In her book, id, Susan Greenfield postulated that the mind is the personalized connectivity of the brain. In the first 2 years of life, the connections among the brain cells grow rapidly, matching the development of different functions of the brain. A second phase of brain development lasts until early adolescence, and is characterised by a greater number of easy forming connections, which is exquisitely sensitive to the environment - the brain is at its most plastic stage. At the end of this stage the brain is maximally connected. The final phase of late adolescence involves heavy pruning, as much as 50%. Unused connections are lost. The connections become localized and modular. Thus is the mind of each of us formed.
With diseases such as Alzheimer’s, the connections of parts of the brain die, the brain shrinks. In some cases you lose your memory for facts, things no longer make sense, people treat you differently, you will behave like a different person. In some cases, you lose the time and space precision of memories, memories become like vivid dreams. You are losing your mind, and identity.
Psychoses such as schizophrenia entail a departure from reality. They share some common characteristics with children. They cannot rationalize their fears or other emotions by recourse to the normal adult mind; they exhibit eccentric thought characterized by lose, tangential associations; they cannot interpret metaphors; they are easily distracted by sensations of the outside world; they do not appreciate that different brains think differently. The children have not yet developed the ability - their minds are not fully developed yet. The schizophrenics, sadly, have lost their minds.
All drugs affect brain function by interfering with the operations of chemical messengers, transmitters at the synapses, connections between brain cells. Amphetamine prolong the availability of dopamine and therefor its action, while cocaine slows down their removal. Ecstasy triggers the explosive release of serotonin. Tranquillizers block the handshake between a transmitter and its receptor. Heroin can act as an impostor and trick the brain into believing that a natural transmitter has been released.
As a result, cannabis impairs driving ability as well as motor skills for up to five days after taking the drug. It modify synapses between brain cells and hence neuronal plasticity and hence the mind. It could demotivate you, disrupt your memory and shorten your attention span. A user may not realize natural intellectual potential and may arguably be a different person. If the receptor becomes less sensitive due to being over stimulated by the persistent drug, more will be needed for normal function - addiction.
There are other types of dysfunctions. The obese individual living in the moment for the taste of food, and the reckless computer gamer high on the excitement of scoring, are placing a premium on the sensation of the experience of the moment rather than considering the consequences - the same pattern of behaviour seen in children and schizophrenics.
Some people lose their minds because of disease or psychoses. Others, sadly, lose their minds voluntarily. They are essentially throwing their minds away.