New findings:

https://www.sciencedaily.com/releases/2022/06/220613140733.htm

"There are many different types of synapses that form between neurons, including "excitatory" or "inhibitory," and the exact mechanisms by which these structures are generated remain unclear to scientists. A Colorado State University biochemistry lab has uncovered a major insight into this question by showing that the types of chemicals released from synapses ultimately guide which kinds of synapses form between neurons.

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"In the lab, Chanda and colleagues were able to make synapses changes between excitatory and inhibitory types, using only enzymes, by making the neurons express just a few genes that induced a cascade of changes in the synapses' machinery. Such a breakthrough could have major implications for treating brain diseases that are caused by malfunctions in synaptic information processing and exchange.

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"Their results show that the cell-adhesion proteins expressed in the synaptic junction area are not the only purveyors of the synapses' function, as some have thought; rather, chemicals called neurotransmitters that are released from the presynaptic site (where the information is coming from) also seem to play a major role in controlling which types of synapses form, and where.

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"'Synapses need lots of other machinery; the neurons took care of all that and turned excitatory synapses into inhibitory ones -- a fundamental change in their identity," Xu-Friedman said."

Comment: the important information is that synapses also have enzyme controls. Because enzyme molecules are so huge and complex, this adds another layer to the design of the brain's functions.