Muscarinic elicitation of EEG asymmetry in freely moving rats.

Averaged frequency spectra (0.5-30 Hz) of electroencephalogram (EEG) were studied in six freely moving rats with chronically implanted electrodes in symmetrical areas of somatosensory cortex. Hemispheric asymmetry in spectra of an ongoing EEG was expressed as a power decrease in 15.6-17.2 Hz band on the left hemisphere and as that in 25.2-27.8 Hz band on the right one. Physostigmine subcutaneous (s.c.) injection (0.25 mg/kg) provoked appearance of the significant left brain bias in 4.7-8.6 Hz range of EEG spectra and the right brain bias in 19.3-21.3 Hz band. These physostigmine effects were counteracted by scopolamine (1.5 mg/kg, s.c.) injected 30 min before. It is suggested that a muscarinic component may be involved in the interhemispheric cooperation associated with cortical theta activity in rats.