SPONTANEOUS SEIZURE ELECTROCORTICAL ACTIVITY IN RATS - RELATION TO AROUSAL LEVEL

The relationship between neocortical high voltage spindle activity (HV S) and the level of arousal (state of vigilance) was investigated in i mp-DAK rats. Two groups of single records (6 h and 24 h) and one group of repeated ones (6 h daily for three consecutive days) were analysed . Five levels of arousal (states) were distinguished on the basis of h ippocampal and neocortical EEG: high arousal (HA), moderate arousal (M A), low arousal (LA), slow wave sleep (SWS) and paradoxical sleep (PS) . The number of HVS episodes and the cumulative amount (i.e. summed du ration) of each state was calculated for each successive hour of recor ding. It was found that the number of HVS episodes correlated positive ly with the amount of the MA state, but not with the amount of the rem aining states. The rate of HVS occurrence during the MA state, however , was not stable. It decreased along with the decrease in amount of MA in successive recording hours of the same recording session. However, at the beginning of each successive session, the HVS episodes became more numerous, whereas the MA amount decreased. The accompanying chang es in the cumulative amount of the remaining states confirm indirectly the supposition that HVS occurrence is related to transitions from on e state to another rather than to a given state itself.