Pleasure is a broad class of mental states that humans and other animals experience as positive, enjoyable, or worth seeking. It includes more specific mental states such as happiness, entertainment, enjoyment, ecstasy, and euphoria. The early psychological concept of pleasure, the pleasure principle, describes it as a positive feedback mechanism that motivates the organism to recreate the situation it has just found pleasurable, and to avoid past situations that caused pain.
The experience of pleasure is subjective and different individuals experience different kinds and amounts of pleasure in the same situation. Many pleasurable experiences are associated with satisfying basic biological drives, such as eating, exercise, hygiene, sleep, and sex. The appreciation of cultural artifacts and activities such as art, music, dancing, and literature is often pleasurable.
Based upon the incentive salience model of reward - the attractive and motivational property of a stimulus that induces approach behavior and consummatory behavior - an intrinsic reward has two components: a "wanting" or desire component that is reflected in approach behavior, and a "liking" or pleasure component that is reflected in consummatory behavior. While all pleasurable stimuli are rewards, some rewards do not evoke pleasure.
Pleasure is a component of reward, but not all rewards are pleasurable (e.g., money does not elicit pleasure unless this response is conditioned). Stimuli that are naturally pleasurable, and therefore attractive, are known as intrinsic rewards, whereas stimuli that are attractive and motivate approach behavior, but are not inherently pleasurable, are termed extrinsic rewards. Extrinsic rewards (e.g., money) are rewarding as a result of a learned association with an intrinsic reward. In other words, extrinsic rewards function as motivational magnets that elicit "wanting", but not "liking" reactions once they have been acquired.
The reward system contains pleasure centers or hedonic hotspots - i.e., brain structures that mediate pleasure or "liking" reactions from intrinsic rewards. As of October 2017, hedonic hotspots have been identified in subcompartments within the nucleus accumbens shell, ventral pallidum, parabrachial nucleus, orbitofrontal cortex, and insular cortex. The hotspot within the nucleus accumbens shell is located in the rostrodorsal quadrant of the medial shell, while the hedonic coldspot is located in a more posterior region. The posterior ventral pallidum also contains a hedonic hotspot, while the anterior ventral pallidum contains a hedonic coldspot. Microinjections of opioids, endocannabinoids, and orexin are capable of enhancing liking in these hotspots. The hedonic hotspots located in the anterior OFC and posterior insula have been demonstrated to respond to orexin and opioids, as has the overlapping hedonic coldspot in the anterior insula and posterior OFC. On the other hand, the parabrachial nucleus hotspot has only been demonstrated to respond to benzodiazepine receptor agonists.
Hedonic hotspots are functionally linked, in that activation of one hotspot results in the recruitment of the others, as indexed by the induced expression of c-Fos, an immediate early gene. Furthermore, inhibition of one hotspot results in the blunting of the effects of activating another hotspot. Therefore, the simultaneous activation of every hedonic hotspot within the reward system is believed to be necessary for generating the sensation of an intense euphoria.
Pleasure is considered one of the core dimensions of emotion. It can be described as the positive evaluation that forms the basis for several more elaborate evaluations such as "agreeable" or "nice". As such, pleasure is an affect and not an emotion, as it forms one component of several different emotions. Pleasure is sometimes subdivided into fundamental pleasures that are closely related to survival (food, sex, and social belonging) and higher-order pleasures (e.g., viewing art and altruism). The clinical condition of being unable to experience pleasure from usually enjoyable activities is called anhedonia. An active aversion to obtaining pleasure is called hedonophobia.
Pleasure is often regarded as a bipolar construct, meaning that the two ends of the spectrum from pleasant to unpleasant are mutually exclusive. This view is e.g. inherent in the circumplex model of affect. Yet, some lines of research suggest that people do experience pleasant and unpleasant feelings at the same time, giving rise to so-called mixed feelings.
The degree to which something or someone is experienced as pleasurable not only depends on its objective attributes (appearance, sound, taste, texture, etc.), but on beliefs about its history, about the circumstances of its creation, about its rarity, fame, or price, and on other non-intrinsic attributes, such as the social status or identity it conveys. For example, a sweater that has been worn by a celebrity is more desired than an otherwise identical sweater that has not, though considerably less so if it has been washed. Another example was when Grammy-winning, internationally acclaimed violinist Joshua Bell played in the Washington D.C. subway for 43 minutes, attracting little attention from the 1,097 people who passed by, and earning about $59 in tips. Paul Bloom describes these phenomena as arising from a form of essentialism.
Epicurus and his followers defined the highest pleasure as the absence of suffering and pleasure itself as "freedom from pain in the body and freedom from turmoil in the soul". According to Cicero (or rather his character Torquatus) Epicurus also believed that pleasure was the chief good and pain the chief evil.
