Volume 16, Number 24,
Issue of December 15, 1996
pp. 8067-8078
Copyright ©1996 Society for Neuroscience
Local Control of Leg Movements and Motor Patterns during Grooming
in Locusts
Received May 15, 1996; revised Aug. 27, 1996; accepted Sept. 20, 1996.
Ari Berkowitz and
Gilles Laurent
Division of Biology, California Institute of Technology, Pasadena,
California 91125
This study demonstrates that the thoracic and abdominal nervous
system of locusts is sufficient to mediate several site-specific and
distinct grooming leg movements. Locusts can use a hindleg or middle
leg to groom at least four ipsilateral thoracic and abdominal sites,
without input from the brain, subesophageal ganglion, or prothoracic
ganglion. The hindleg is used to groom the posterior abdomen, the
ventral or posterior hindleg coxa, and the ear; the middle leg is used
to groom the anterior hindleg coxa. Grooming movements are often
rhythmic and display site-specific intralimb coordination patterns.
During grooming of the posterior abdomen or ventral hindleg coxa, for
example, hindleg tibial extension occurs nearly simultaneously with
femur elevation, in contrast with locust hindleg movements during
walking. Electromyographic (EMG) recordings during these movements show
that rhythmic bursts of tibial extensor activity occur nearly in-phase
with those of trochanteral levators, in contrast to hindleg EMGs during
walking. During grooming of the ear, hindleg tibial extension/flexion
and tibial extensor/flexor muscle bursts can occur independently of the
femur elevation/depression and trochanteral levator/depressor muscle
bursts, suggesting that the neural modules controlling tibial and
femoral movements can be uncoupled during this behavior. Tibial
extension can occur before, or even in the absence of, tibial extensor
muscle activity, suggesting that spring-like properties of the leg and
energy transfer from femur motion may play important roles in such leg
movements. Adjacent legs sometime show coordinated femur movement
during grooming with one hindleg, suggesting that grooming may also
involve interlimb coordination.
Key words:
scratching;
motor control;
insect;
thoracic;
ganglia;
central pattern generation;
locomotion
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