Re: If the brain is all about electrical signals why cant we just use signals?

This is a good question!  The shortest answer is that scientists have been 
trying to reproduce the brain's signals for many years, but the technology 
isn't good enough yet to either measure or reproduce the signals 
accurately.  It is impossible right now, but maybe not in the future.

I will explain more, but first, a little background.  The brain does 
process information using electrical signals, called action potentials, 
which are small, fast electrical pulses.  Scientists study the electrical 
signals, or action potentials, by recording them on specialized equipment. 
More about this equipment and its limitations later.

We will use vision as an example, as in your question. In the retina are 
cells, which sense light, dark, and color (called rods and cones).  These 
cells are connected to nerve cells (called retinal ganglion cells) which 
together make up the optic nerve, which sends action potentials to the 
brain.   There are about a million ganglion cells, which make up the optic 
nerve.  Once in the brain, these cells connect to millions of other nerve 
cells, which interpret the information and form an image of what you see.

To reproduce the information this nerve is sending about what you see, we 
must know what every single nerve cell is doing - whether or not it is 
sending action potentials, how many it sends, and when it sends them.  Each 
of these thousands of nerve cells is going to be sending different 
information, and we need to know all of it.  As you may imagine, no 
technology exists to record all these different signals at once.

The second problem is this: how would we create something that would hook 
up correctly to all those different nerve cells, and stimulate them so that 
they fire action potentials in just the right pattern?  Nerve cells are 
very small - around 10 microns, or 1/100 of a millimeter.  Individual nerve 
fibers are even smaller - less than 1 micron, or 1/1000 of a millimeter.  
We don't have equipment small enough to do that in the eye.  There are 
cochlear implants, though, which stimulate auditory nerve fibers, helping 
deaf people to hear.  They do not connect to every nerve fiber, but they 
can reproduce some parts of what we hear.  For more information on how your 
idea is already being used, see http://www.deafblind.com/cochlear.html.  
This technology has limitations - there are usually about 20 different stimuli 
being delivered to the nerve fibers in a cochlear implant, as opposed to 20,000 
in the normal ear.

The smell molecule question is entirely different.  We can make artificial 
smell molecules, and much of what you smell every day is "artificial".  
Chemical smells such as burning plastic or nail polish do not exist in 
nature, but you are able to smell them.  Your nose and brain process these 
odors the same way they process "natural" smells such as grass or flowers.

If you have other questions, or need clarification of this one, please 
contact me!

Brenda