The Peripheral Nervous System
The Central Nervous System The
Spinal Cord The Brain
The Hind BrainThe Mid Brain The Fore Brain Thalamus The Limbic System
The Cerebral Cortex The Mind-Brain The "Left" and "Right" Brain
Learning and Memory The Memory Regions of the brain The Mind
The Mid Brain
The midbrain is extremely reduced in humans,
but an important relay center, the reticular formation, passes through
it. The neurons of the reticular formation extend all the way from the
central core of the medulla, through the pons, the midbrain, and on into
lower regions of the forebrain. It recieves input from virtually every
sense and every part of the body and from many areas of the brain as well.
The reticular formation plays a role in sleep and arousal, emotion, muscle
tone, and certain movements and reflexes. It filters sensory inputs before
they reach the conscious regions of the brain, although the selectivity
of the filtering seems to be set by higher brain centers. Through a combination
of genetically determined wiring and learning, the reticular formation
"decides" which stimuli require attention. Important stimuli are forwarded
to the conscious centers for processing, and unimportant stimuli are suppressed.
The fact that a mother wakens upon hearing the faint cry of her infant
but sleeps through loud traffic noise outside her window testifies to the
effectiveness of the reticular formation in screening inputs to the brain
and to the role of learning in determining the importance of sensory stimulation.