bethanbloodrose (bethanbloodrose) wrote in ed_ucate,
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Following on from this post.



25. Disgust - the forgotten emotion of psychiatry

The British Journal of Psychiatry
(C) 1998 The Royal College of Psychiatrists
Volume 172(5), May 1998, pp 373-375

Disgust - the forgotten emotion of psychiatry

PHILLIPS, M. L.; SENIOR, C.; FAHY, T.; DAVID, A. S.
M. L. PHILLIPS, MRCPsych, C. SENIOR, BSc, Department of Psychological Medicine,
Institute of Psychiatry, London; T. FAHY, MRCPsych, Maudsley Hospital, London;
A. S. DAVID, MD, Department of Psychological Medicine, Institute of Psychiatry,
London.


If asked to name common emotions, most people, including those interested in
psychiatric topics, would start with happiness, sadness, and go on to fear and
anger. Few would consider the emotion of disgust. We will argue that this basic
emotion is important not only to many aspects of our daily lives but is also
central to a range of psychiatric phenomena.

EMOTIONS

What are emotions? Dualist, or 'feeling', theories proposed by Descartes and
later by James (1890) [14] describe emotions as epiphenomena, or non-functional
feelings, derived from physiological changes or behaviour in response to
provoking stimuli. Behaviourists, such as Skinner (1974) [27] define emotions in
terms of reinforced patterns of behaviour. However, ever since Aristotle, others
have emphasised the importance of cognitions (thoughts, memories) as causal to
emotions, with theorists such as Lyons (1992) [16] describing the appraisal or
interpretation of events, which then leads to physiological changes, as central
to the formation of an emotion. An emotion could be defined as the value
ascribed to events. Ekman (1992), [8] has described emotions as "having evolved
through their adaptive value in dealing with fundamental life-tasks". He argues
that there are a finite number of emotions, each characterised by a distinctive
facial expression, physiology, antecedents and presence in other primates.

How many different emotions are there? One theory (Lyons, 1992) [16] argues
against separate emotions, but instead suggests that a general level of arousal
will be interpreted or 'coloured' by the individual in terms of the events and
evaluations with which it is associated. Davidson (1992) [7] has proposed a
single emotion dimension built upon primitive adaptive responses: approach
(positive) through to withdrawal (negative). The other type of theory (Darwin,
1872; Ekman, 1992) [6,8] argues for the existence of separate, basic emotions,
proposing six: sadness, happiness, anger, surprise, fear and disgust. In
psychiatry, fear and sadness have been considered important as underlying
several disorders, including specific and generalised anxiety and obsessive-compulsive
disorder (OCD), and effective disorders, respectively. Evidence for abnormal
perception of disgust as important in the genesis of specific psychiatric
conditions is beginning to emerge and will be discussed below. We will firstly
describe the defining characteristics of this otherwise neglected basic emotion.

DISGUST

Disgust (literally - bad taste) has been defined in terms of a food-related
emotion. Darwin (1872) [6] wrote that disgust was "... something offensive to
the taste", and later authors (Rozin & Fallon, 1987) [24] describe the emotion
as "revulsion at the prospect of (oral) incorporation of an offensive object".
The prototypical objects of disgust have been identified as waste products of
the human and animal body but extend to other biological substances such as
blood, saliva, sweat and hair. In addition, the concept of disgust can be
expanded to involve violation of body borders at points other than the mouth
(Rozin & Fallon, 1987) [24]. This concept of core disgust can be further
elaborated to include: animal-origin disgust, with the tendency of humans to
emphasise the human-animal boundary (Rozin & Fallon, 1987); [24] interpersonal
contamination, with disgust elicited by physical contact with unpleasant or
unknown people (Rozin et al, 1994); [25] and, finally, the moral or socio-cultural
domain of the emotion (Miller, 1997), [18] with disgust at certain beliefs or
behaviours, such as sexual abuse of children, acting as a powerful means of
transmitting social values (Rozin & Fallon, 1987) [24].

