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A star in the brainstem reveals the first step of cortical magnification.

Catania KC, Leitch DB, Gauthier D - PLoS ONE (2011)

Bottom Line: These measures were compared to fiber counts and primary cortical areas from a previous investigation.Our results indicate that PrV provides the first step in magnifying CNS representations of important afferents, but additional magnification occurs at higher levels.The early development of the 11(th), foveal appendage could provide a mechanism for the most important afferents to capture the most CNS space.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America. ken.catania@vanderbilt.edu

ABSTRACT
A fundamental question in the neurosciences is how central nervous system (CNS) space is allocated to different sensory inputs. Yet it is difficult to measure innervation density and corresponding representational areas in the CNS of most species. These measurements can be made in star-nosed moles (Condylura cristata) because the cortical representation of nasal rays is visible in flattened sections and afferents from each ray can be counted. Here we used electrophysiological recordings combined with sections of the brainstem to identify a large, visible star representation in the principal sensory nucleus (PrV). PrV was greatly expanded and bulged out of the brainstem rostrally to partially invade the trigeminal nerve. The star representation was a distinct PrV subnucleus containing 11 modules, each representing one of the nasal rays. The 11 PrV ray representations were reconstructed to obtain volumes and the largest module corresponded to ray 11, the mole's tactile fovea. These measures were compared to fiber counts and primary cortical areas from a previous investigation. PrV ray volumes were closely correlated with the number of afferents from each ray, but afferents from the behaviorally most important, 11(th) ray were preferentially over-represented. This over-representation at the brainstem level was much less than at the cortical level. Our results indicate that PrV provides the first step in magnifying CNS representations of important afferents, but additional magnification occurs at higher levels. The early development of the 11(th), foveal appendage could provide a mechanism for the most important afferents to capture the most CNS space.

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A parasagittal section of the star-nosed mole brain showing the relative size and location of the trigeminal nuclei, cranial nerve 5 (V) and the trigeminal ganglion (Vg).
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pone-0022406-g002: A parasagittal section of the star-nosed mole brain showing the relative size and location of the trigeminal nuclei, cranial nerve 5 (V) and the trigeminal ganglion (Vg).

Mentions: In contrast, the principal nucleus of the star-nosed mole (Figure 1 C, D) was greatly enlarged, oval in shape, and extended far rostrally to partially invade the trigeminal nerve (V). This rostral expansion was so great that in some coronal sections portions of the trigeminal nerve and PrV appeared separate from the rest of the brainstem (not shown). Figure 2 shows the extent of the star-nosed mole trigeminal complex in a parasagittal, nissl stained section, further illustrating this rostral expansion and the relationship of the trigeminal ganglion to PrV. In addition to its large size (see next section for volumes), PrV was subdivided into a series of modules separated by light septa. These subdivisions seemed similar to the stripes that represent the star in the mole's somatosensory cortex [15]. This impression was strengthened when reconstruction of horizontal sections revealed a total of 11 stripes, corresponding to the number of nasal rays on each side of the star. To further investigate the relationship between the brainstem stripes and the star, multiunit electrophysiological recordings were made from PrV. At the same time, we experimented with different angles for sectioning the brainstem that allowed for the best visualization of the modules in single sections.


A star in the brainstem reveals the first step of cortical magnification.

Catania KC, Leitch DB, Gauthier D - PLoS ONE (2011)

A parasagittal section of the star-nosed mole brain showing the relative size and location of the trigeminal nuclei, cranial nerve 5 (V) and the trigeminal ganglion (Vg).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3139641&req=5

pone-0022406-g002: A parasagittal section of the star-nosed mole brain showing the relative size and location of the trigeminal nuclei, cranial nerve 5 (V) and the trigeminal ganglion (Vg).
Mentions: In contrast, the principal nucleus of the star-nosed mole (Figure 1 C, D) was greatly enlarged, oval in shape, and extended far rostrally to partially invade the trigeminal nerve (V). This rostral expansion was so great that in some coronal sections portions of the trigeminal nerve and PrV appeared separate from the rest of the brainstem (not shown). Figure 2 shows the extent of the star-nosed mole trigeminal complex in a parasagittal, nissl stained section, further illustrating this rostral expansion and the relationship of the trigeminal ganglion to PrV. In addition to its large size (see next section for volumes), PrV was subdivided into a series of modules separated by light septa. These subdivisions seemed similar to the stripes that represent the star in the mole's somatosensory cortex [15]. This impression was strengthened when reconstruction of horizontal sections revealed a total of 11 stripes, corresponding to the number of nasal rays on each side of the star. To further investigate the relationship between the brainstem stripes and the star, multiunit electrophysiological recordings were made from PrV. At the same time, we experimented with different angles for sectioning the brainstem that allowed for the best visualization of the modules in single sections.

Bottom Line: These measures were compared to fiber counts and primary cortical areas from a previous investigation.Our results indicate that PrV provides the first step in magnifying CNS representations of important afferents, but additional magnification occurs at higher levels.The early development of the 11(th), foveal appendage could provide a mechanism for the most important afferents to capture the most CNS space.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee, United States of America. ken.catania@vanderbilt.edu

ABSTRACT
A fundamental question in the neurosciences is how central nervous system (CNS) space is allocated to different sensory inputs. Yet it is difficult to measure innervation density and corresponding representational areas in the CNS of most species. These measurements can be made in star-nosed moles (Condylura cristata) because the cortical representation of nasal rays is visible in flattened sections and afferents from each ray can be counted. Here we used electrophysiological recordings combined with sections of the brainstem to identify a large, visible star representation in the principal sensory nucleus (PrV). PrV was greatly expanded and bulged out of the brainstem rostrally to partially invade the trigeminal nerve. The star representation was a distinct PrV subnucleus containing 11 modules, each representing one of the nasal rays. The 11 PrV ray representations were reconstructed to obtain volumes and the largest module corresponded to ray 11, the mole's tactile fovea. These measures were compared to fiber counts and primary cortical areas from a previous investigation. PrV ray volumes were closely correlated with the number of afferents from each ray, but afferents from the behaviorally most important, 11(th) ray were preferentially over-represented. This over-representation at the brainstem level was much less than at the cortical level. Our results indicate that PrV provides the first step in magnifying CNS representations of important afferents, but additional magnification occurs at higher levels. The early development of the 11(th), foveal appendage could provide a mechanism for the most important afferents to capture the most CNS space.

Show MeSH
Related in: MedlinePlus