amphibia

Evolution. 1. Collectively, those older parts of the human brain which developed during the amphibian transition from water to land in the Devonian period of the Paleozoic Era. 2. Specifically, those modules of the amphibian midbrain and forebrain which evolved to further life above the waterlines of ancient seas. 3. Those amphibian-inspired paleocircuits a. for hearing and seeing in a higher, drier world, and b. for postural stance in terra firma's gravitational pull.

Usage: Several common gestures and postures (derived, e.g., from the auditory startle and the high-stand display) originated ca. 380 m.y.a. in modules of the amphibian brain. (The latter itself evolved from modules and paleocircuits of the aquatic brain.) Today these play key roles in the expression of dominance and submission.

Media. Sudden movements, looming objects, and bright lights trigger midbrain vision centers which reflexively orient our face and eyes to novel or dangerous stimuli. Meanwhile, midbrain hearing centers stay tuned to abrupt changes in sound. Thus, with its fluctuating cuts in scenery, camera angle, and volume, TV addresses the amphibian brain.

Neuro-notes I: midbrain. As amphibian ancestors emerged from primeval lakes and seas to live part of their lives on land, seeing and hearing sharpened. Two paired centers of the amphibian midbrain--the inferior and superior colliculi--evolved as processing stations for audiovisual cues. The former's hearing centers (the auditory lobes) unconsciously prompt us to crouch from loud noises. The latter's vision centers (the optic lobes) reflexively focus our attention on body motions, gestures, and objects that move.

Neuro-notes II: forebrain. Unlike water's buoyancy, land presents an incredibly heavy environment in which antigravity signs (e.g., the reptilian press-up to a high stand) evolved. The forebrain module in charge of the earliest aggressive "pushup" was a motor area presently called the striatal complex. What remain of its paleocircuits (see BASAL GANGLIA) inspire us to extend our limbs to show dominance as John Wayne did in the 1960 movie, The Alamo, by similarly "standing tall."

See also PALM-DOWN, REPTILIAN BRAIN.