DAVID: It is obvious that if the brain increases its complexity by simply adding synapses it might get into an overload situation in which the neurons could not handle all the new connections. What happens is that as new synapses start or become stronger others become more quiet:
https://medicalxpress.com/news/2018-06-scientists-fundamental-brain-plasticity.html

QUOTE: "As the synapse for the new receptive field grew, the researchers could see under the two-photon microscope that nearby synapses also shrank.”

This would seem to support my proposal that shrinkage in the sapiens brain has been caused by the increased efficiency of complexification.