A hormone is a type of chemical messenger secreted by certain cells that affects cells in other parts of the body. Hormones are often transported in the blood. Humans (and other vertebrates) have three types of hormones: amines, peptides, and lipids. Amines, derived from the amino acids tryptophan and tryrosine, include catecholamines (adrenaline and noradrenalien) and thyroxine (a thyroid hormone). Peptides include insulin, growth hormones, testosterone, and cortisol (a stress hormone). The main lipids are steroids, derived from cholesterol and eicosanoids. Prostoglandins, which are involved in pain perception, inflammation, and hormone regulation, are a type of eicosanoid. Enkephalin is a hormone involved in pain regulation.

Hormones serve various functions, including regulation of growth, mood, hunger cravings, immune function, metabolism, pain, and the reproductive cycle. Hormones such as adrenaline and noradrenaline prepare the body for fight or fligh (in response to a threat). Hormones also prepare the body for a new phase of life (e.g., puberty, pregnancy and childbirth, and menopause). Melatonin, found in the pineal gland, is an antioxidant that can cause drowsiness. Melatonin is sometimes used to regulate the sleep cycle (e.g., with jet lag). Serotonin is a hormone that affects mood, appetite, and sleep. Insulin and glucagon (both peptides) affect blood sugar. The peptide orexin affects wakefulness, appetite, and energy level. Oxytocin—sometimes referred to as the love hormone—is interal to the birth process, release of breast milk, and orgasm and has been implicated in buiding bonds and trust between people (Anderson & Middleton, 2006).

While testosterone is considered a male hormone and estrogen a female hormone, both males and females have some amount of both hormones. Testosterone is a steroid that increases muscle mass, strength, and bone density. Testosterone is involved in male maturation, including development of male secondary sexual characteristics (e.g., facial hair growth, deepening of voice). Testosterone levels in males may affect muscle mass, strength, energy level, sleep, sex drive (libido), concentration, memory, and mood. A decrease in testosterone levels due to aging is sometimes referred to as andropause.

Female steroids, including estrogen (estradiol) and progesterone, serve many functions. These include promoting the formation of female secondary sexual characteristics (e.g., breast development), supporting pregnancy, growth and metabolism, and maintenance of bone density. Estrogen levels in females may affect energy level and mood. Fluctuating levels of estrogen and other (e.g., serotonin and beta-endorphins) hormones may manifest as mood swings, depression, anxiety, or irritability at different points in the menstrual cycle (Dickerson, Mazyck, & Hunter, 2003). Depending on the pattern and severity of symptoms, women may be diagnosed with premenstrual syndrome (PMS) or premenstrual dysphoric disorder. Levels of female and other (e.g., thyroid and cortisol) hormones change dramatically after childbirth and may be associated with postpartum depression (Harris, 1996). Female hormones decrease with age. When a woman’s ovaries stop producing eggs and female hormone levels drop, her menstrual periods cease and she experiences menopause. While some women experience menopause symptoms, including depression, irritability, mood swings, decreased libido, sleep problems, night swearts, and hot flashes, many women have no symptoms (Liu et al., 2009).

Adrenaline (also known as epinephrine) prepares the body to fight or flee (escape) in response to a threat. An increase in adrenaline also increases heart rate, dilates blood vessels and pupils, suppresses digestion, and suppresses the immune system. High levels of chronic stress can repeatedly activate the adrenaline (fight-or-flight) system. This can result in repeated suppression of the immune system and may be associated with stress-related illnesses. Adrenocorticotropic hormone (ACTH) is often produced in response to stress. It increases the production of androgens (e.g., testosterone) and the stress hormone cortisol. Cortisol is a steroid that stimulates the breakdown of fat cells, has anti-inflammatory properties, and suppresses the immune system. Prolactin is a peptide hormone primarily associated with lactation (producting breast milk). Prolactin levels seem to increase with emotional crying. Some postulate that crying may have beneficial effects, including relieving stress and tension (Walter, 2006). Prolactin levels—as well as levels of noradrenaline, cortisol , and ACTH—have been shown to vary with the elicitation of different emotions (pleasant and unpleasant feelings; Codispoti et al., 2003). Levels of prolactin, ACTH, and cortisol all have been found to increase in response to stress. Greater stress reactivity may be associated with greater risk of developing alcoholism and increased subjective perception of stress in children of alcoholics (Uhart et al., 2006).

