Without an average size reference, it’s wrong to say whether one is too large or the other is “atrophied”.

There's an old story I remember but can't find a good citation to, that discussed a medical investigation into SIDS during the early 20th century. In an effort to determine the cause of these dead infants, a series of autopsies was performed and compared against adults. One finding in the autopsy was the size of the pituitary gland, which was quite small in the adults but comparatively large in the infants. The investigators concluded that an over-large pituitary was contributing to the infant death and therefore recommended irradiating the necks of babies as a precautionary measure.

Of course, this did not decrease the rate of SIDS in the targeted population. Just the reverse.

The problem in the methodology was that the town in question had a number of large coal stacks that rained toxic soot on the population. Long exposure to this fallout was functionally irradiating the population. Furthermore, the adult corpses being studied were all industrial workers with unusually high exposure. The infants being studied had healthy glands, and the adults were the ones with a chronic condition.

The answer is simply that the liberal brainworm tends to move around after it consumes neurons while the conservative brainworm likes to stay in one spot.

I contend that its lead poisoning all the way down.