For years the brain’s reward system, involving domaminergic neurons in the ventral tegmental area which project to the nucleus accumbens and frontal cortex, was thought to be the basis of pleasure . The idea was that dopamine release made feeding, reproduction, and care of the young feel good, which motivated animals to carry out behaviors good for evolutionary success. Drug abuse was thought to represent the choice of short-term pleasure over long-term well-being. But, to borrow words from Francis Crick, “It would be so pretty if it were true.” The dopamine reward system turns out to have much more to do with reinforcing adaptive behaviors and associating them with environmental cues than with producing feelings of pleasure.
At a basic level, the reward system is concerned with homeostasis. The body has elaborate systems to monitor temperature, hydration, salt balance, blood pressure, food intake, and energy expenditure. The brain’s motivational systems respond to this information by changing behavior when the system is out of balance. It also learns to make adjustments in anticipation of upcoming changes. Peter Shizgal and Steven Hyman note that camels conserve water by letting their body temperatures cool below normal at night, delaying the need to sweat as the temperature rises during the day. They also note that motivational states arise in response to both internal and external inputs—the time since an animal has eaten and whether she is lactating, and also the opportunities in the environment to acquire resources like food and water. In addition, motivational systems respond to non-homeostatic needs such as reproduction and care of young.
Stressful as well as pleasurable stimuli affect dopamine release. In a review of the brain's mechanisms of pleasure and displeasure, Kent Berridge and Morten Kringelbach describe research indicating that dopamine is released in response not to pleasurable stimuli, but to unexpected rewards. Since dopamine is involved in learning, i.e. the encoding of such information in memory, dopamine release motivates animals to maximize future rewards and avoid fruitless pursuits. None of this requires emotions of pleasure.
Berridge and Kringelbach note that while pleasures differ qualitatively—enjoyment of food differs from that of sex or music—there is considerable overlap in the brain regions activated in scans of people engaging in various pleasurable activities. These include the orbitofrontal, anterior cingulate, and insular cortices as well as the nucleus accumbens, ventral pallidum, amygdala, and mesolimbic tegmentum. The most consistently activated area is in the mid-anterior orbitofrontal cortex.
In contrast to these areas which activate in imaging studies of human subjects, animal brain stimulation studies identify more subcortical areas involved in the production of “liking” reactions. Here we encounter the problem of interpreting emotional responses of animals. Berridge and Kringelbach use facial expressions, gestures, and vocalizations which are homologous across species to indicate positive reactions. Most of their work involves liking responses to sweet drinks. They found the mesolimbic dopamine system involved in reward and motivation, but not in liking. Liking is produced by stimulation of a number of small “hotspots” in parts of the nucleus accumbens and ventral pallidum. The two hotspots appear to function as an integrated hedonic circuit. Rather than dopamine, opioid and endocannabinoid signals generate pleasure, but only in these hotspots. Opioid stimulation of the rostral nucleus accumbens hotspot produces both liking and wanting, while stimulation with dopamine or glutamate produces only wanting.
To bring this to the level of clinical work, the reward system would seem to modulate the clinician’s engagement with the patient. When a clinician encounters a patient, she may expect gratification of her needs for social rewards, such as admiration; satisfaction at doing a good job; and financial compensation. Since the reward system responds primarily to the unexpected, she may be motivated to engage with the patient by changes in these and other stimuli. This brings to mind Atul Gawande's recommendation to ask an unscripted question at every patient visit, so “the machine begins to feel less like a machine” and the clinician remains engaged. Patient behaviors that provide unexpected stimulation of the clinicians caretaking, sexual, and social play systems should reinforce the clinician’s engagement with the patient. New or varying stimuli with negative valences of anger, fear, disgust, or loss should elicit negative reinforcement.
Berridge and Kringelbach note that different small regions of the shell of the nucleus accumbens may balance positive and negative responses such as desire and dread. The balance between the two can be adjusted by top-down psychological input. Extending this to the clinical situation, a patient’s flirtatious behavior may stimulate the clinician’s sexual response system and thereby motivate increasing engagement with the patient, but this may be modified by understanding of her professional responsibility to maintain boundaries. Patients’ provocation of fearful or angry responses may turn down the dopamine reward system and motive disengagement, balanced by intellectual interest in the patient’s psychology, a desire to care and help, or by reframing the patient’s behavior as the product of a disorder the clinician feels competent to treat.
For me, the main lesson of all this is to pay more attention to my motivation to engage or disengage with the patient, for it is basic to the therapeutic alliance. By identifying clinician motivation as a primary element in every encounter, one can then step back and look at what may be promoting engagement in helpful or unhelpful ways, and what may interfere.
Peter B. Shizgal and Steven E. Hyman, Homeostasis, Motivation, and Addicive states, in Principles of Neural Science, Fifth Edition, Eric R. Kandel, James H. Schwartz, Thomas M. Jessell, Steven A. Siegelbaum, and A.J. Hudspeth, editors, 2013. pp 1095-1115