decreased brain size abnormal forebrain size decreased forebrain 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) MP:0012138 2013-10-09T15:20:00Z MPheno.ontology csmith small prosencephalon truncated prosencephalon reduced prosencephalon size reduced forebrain size decreased prosencephalon size small forebrain truncated forebrain