Speech and Language
Although mechanisms of action are the same and the elements of the neuronal structure (neurons, synapses, neurotransmitters, etc.) are shared with other species, it is believed that language is a uniquely human ability with its biological substrate. This is particularly true of speech: whereas some form of language-like symbolic communication is possible in some primates (e.g., chimpanzees), speech communication is used only by humans (Lieberman, 1991). There is evidence that nonhuman primates use vocalizations for more than just signaling simple emotional and behavioral situations; some form of “conversation” exists among members of some primate species, which suggests a relatively elaborate cortical organization of their vocalizations, similar to humans’ (Aitkin, 1990). However, cortical and subcortical pathways in humans and other primates differ, and human cortical areas devoted to speech do not correspond anatomically to those involved in primate vocalizations. Moreover, the consequences of injuries to relevant areas involved in human speech and primate vocalizations are not identical.