Hippocampal sleep spindles revisited: physiologic or epileptic activity?

Objective: Few reports have described sleep spindles in intracranial electr ode recordings from human hippocampus. Controversy exists regarding whether hippocampal spindles represent a physiologic or epileptic phenomenon. Methods: We reviewed hippocampal recordings in 8 subjects to characterize e vents resembling sleep spindles. Results: In 6 subjects, events occurred exclusively during non-rapid eye mo vement (NREM) sleep, were similar in morphology to surface spindles, occurr ed simultaneously or independently of surface spindles, and did not show a consistent relationship to the epileptic region. In an additional subject, a proportion of the hippocampal activity recorded differed slightly in morp hology from surface spindles, was present during both NREM and rapid eye mo vement (REM) sleep, occurred in the same channels as isolated interictal ep ileptiform discharges, attenuated just prior to seizures, and occurred post ictally as repetitive discharges. This activity occurred simultaneously or independently of surface spindles, but differed from surface spindles by bo th visual and signal analysis measures. Conclusions: Most examples of hippocampal activity resembling spindles are probably physiologic, originating within the hippocampus or propagated from neighboring regions. However, in one subject, spindle activity and epilept iform discharges may have coincided, supporting experimental evidence that neurophysiological processes associated with spindle generation and NREM sl eep contribute to the activation of epileptiform discharges. (C) 1999 Elsev ier Science Ireland Ltd. All rights reserved.