Disgust and OCD Flashcards
What are obsessions?
A series of intrusive thoughts or images or impulses that are repetitive and unpleasant. Common obsessions: Contamination Losing control Perfectionism Superstitious fears Hoarding Obsessions are a cognitive interpretation of compulsive urges, which reinforce them in a positive feedback loop
What are compulsions
Repetitive behaviours or mental acts that the person feels driven to perform in response to an obsession
Common compulsions:
Washing
Checking
Repeating
Arranging
A person must spend at least an hour each day fulfilling their compulsions to be diagnosed with OCD
OCD epidemiology
1.6% lifetime prevalence
Onset in early childhood or late adolescence
Usually chronic
No gender difference
High comorbidity with depression and anxiety
4th most common psychiatric disorder
10th highest cause of disability worldwide
Neurobiological account of OCD
PET scans implicate head of the caudate, putamen, thalamus, amygdala, OFC. Caudate and mOFC bias towards habit formation, which interacts with trait anxiety (amygdala) to produce compulsions.
Ahmari et al 2013 - stimulated rat neurons projecting from PFC to ventral striatum. Noted both acute and chronic increases is compulsive grooming behaviour.
OCD and threat detection
Bozikas et al 2009 - OCD patients are normal at recognising fearful faces (or any other faces), when you don’t distinguish between types of OCD
Daros et al 2014 - contamination-based OCD patients are worse at recognising disgust, anger and sadness in faces
Lavy et al 1994 - you see threat-biased attention if you use symptom-specific stimuli, but this study was complicated by comorbid depression
Morein-Zamir et al 2013 - controlled for symptom-specific stimuli and depression. Found normal unpleasantness rating of negative stimuli, but slower reaction times, and patients called negative stimuli ‘disgusting’ rather than ‘scary’.
What is disgust?
Disgust is a universal emotion characterized by the feeling of revulsion or profound disapproval of something
unpleasant or offensive.
Evolutionary function of contamination and disease avoidance.
Characterised by aversion behaviour and the tendency to
distance oneself from the offensive stimulus.
Disgust is evolving - there’s moral disgust now too.
Neurobiology of disgust
Striatum is active for both pleasant and unpeasant stimuli
The insula is the only area with no overlap - only active for unpleasant stimuli
Insula is active for both disgusting and scary stimuli
Ho and Berridge 2014 - in rats, excitotoxic lesions or GABA inactivation of the posterior striatum cause increased disgust responses to sucrose. Degree of cell death in lesioned subjects correlated with disgust sensitivity. This region had previously been noted as a ‘liking’ hotspot.
Disgust in OCD - psychology
Questionnaires suggest people who rate things as more disgusting are more likely to exhibit obsessive-compulsive tendencies
Patients with contamination-based OCD (i.e. washers) rated both normal disgusting stimuli and contamination-specific stimuli as more disgusting than patients with other OCD types.
Tolin et al 2002 - OCD patients are worse at suppressing intrusive thoughts than anxious and non-anxious controls
OCD patients showed more distress at disgusting stimuli, and better memory for contaminated items.
Armstrong et al 2010 - Contamination-based OCD patients orient to fear faces as controls, but orient more strongly to disgust faces. Excessive visual fixation.
Daros et al 2014 - contamination-based OCD patients are worse at recognising disgusted faces (note that this is not true of other types of OCD)
BUT Jhung et al 2010 found no difference between OCD and controls in recognising any non-ambiugous facial expression. Patients were more likely to call an ambiguous expression ‘disgust’, and contamination-based patients the most so.
Connolly et al 2009 - contamination-based OCD patients overestimated the covariance of disgusting scenes with disgusted faces in a scene-face random copresentation paradigm. The same was not true of other faces (e.g. they didn’t say pleasant scenes always occurred with happy faces).
OCD patients rate disgusting tasks as more disgusting, and are less likely to initiate them (avoidance)
Law of contagion
Tolin et al 2004 - Touched a pencil to a toilet, then another pencil etc etc. OCD patients thought the 12th pencil was still contaminated. Anxious and non-anxious controls stopped between 4 and 7.
Specific to ‘disgusting’ stimuli - if you do the same with candy instead of toilet and ask OCD patients whether the 12th pencil is contaminated with candy, they say no.
Law of similarity
Rozin et al 1982 - perceptually similar items are equally threatening. Gave subjects a piece of chocolate fudge, they all ate it. Gave them the same fudge shaped like poo, told them it’s exactly the same, controls ate it but patients didn’t.
Disgust in OCD - neurology
Shapira et al 2003 - OCD patients show greater increases in the insula, parahippocampal and inferior frontal regions to disgust. There were no differences to threat
Different types of OCD have increased activity in different areas. E.g. hoarding mainly in OFC and precentral gyrus
Washers had similar insula activation but less fronto-striatal activation than controls or checkers to disgusting stimuli
Becker et al 2014 - OCD patients are more sensitive to negative and neutral feedback, and show more insulaa activation in these cases (so insula is coding for guilt/shame as well as pure disgust?)
Treatments for OCD
McKay 2006 - peak anxiety decreased over 5 sessions of exposure therapy to disgusting stimuli
~60% of OCD patients respond to an SSRI (cf 40-50% of depressed patients)
OCD and 5-HT
Genotypic variance within the 5-HT system is
associated with OCD - 5-HT binding sites on platelets are disordered in OCD and their first degree but unaffected relatives. So endophenotype?
~60% of OCD patients respond to an SSRI (cf 40-50% of depressed patients)
SSRIs improve OCD symptoms even when controlling for depression severity
ATD increases depressive but not OC symptoms in OCD
Lochner et al 2014 - placebo OCD and controls recognised disgusted faces equally well. SSRIs improved disgust detection in OCD, and reduced it in controls
Tuerke et al 2012 - in the posterior insula, 5-HT3 antagonist reduces LiCl-conditioned disgust responses and 5-HT3 agonist increases them. No effect in anterior insula.
Disgust in schizophrenia
Schizophrenics rate various stimuli as more disgusting than controls, but show reduced insula activation to disgusted facial expressions.
Schizophrenics are worse at recognising any facial expression, but particularly disgust, and cannot recognise ‘microexpressions’
Lindner et al 2014 - In schizophrenics, insula activation to disgust expressions correlates with social loneliness
[[also note…
… this and the sets on anxiety and esp on mania, I didn’t look up any extra papers etc for. So if you have time, or this has caught your attention, maybe do a bit of googling - especially on alternative theories for the neuropsychological bases of these! Anything ~alternative~ and original. I love you, remember your worth is not defined by this exam, and you’re not studying for the exam - you’re studying because you love the brain and how it works!]]
