The complete inability to articulate is called alalia.    From Wordnik.com.  [The Mind of the Child, Part II The Development of the Intellect, International Education Series Edited By William T. Harris, Volume IX.] Reference

The third frontal convolution and the island of Reil were small on both sides, corresponding to the alalia.    From Wordnik.com.  [The Mind of the Child, Part II The Development of the Intellect, International Education Series Edited By William T. Harris, Volume IX.] Reference