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AVP
Shell
NPY
Core
OC
OC
OC
NT
VIP
OC
OC
Figure 1.4 Drawing the localization of peptide-containing neurons in the human SCN.
AVP, arginine vasopressin; NPY, neuropeptide Y; NT, neurotensin; OC, optic chiasm; VIP,
vasoactive intestinal polypeptide.
subdivisions come in a number of forms that have one of two bases. The first
is that the SCN is too complex to fit into such a rigid package, and the sec-
first argument is reminiscent of the debates in the early to mid-twentieth
century about cortical organization. Cytoarchitectonics, the study of the
laminar organization of the cerebral cortex, was initiated by Campbell
93
who described 14 cortical areas for which he proposed distinct functions.
describing 107 areas. No generally accepted map was accomplished by mid-
century, and no further attempts were reported. But the argument was
between “lumpers” and “splitters,” those espousing few areas and those with
many. Recent studies using functional imaging indicate that Brodmann's
areas are a good approximation of real functional areas. The conclusion is
that anatomical descriptions are of value if
they lead to functional
correlations.
The arguments for the core/shell are summarized in
Table 1.3
. They can
be placed in several categories. Core and shell connections differ. Expres-
sions of function such as light responses, intrinsic activity, responses to forced
desynchrony, development of photoperiodic responses versus intrinsic
rhythmicity, and clock gene expression all differ between core and shell.
Some individuals object to the terms “core” and “shell.” The intent in intro-
ducing this designation was twofold. First, anatomically core lies adjacent to
the optic chiasm and is largely surrounded by the shell in most mammalian
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