Neuroscience: Mechanisms Responsible for Epilepsy in Hippocampal Slices Predispose the Brain to Collective Oscillations

Neuroscience: Mechanisms Responsible for Epilepsy in Hippocampal Slices Predispose the Brain to Collective Oscillations

About 90% of the neurons in the CA3 region are pyramidal cells, the principal neurons that supply CA3 output to other parts of the brain (including, in particular, the CA1 hippocampal region and the opposite CA3 region—there is one hippocampus in each cerebral hemisphere). Of particular relevance to epilepsy and probably to normal brain function is the fact that CA3 neurons synaptically excite one another. These connections are called recurrent. The remaining neurons, generally nonpyramidal in shape, are probably all inhibitory and most or all of them use γ-aminobutyric acid (GABA) as their transmitter. Pyramidal neurons have two sets of dendrites, called basilar and apical, with recurrent synaptic connections into both sets of dendrites. Presynaptic neurons release transmitters onto a given postsynaptic neuron causing membrane synaptic currents to flow and possibly initiating intracellular secondary metabolic processes that in turn influence the membrane. There are also synaptic receptors whose primary function is to couple to intracellular biochemical processes. As metabolic processes are, in general, slower than voltage-gated membrane processes, the different receptor coupling mechanisms introduce a range of time scales into neuronal function.