  • Anderson, A., & Middleton, L. (2006). What is this thing called love? New Scientist, 190, 32 – 34.
  • Codispoti, M., Gerra, G., Montebarocci, O. Zaimovic, A., Augusta Raggi, M., & Baldaro, B. (2003). Emotional perception and neuroendocrine changes. Psychophysiology, 40, 863 – 868.
  • Dickerson, L.M., Mazyck, P.J., & Hunter, M.H. (2003). Premenstrual syndrome. American Family Physician, 67, 1743 – 1752.
  • Harris, B. (1996). Hormonal aspects of postnatal depression. International Review of Psychiatry, 8 27 – 36.
  • Liu, D>, Lu, Y., Ma, H., Wei, R.-C., Li, J., Fung, J., et al. (2009). A pilot observational study to assess the safety and efficacy of Menoprogen for the management of menopausal symptoms in Chinese women. Journal of Alternative and Complementary Medicine, 15, 79 – 85.
  • Uhart, M., Oswald, L., McCaul, M.E., Chong, R., & Wand, G.S. (2006). Hormonal responses to psychological stress and family history of alcoholism. Neuropsychopharmacology, 31, 2255 – 2263.
  • Walter, C. (2006). Why do we cry? Scientific American Mind, 17, 44 – 51.
  • Since cognitive science Opens in new window has taken on board this commonsense view of the mind, an important question is how such a relationship to a proposition can be implemented.

    The representation theory of mind (RTM; Field, 1978; Fodor, 1978) assumes that a propositional attitude consists in holding a representation of the proposition and that this representation plays a certain functional role in the economy of mental states. This can be best illustrated with the two core concepts: belief and desire.

    These are core concepts, since knowing what someone believes (thinks) to be the case (e.g., Max thinking the chocolate is in the cupboard and thinking that going there will get the chocolate into his possession) and what that person desires (wants) (e.g., Max wanting the chocolate to be in his possession) allows us to make a behavioral prediction that Max will approach the cupboard. This kind of inference is known since Aristotle as the practical syllogism.

    Searle (1983, after Anscombe, 1957) points out that these two states are mirror images in terms of causal direction and direction of fit. The function of a belief is to be caused by reality and the believed proposition should match reality.

    For instance, the chocolate being in the cupboard should be responsible for Max’s believing that the chocolate is in the cupboard (world to mind causation) and the proposition “the chocolate is in the cupboard” should thus match the relevant state of affairs in the world (mind should fit world).

    The function of desire (want) is to cause a change in the world (mind to world causation) so that the world conforms to the desired proposition (world should fit mind)—for example, if Max wants the chocolate to be in the cupboard, then this desire should cause action leading to a change of the chocolate’s location such that it conforms to what Max desires.

    This trivial-sounding example does highlight the important distinctions.

    Three Important Distinctions

    1. First vs. Third Person

    One important distinction is between first-person and third-person attribution of mental states. A third-person attribution is an attribution to another person and a first-person attribution is one to myself.

    For instance, if Max erroneously believes that the chocolate is still in the cupboard (because he didn’t see that it was unexpectedly put into the drawer), then a third-person observer will attribute a false belief to Max. In contrast, Max himself will make a first-person attribution of knowledge to himself.

    The observer can capture this difference between her own and Max’s subjective view by the second-order attribution that Max thinks he knows where the chocolate is. This is useful to keep in mind when it comes to false memories. Since a memory can only be a recollection of something that actually occurred, a false memory is not a memory by third-person attribution, although it is by first-person attribution.

    1. Sense and Reference

    A related second point has to do with Frege’s (1892/1960) distinction between sense and reference. Since mental states involve representations, they connect us to objects and events in the real (or a possible) world.

    Famously, Oedipus knew and married Iocaste (referent: a particular person), but he did not know or marry her as his mother but as an unrelated queen (sense: how Iocaste was presented to Oedipus’ mind).

    Thus, in third-person parlance we can say that Oedipus married his mother if we use the expression “his mother” to pick out (refer to) the individual whom he married without implying that he knew Iocaste under that description. In first-person description of the event Oedipus would not have used the descriptor “my mother.”

    These distinctions are useful to keep in mind when discussing infants’ ability to remember particular events: Whenever a memory trace of a unique event can be demonstrated then one can conclude (in first-person parlance) as a particular event—that is, that the infant makes cognitive distinctions that represent that event as a particular event.

    1. Having vs. Representing a Mental State

    The third important distinction is that between being in a mental state (or having an attitude) and representing that mental state.

