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The functional organization of the motor map of a rat changes rapidly after transection of the facial nerve. (Reproduced, with permission, from Sanes et al.
1988 and from Jacobs and Donoghue 1991.)
A. A surface view of the rat's frontal cortex shows the normal somatotopic arrangement of areas representing forelimb, whisker, and periocular muscles.
Within minutes after transection of the branches of the facial nerve that innervate whiskers, stimulation of cortical sites that formerly activated whisker
muscles causes contraction of forelimb and periocular muscles.
B. Elimination
of theVoluntary
sensory inputs
after transection
the facial
nerve
may lead
to rapidScience,
changesFifth
in the
balance of local inhibitory circuits in the motor
Source:
Movement:
The PrimaryofMotor
Cortex,
Principles
of Neural
Editon
cortex. UnderCitation:
normal Kandel
conditions
(top)
the
excitatory
effect
of
horizontal
axonal
projections
between
different
of theScience,
motor map
subject2012
to inhibition
ER, Schwartz JH, Jessell TM, Siegelbaum SA, Hudspeth AJ, Mack S. Principlesparts
of Neural
FifthisEditon;
Available
mediated by local at:
inhibitory
interneurons,
so
that
electrical
stimulation
of
a
whisker
site
evokes
contractions
of
only
whisker
muscles
and
not
forelimb
http://mhmedical.com/ Accessed: May 14, 2017
muscles. Iontophoretic
injection
of bicuculline
into a forelimb
site reserved
in the motor map blocks local GABA-mediated inhibition (bottom). As a result, stimulation
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of whisker sites can excite output neurons in forelimb and periocular sites through horizontal axonal collaterals whose influence is normally restricted by