Imagine what 'catastrophe' would be if, during sleeping and dreaming, we wouldn't have brain mechanisms which work to inhibit our movements and actions!
When we are sleeping, we have an adaptative
mechanism that protect us from ourselves or from injuries to other people.
The same mechanisms of the brain stem that control the sleep processes
of the forebrain also inhibit the spinal motor neurons, preventing the
descending motor activity from expressing itself as actual movement.
Systems that inhibit
movement in REM sleep. A.
In normal REM sleep the pons strongly
In REM sleep the pons is activated, exciting the medullary
inbibitory area by projections (tegmento-reticular tract) which
connects the pons to the inhibitory center. The medullary center
inhibits the motor neurons and gives rise to atonia.
A lateral locomotor strip, down the outside of the brain
stem, plays an important role in the reduction of motor drive.
It is connected to structures in the spinal cord. In REM
sleep the pons stimulates the inhibitory zone, turning
off the locomotor strip and shutting down motor drive.
People who act out during their dreams have a rare disorder known as REM sleep behavior disorder. These people often sustain repetead injuries and even their brother, siters, spouses and husbands have fallen victims to their nocturnal failings. The basis for this REM disorder seems to be a disruption of the brain stem systems that normally mediate REM atonia.
Experimental lesions in certain parts of
the pons can cause a similar condition in cats. During REM periods, they
may seem to chase imaginary mice or investigate invisible intruders.
Center for Biomedical
State University of Campinas, Brazil
Copyright 2000 Silvia Helena Cardoso, PhD