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Summary: September 2008 | Volume 2 | Article 4 | www.frontiersin.org
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Recently, the vibrissal compartment of the VPM was shown
to be supplied by two different ascending pathways [from the
principal trigeminal nucleus (PrV) to the dorsomedial part of
the VPM (VPMdm), and from the caudal division of the inter-
polaris nucleus (SpVi) to the ventrolateral part of the VPM
(VPMvl)] and to project to different targets (Pierret et al., 2000;
Veinante and Deschenes, 1999). Functionally, the two sub-nuclei
were found to convey different sensory signals: contact signals by
the VPMvl and complex whisking-touch signals by the VPMdm
(Yu et al., 2006). Yet, the structural boundaries between the two
sub-nuclei had only been partially described. A third pathway,
ascending through the "heads" of the barreloids, has recently
been reported (Urbain and Deschenes, 2007).
The VPM contains head representations (Waite, 1973), with
its dorsolateral part containing representations of the contralat-
eral vibrissae (Sugitani et al., 1990; Vahle-Hinz and Gottschaldt,
1983). In the VPM, each vibrissa is represented by a cluster of
neurons called a"barreloid".These arrays of rod-shaped domains
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