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INTERNAL
STRUCTURE
OF
CEREBRAL
CORTEX
intrinsic cortex is larger than the
homologous human cortex, and its
ratio
is very dose to man's, what then,
gives the human brain any superiority
at all?
Kruger proposes the answer. But
his cogent rcasoning is cven more
interesting. To understand either, we
must first learn about the microscopic
appearance of cerebral cortex. The
cell bodies of the bilJions of neurons
seem to be horizontally arranged in
various layers - called "laminars.".>
As mammals increase in mental
complexity from rabbit to cat to chimp
to man, there is a general tendency
for these laminars to become more
stratified and more distinct. Now what
3
Each l:tminnr, .seen in mtcroscupic cross
Sl'..,ctirm
as a "laycr,"
is
actually
3
"laycred t;heet"–
each one runnin.R parallel
to
thc cortical
surface
at its own <p<eifi<-d depth. The accepted sysrem
ct.ssifies six <uch l•yers. Hn"ev<r. in m:an. there
has b«n diS3Jtre<mcnt •s tn hnw many layers.
subl>yer<, ere.. there are in any j.livcn cortical
locus.
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The cerebral cortex is the seat
of all higher mental activity.
Shown to the right are cross–
sections of the human (
1/ 6
inch th ick), chimp, rat and
dolphin cortex. Notice six
dis–
tinct
ce//u/or
layers
in the human
ond chimp - and the
lack
of
such distinct loyers in the rot
ond dolphin. Could this help
exploin intelligence?
about the cetaceans? Well, brain re–
search has finally uncovered the long–
sought "good criterion for insisting
upon man's superiority." Because in
cetaceans this laminar arrangement is
largely
absent.
Notice how Kruger
phrases his conclusion:
lf
we were forced m choose the
criteria
of
greatest relevance
10
intellec–
rual development, the mere fact that
three mamn1alian orde rs (Cetacean,
Primates and Proboscidca [clephants})
presumably develop extcnsive "asso–
ciation" cortex would seem
to
suggest
that the degree
of
laminar differeotia–
tion is the most evident characteristic
thar can be claimed
for
superiority in
the human brai n, unless one wishcs
to
claim that dolphins aod clcphants are
as clever
as man.
Why, asks Kruger, are human
be–
ings mentally superior to whales, dol–
phins, and elephants when the brains
of the lattcr are enormously larger
in size and almost equal with respect
to all the traditional standards?
Kruger has
no
alternativc - he
. ...
..
has only onc viable point m which
human brain is supreme:
laminar
differentiation
-
human cortical cells
are arranged neatly in layers.
Circular reasoning has dictated this
judgment - and Kruger tells us so!
His logical appraisal is as sound as
it is forthright and honest. He
kneu
that man's brain
mmt
be
the most
advanced - yet he saw every tradi–
tional neurological yardstick dcny it.
Though other authors would cling to
these ill-adviscd criteria -
which
supposedly prO\'Cd human brain su–
perior to cctacean brain when in fact
they suggested guite the reverse -
Krugec candidly eliminated them. As
a result, he had to nominatc the only
conceivable way in which human brain
could
possibty
be supreme: the ar–
rangement of human cortical cell
bodies in layers and the absence of
such laminar stratification in cetacean
cerebral cortex.
PlAIN TRUTH Moy 1972