‘GABAergic and Glutamatergic neurons in the zebrafish brain’ by Steve Wilson and Kate Turner. CC BY
Behold, a brain in balance. In addition to firing or not firing, neurons act along another critical dimension. They can make it easier for their neighbors to fire, exciting them. Or, they can try to stop them from firing, inhibiting them. This four-day-old zebrafish brain showcases both types. Excitatory neurons glow purple while inhibitory neurons shine green.
Nearly every function of the brain depends on these two types of neurons keeping each other in check. Too much inhibition will stop signals in their tracks before they get to their destination. Perfect excitation (where one neuron triggers two, which trigger four, and then eight, and so on) leads to electrical storms and seizures. Modern research on the brain suggests that healthy functionality depends on walking the line between these two extremes.