Non-invasive electrophysiological neuroimaging of sleep

Abstract

Neuroimaging of sleep by means of low-resolution brain electromagnetic tomography (LORETA) can localize generators of electrical activity in the brain with high temporal resolution based on non-invasive multichannel EEG recordings. In 10 normal healthy subjects aged 20–35 years, delta waves in S4 as well as sleep spindles in S2 were marked visually. For these epochs, the spectral power density was calculated and LORETA was applied. For frequencies below 1 Hz (slow cortical oscillations), LORETA activity was maximal in posterior regions in the precuneus. In the delta frequency range of 1.6–4 Hz, LORETA activity was maximal in the medial prefrontal cortex and spread into the anterior cingulate and orbitofrontal cortex. For sleep spindles, LORETA revealed distributed sources in the prefrontal cortex, oscillating with a frequency below 13 Hz, and in the precuneus, oscillating with a frequency above 13 Hz. The observed LORETA sources are in accordance with recent results of local, use-dependent aspects of sleep. The enhanced delta activity in prefrontal regions is in line with hypotheses concerning the functional significance of slow-wave sleep. Moreover, the localized cortical brain regions have principal connections to adjacent parts of the dorsal thalamus where thalamic delta and spindle oscillations are generated.