What constitutes a disgusting stimulus, at the margins of the definition, is
clearly influenced by culture and individual differences. Such influences may be
enshrined in religious dietary laws and national dietary preferences (consider
the French taste for snails, horsemeat and steak tartar and British preference
for black pudding and tripe). Lack of tolerance for sweat and body odour seem to
be a recent concern in Western cultures. It has also been argued that complex
emotions, such as shame, guilt and embarrassment, are derived from the basic
emotion of disgust, with the focus being on the self (Power & Dalgleish, 1997)
[21]. Any emotion could be derived from combinations of basic emotions in the
same way that an infinite number of hues can be derived from three basic
colours.

Psychoanalytic theories

Freud (1908) [10] considered disgust to be a reaction formation, that is a
defence mechanism involving the repudiation of the desired object. This could
become elaborated according to the developmental context so as to facilitate
weaning, toilet training and sexual restraint. Modern versions of such theories
stress disgust as a reaction against threats to the integrity of the self and as
a means of imposing distance between self and object (Miller, 1993) [17].

The biology of disgust

The reaction of a person to a disgusting object includes a characteristic facial
expression (Rozin & Fallon, 1987), [24] with narrowing of the nostrils and
raising of the upper lip (activity on the levator labii muscles), in addition to
wrinkling of the brow (activity in the corrugator region). The purpose of the
facial expression is to inhibit oral ingestion and includes the accompanying
nausea and excessive salivation, but may extend to vocalisations ('yuk!',
'ugh!') and the shudder response.

Although non-human species do not demonstrate disgust, most avoid decaying meat,
suggesting that they have an analogous form of food rejection. Perception of
disgust in humans is absent at birth, with young children appearing to be
tolerant of odours associated with decay, and children in the first two years of
life demonstrating the well known tendency to put anything into their mouths.
The disgust facial expression can, however, be elicited in young children in
response to unpleasant tastes. Rozin & Fallon (1987) [24] concluded that
perception of disgust develops at a later stage in childhood, between the ages
of two and three and further at seven to nine years, probably as a result of
cognitive development leading to ideational rejection of initially distasteful
stimuli.

The neurology of emotion perception

There has been much recent interest in the investigation of the neural
correlates of perception of positive and negative emotion. Lesion studies have
implicated both the left hemisphere (Young et al, 1993) [30] and right
hemisphere (Adolphs et al, 1996) [2] in the perception of facial expressions per
se. The right hemisphere, however, has been demonstrated to have a role in the
perception of negative emotions, in particular, sadness and fear (Adolphs et al,
1996; Gur et al, 1994) [2,13].

There have been several studies investigating the specific neural substrate for
perception of fear, with the amygdala emerging as critical to the perception of
fearful facial expressions (Adolphs et al, 1994; Morris et al, 1996) [1,19].
However, there has been little investigation of the neural correlates of
perception of disgust. Recent studies have demonstrated impaired recognition of
disgust in people with Huntington's disease (Sprengelmeyer et al, 1996) [28].
This suggests that perception of disgust may involve palaeocortical structures
atrophied in Huntington's disease, such as periamygdalar and piriform cortex.
Other important structures are those implicated in appreciation of offensive
stimuli, including a specific cortico-striatal-thalamic circuit identified in
primates (Alexander et al, 1990) [3]. Evidence for the involvement of this
circuit in perception of facial expressions of disgust, in addition to
involvement of the anterior insula, identified as gustatory cortex in primates
(Rolls et al, 1994) [23] has been found in a recent functional imaging study
(Phillips et al, 1997) [20]. The authors concluded that the neural response to
facial expressions of disgust in others is thus closely related to appraisal of
distasteful stimuli.

DISGUST AS AN EMOTION UNDERLYING PSYCHIATRIC DISORDERS

There are several lines of evidence to suggest that abnormal perception of
disgust may underlie various psychiatric disorders, including OCD, phobias,
depression, eating disorders, certain sexual dysfunctions and uncommon
psychiatric syndromes.

