Postoperative changes of rat EEG variance.

Concerning an EEG parameter variance, the long-term postoperative changes were observed in rats chronically implanted with bipolar depth electrodes for EEG recordings. The cortico-hippocampal EEG signals were continuously digitized and their variances were computed for each 1 min in real time. Daily mean of the EEG variance gradually increased over 2 weeks after surgery for the implantation of chronic electrodes and, then, reached a plateau. To observe the absolute quantity of the depth EEG in the rat, at least 2 weeks are required before data collections.