The Journal of Neuroscience, December 15, 1998, 18(24):10603-10618
Anatomic Evidence of a Three-Dimensional Mosaic Pattern of
Tonotopic Organization in the Ventral Complex of the Lateral Lemniscus
in Cat
Manuel S.
Malmierca1,
Trygve B.
Leergaard2,
Victoria M.
Bajo1,
Jan G.
Bjaalie2, and
Miguel A.
Merchán1
1 Laboratory for the Neurobiology of Hearing,
Department of Cellular Biology and Pathology, University of Salamanca,
and the Institute of Neuroscience of "Castilla y León"
(INCyL) at Salamanca, E-37007 Salamanca, Spain, and
2 Department of Anatomy, Institute of Basic Medical
Sciences, University of Oslo, N-0317 Oslo, Norway
The ventral complex of the lateral lemniscus (VCLL, i.e., the
ventral and intermediate nuclei) is composed of cells embedded in the
fibers of the lateral lemniscus. These cells are involved in the
processing of monaural information and receive input from the
collaterals of the fibers ascending to the inferior colliculus. Whereas
tonotopic organization is a feature of all other nuclei of the auditory
system, this functional principle is debated in the VCLL. We have made
focal injections of the tracer biotinylated dextran amine into
different frequency band representations of the inferior colliculus in
cat. Retrogradely labeled cells and terminal fibers (collaterals of
efferent local axons and other ascending lemniscal fibers) were found
in the ipsilateral VCLL. The spatial distribution of the labeling was
analyzed using three-dimensional (3-D) reconstruction and computer
graphical visualization techniques. A complex topographic organization
was found. In all cases, labeled fibers and cells were distributed in
multiple clusters throughout the dorsoventral extent of the VCLL. The
shape, size, and location of the labeled clusters suggest an
interdigitation of clusters assigned to different frequency-band
representations. But an overall mediolateral distribution gradient was
observed, with high frequencies represented medially and lower
frequencies progressively more laterally.
We conclude that the clusters may represent discontinuous
frequency-band compartments as a counterpart to the continuous laminar compartments in the remaining auditory nuclei. The 3-D orderly mosaic
pattern indicates that the VCLL preserves the spectral decomposition
originated in the cochlea in a way that facilitates across-frequency integration.
Key words:
auditory system; inferior colliculus; ventral complex of
the lateral lemniscus; monaural system; tonotopic organization; frequency-band laminae; computer-assisted 3-D reconstruction; across-frequency integration
Copyright © 1998 Society for Neuroscience 0270-6474/98/182410603-16$05.00/0
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