In the 12th century Razi's "Treatise of the Self and the Spirit" (Kitab al Nafs Wa'l Ruh) analyzed different types of pleasure, sensuous and intellectual, and explained their relations with one another. He concludes that human needs and desires are endless, and "their satisfaction is by definition impossible."
In the past, there has been debate as to whether pleasure is experienced by other animals rather than being an exclusive property of humankind; however, it is now known that animals do experience pleasure, as measured by objective behavioral and neural hedonic responses to pleasurable stimuli.
Rewards in operant conditioning are positive reinforcers. ... Operant behavior gives a good definition for rewards. Anything that makes an individual come back for more is a positive reinforcer and therefore a reward. Although it provides a good definition, positive reinforcement is only one of several reward functions. ... Rewards are attractive. They are motivating and make us exert an effort. ... Rewards induce approach behavior, also called appetitive or preparatory behavior, and consummatory behavior. ... Thus any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward. ... Rewarding stimuli, objects, events, situations, and activities consist of several major components. First, rewards have basic sensory components (visual, auditory, somatosensory, gustatory, and olfactory) ... Second, rewards are salient and thus elicit attention, which are manifested as orienting responses (FIGURE 1, middle). The salience of rewards derives from three principal factors, namely, their physical intensity and impact (physical salience), their novelty and surprise (novelty/surprise salience), and their general motivational impact shared with punishers (motivational salience). A separate form not included in this scheme, incentive salience, primarily addresses dopamine function in addiction and refers only to approach behavior (as opposed to learning) ... Third, rewards have a value component that determines the positively motivating effects of rewards and is not contained in, nor explained by, the sensory and attentional components (FIGURE 1, right). This component reflects behavioral preferences and thus is subjective and only partially determined by physical parameters. Only this component constitutes what we understand as a reward. It mediates the specific behavioral reinforcing, approach generating, and emotional effects of rewards that are crucial for the organism's survival and reproduction, whereas all other components are only supportive of these functions. ... Rewards can also be intrinsic to behavior (31, 546, 547). They contrast with extrinsic rewards that provide motivation for behavior and constitute the essence of operant behavior in laboratory tests. Intrinsic rewards are activities that are pleasurable on their own and are undertaken for their own sake, without being the means for getting extrinsic rewards. ... Intrinsic rewards are genuine rewards in their own right, as they induce learning, approach, and pleasure, like perfectioning, playing, and enjoying the piano. Although they can serve to condition higher order rewards, they are not conditioned, higher order rewards, as attaining their reward properties does not require pairing with an unconditioned reward. ... These emotions are also called liking (for pleasure) and wanting (for desire) in addiction research (471) and strongly support the learning and approach generating functions of reward.
In the prefrontal cortex, recent evidence indicates that the [orbitofrontal cortex] OFC and insula cortex may each contain their own additional hot spots (D.C. Castro et al., Soc. Neurosci., abstract). In specific subregions of each area, either opioid-stimulating or orexin-stimulating microinjections appear to enhance the number of liking reactions elicited by sweetness, similar to the [nucleus accumbens] NAc and [ventral pallidum] VP hot spots. Successful confirmation of hedonic hot spots in the OFC or insula would be important and possibly relevant to the orbitofrontal mid-anterior site mentioned earlier that especially tracks the subjective pleasure of foods in humans (Georgiadis et al., 2012; Kringelbach, 2005; Kringelbach et al., 2003; Small et al., 2001; Veldhuizen et al., 2010). Finally, in the brainstem, a hindbrain site near the parabrachial nucleus of dorsal pons also appears able to contribute to hedonic gains of function (Söderpalm and Berridge, 2000). A brainstem mechanism for pleasure may seem more surprising than forebrain hot spots to anyone who views the brainstem as merely reflexive, but the pontine parabrachial nucleus contributes to taste, pain, and many visceral sensations from the body and has also been suggested to play an important role in motivation (Wu et al., 2012) and in human emotion (especially related to the somatic marker hypothesis) (Damasio, 2010).
Here, we show that opioid or orexin stimulations in orbitofrontal cortex and insula causally enhance hedonic "liking" reactions to sweetness and find a third cortical site where the same neurochemical stimulations reduce positive hedonic impact.
So it makes sense that the real pleasure centers in the brain - those directly responsible for generating pleasurable sensations - turn out to lie within some of the structures previously identified as part of the reward circuit. One of these so-called hedonic hotspots lies in a subregion of the nucleus accumbens called the medial shell. A second is found within the ventral pallidum, a deep-seated structure near the base of the forebrain that receives most of its signals from the nucleus accumbens. ...
On the other hand, intense euphoria is harder to come by than everyday pleasures. The reason may be that strong enhancement of pleasure - like the chemically induced pleasure bump we produced in lab animals - seems to require activation of the entire network at once. Defection of any single component dampens the high.
Whether the pleasure circuit - and in particular, the ventral pallidum - works the same way in humans is unclear.