Re: Which affects more in a mature peronality:Genes or experience?

Hi Mariza!

This is a fun question; I don't know if it can be completely answered at
this stage of scientific discovery.  So, I'll weigh in with my $ 0.02.  I
hope that my response doesn't so much answer your question as give you 
incentive to do further study into this fascinating and complicated topic.

My response will touch on two stages: early brain development, and adult
brain function.  The helpful aspect of studying early development is that you
can do well-controlled experiments to answer specific questions.  The problem
is that the outcome of these experiments may or may not mirror what's actually
relevant for the adult brain.  It's much harder to do experiments on adult 
brains, because those brains have been influenced by a lifetime's experiences.
Empirical study and everyday experience suggest that genes and environment are 
both important determinants of personality in the mature brain.

So, how does a brain develop?  A lot of researchers striving to answer this
question have turned to the study of the visual cortex, that area of the
brain that processes information from the retina of your eye. There's been a
raging debate for at least the last 25 years centering around the topic of, "Is
it activity (experience) or molecules (genes) that patterns the cortex?"
Early studies on the development of visual cortex (notably those by Stryker and
colleagues) pinpointed the role of activity in cortical development.  For
instance, if you deprive an eye of activity by suturing the eyelid closed or
preventing the neurons from firing action potentials, the cortex develops
abnormally.  Score one for activity.  BUT, with tremendous advances in
molecular and microscopy techniques over the last decade or so, evidence has 
also developed to support a role for molecules playing a critical role in the 
early patterning of cortex -- the Katz lab at Duke has had some very 
provocative papers on this topic over the last several years.

That's not the whole story, though:  recently, the Sur lab at MIT has 
developed a technically brilliant method of "rewiring" the brain so that neurons
from the eye form circuit connections with the auditory cortex.  Auditory 
cortex and visual cortex normally look and function in different fashions.  
However, the Sur lab's technique has shown that "rewired" auditory cortex looks 
and functions like visual cortex -- suggesting that an awful lot of cortical 
development can be explained by primarily activity-dependent models.

So, the question is still open, with strong evidence on BOTH sides that
genes and activity are responsible for early cortical development.

What about in the mature brain?  On a molecular level, studies have
shown that the brain is highly dynamic, with neurons constantly forming and
changing synaptic connections.  Sets of genes are intimately involved with the
ways that neurons communicate with each other and "remember" what has happened
(from 5 minutes ago to 5 decades ago).  Activity and genes work together to form
and erase memories.

Let's zoom out from cells to the whole brain now.  How does what's happening at
the cellular level reflect what the whole brain does?  Many studies have also 
shown that genes/molecules play a role in shaping moods, emotions, and other 
complex aspects of a person's character.  For instance, alterations in the 
brain's responisveness to the neurotransmitter serotonin can result in clinical 
depression; drugs which boost serotonin signaling between neurons (such as 
Prozac/fluoxetine) are often very effective treatments for depression.

That work can be regarded as a real sign of encouragement ("if we know
the molecular basis of disorders, we can find drugs to cure them"), or as a
scary, deterministic view of the mind ("if genes produce behavior and we can't
control our genes, then how can we control our minds?").

I tend to believe that having a better understanding of the molecular
underpinnings of personality IS beneficial and not scary.  I also think
it is important, however, to recognize that genes are NOT the be-all and
end-all of personality determination.  Our formative childhood experiences, role
models, educations, social involvements, day-to-day experiences, and so forth
can have a *profound and changing* effect on our personality. I don't think it's
really possible to quantitate this effect, though -- for specific examples one
can probably point to a strong genetic or environmental determinant, but not
for all cases.

Some further examples: many researchers are working to identify genes
that "cause" conditions as diverse as Alzheimer's disease, alcoholism,
obesity, schizophrenia, perfect musical pitch, and narcolepsy.  The 
overwhelming conclusion of these studies is that human traits tend to involve
multiple genes, rather than being exclusively caused by single genes. The 
severity of a condition can be greatly affected by the interaction of these 
suites of genes, AND by environmental effects.

Now, for some references: you can look up scientific abstracts for free
on PubMed, at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed .
Type in the authors' last names to locate a specific paper, or use keywords to 
do a search on an interesting topic.  For some journals, you can even see the 
articles for free.  "Reviews" offer a broader view of a field than "articles," 
which tend to report specific findings.

On early development of the visual system, I've referenced papers by
Stryker, Shatz, and LeVay; Crowley and Katz; and Von Melchner and Sur.

On genes and the adult brain: Baharloo and Freimer have a paper on
perfect pitch; McInnes and Freimer have a review on mapping other traits; Lin 
and Mignot describe a gene for canine narcolepsy.

Two other good resources are the Principles of Neural Science text by
Eric Kandel (who recently won an Nobel prize), and this site: http://faculty.washingt
on.edu/chudler/neurok.html

Hope this gives you some food for thought,
Amanda Kahn