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Control
Experimental
A
somatosensory
cortex
visual cortex
SC
LGN
VBN
VBN
Eye
Eye
Skin
Skin
elimination of
transient projection
transient projection
remains
VBN
VBN
Eye
Eye
Skin
Skin
Control
Experimental
B
Visual Cortex
LGN
Auditory Cortex
Auditory Cortex
LGN
MGN
MGN
Cut auditory
pathway to MGN
C
Normal
Experimental
EphA2, EphA5
double knockout
expression
EphA2, EphA5
expression
LGN
LGN
MGN
MGN
Cut auditory
pathway
Cut auditory
pathway to MGN
FIGURE 6.7 Cross wiring of visual signals to the somatosensory and auditory and cortex. A. In a normal
ferret, the auditory input goes indirectly to the medial geniculate nucleus of the thalamus and from there to
the auditory cortex. Retinal input is to the LGN and then on to the visual cortex. B. When the auditory
pathway is cut and then is left to degenerate by ablation of the visual cortex, the visual input sprouts into
the MGN, which projects as usual giving visual physiological properties to the auditory cortex. C. EphrinA2
and EphrinA5 are expressed at the border between the LGN and the MGN. Even though the auditory
pathway to the MGN has been cut, the retinal fibers do not invade the MGN, but they do so in EphrinA2,
EphrinA5 double knockouts. (After Metin and Frost, 1989; Roe et al., 1992; Lyckman et al., 2001)
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