Brain imaging studies led by senior scientist Ysbrand Van Der Werf aim to elucidate brain mechanisms involved in the favourable and disruptive effects on cognition of, respectively, sleep and sleep disturbances. We focus on (1) the functional significance of the slow oscillations (<4 Hz) typical of ‘deep’ sleep and on (2) the functions and brain areas affected most in insomnia, the most frequently occurring sleep complaint and characterized by ‘shallow’ sleep.
With respect to the functional significance of the slow oscillations we use magneto-encephalography (MEG) to investigate how the spatial map of cortico-cortical synchronization during sleep is affected by pre-sleep cognitive activity. We furthermore apply subtle experimental suppression of slow oscillations and use Magnetic Resonance Imaging (fMRI) to investigate its effects on subsequent task-related activation (blood-oxygen level dependent (BOLD) functional MRI, fMRI) and ‘resting-state’ perfusion (Arterial Spin Labelling, ASL). A new project has started to further investigate the role of slow oscillations on the resting state network. Using novel techniques for manipulation of the sleep slow oscillations we will test the hypothesis that they serve to ‘refresh’ the brain networks used the previous day by evaluating how wake experiences (or rather the accompanying activated brain networks) affect the appearance of slow waves during the night, and secondly, how these slow waves in turn serve to specifically ‘rejuvenate’, or prepare those brain networks for renewed function.
With respect to the functions and brain areas affected most in insomnia, we demonstrated that insomniacs are prone to show a dysbalance of faster responses in simple reaction time tasks and slower responses in a more difficult reaction time task (Altena et al., 2008). We were the first to apply fMRI in insomnia and demonstrated that, in spite of a normal to high performance on verbal fluency tasks, insomniacs show a decreased activation of the dorsolateral prefrontal cortical area typically involved in performing this task (Altena et al., 2008). We presently investigate how insomnia affects performance and BOLD-responses during other tasks that involve prefrontal, parietal and medial temporal lobe activation (fMRI); how it affects ‘resting-state’ perfusion (ASL); how it affects grey and white matter density (voxel-based morpho¬metry, VBM); and how it affects intra-cortical inhibition and facilitation (Transcranial Magnetic Stimulation, TMS).