Clinical aspects of the "third rhythm" of the temporal lobe.

We studied clinical aspects of the "third rhythm," which was first described by Niedermeyer as alpha-like activity of the temporal lobe. By scalp EEG, temporal alpha-like activity was recorded in 15 (0.30%) of 4929 patients over 20 years of age. The temporal alpha-like activity was observed in 5 patients who had clinical and brain imaging findings indicating the presence of a cerebrovascular disorder. The alpha-like rhythm of these patients was left-sided, and wicket spikes appeared in the same region as the alpha-like rhythms in 4 of the 5 patients. In 8 of the 15, the temporal alpha-like rhythm was recorded over the defective bone or replacement bone after intracranial surgery. The alpha-like rhythm of these patients was similar to breach rhythm in the temporal region. The remaining 2 patients had not undergone intracranial surgery nor did they show symptoms of cerebrovascular disorders. The temporal alpha-like rhythms in one of these 2 might be a physiological third rhythm detected by scalp EEG through congenital bone thinning. Our observation supports the existence of intrinsic activity of the temporal lobe (the third rhythm). The third rhythm can be recorded by routine scalp EEG in some clinical conditions, and it is important to recognize this rhythm when one encounters temporal rhythmic activity independent of alpha rhythm of the occipital lobe.