I follow the Brain Identity Theory. This theory, sometimes called the mind/brain identity theory, is the idea that, whatever "mind" and "intelligence" are, they are rooted strictly in the brain, and do not make use of, depend on, or interact with anything non-physical. You are free to agree or disagree with this; I am simply stating it so you have a better feel for my perspective over these notes.
The human brain is made of approximately 100-billion nerve cells, called neurons. Neurons have the amazing ability to gather and transmit electrochemical signals. Neurons share the same characteristics and have the same parts as other cells, but the electrochemical aspect lets them transmit signals over long distances (several feet or meters) and pass messages to each other. Brain cells possess dendrites, or nerve endings. These small, branch-like projections of the cell make connections to other cells and allow the neuron to talk with other cells or perceive the environment. Dendrites can be located on one or both ends of the cell.
The simplest possible creatures have incredibly simple nervous systems made up of nothing but reflex pathways. For example, flatworms and invertebrates do not have a centralized brain. They have loose associations of neurons arranged in simple reflex pathways. Flatworms have neural nets; individual neurons linked together that form a net around the entire animal.
Most invertebrates (such as the lobster) have simple "brains" that consist of localized collections of neuronal cell bodies called ganglia. Each ganglion controls sensory and motor functions in its segment through reflex pathways, and the ganglia are linked together to form a simple nervous system. As nervous systems evolved, chains of ganglia evolved into more centralized simple brains.
The brain, when it has a thought, is like a thundercloud. The synaptic clef, is the sky between the storm and the earth, the earth being the receptor. Lighting striking is then thought processing amongst the neural net. When a coherent thought is made, the brain looks like a thunderstorm viewed from space.
Neurons have tiny branches that spread out and connect with other neurons which form a neural net. Each place where these branches connect is representative of a memory. The brain builds up all its concepts by law of associative memory. Ideas and thoughts are all constructed, and interconnected in this neural net. The concept of happiness, for instance, is stored in this vast neural net.
Physiologically, nerve cells that fire together, wire together. When we practice something over and over, the nerves involved with this process have a long term relationship. Similarly, nerve cells that do not fire together do not wire together. They lose their long term relationship. This results when we interrupt the thought process that produces a chemical response in the body. Those nerve cells that are connected to each other, start breaking the long term relationship. This means, that our emotions are imprinted chemicals in our brain, mapped to us by many previous engagements.
The hypothalamus is a small factory in our brain that creates certain chemicals that matches our current experience. These chemicals are called peptides, and they are small links of amino acids sequences. If we experience an emotion, the hypothalamus assembles the peptide, and releases it through the pituitary to the blood stream, where they travel to different cells in the body. Every single cell acts accordingly.
I explained how an atom reacts with another atom, so now we can focus on larger components. So, we start with another small unit in the brain: 1 brain cell. This cell that will act in a certain way as governed by the laws of physics. It may split, or move, float, or act, based on billions of stimuli: gravity, other cells pushing on it, nerve receptors firing, etc. If you have two brain cells, they will act again in a certain way, but the ability to predict what they will do has now grown exponentially because you are dealing with two brain cells with the same number of conditions effecting them both.
Now, when you get enough brain cells together, and several nerve endings, these will act in a certain way. Each cell having a billion stimuli, and each nerve ending having a billion more stimuli, make prediction very hard, quite impossible by our current means, but they will in fact act in a certain way, as you cannot have a physical entity such as a cell or nerve ending, deviate from the laws of physics.
Zoom out. When we were say, five years old, we burnt our hand on a stove, which made our brain cells and neurons interact with each other accordingly. This created a very specific new wiring in our brain. This very specific new wiring was based on billions of past actions, emotion and how we are in general. The brain will reconstruct itself precisely due to this. The brain will not cause nerves to form that will cause us to moo like a cow, for instance.
Now, say you have a completely functional person based on all of these past experiences. When the person sees their hand on a stove, light will reflect on the stove, and will enter your eye. Based on billions of light particles, and billions of imperfections and physical characteristics of your eyes, your brain will perceive the stove in an exact way. Say there is a nerve that doesn't work somewhere, and a slight perception of this stove is off. This is what helps mold your brain's instant perception of this stove.
So your body will thus react to this stove in a certain way immediately. Remember my original example with 1 brain cell having 1 billion stimuli, causing it to act in a certain way. If you have 2 brain cells, you have an exponential growth in possible outcomes. Now, add the culmination of the reaction ten trillion brain cells, along with trillions of nerves telling these brain cells what to do, based on what it just saw.
We continue, saying that your hand is being burnt on a stove. Your neural net will react based on the way your body has developed. A signal is sent through your arm, through individual nerves. Given enough time, we can analyze each variable that influences the passage of each signal, from the tip of your fingers all the way to your brain. We can watch an atom-by-atom reaction of the signal moving up your arm. The very first atom at the very tip of your finger excites the second one, which excites the third, and very quickly, you have a whole cell that has warmed, from touching the stove. (this is a micro-analyzed event, because in all actuality, trillions of atoms would be heating up at the same time). The second layer of skin then warms up as a result of the first layer warming, and so on, until atom-by-atom, the signal reaches your brain.
Imagine two atoms that directly influence each other. They are as two dominos. One domino falling has the exact same effect each time it falls: the second domino is hit and starts to act. No matter how many times we repeat the experiment, the first domino falling towards the second will cause the second to react, assuming the exact same variables are there. Imagine video taping the two dominos falling. No matter how many times you watch the video, they will always commit the same event because in this video, the variables never change. Now, if outside stimuli were to push the first domino in another direction, then the second domino would never be touched, no matter how many times your replayed the experiment.
Similarly, trillions of atoms and particles act, in a domino-like effect, sending a signal to the brain. With the same exact set of variables, the signal will reach the brain at the exact same time, every time the experiment is conducted.
Next, your brain reacts. A snap shot of your brain is our control. This snap shot of your brain is made up of many, many atoms that only arrived in this state from the immediate past. It will react again in the immediate future with every atom in your brain being a variable acting upon countless other atoms in your brain, thus resulting in the immediate future. This means that all of our brain cells will react accordingly, and the immediate future will see a result only possible because of the immediate past's influence. This is a highly complicated event of dominos. In the real game of dominos, each block is a simple rectangle. However in our brain's game of dominos, each block is a billion billion billion atoms. The same holds true, however. If we were to take any two immediate snap shots of our brain, the second would be derived from the first every time the variables acting upon the control were the same.
The obvious question is, what if an event happens that alters our experiment. Say, a baseball comes through the window and hits us while we are reacting to the stove over and over again. I say there is no atom in this universe that does not have an immediate past that could not have put the atom there. Therefore, if one had the imagination, one could take all atoms in the universe, using them as a part of our domino, thereby making no outside stimuli. This means that the baseball would already be part of our dominos experiment, and it would have been added as a variable in the first place. However, in our cosmic game of dominos, this baseball was not there, and it could not be produced from nothing so that it came into being, and alter our snap-shot results. This is because if a baseball were there in one of our experiments, we would be able to trace each atom in the baseball, back to the time immediately following the big bang. There would be a step that escaped physical law, and that step is when the baseball materialized so that it became part of our experiment.
When you react to your hand touching a hot stove, your brain will act precisely, determined by every event and every variable (trillions and trillions of events happening in your brain at a precise moment). Therefore making a predictible outcome.
This does not mean that cognitive science is false in studying intelligence. Perception, self awareness, and intelligence are still very much existent, even if free will did not exist.
At this point, we witness the breakdown of free will, as every chemical, amino acid, and decision, is based on an immediately previous physical snap shot.