It has long been known that the EEG relates in a general fashion to cerebral metabolism and blood flow. At an early stage it was found that, for example, comatous states with their slow wave EEG pattern showed a reduced cerebral metabolism and blood flow as measured with the Kety nitrous oxide technique. Vice versa, in states with an increased metabolism, such as hyperthyroidism and epileptic seizures with a high frequency EEG pattern, there was increased metabolism and blood flow. These observations suggested that the EEG carries information on the neuronal metabolic work and which in its turn controls the blood flow via the so-called metabolic regulation. The present opinion is that the EEG is ultimately determined by fluctuating rhythmic brain potentials in synchronized masses of neuropile in the cerebral cortex. These rhythmic changes ultimately depend upon membrane activities involving ionic transport, which in its turn requires oxidative metabolism. Possibly the EEG thus reflects energy consuming processes in neuronal cortical membranes mainly in the so-called neuropile (Creutzfeldt). Recent studies of the frequency content of the human EEG have shown that it correlates distinctly to the over-all cerebral oxygen uptake as well as blood flow. Correlations between EEG and specific regions of the brain are also being studied. Thus, the normal waking state in undisturbed subjects, when the alpha rhythm shows its typical parieto-occipito-temporal distribution and higher frequencies frontally, is accompanied by a significant increase in the cerebral blood flow (and metabolism) in frontal areas and lower flows and by metabolism in posterior regions. This state, which can be understood as a prerequisite for consciousness, has been interpreted as due to higher activities in efferent 'behavioral' parts of the cerebral cortex and inhibition of afferent-gnostic regions where the alpha rhythm prevails. Results relating to this concept and also to regional EEG analyses during voluntary movements, speech, conditioning experiments, etc, will be discussed as will implications of the general concept presented, i.e., that the typical EEG of a focal lesion due to epilepsy, tumors, cerebrovascular disorders, etc, implies altered cerebral metabolism and blood flow. In general it appears that the normal EEG as well as EEG abnormalities may be interpreted in cerebral metabolic and circulatory terms.
