Influence of immobilization and motor loading on the 4.5--12 Hz frequency range of the EEG in rats

The changes in the rhythmic structure of the background bioelectrical activity in the 4.5-12 Hz range in the hippocampus (Hipp.), the mesencephalic locomotor region (Mes LMR) and the sensomotor cortex (MC) in rats are studied under conditions of prolonged immobilization and motor loading. The different motor regimes are found to result in a lasting transformation in the background rhythmic characteristics of the formations studied. While in the immobilized rats there is prevalence of rhythms in the 4.5--7 Hz range and a decrease between 7.5 and 9 Hz, in motor-loaded rats rhythms prevail in the 7.5--9 Hz range. Moreover, in the case of motor-loaded rats there is a characteristic shifting of the rhythms towards the higher frequency within the 9.5--12 Hz range compared with the controls. Similar results have also been found as a direct result after each training session. The data obtained are interpreted on the basis of the EEG correlates described in the literature of the respective behaviour--"movement" and "immobility" slow rhythmic hippocampal activity (RSA). It is pointed out that: (1) Different motor regimes lead to lasting transformations in the background EEG; (2) The observed transformation concerns not only the hippocampus but also other cerebral structures as well, connected with the control of motor behaviour, namely MC and MesLMR.