This is a review of the studies about MSG and its influence on different systems in humans. Effects of injected MSG into rats included neuron damage, and prefrontal cerebral cortex changes, but such tests cannot be done on humans, who are not injected with MSG anyway (except in some vaccines which were not discussed in this article).
Rats given MSG mixed with their food, however, also showed degenerative changes and inflammation in various brain areas. Mice born to mothers fed MSG had impaired maze learning although no neuronal damage was visible. Also, low doses given orally to young rats led to learning problems in adulthood.
QUOTE: “… early-life MSG exposure could lead to subtle behavioral aberrations in adulthood.”
The author says more research on doses approximating those used by humans are needed.