In article <6morh0$j4s$1 at fremont.ohsu.edu>, Matt Jones <jonesmat at ohsu.edu>
> In article <6mn56k$gai at dfw-ixnews3.ix.netcom.com> F. Frank LeFever,
>flefever at ix.netcom.com writes:
> >Maclean's "tripartate" brain (reptilian, amphibian, etc.) was an
> >imaginative but almost metaphorical expression.
>> These are good points, and obviously such a simple scheme is likely to be
> inaccurate in the details. However, in terms of which parts are necessary
> and sufficient for various levels of function, is it not true that
> animals that have been surgically decerebrated can still breath, their
> hearts beat, they secrete hormones, they have gastrointestinal functions?
> I would say that is evidence of a real functional segregation between
> "higher" and "lower" operations.
>> Matt Jones
Admittedly, I know little about Maclean's intention for his "tripartate"
brain. By calling it metaphorical, I can almost let it slide. Howver,
one cannot break the brain down into layers or parts based on age. It is
utterly incorrect to say that "the most primitive part of the human brain
can be described as the amphibian brain" or whatever. This is the case
for at least two reasons: 1) Evolution is not linear and 2) All brains
have evolved, even those of reptiles, etc. With regard to #1, mammals
existed on this planet before the dinosaurs. Yet, in the modern schema,
the mammalian brain is considered of a "higher order" than all others
becuase it is thought of as the most recent product of evolution. In
short, the employment of an evolutionary "line" of progression as a basis
of comparision is inherently flawed. As for #2, many adjustments have
been made over time to the brain in many, even, perhaps, all species.
These changes don't necessary reflect a change (ie an increase) in IQ, a
conclusion which many may jump to after a claim such as this one is made,
but modifications due to random mutation and, to a lesser extent, natural
selection, are continual, especially when considered on the time scale
suggested by Maclean's theory (ie 100's of millions of years). A more
direct way of arguing for my #2 is the following: One cannot point to any
part of the human brain and say "there, that section there is what a
lizard's brain looks like." Lizards have brainstems, limbic systems,
cerebelli, and even cortices. As for Mr. Jones' comment, first a
decerecrate animal is not an animal with its cortex disconnected from its
lower (spatially) brain structures as he is apparently implying. Rather,
in a decerebrate preparation, the entire brain is separated from the
spinal cord - a decerebrate animal cannot show the separation of "higher
and lower" brain areas. Secondly, yes the heart beats and the GI tract
maintains peristalsis - these activities are propertiews of the cardiac
and smooth muscle and can function without nervous input. These animals
do NOT breathe. If any hormonal action takes place, it is spontaneous and
not the result of neural input.