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What is the mind, and where does it come from ? Is the mind the same as the "soul", and thus sepparate from the brain, or is it just a product of the pysical activity of the brain ? To answer this question, lets consider what happens when we get intoxicated from drinking beer, and what happens when we take Prozac for our depression.
Ethanol in beer is a physical substance, and it binds to the physical entity of a GABA receptor on neurons and thus accentuates the inhibitory effect of the neurotransmiter GABA (gamma-amino butiric acid) on the brain. Thus we get a slurring of our speach, and a stumbling in our steps. Similarly for psychoactive drugs like anti-depressents, they effect the activity of neurotransmitters. Serotonin reuptake inhibitors block the enzyme that takes the neurotransmitter serotonin back into the presynaptic terminals. Thus serotonin remains in the synaptic cleft, and continues to activate its receptors on the postsynaptic side. This leads to elevation of person's mood and reduction in depression.
The brain is made up of physical entities such as neurons and neurotransmitters and receptors. There is no "soul" inside our scull.
The mind is created by the different components of the brain. Just like the brain is not one monolythic organ, the mind which is its product, is not one unified "soul". Each part of the brain creates a distinct segment of the mind, and we get the illusion that our mind is one unified entity, when in fact it is not. The brain can suffer selective damage to distinct nuclei whithin it. This will cause a selective destruction of that part of the mind which arises from that part of the brain. Loss of the hypocampus will lead to loss of new memory formation. Loss of the amygdala will lead to loss of emotional response. Damage to cerebellum will lead to loss of motor control. The most dramatic example is split personality disorder, which is basically a shattering of the mind, leading to multiple personalities. Such a patient obviously does not aquire multiple "souls", but suffers from a fragmentation of his/her mind.
Minds are simply what brains do. Or more accurately, the mind is an illusion created by the amalgamation of its various components, each created by a distinct part of the brain. There is no such thing as the "immortal soul". When the brain dies, so does the mind.