MH Lecture 6 - Schizophrenia and ADHD

Dopamine

• not exactly the “pleasure neurotransmitter”

• critical for motivated behaviour and learning

• helps us direct our attention to meaningful stimuli

Dopamine and Learning

• prior to CS-US training — dopamine (DA) spikes at food/reward delivery (R)

• after conditioning — DA spikes at CS presentation

• DA helps us learn CS-US associations

What gets our attention — Predictive Stimuli 

the predictiveness principle — we pay more attention to stimuli if they are “predictive” 

• we pay more attention if they predict something that we like or dislike 

What do we ignore 

ignoring without learning 

• stimuli that lacks salience 

things we learn to ignore

• non-predictive stimuli 

Schizophrenia Diagnostic Criteria

2 or more of the following (incl at least 1,2, or 3)

1. delusions

2. hallucinations

3. disorganised speech

4. grossly disorganised or catatonic behaviour

5. negative symptoms

• Symptoms must cause dysfunction

• continuous signs of disturbance persist for at least 6 months

• exclusions for other conditions

Schizophrenia Symtom Clusters

• positive symptoms (added)

• negative symptoms (taken away)

• cognitive symptoms

Schizophrenia Positive Symptoms

• Delusions

  • persecutory, grandiose, referential

• Hallucinations

  • most commonly auditory, can involve other senses

• Disorganised speech/thinking

  • word salad

• Disorganised behaviour

  • agitated or repetitive motor behaviours, difficulty w basic tasks

• Catatonic behaviour

  • unresponsive/frozen

Dopamine hypothesis of Schizophrenia 

• excess dopamine activity in the striatum causes “aberrant salience” and “failures to ignore”

• attention is attracted by meaningless stimuli 

• hallucinations/delusions develop as a result 

Latent Inhibition

tests normal processes of learning to ignore irrelevant stimuli

• people w schizophrenia do not show strong latent inhibition effect

  • failure to ignore is a feature of the condition

ADHD Presentation — Inattention 

more than 6 (kids) — more than 5 (adults) 

• lack of attention to detail 

• difficulty sustaining attention in play or work 

• does not appear to attend when spoken to directly 

• leaves tasks unfinished 

• difficulties w organisation 

• avoid tasks that require sustained mental effort 

• loses things necessary for tasks/activities 

• easily distracted by extraneous stimuli/unrelated thoughts 

• forgetful in daily activities

ADHD Presentation — Hyperactivity  

more than 6 (kids) — more than 5 (adults) 

• fidgets 

• leaves seats in inappropriate situations 

• runs about or climbs in inappropriate situations 

• unable to play/engage in leisure activities quietly 

• on the go

• talks excessively 

• prematurely blurts out answers 

• difficulty waiting turn 

• interrupts 

ADHD Diagnostic Criteria 

• persistant pattern of inattention and/or hyperactivity

• symptoms present before 12 years of age

• symptoms present in 2 or more settings

• causes dysfunction

• not explained by schizophrenia

Dopamine Hypothesis of ADHD

• evidence of disrupted DA activity

• hyperactive DA transporter

• decreased sensitivity of DA receptors

Representation of Dopamine Signalling

SCZ Treatment 

Antipsychotics

• dopamine antagonists

  • block activity at a specific subtype of DA receptor (dampens down the excess dopamine and calms down some of the positive symptoms)

ADHD Treatments

Amphetamines

• dopamine agonists

  • increase release and/or prevent reuptake of dopamine

  • d-amphetamine not methamphetamine given

Problem of Symptom Similarity

• prior to onset of first psychotic episode — person w prodromal schizo may experience attentional challenges and be diagnosed w ADHD (many people w SCZ have additional diagnosis of ADHD)

• what would happen if person w SCZ given amphetamine — induces psychotic episodes

• common symptom of disrupted attentional filtering is the same but biological mechanisms are polar opposites