Obsessive Compulsive Disorder

Question 1

What is Obsessive-Compulsive Disorder (OCD)?

Answer 1

OCD is a severe, often chronic and disabling mental health disorder that presents numerous challenges for neuroscience.

Question 2

What are the core deficits of OCD according to the DSM-5?

Answer 2

The core deficits are obsessions and compulsions.

Question 3

What are obsessions in the context of OCD?

Answer 3

Obsessions are recurrent and persistent thoughts, urges, or images that are experienced as intrusive and unwanted. They can commonly relate to hygiene/contamination, aggression, catastrophic themes, etc.

Question 4

What are compulsions in the context of OCD?

Answer 4

Compulsions are repetitive behaviours or mental acts that an individual feels driven to perform in response to an obsession. Examples include cleaning, checking, symmetry/counting, or other rituals.

Question 5

How common is OCD?

Answer 5

The prevalence is 2-3% of the population, making it the 4th most common mental health disorder.

Question 6

Why is OCD sometimes called a ‘hidden disorder’?

Answer 6

It is often considered a hidden disorder due to stigma, leading to a significant delay of 10-15 years of illness before diagnosis.

Question 7

Is OCD typically a short-term or chronic disorder?

Answer 7

OCD is often chronic. It is ranked as the 10th most debilitating of illnesses and carries a 10-fold risk for suicide.

Question 8

What is the most common form of cognitive behavioural therapy (CBT) for OCD?

Answer 8

The most common form is Exposure Response Prevention (ERP).

Question 9

How does ERP work?

Answer 9

ERP involves systematic exposure to stimuli that would normally induce fear and trigger obsessions and compulsions, followed by response prevention of compulsive rituals.

Question 10

What is the first-line pharmacotherapy used for OCD?

Answer 10

SSRIs (selective serotonin uptake inhibitors) are the first line, with sertraline being the most commonly used.

Question 11

How effective are SSRIs for OCD?

Answer 11

Approximately ~50% respond, likely due to the heterogeneous nature of the disorder. Symptom reduction is typically around ~35%.

Question 12

How quickly do SSRIs work for OCD?

Answer 12

Response is slow and gradual (over weeks and months), with continued improvement possible up to 2 years.

Question 13

What is a common treatment strategy for individuals who do not respond to SSRIs alone?

Answer 13

They may receive SSRI + risperidone. Risperidone is an antipsychotic with D2/5-HT antagonism.

Question 14

What is suggested about different symptom subtypes of OCD and treatment response?

Answer 14

It is likely that different symptom subtypes are driven by dysfunction within different components of fronto-striatal circuitry and/or neurotransmitter action.

Question 15

Is there direct evidence for neurochemical changes in OCD consistent with changes in 5-HT function?

Answer 15

Direct evidence is limited.

Question 16

What are some hypotheses for how SSRIs reduce symptom severity in OCD?

Answer 16

One hypothesis is that they cause anxiety reduction, which diminishes automatic cycles of thoughts and actions. An alternative hypothesis is that SSRIs re-engage the goal-directed brain system.

Question 17

What are some alternative treatments mentioned for OCD?

Answer 17

Alternative treatments include deep-brain stimulation and psychedelics (e.g., psilocybin).

Question 18

What is the fronto-striatal network hypothesis of OCD?

Answer 18

This hypothesis focuses on cortico-striatal or cortico-striato-thalamic loops, which are semi-segregated neural networks between cortical regions and subcortical areas.

Question 19

What neurotransmitter largely modulates the activity of fronto-striatal loops?

Answer 19

The activity of these loops is largely modulated by catecholaminergic neurotransmitters such as dopamine.

Question 20

How is dopamine dysfunction linked to OCD?

Answer 20

Dopamine dysfunction in Parkinson’s disease is presented as reflective of an individual with OCD.

Question 21

How is computational psychiatry used to study OCD?

Answer 21

It is used to help elucidate the possible brain mechanisms underlying specific behaviours.

Question 22

What is reinforcement learning, and what role does reward prediction error (RPE) play?

Answer 22

Reinforcement learning involves learning through signalling reward prediction error (RPE).

Question 23

Where are RPE signals processed in the brain?

Answer 23

RPE signals are encoded by the dopaminergic midbrain and processed in fronto-striatal loops.

Question 24

How are aberrant RPEs linked to OCD?

