The most powerful substance in the human brain for neuronal communication is glutamate. It is by far the most abundant, and it’s implicated in all kinds of operations. Among the most amazing is the slow restructuring of neural networks due to learning and memory acquisition, a process called synaptic plasticity. Glutamate is also of deep clinical interest: After stroke or brain injury and in neurodegenerative disease, glutamate can accumulate to toxic levels outside of neurons and damage or kill them.