In addition, resting state activity in itself potentially contains unique information on the large scale organization of neuronal networks and reveals information about functional abnormalities related to disease processes. Study Population. To avoid confounding factors related to disease processes, subjects for this study will be recruited from the normal adult population. In addition, subjects will be screened for sleep behavior, and subjects with abnormal sleep behavior will be excluded. Design. The study is designed to facilitate MRI detection of cerebral metabolic differences between the sleep and awake states. Wakefulness and sleep, and the various stages will be classified in accordance with the EEG criteria, consistent with the guidelines of Rechtschaffen and Kales (Rechtschaffen, 1968). For this purpose, we will optimize the methodology for the concurrent acquisition of EEG and fMRI signals. Using concurrent EEG and state-of-the-art MRI, we plan to establish the precise spatial distribution of changes in brain activity that are associated with changes in the sleep/wake state and the various stages of sleep, specifically early sleep (stage 1 and 2). Secondly, we plan to investigate whether changes in regional brain metabolism as measured by MRI correlates with transitory EEG phenomena during sleep, including fluctuations in band-specific power, sleep spindles, and K-complexes. Outcome Measure. As an outcome of this study, an atlas of activity clusters in normal subjects will be established, both during waking conditions, as well as during several sleep stages. Further outcomes will be spatial patterns of covariance with EEG band-specific power, spindles, and K-complexes. These data will serve as a baseline for comparison with activity patterns in patients.