Answer 24

Changes in RPE processing directly impact fronto-striatal loop activity, altering decision making and learning.

Question 25

How did a computational model describe choice behaviour in OCD patients during a probabilistic reversal learning task?

Answer 25

The model included a parameter for perseveration. It found that OCD patients were less 'sticky' in their choices.

Question 26

How does dopamine pharmacotherapy affect RPEs in OCD patients according to one study?

Answer 26

Administration of both a dopamine agonist and an antagonist normalised abnormally strong RPE signals.

Question 27

What does the finding that both DA agonists and antagonists normalize ACC signals suggest about dopamine's role?

Answer 27

It suggested that ACC signals were dopaminergic in origin and that both increasing and decreasing DA had the same effect.

Question 28

What is excessive checking, and how is it related to behaviour in OCD?

Answer 28

Excessive checking is a common, debilitating symptom. It may be associated with impairments in goal-directed behaviour.

Question 29

What brain circuits and neurochemical systems are thought to be involved in compulsivity, including checking?

Answer 29

Compulsivity is believed to involve dysfunction of cortico-striato-thalamo-cortical circuits.

Question 30

How have rodent models investigated checking behaviour and dopamine?

Answer 30

Rodent models using the Observing Response Task (ORT) quantify 'checking-like behaviours' by measuring non-functional lever presses.

Question 31

How were findings from rodent checking models translated to humans?

Answer 31

Researchers used a free-operant task (ORT) in humans, showing similar behavioural patterns to rodents.

Question 32

What did the results of the human ORT study suggest about OCD patients?

Answer 32

They suggested that OCD patients might be less sensitive to punishment or were already checking at a 'ceiling level'.

Question 33

What is the habit theory of compulsions in OCD?

Answer 33

The habit theory suggests that OCD patients may have overactive habitual systems or dysfunctional goal-directed systems.

Question 34

How is habitual behaviour quantified in research?

Answer 34

It is quantified using methods like contingency degradation and outcome devaluation tasks.

Question 35

Which brain regions are suggested to underlie goal-directed actions and habits?

Answer 35

The medial PFC and the caudate nucleus are suggested to underlie goal-directed actions.

Question 36

What evidence supports the habit theory from studies on OCD patients?

Answer 36

Studies found deficits in OCD patients' ability to inhibit previously learnt stimulus-response associations.

Question 37

What are some caveats or limitations of the habit account of OCD?

Answer 37

Habit perseveration has often been inferred from failures in goal-directed control rather than measured directly.

Question 38

What is the relationship between hyperactivity in cortical areas (cortical-striatal loops) and neurotransmitter balance in OCD?

Answer 38

Hyperactivity in cortical areas is thought to be due to an excitatory/inhibitory imbalance across SMA and ACC.

Question 39

What is the dual-system theory of learning regarding model-based and model-free systems?

Answer 39

Computational models describe learning as occurring via two systems: 'model-free' and 'model-based' learning.

Question 40

How is dopamine traditionally associated with these learning systems?

Answer 40

Traditionally, dopamine is associated with model-free learning, representing a teaching signal.

Question 41

How does dopamine influence model-based learning according to research?

Answer 41

Studies suggest that increased presynaptic ventral striatal dopamine levels are associated with a behavioural bias towards model-based control.

Question 42

How does serotonin influence model-based vs model-free learning?

Answer 42

Decreasing serotonin through tryptophan depletion can influence the balance between model-based and model-free systems.

Question 43

What is the Metacognitive Theory of OCD?

Answer 43

This theory proposes that compulsions originate as a consequence of intrusive thoughts due to patients' overestimation of the credibility of their thoughts.

Question 44

What does it mean that OCD is 'egodystonic'?

Answer 44

OCD is egodystonic in nature, meaning patients recognize their thoughts are irrational and actions are exaggerated.

Question 45

What is metacognitive sensitivity?

Answer 45

Metacognitive sensitivity reflects the idea of being aware of your actions.

Question 46

What evidence suggests metacognitive deficits in OCD?

Answer 46

Empirical evidence suggests metacognitive deficits, with subjective appraisal similar to controls despite exaggerated actions.

Question 47

What neurotransmitter is suggested to modulate metacognition?

Answer 47

Metacognition seems to be modulated by noradrenaline.

Question 48

How does manipulating noradrenaline affect metacognition?

Answer 48

A noradrenaline antagonist (propranolol) increased metacognitive performance.