In article <Pine.OSF.3.91.950217021735.1757A-100000 at duke.usask.ca> Kevin,
keh134 at duke.usask.ca writes:
>I am interested in obtaining information concerning the differences in
human
>and dolphin brain biology.
There are several scientists studying the anatomy of the dolphin brain,
especially the cerebral cortex. A good reveiw article on dolophin cortex
with lots of references(although it was published in 1990-5 years ago) is
"Comparative and Evolutionary Anatomy of the Visual Cortex of the
Dolphin" by Peter J. Morgaine, Ilya I Glezer, and Myron S. Jacobs,
published in volume 8b (Comparative Struvture and Evolutuion of Cerebral
Cortex, part II; pages 215-262) of the Cerebral Cortex book series E.G.
Jones and Alan Peters, eds.
They show that, although dolphin neocortex is very extensive, it has a
relatively primitive, undifferentiated structure. The layers of cortex
are not very well defined, and there appear to be fewer cell types than
in primates. This is lack of differentiation is especially notable in
primary visual cortex (V1). In cats or primates, e.g., V1 has a very
specialized layer 4 that is both highly granular (tiny stellate cells,
closely packed) and divided into sublayers that receive different classes
of inputs from the lateral geniculate nucleus. In the visual cortex of
the dolphin, layer 4 is hardly visible as a distinct layer.
In its simple organization, dolphin cortex appears to resemble that of
hedgehogs, which have an ancient lineage, fossil hedgehogs being present
in the fossil record over 70 million years ago. Morgane et al. argue
that, as the dolphin's ancestors entered the oceans more than 50 million
years ago, they have "...preserved characteristic features of the
original structure of the brain of primitive mammals in far greater
measure than have more advanced land animals." Sorry Flipper. So
dolphins, according to Morgaine et al. became smart by greatly increasing
the siurface area of their neocortex, without much change in its
complexity, while some terrestrial mammals became smart by greatly
increasing the complexity of neocortex, with smaller increases in extent.
Jamie Boyd
Dept. of Ophthalmology
University of British Columbia
Vancouver, B.C. Canada
boyd at org.ecc.ubc.ca