    For understanding or knowing that a person is in a mental state, or to reflect on one’s own mental states, one has to be able to represent that state. In order to be able to represent a state, one needs a concept of that state—that is, a rich enough theory of mind.

    The study of how children acquire the requisite theory of mind is therefore essential for our understanding of how children come to understand memory. Furthermore, since some memorial states are reflective or self-referential, children need a theory of mind for being in such states or having such memories.

    Why We Need a Theory of Mind for Memory

    We probably do not need a theory of mind for implicit (nondeclarative Opens in new window) memory, but for explicit (declarative Opens in new window) memory we do, since “explicit memory is revealed when performance on a task requires conscious recollection of previous experiences.” (Schacter, 1987).

    To be conscious of a fact one requires to be also aware of the state with which one beholds that fact. The higher-order-thought theories of consciousness make this their core claim (Armstrong, 1980; Rosenthal, 1986).

    For instance, if one sees a state of affairs X (e.g., that the chocolate is in the cupboard), then this seeing is a first-order mental state (attitude).

    To be conscious of this state of affairs means, according to theory, that one entertains a second-order thought about the seeing—that is, the second-order thought represents the first-order seeing.

    A weaker version does not require that one has to entertain the second-order thought, but only that one has to have the potential for having the second-order thought (Carruthers, 1996). That some such condition must be true can be seen from the following consideration:

    “Could it ever be that I can genuinely claim that I am consciously aware of the chocolate being in the cupboard, but claim ignorance of the first-order mental state by which I behold this state of affairs—that is, by claiming that I have no clue as to whether I see, or just think of, or want the chocolate being in the cupboard?”

    The important point of these conceptual analyses is that to be conscious of some fact requires some minimal concept of knowledge or of some perceptual state like seeing.

    Unfortunately, there is no clear evidence when children understand a minimal state of this sort. There is some evidence of understanding (mother’s) emotional reactions and seeing (direction of gaze) in the first year of life (see Perner, 1991, chap. 6; Baldwin & Moses, 1996; Gopnik & Meltzoff, 1997, for summaries and discussion of problems of interpretation).

    There is also some recent evidence that between 8 and 12 months children might be inferring people’s intentions to grasp an object from where that person looks (Spelke, Philips, & Woodward, 1995) and even between 5 to 9 months from how a person touches an object (seemingly intentional or accidentally).

    And by 18 months (where children’s understanding of mental phenomena seems to flourish in general) children imitate people’s intended actions even when they observe a failed attempt (Meltzoff, 1955a) and they understand differences in preferences (e.g., that someone else can prefer cauliflower over biscuits, Repacholi & Gopnik, 1997).

    Evidence that children distinguish their knowledge from ignorance is available at a relatively late age. Povinelli, Perilloux, and Bierschwale (1993) asked children to look for a sticker under one of three cups.

    Children were first trained to look under the cup at which the experimenter had pointed. After some training even the youngest were able to do this.

    When asked to look without the experimenter pointing, an interesting developmental difference emerged. Children older than 2 years and 4 months acted without hesitation when they knew which the cup the sticker was under, but hesitated noticeably when—in the absence of the experimenter’s poining—they had to guess where it was.

    Interestingly this is also the age at which children start using the phrase “I don’t know” (Shatz, Wellman, & Silber, 1983). In contrast, children younger than that showed no comparable difference in reaction time. This may indicate that young 2-year-olds do not yet reflect on what they do and do not know.

    So, theory of mind research is not yet able to give a guideline for when infants might develop explicit, conscious memories. Memory development may help out on this point.

    Meltzoff (1985, 1995b) demonstrated that 14-month-old infants can reenact a past event (e.g., they imitate the experimenter leaning forward to touch a panel with forehead so that panel lights up) after several months. Recently this has been demonstrated in 11-month-olds with a delay of 3 months.

    Since this is achieved from a brief observational period and does not require prolonged learning, and since patients with amnesia cannot do this (McDonough, Mandler, KcKee, & Squire, 1995), it is tempting to conclude that such enactment demonstrates explicit, conscious memory.

    One should, though, keep in mind that delayed imitation that is based on a single event (third-person view) is not to be equated with a memory (knowledge) of that event as a single, past event (first-person view).

    Keep on learning:
      Adapted from: The Oxford Handbook of Memory. Authored by ENDEL TULVING (ED.), Fergus I. M. Craik