Give thy thoughts no tongue . . . . --Shakespeare (Hamlet, I, 3)
Evolution. 1. Collectively, those modules, centers, and circuits of the brain which developed ca. 4 million-to-200,000 years ago in members of the genus, Homo. 2. Specifically, those areas of the primate forebrain, midbrain, and hindbrain adapted for a. emotional communication, b.linguistic communication, c. sequential planning, d. tool-making, and e. rational thought.
Usage I: The human brain is both verbal (see SPEECH and WORD) and nonverbal. Sometime between ca. 4 million and 200,000 years ago (anthropologists are not sure when) human beings began to speak. And yet, despite the immense power of words, nonverbal signals are still used a. to convey emotions, feelings, and moods; and b. to express the highs and lows of social status. Moreover, vocalizing itself--perhaps because speech and manual signing co-evolved--is accompanied in every culture by a panoply of palm-up, palm-down, pointing, and mime cues. (N.B.: Mime cues pantomime shapes, relationships, and concepts largely unexpressed until Homo set foot in Nonverbal World.)
Usage II: Incredibly little is new in the human brain that cannot be found (on a simpler scale) in the aquatic, amphibian, reptilian,mammalian, and primate brains preceding it. Yet, from a nonverbal perspective (i.e., one focusing on communication), what sets our brain apart are those highly specialized areas which control fine motor movements of the fingers, lips, and tongue, all of which evolved as neurological "smart parts."
Mental imagery. The brain creates its own nonverbal imagery (i.e., "sees" without external visual input, through the "mind's eye") by activating ". . . the dorsal (area 19) and ventral (fusiform gyrus) visual association areas, superior and inferior parietal cortex, as well as other nonvisual cortices such as the dorsolateral prefrontal cortex and angular gyrus" (Miyashita 1995:1719).
Neuro-notes II. To the primate brain's hand-and-arm gestures, our brain added precision to fingertips by attaching nerve fibers from theprimary motor neocortex directly to spinal motor neurons in charge of single muscle fibers within each digit. Direct connections were made through the descending corticospinal tract to control these more precise movements of the hand and fingers.
Neuro-notes III. With practice we can thread a needle, while our closest animal relative, the chimpanzee, cannot. No amount of practice or reward has yet trained a chimp to succeed in advanced tasks of such precision; the primate brain simply lacks the necessary control.
Neuro-notes IV. As our digits became more precise, so did our lips and tongue. These body parts, too, occupy more than their share of space on the primary motor map (see HOMUNCULUS).
Neuro-notes V. Using the mammalian tongue's food-tossing ability as a start, our human brain added precision to the tongue tip just as it did to the fingertips. Nerve fibers from the primary motor cortex were linked directly to motor neurons of the hypoglossal nerve (cranial XII) in charge of contracting individual muscle fibers within the tongue. Direct connections were made through the descending corticobulbar tract to precisely control movements of the tongue tip needed for speech.
See also NONVERBAL BRAIN.
Photo of imaged brain (from Kandel et al. 1991; copyright 1991 by Appleton & Lange)