The experience of all the above-mentioned sensations directly comes from the individual. Fear can involve a fast and weak heartbeat, muscles that are trembling with no effect, and clammy hands. Anger can involve a fast and strong heartbeat, tense and hyperactive muscles, and a red face. Pleasure can involve relaxed muscles, stable respiration and heartbeats. These sensations and experiences become part of an individual’s memory. Usually, they are related to special and memorable events, comprising part of the signals of original emotional reactions, through which one can recall the related body reactions. Through memory fixation, sensation of body reactions to specific conditions becomes internalized as part of high-level function which doesn’t require special stimulus to arouse them.

The memory of sensation is part of the neocortex. Linking downward through the limbic system, the hypothalamus, the brain stem, and the spinal cord, it arouses the same feelings caused by the original condition or sensory stimulus. One can experience and report a kind of sensation, which means he can sense fear, anger, or pleasure without any present external causes. The memory of sensation is the major reason for one’s failure to efficiently control such emotions as anxiety, anger, and fear, etc. It is a normal function of the coordinated electrochemical activity of the nervous system in the human body. And it also makes humans unable to resist some drugs, such as cocaine, which can evoke addictive, near-collapse cravings.

After a person smokes or snorts cocaine, cocaine molecules will first enter the body from the nasal cavity and then travel through the blood- brain barrier (BBB) to the brain. BBB is a regulatory interface between the capillaries and the neural tissue in the brain and spinal cord and many large therapeutic molecules cannot pass through it. After entering the brain, the cocaine molecules then control dopamine transporters on the brain cell membrane in the region responsible for such pleasurable feelings as desire for food and sex. The basic function of these dopamine transporters is to uptake dopamine back to the cells to control the amount of dopamine released from the synapses.  The cocaine molecules just go inside the cell to exchange and release dopamine. Such kind of neurotransmitter mainly works on a brain area called the nucleus accumbens, which is full of neurons producing and responding to dopamine. Chronically stimulating the neurons to release dopamine will keep on generating pleasurable feelings, evoking addictive, near-collapse cravings (See the upper-right picture).