Regardless, the author is optimistic that eventually technology will refine our understanding. We can define pain with physical descriptors and emotional words, but how and why such a wide range of information inputs and memories should stimulate the VTA is not clear. One issue is the concept of pleasure itself.
Linden is clear that there are many unanswered questions. While this may offer strategies for drugs to fight addiction, it also raises legal and ethical issues should genetic testing be proposed. The author suggests that the genetic risk of addiction may be as high as 50 percent and involve gene variants in dopamine types and receptors. In some people, such behaviors can progress to addiction, a pathological process that changes the structure and function of the VTA, transforming pleasure to craving. (Cocaine and other drugs block this re-uptake, flooding the circuitry with dopamine to increase the “high.”) Linden details brain-imaging experiments which indicate that the VTA is activated not only to aid human survival by affording the pleasures of eating and the joys of sex, but also in connection with behaviors ranging from consuming fatty foods, charitable giving, exercise, gambling and certain types of learning and ideas. A dopamine transporter takes up the released dopamine so the cell can fire again. When certain neurons in this area are excited, they release dopamine to target neurons in the prefrontal cortex and in selected emotional, motivational and memory centers.
The human equivalent of this pleasure circuit is the ventral tegmental area (VTA). The author notes that it was back in the 1950s that McGill University scientists discovered that rats with electrodes implanted in a specific part of their brains would press a lever repeatedly to stimulate the area, to the exclusion of food, water or sex. The Accidental Mind: How Brain Evolution Has Given Us Love, Memory, Dreams, and God, 2007) probes the anatomy of pleasure in this review of what happens in the brain when we “feel good.”
Journal of Neurophysiology editor in chief Linden (Neuroscience/Johns Hopkins Univ.
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