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In-Depth Information
A
Removed from
host lumbosacral
spinal cord
M-cell
M-cell homologue MiD2em
M-cell homologue MiD3em
Wing
region
Leg
region
Graft from
donor brachial
and thoracic
spinal cord
M-cell
fluorescence
increases
Hopping chicken
that moves both
legs together
B
Tap applied
to tail
Removed from
host brachial and
thoracic spinal cord
Wing
region
FIGURE 10.6 Visualizing the neural basis of behavior in
zebrafish. In a newly post-hatched zebrafish larva, the descending
cells including the giant Mauthner neuron (M-cell) and its two
homologs in the hindbrain have been filled with a fluorescent
calcium indicator. The panel below shows a trial consisting of a
sequence of images during which an escape was elicited by an ipsi-
lateral touch to the head or tail. The color scale represents fluores-
cence intensity (blue, lowest; red, highest). Simultaneous imaging of
both the Mauthner cell (left) and one of its segmental homologs (far
right). The top row shows that with a head stimulus, both cells
respond. The bottom row shows the result from a tail stimulus. The
Mauthner cell responds but not its homolog. (Adapted from
O'Malley et al., 1996)
Graft from
donor lumbosacral
spinal cord
Leg
region
Chicken that moves
wings alternatively
FIGURE 10.7 Flapping legs and walking arms. A. The lumbar
cord of one chick embryo is replaced by the brachial cord of a donor
embryo. When the chick hatches, instead of walking, it jumps in the
rhythm of flapping wings. B. The reciprocal experiment leads to a
chick that has alternating wing movements instead of normal flap-
ping ones. (Adapted from Narayanan and Hamburger, 1971)
them under control. Voluntary movements are initi-
ated in the cerebral cortex of primates, and so it is
not until the corticospinal tract develops fully that
macaque monkeys are able to make fine finger move-
ments and exhibit mature manual dexterity (Armand
et al., 1994).
wonders how much behavior is built into the nervous
system. Are activity patterns and repetitive practice of
simple movements important for the proper develop-
ment of later movements? The deafferentation experi-
ments mentioned above imply that sensory input is
not necessary for the initiation of behavior. More
remarkably, similar experiments show that neural
activity altogether is not involved in the coordination
and maturation of very early motor behaviors. Perhaps
the most revealing experiments having to do with
the role of activity in the maturation of early motor
THE ROLE OF ACTIVITY IN
THE EMERGENCE OF
COORDINATED BEHAVIOR
If the exchange of pieces of nervous system can lead
to predictable abnormalities in behavior, then one
 
 
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