The Journal of Neuroscience, January 15, 2002, 22(2):569-576
Lid Restraint Evokes Two Types of Motor Adaptation
Edward J.
Schicatano1,
Jessica
Mantzouranis2,
Kavita R.
Peshori2,
Jill
Partin3, and
Craig
Evinger2
1 Department of Psychology, Wilkes University,
Wilkes-Barre, Pennsylvania 18766, and Departments of
2 Neurobiology and Behavior and Ophthalmology and
3 Pediatrics, State University of New York Stony Brook,
Stony Brook, New York 11794
Unilateral reduction in eyelid motility produced two modes of blink
adaptation in humans. The first adaptive modification affected both
eyelids. Stimulation of the supraorbital branch of the trigeminal nerve
(SO) ipsilateral to the upper eyelid with reduced motility evoked
bilateral, hyperexcitable reflex blinks, whereas contralateral SO
stimulation elicited normally excitable blinks bilaterally. The
probability of blink oscillations evoked by stimulation of the
ipsilateral SO also increased with a reduction in lid motility. The
increased probability of blink oscillations correlated with the
enhanced trigeminal reflex blink excitability. Thus, the trigeminal
complex ipsilateral to the restrained eyelid coordinated an increase in
excitability and blink oscillations independent of the eyelid
experiencing reduced motility. The second type of modification appeared
only in the eyelid experiencing reduced motility. When tested
immediately after removing lid restraint, blink amplitude increased in
this eyelid relative to the normal eyelid regardless of the stimulated
SO. A patient with seventh nerve palsy exhibited the same two patterns
of blink adaptation. These results were consistent with two forms of
adaptation, presumably because unilateral lid restraint produced two
error signals. The corneal irritation caused by reduced blink amplitude
generated abnormal corneal inputs. The difference between
proprioceptive feedback from the blink and expected blink magnitude
signaled an error in blink amplitude. The corneal irritation appeared
to drive an adaptive process organized through the trigeminal complex, whereas the proprioceptive error signal drove an adaptive process involving just the motoneurons controlling the restrained eyelid.
Key words:
motor learning; reflex blinks; facial nerve palsy; motor
adaptation; trigeminal; adaptive plasticity
Copyright © 2002 Society for Neuroscience 0270-6474/02/222569-08$05.00/0
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