Synapses, Neurons and Circuits Generating EEG Signals M. Bruce MacIver (Professor (Research) of Anesthesiology, Perioperative and Pain Medicine, Stanford University, Stanford, CA ) PL13
Our lab uses micro-electrode recordings of synaptic activity, neuronal discharge and field potentials from humans, freely moving animals and brain slices to characterize oscillations that are prominent in EEG recordings. This talk will focus on brain networks that generate theta rhythms (4 to 12 Hz sinusoidal waveforms) - these are largest amplitude and best characterized of the major oscillatory EEG signals. Theta is observed during learning, especially for movement directed tasks. This EEG activity is generated by synchronized synaptic oscillations and discharge activity among many thousands (likely millions) of midbrain, hippocampal and neocortical neurons subserving navigation, motor planning and limbic system integration. The sensory/motor integration circuitry that drives theta EEG activity can be separated into two ascending pathways: Type 1 and 2, distinguished by behavior and drug sensitivity, based on different synaptic, circuit and network properties associated with these two brain rhythms. New results from studies on gamma frequency (~ 40 Hz) oscillations will also be presented. It will be shown that local field potential (micro-EEG) signals are generated by synchronous synaptic inputs that produce membrane potential oscillations in pyramidal neurons and that neuronal action potential discharge contributes very little to these signals. Inhibitory interneurons are major contributors to the synaptic inputs driving both theta and gamma micro-EEG oscillations of pyramidal cells. Circuitry intrinsic to neocortex augments ascending rhythmical inputs to produce membrane potential oscillations that are synchronized across large numbers of cortical pyramidal neurons.