The Journal of Neuroscience, March 15, 2002, 22(6):2283-2298
Using Optical Flow to Characterize Sensory-Motor Interactions in
a Segment of the Medicinal Leech
Davide
Zoccolan and
Vincent
Torre
Scuola Internazionale Superiore di Studi Avanzati and
Istituto Nazionale di Fisica della Materia, Unita' di
Trieste, c/o Scuola Internazionale Superiore di Studi Avanzati, 34014 Trieste, Italy
Activation of motoneurons innervating leech muscles causes the
appearance of a two-dimensional vector field of deformations on the
skin surface that can be fully characterized using a new technique
(Zoccolan et al., 2001) based on the computation of the optical flow,
the two-dimensional vector field describing the point displacements on
the skin. These vector fields are characterized by their origin (i.e.,
the singular point) and by four elementary components that combine
linearly: expansion (or compression), rotation, longitudinal shear, and
oblique shear. All motoneurons can be classified and recognized
according to the components of the deformations they elicit:
longitudinal motoneurons give rise almost exclusively to longitudinal
negative shear, whereas circular motoneurons give rise to both positive
longitudinal shear and significant negative expansion. Oblique
motoneurons induce strong oblique shear, in addition to longitudinal
shear and negative expansion. Vector fields induced by the contraction
of longitudinal, circular, and oblique fibers superimpose linearly.
Skin deformations can therefore be attributed rather reliably to the
contraction of distinct longitudinal, circular, and oblique muscle
fibers. We compared the deformation patterns produced by touching the skin with those produced by intracellular stimulation of P, T, and N
cells: vector fields resulting from the activation of P cells were
almost identical to those produced by mechanical stimulation. Therefore, motor responses triggered by light or moderate touch are
almost entirely mediated by excitation of P cells, with minor contributions from T and N cells.
Key words:
sensory-motor interaction; motoneurons; optical flow; videomicroscopy; leech; mechanosensory neurons; computer vision
Copyright © 2002 Society for Neuroscience 0270-6474/02/2262283-16$05.00/0
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