Once you focus on “parts” of the brain, you’re restricting consideration to mechanisms that are activated at sufficient scale to need to balloon up. I would expect the rarely-activating mechanisms to be much smaller in a physical sense than “parts” of the brain are
Counterpoint: brain is extremely energy-demanding and every part of it that is not working often gets brutally selected out.
Once you focus on “parts” of the brain, you’re restricting consideration to mechanisms that are activated at sufficient scale to need to balloon up. I would expect the rarely-activating mechanisms to be much smaller in a physical sense than “parts” of the brain are