Sleep spindles recorded from deep cerebral structures in man.

The depth and scalp EEG findings in 73 patients with intractable epileptic seizure disorder and in 14 patients with intractable pain were reviewed; stress was laid on the area of earliest spindle activity. It was found that sleep spindles frequently occurred first in frontal depth leads and especially in the superior frontal region (supplementary motor region). In some cases, spindles in frontal depth leads occurred while the patient showed early drowsy activity or even waking activity (with posterior basic rhythm) in the scalp leads. In patients with thalamic implants, spindles tended to appear on the thalamus before appearance on the scalp. The general rule that sleep onset (NREM) is characterized by the appearance of spindles is valid for the scalp EEG only. Deep spindle activity occurs much earlier and probably requires a certain degree of synchronization before spindle activity is noticeable in scalp leads. The superior frontal region is likely to be the starting point of spindle activity.