Palatability (or palatableness) is the
hedonic reward (i.e.,
pleasure
Pleasure refers to experience that feels good, that involves the enjoyment of something. It contrasts with pain or suffering, which are forms of feeling bad. It is closely related to value, desire and action: humans and other conscious anima ...
) provided by foods or fluids that are agreeable to the "
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
", which often varies relative to the
homeostatic
In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
satisfaction of
nutrition
Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient n ...
al,
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
, or
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of heat a ...
needs. The palatability of a food or fluid, unlike its
flavor
Flavor or flavour is either the sensory perception of taste or smell, or a flavoring in food that produces such perception.
Flavor or flavour may also refer to:
Science
*Flavors (programming language), an early object-oriented extension to Lis ...
or
taste
The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
, varies with the state of an individual: it is lower after
consumption
Consumption may refer to:
*Resource consumption
*Tuberculosis, an infectious disease, historically
* Consumption (ecology), receipt of energy by consuming other organisms
* Consumption (economics), the purchasing of newly produced goods for curren ...
and higher when
deprived. It has increasingly been appreciated that this can create a hunger that is independent of homeostatic needs.
[Lowe MR, Butryn ML. (2007). Hedonic hunger: a new dimension of appetite? Physiol Behav. Jul 24;91(4):432-9. ]
Brain mechanism
The palatability of a substance is determined by
opioid receptor
Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin ...
-related processes in the
nucleus accumbens
The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypotha ...
and ventral
pallidum
The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rod ...
.
[Wassum KM, Ostlund SB, Maidment NT, Balleine BW. (2009). Distinct opioid circuits determine the palatability and the desirability of rewarding events. Proc Natl Acad Sci U S A. 106:12512–12517 ] The opioid processes involve
mu opioid receptors and are present in the rostromedial shell part of the nucleus accumbens on its
spiny neurons. This area has been called the "opioid eating site".
The rewardfulness of consumption associated with palatability is dissociable from desire or incentive value which is the motivation to seek out a specific commodity.
Desire or incentive value is processed by opioid receptor-related processes in the
basolateral amygdala.
Unlike the liking palatability for food, the
incentive salience
Motivational salience is a cognitive process and a form of attention that ''motivates'' or propels an individual's behavior towards or away from a particular stimulus (psychology), object, perceived event or outcome. Motivational salience regulat ...
wanting is not downregulated by the physiological consequences of food consumption and may be largely independent of homoeostatic processes influencing food intake.
Though the wanting of incentive salience may be informed by palatability it is independent and not necessarily reduced to it.
It has been suggested that a third system exists that links opioid processes in the two parts of the brain: "Logically this raises the possibility that a third system, with which the accumbens shell, ventral pallidum, and basolateral amygdala are associated, distributes the affective signals elicited by specific commodities across distinct functional systems to control reward seeking... At present we do not have any direct evidence for a system of this kind, but indirect evidence suggests it may reside within the motivationally rich circuits linking hypothalamic and brainstem viscerogenic structures such as the parabrachial nucleus.
It has also been suggested that "hedonic hunger" can be driven both in regard to "wanting" and "liking"
and that a palatability subtype of neuron may also exist in the basolateral amygdala.
Satiety and palatability
Appetite
Appetite is the desire to eat food items, usually due to hunger. Appealing foods can stimulate appetite even when hunger is absent, although appetite can be greatly reduced by satiety. Appetite exists in all higher life-forms, and serves to regu ...
is controlled by a direct loop and an indirect one. In both the direct and indirect loops there are two feedback mechanisms. First a positive feedback involving its stimulation by palatability food cues, and second, a negative feedback due to satiation and satiety cues following ingestion. In the indirect loop these cues are learnt by association such as meal plate size and work by modulating the potency of the cues of the direct loop. The influence of these processes can exist without subjective awareness.
The cessation of a desire to eat after a meal "satiation" is likely to be due to different processes and cues. More palatable foods reduce the effects of such cues upon satiation causing a larger food intake. In contrast, unpalatability of certain foods can serve as a deterrent from feeding on those foods in the future. For example, the
variable checkerspot butterfly contains
iridoid
Iridoids are a type of monoterpenoids in the general form of cyclopentanopyran, found in a wide variety of plants and some animals. They are biosynthetically derived from 8-oxogeranial. Iridoids are typically found in plants as glycosides, mos ...
compounds that are unpalatable to avian predators, thus reducing the risk of
predation
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...
.
[Bowers, M. D. "Unpalatability as a Defense Strategy of Western Checkerspot Butterflies (Euphydryas Scudder, Nymphalidae)." Evolution 35.2 (1981): 367-75.]
See also
*
Acquired taste
An acquired taste is an appreciation for something unlikely to be enjoyed by a person who has not had substantial exposure to it. It is the opposite of innate taste, which is the appreciation for things that are enjoyable by most persons without ...
*
Flavor
Flavor or flavour is either the sensory perception of taste or smell, or a flavoring in food that produces such perception.
Flavor or flavour may also refer to:
Science
*Flavors (programming language), an early object-oriented extension to Lis ...
*
Food craving
Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ing ...
*
Motivation
Motivation is the reason for which humans and other animals initiate, continue, or terminate a behavior at a given time. Motivational states are commonly understood as forces acting within the agent that create a disposition to engage in goal-dire ...
*
Nutrition
Nutrition is the biochemical and physiological process by which an organism uses food to support its life. It provides organisms with nutrients, which can be metabolized to create energy and chemical structures. Failure to obtain sufficient n ...
*
Pleasure center
The reward system (the mesocorticolimbic circuit) is a group of neural structures responsible for incentive salience (i.e., "wanting"; desire or craving for a reward and motivation), associative learning (primarily positive reinforcement and clas ...
References
External links
The effect of palatability on satiety{dead link, date=March 2018 , bot=InternetArchiveBot , fix-attempted=yes Martin R Yeomans
Behavioral neuroscience
Gustation
Gustatory system