Re: Is there firm evidence for the exsistence of a subconscious?

The short answer is that there are most definitely subconscious parts of 
brain function and that they profoundly influence our thoughts and actions. 
The difficult thing is to decide exactly how to define the subconscious.

The first person to really start thinking about the subconscious (as you 
are probably defining it) was Sigmund Freud.  In fact, the subconscious 
basically forms the basis for his invention of the technique of 
psychotherapy and his ideas of the subconscious are still used basically 
unchanged to this day by psychologists in their analysis of human behavior. 
However, we have learned an incredible amount about the brain since the 
time of Freud - and now we realize that most of his ideas were extremely 
over-simplistic and mostly wrong.  Though Freud was revolutionary for his 
time of course.

So what does modern neuroscience tell us about the subconscious?  I think 
the first thing to keep in mind is that we have found that the subconscious 
is not "one" thing, but in fact a collection of separate subconsciouses - 
if you will.  

Basically, let us define subconscious mental activity as mental activity 
that is not present in our immediate consciousness.  There are of course 
many levels of this.  Sex hormone secretion or heart rate, both controlled 
by the brain, cannot be influenced by our consciousness.  However, 
breathing for example is controllable - we can hold our breath, breathe 
deeply, breathe fast or slow, etc.  But most of the time, we don't think 
about our breathing - in a sense it is completely automatic.  Thus, you can 
consider breathing to be a subconscious mental activity.  There are in fact 
many automatic aspects of brain activity (such as keeping one's balance) 
that can be overridden by conscious mental activity when we choose.  

There are much more sophisticated forms of subconscious activity as well.  
For example, there are two pathways in the visual system - one that goes 
through the visual cortex (which is what we would call our conscious vision 
process) and then there is a more primitive process that goes through the 
brain stem.  Since we are not conscious of this more primitive form of 
vision, it can be considered subconscious.  However, it is measurable.  For 
example, there are people who, due to some form of brain damage, have lost 
the "conscious" part of vision and are therefore blind.  However, many of 
these people have what we call "blind sight."  That is you can put one of 
these people in front of a mailbox, hand them a letter, and ask them to 
place it into the mailbox.  Of course, they believe that they are blind and 
will tell you that you are asking the impossible.  But if you say to them 
"Oh, just make your best guess" they will invariably place the letter 
perfectly into the box in the correct orientation.  So clearly they can see 
the box, but they are not conscious of this!  There are in fact ways to 
show that normal people also have this subconscious aspect of vision as 
well.

Now think of memory.  When we remember a fact, it somehow gets stored in 
the brain as a memory.  However, most of the time this memory is not in 
your conscious mind.  Only when you specifically attempt to recall the 
piece of information does it enter into the consciousness.  Thus, normal 
memory can be thought of as subconscious.  In fact, sometimes we may have 
great difficulty recalling a certain memory (like the name of some actor, 
for instance) - but often we will finally be able to recall it, though 
sometimes after 30min or so of effort.  Thus, clearly this memory is IN the 
brain, but not immediately accessible by the conscious mind.  The modern 
way of thinking about memory recall is in fact not that we have lost the 
memory, but in fact that our brains are actively repressing the memory.  It 
is very important to keep our minds clear of clutter - so our brains 
purposely repress memories when they are not needed.  There are in fact 
cases of people with certain types of brain damage where this repression 
process no longer functions.  These people are completely unable to function in 
normal society.  They are literally driven crazy by their own memories!

There are actually several types of memory - not just memory for facts - 
which we would call declarative memory.  We also have emotional memories.  
For example, say someone ate an entire jar of peanut butter as a child and 
got a stomach ache.  This can form such a deep-rooted, long-lasting memory 
that this person may never touch peanut butter again!  This form of memory 
is more primitive than declarative memory, but certainly can have a 
profound influence on behavior.  This type of memory might also be the 
cause of phobias, as described by Freud.  And they are completely 
subconscious.

If you would like to learn more information about the subconscious and even 
the nature of consciousness itself, I urge you to pick up a copy of a 
fantastic recently published book called "Phantoms in the Brain : Probing 
the Mysteries of the Human Mind" by V. S. Ramachandran and Sandra 
Blakeslee.  It's very readable and addresses these sorts of questions 
directly and scientifically.

I hope this answered most of your questions.

Take care,
Dave