paleo

PALEOCIRCUIT

Neuro term. 1. A preconfigured pathway or network of nerve cells in the forebrain, brain stem, or spinal cord utilized in nonverbal communication. 2. A pre-established neural program of great age for sending or receiving nonverbal signs. 3. An ancient, neural platform for bodily expression, configured millions of years before the advent of cortical circuits for speech.

Usage: Paleocircuits are modules and passageways preserved in living nervous tissue, much as fossils solidify no longer living tissues into lifeless stone. Tracing the paleocircuits of nonverbal signs helps us unravel their origin, evolution, and meaning.

Anatomy. Paleocircuits channel electrochemical impulses required for muscles to contract--e.g., as visible signs of happiness or sadness in the nonverbal present. As "living fossils," paleocircuits preserve information about gestures from the nonverbal past as well.

Evolution. In the aquatic brain and spinal cord, ancient networks of motor neurons and interneurons evolved to control body movements of our oldest animal ancestors, the jawless fishes. From these ancient neuronal micropaths, instructions reached local muscle groups to move individual body parts. From the beginning of vertebrate life, microscopic systems of spinal interneurons stood between motor neurons and sense receptors, affecting the input and outflow of nonverbal signs. Thus, it was established early on that the spinal cord should be more than a passive pipeline to carry sensory messages to the brain and motor signals back to the body. Like the brain itself, our spinal cord is replete with paleocircuits which have "minds of their own" (e.g., for managing tactile withdrawal and the oscillating, rhythmic movements of walking).

Neuro-notes. 1. Paleocircuits are subcortical nerve nets and pathways which link bodily arousal centers (of the reticular activating system), emotion centers (of the hypothalamus, amygdala, and cingulate gyrus), and motor areas of the forebrain (basal ganglia) and midbrain (superior and inferior colliculi), with muscles for the body movements required to produce nonverbal signs. 2. "Only a few of the descending [motor] pathways [from the brain] synapse directly on spinal cord motor neurons. Instead, most of the descending projections influence the activity of interneurons that are interposed in reflex circuits and thus alter ongoing spinal reflex activity" (Willis 1998E:186).