[Neuroscience] Re: Question for a neurosurgeon

Matthew Kirkcaldie m.kirkcaldie at removethis.unsw.edu.au
Sun Jan 8 18:38:40 EST 2006

In article <84ed8$43c16d64$43888dc7$18078 at DIALUPUSA.NET>,
 "BeardIron" <noemail at anywhere.123> wrote:

> Is there a place in the brain where you can touch that
> will stimulate hunger and thurst and sex drives and so forth ?
> Also I understand the human brain to be a marvel of evolutionary
> process with older and newer parts to it...There supossedly is
> a reptile brain imbedded in the newer human brain....what
> is the proper medical term given to this reptile brain
> and what happens when it is stimulated/probed during brain
> surgery ????

Most of the surface-stimulation experiments tap into cortical functions 
- so-called "higher" abilities like memory, sensation, etc.  The 
functions you describe are generally governed by the hypothalamus, which 
is a tiny structure buried deep underneath the rest of the brain, 
roughly in the middle of a line between the temples.  It does a lot of 
very basic, vital function in the nervous system and hence surgeons are 
VERY reluctant to mess about with it, even just to stimulate it.  These 
kinds of stimulation experiments have been done on other mammals, 
especially rats, and shown to induce or suppress these kinds of drives.  
Furthermore, humans with damage to or tumours growing in this part of 
the brain often have their basic drives altered.

When people talk about the "reptile brain" it's really a figure of 
speech - they refer to the limbic system and brainstem, which includes 
the hypothalamus and some other basic regulatory mechanisms.  Mammals 
have several other systems "on top of" the limbic system, notably the 
thalamus and the cerebral cortex, and these are the seat of more complex 
perception and behaviour.  It's inappropriate to call reptile brains 
"older" since they and we descended from the same original multicellular 
ancestors.  Their brains and ours have been evolving for exactly the 
same amount of time - it's just that reptiles live in ways which don't 
require a thalamus and a cortex.  We live in more challenging 
environments in which it's an advantage to make more sophisticated 
sensory discriminations and to reason about things in a more abstract 
way.  Otherwise we wouldn't have bothered growing such a complex brain 
that's expensive and tricky to maintain!

      Cheers, MK.

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