Frontal intermittent rhythmical delta activity and anterior bradyrhythmia.

Rhythmical intermittent delta activity was found in 162 patients (out of a total of 5,542 patients; i.e. 2.9%). The typical features of frontal rhythmical intermittent delta activity (FIRDA) were noted in 105 patients while in 43 the pattern of anterior bradyrhythmia (AB) was present. Mental decline with delirium or dementia was the most common clinical correlate in cases of FIRDA, whereas cerebrovascular disorder represented the by far most frequent etiology in cases of AB. The patient group with AB proved to be older than the population with FIRDA. Stress was laid on the distinctive EEG features of FIRDA and AB as well as their relationship to the level of vigilance. FIRDA invariably showed a maximum over the frontopolar region whereas AB was maximally developed either over frontopolar or over superior frontal areas. There is reason to presume that a superior frontal maximum is related to arousal mechanisms (with input into the supplementary motor zone). On the other hand, it is hypothesized that the frontopolar maximum of FIRDA reflects thought processes in a frontal lobe with compromised circulation.