[Clinical value of EEG coherence as electrophysiological index of cortico-cortical connections during sleep]

The technique of EEG coherence gives a non-invasive objective index of the functional relations between the different regions of the cerebral cortex. The main objectives of this study were firstly to obtain methodological information to facilitate its use in any context, whether clinical or in investigation, and secondly to draw attention to the results obtained with this technique during the different phases of sleep, both in healthy persons and in certain clinical conditions where its use in evaluation and/or diagnosis has been shown.

The results derived from the application of coherence analysis during normal sleep show the existence of a high level of interhemisphere connectivity during all phases of sleep. This result has fomented its use in the evaluation and diagnosis of disorders in which it is suspected that there are anomalies in the relation between the two hemispheres, such as neurological changes (agenesis of the corpus callosum, AIDS), psychiatric disorders (depression) and in the prognosis of states of coma. Also, progressive neurone degeneration and neurochemical deficits characteristic of Alzheimer-type dementia suggest that the coherence EEG during the REM phase may give electrophysiological indices in the establishment of the diagnosis and prognosis of the disorder.

This study shows that the coherence technique is a useful tool when establishing the pattern of cortico-cortical interactions subjacent to different functional states of the brain, both in healthy persons and in those with the different diseases in which there are alterations in cerebral function.