Synaptic mechanisms of synchronized neocortical micro-EEG activity

Synchronized neuronal activity underlies a myriad of cognitive processes. The study of synchronous activity has been approached from both cellular and predictive perspectives. At the cellular level, studies have focused on unraveling synaptic mechanisms of neuronal synchrony, while at the predictive level, synchronous neuronal EEG activity has been used to monitor underlying brain states. Experiments described in this thesis contribute to both levels of understanding by examining three aspects of neuronal synchrony: (1) mechanisms of generation, (2) anesthetic-induced modulation, and (3) external monitoring.;Mechanisms of synchronous theta frequency micro-EEG oscillations were investigated in neocortical rat brain slices. Experiments using specific pharmacological probes demonstrated that theta frequency oscillations required muscarinic receptor activation, GABA;Anesthetic-induced alterations in synchronous patterned micro-EEG activity were investigated using the neocortical brain slice system described above. Similar to effects seen in vivo, clinically relevant concentrations of thiopental, propofol and isoflurane evoked a steady progression of micro-EEG states; theta oscillations slowed to delta frequencies followed by transitions to burst suppression and then isoelectric activity. Prolonged inhibitory currents were associated with transitions from theta to delta activity, while burst suppression activity required increased levels of tonic inhibition. Whole cell recordings revealed robust glutamatergic transmission during burst suppression micro-EEG activity. These glutamate-mediated events were significantly depressed by anesthetic concentrations capable of eliciting isoelectric activity. This finding, coupled with the fact that glutamate receptor antagonists forced transitions from burst suppression to isoelectric activity, suggests that anesthetic-induced depression of excitatory transmission underlies the transition from burst suppression to isoelectric activity.;EEG activity was monitored in rats exposed to high G-forces with the hope of identifying EEG measures which correlated with increasing +G;Thus, results described in this thesis contribute to our understanding of synchronized neuronal activity at both the cellular mechanistic level, and at the level of in vivo predictability.