QUANTAL ORGANIZATION OF REFLEX AND CONDITIONED EYELID RESPONSES
JOS A. DOMINGO, AGNES GRUART, AND JOS M. DELGADO-GARCA
Laboratorio de Neurociencia, Facultad de BiologĦa, Universidad de Sevilla,
41012-Sevilla, Spain
APStracts 4:152N, 1997.
ABSTRACT
Upper lid movements and the electromyographic activity of the orbicularis
oculi muscle were recorded in behaving cats during spontaneous and
experimentally-evoked reflex blinks, and conditioned eyelid responses. Reflex
blinks evoked by the presentation of air puffs, flashes, or tones consisted of
a fast downward lid movement followed by late, small downward waves, recurring
at ÷ 50-ms intervals. The latency, maximum amplitude, peak velocity, and
number of late waves depended upon the modality, intensity and duration of the
evoking stimulus. The power spectra of acceleration records indicated a
dominant frequency of ÷ 20 Hz for air-puff-evoked blinks. Flashes and tones
usually evoked small and easily-fatigable reflex responses of lower dominant
frequencies (14-17 and 9-11 Hz respectively). A basic ÷ 20 Hz oscillation was
also noticed during lid fixation, and ramp-like lid displacements evoked by
optokinetic stimuli. Five classical conditioning paradigms were used to
analyze the frequency-domain properties of conditioned eyelid responses. These
learned lid movements differed in latency, maximum amplitude, and profile
smoothness depending on the modality (air puff, tone), intensity (weak,
strong), and presentation site (ipsi-, contralateral to the unconditioned
stimulus) of the conditioned stimulus. It was found that the characteristic
ramp-like profile of a conditioned response was not smooth, but appeared to be
formed by a succession of small waves at a dominant frequency of ÷ 20 Hz. The
amplitude (and number) of the constituting waves depended on the
characteristics of the conditioned stimulus and on the time interval until
unconditioned stimulus presentation. Thus, conditioned responses seemed to be
formed from lid displacements of 2-6 deg in amplitude and ÷ 50 ms in duration,
that increased in number throughout conditioning sessions, until a complete
(i.e., lid closing) conditioned response was reached. It is suggested that a ÷
20-Hz oscillator underlies the generation of reflex and conditioned eyelid
responses. The oscillator is susceptible to being neurally modulated in order
to modify the velocity of a given quantum of movement, and the total duration
of the lid response. Learned eyelid movements are probably the result of a
successively-longer release of the oscillator as a function of the temporal-
spatial needs of the motor response.
Received 3 March 1997; accepted in final form 14 July 1997.
APS Manuscript Number J179-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 27 August 1997