Obsessive-compulsive disorder

There is accumulating evidence for the non-homogeneity of OCD from study of the
onset, symptom profile, treatment and underlying brain dysfunction (Blanes &
McGuire, 1997) [4]. There is a subgroup of people with OCD, with a chronic,
deteriorating course, earlier age of onset and more severe symptoms. This
subgroup is more common in males and can be linked with basal ganglia dysfunction.
A second subtype, which is more in females, is associated with a later onset,
mood and anxiety disorders, frontal lobe dysfunction and a good response to
serotonergic antidepressants. One question is whether these two subgroups can be
distinguished on the basis of perception of disgust, since a prominent theme of
obsessional thoughts concern dirt/contamination and washing, or checking. The
cleaning/washing obsessions occur more often in females with a later age of
onset of OCD, suggesting the relevance of disgust to this group in particular.

Perhaps more compelling evidence in favour of disgust as an emotion underlying
OCD is demonstrated by the results of the functional neuroimaging studies, and
the relationship of these with the findings from work investigating the neural
correlates of perception of disgust. Reviews have highlighted increased
metabolism, blood flow in orbitofrontal and striatal regions (Breiter & Rauch,
1996) [5]. Increased activation in similar brain regions has been demonstrated
during perception of facial expressions of disgust (Phillips et al, 1997) [20].

Phobias

In their recent review, Power & Dalgleish (1997) [21] discuss evidence
suggestive of a role for disgust in the genesis of certain phobias. Certain
animal phobias may be disgust-based reactions to contamination or association
with particular animal products such as mucus and faeces. Furthermore, they
suggest that social phobia, in which the person imagines that he will be
humiliated in public, may also have as its basic emotion self-directed disgust,
or shame, a complex emotion perhaps related to disgust, as described above.
Finally, they note that the physiological response to blood demonstrated by
people with blood phobias (bradycardia and hypotension) is similar to that for
perception of disgust, and very different from the usual phobia-induced
fight-or-flight response (tachycardia).

Depression

The importance of shame in the development of self-esteem and relationship with
others has been reviewed extensively (Gilbert, 1997) [12]. Low self-esteem is
known to be an important component of depression, and self-loathing, or
self-disgust, in addition to sadness, may represent part of the core phenomenological
state of depression. Disgust would therefore appear to play an important role in
the genesis of depression.

Eating disorders

People with anorexia nervosa and bulimia often experience disgust with respect
to sexuality, parts of their bodies, and towards certain foods, especially those
which are fattening or have a high calorie content. Those with bulimia nervosa
appear to be able to overcome the normal response to satiety, and overeat, or
'binge', frequently enjoying the sensation of eating. However, the experience of
self-directed disgust, characterised by feelings of being unattractive and
overweight, after such binges (Russell, 1979) [26] appears to contribute to the
switch to the vomiting and purging part of the cycle. Individuals occasionally
describe choosing repellent foodstuffs during a binge as an attempt to control
the binge urge and perhaps as part of self-punishment.

It will be interesting in the future to investigate the perception of disgust,
and the neural substrate underlying this, in people with eating disorders.

Dysmorphophobia

Dysmorphophobia, the persistent preoccupation with a presumed deformity or
disfigurement and the refusal to accept advice and reassurance from others to
the contrary, can also be linked with disgust (Thomas & Goldberg, 1995) [29].

Other psychiatric disorders

Coprophagia - usually defined as the ingestion of one's own faeces, is seen in
the extremes of life in people with severe learning disabilities or dementia.
Bilateral damage to the temporal lobes-amygdala complex is often implicated
(Ghaziuddin & MacDonald, 1985) [11].

Self-related disgust can be related to various sexual dysfunctions, including
vaginismus, dyspareunia, premature ejaculation, erectile and orgasmic dysfunction
(Power & Dalgleish, 1997) [21] and perversions. Uncommon psychiatric syndromes,
such as lycanthropy, a delusion of metamorphosis into a wolf-like animal often
in the context of sexual conflict, and vampirism, blood ingestion resulting in
erotic satisfaction (Fahy et al, 1988), [9] may also be associated with
distorted perception of disgust. As for klismaphilia (the erotic enema
deviance), urolagnia (ingestion of urine for sexual purposes), necrophilia/phagia,
bestiality (Rebal, 1982), [22] one could speculate that the intense emotional
response induced by disgusting stimuli and activities becomes associated with
sexual arousal (Kraft-Ebing, 1886) [15]. Nevertheless, 'normal' eroticism from
kissing onwards, presumably involves a similar but limited process, specific and
personalised to the sexual partner.
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