decreased brain size abnormal forebrain size decreased forebrain size 2013-10-09T15:20:00Z MP:0012138 MPheno.ontology csmith decreased prosencephalon size reduced forebrain size reduced prosencephalon size size reduction or truncation of the anterior of the three primary divisions of the developing chordate brain or the corresponding part of the adult brain (in vertebrates, includes especially the cerebral hemispheres, the thalamus, and the hypothalamus and especially in higher vertebrates is the main control center for sensory and associative information processing, visceral functions, and voluntary motor functions) small forebrain small prosencephalon truncated forebrain truncated prosencephalon