Journal of Neuroscience, Vol 6, 507-513, Copyright © 1986 by Society for Neuroscience
Receptive fields of motor neurons underlying local tactile reflexes in the locust
MV Siegler and M Burrows
The receptive fields of motor neurons to a hind leg were mapped by
recording intracellularly from their cell bodies or from the muscle fibers
they innervate while stimulating mechanoreceptors on the surface of that
leg. Each motor neuron is affected by a specific array of receptors that
make up its receptive field. Boundaries along the anteroposterior or
dorsoventral axes of the leg divide the receptive fields into excitatory
and inhibitory regions. Proximodistal boundaries may correspond to the
articulations between parts of the leg. Motor neurons that innervate
antagonistic muscles have complementary receptive fields, so that the
region that is excitatory for one is inhibitory for the other. The
receptive fields of the motor neurons overlap. Tactile stimulation
therefore leads to a specific local reflex that involves the coordinated
movement of the segments of a leg. Five local reflexes are described, each
of which moves the leg away from the site of stimulation. Afferents from
the external mechanoreceptors do not synapse directly on the motor neurons,
but instead on spiking local interneurons, some of which then synapse
directly on motor neurons. These local interneurons have smaller receptive
fields delineated by the same boundaries, so that the receptive fields of
the motor neurons can be constructed from appropriate combinations of them.
It is suggested that receptive fields are organized as "functional maps"
that are appropriate for particular behavioral responses rather than solely
to preserve or refine spatial information.
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