Alpha-like rhythmical activity of the temporal lobe.

In addition to the classical posterior alpha rhythm and Rolandic mu rhythm, a third type of rhythmical activity in alpha- (or sub-alpha-) frequency can be recorded over the temporal lobe and especially over the midtemporal region. This rhythm usually escapes detection in the scalp EEG but is commonly seen over bone defects ("breach rhythm"). With the use of epidural electrodes, however, this rhythm becomes quite prominent and dominates the activity of the temporal lobe unless there is excessive local EEG abnormality and/or pathology. This temporal rhythm lies in the range of 6-11/sec and thus often extends into the theta frequency range. There is no proven blocking effect; this mere fact sets it apart from posterior alpha and Rolandic mu rhythm. It is essentially a rhythm of the waking state but may linger into drowsiness and even into light NREM sleep. It is also separable from the highly controversial frontotemporal "kappa rhythm" of bygone times. EEG recordings from the depth of the temporal lobe (limbic structures) do not demonstrate such a rhythm that is likely to originate from the neocortical portion. Its neurophysiological and psychophysiological significance is enigmatic.