What is more, the main purpose of a large number of these connections is actually to inhibit – in other words to stop the other hemisphere interfering. Neurones can have an excitatory or inhibitory action, excitatory neurones causing further neuronal activity downstream, while inhibitory neurones suppress it. Although the majority of cells projecting to the corpus callosum use the facilitatory neurotransmitter glutamate, and are excitatory, there are significant populations of nerve cells (those that use the neurotransmitter gamma-amino butyric acid, or GABA for short) whose function is
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