The “Third Rhythm”: Further Observations

Abstract

Earlier personal observations have indicated the existence of an alpha-like rhythm in the temporal lobe. This rhythm shows no relationship to the posterior alpha and the central mu rhythm; for this reason, it may be called the "third rhythm." This activity is undetectable in scalp leads but may turn into a "breach rhythm" under bone defects. The assessment of a young adult as a possible candidate for temporal lobectomy with the use of epidural electrodes yielded an unusually good demonstration of the "third rhythm." As a matter of fact, there were two types of rhythmical alphoid activity. One of them was more anteriorly located over the temporal lobe and more prominent over the left (epileptologically chiefly involved) hemisphere. This rhythm was often visualized in the temporal scalp electrodes and was felt to be an abnormal phenomenon. The other type of rhythmical activity was maximal in the midsection of the temporal lobe, better developed on the right (epileptologically less affected) side and essentially undetectable in scalp leads. This rhythm appears to be the true physiological "third rhythm". The responsiveness of this rhythm remains unclear. Attenuation on the right side occurred while the patient was singing.