frontal lobe

Jennifer Mull Psychology Human speech makes possible the expression and communication of thoughts, needs, and emotions through vocalization in the form of words. It is a process whose specialized adaptations differentiate it from the mere making of sounds--a capacity humans share with most animals. In addition to the capacity for laryngeal production of sound (which some animals also possess), speech requires a resonance system for modulation and amplification of that sound and an articulation process …

…speech function (sensory aphasia); and damage to the motor control functions of the speech centers (motor aphasia). (Health Central)The basic aspect of aphasia--whether due to stroke, paralysis, head injury, or disease--is the loss of the capacity for the meaning of language or its comprehensible organization into words or word sequences. In other cases the intellectual functions appear to be retained, whereas the vocalization system cannot be utilized to emit words but rather only sounds.