A Framework for Constructing Neural Models of Dopaminergic Contributions to Personality Alan Pickering Department of Psychology

My Objectives Construct models accounting for association between dopamine- (DA-) related personality traits and specific (lab) behaviours Models will ultimately be computational Models will be biologically constrained

A 5-Step Strategy: Steps Identify traits associated with variations in DA neurotransmission candidate trait approach 2.Characterise specific processes by which DA affects cognition and behaviour 3.Construct matched tasks which differ in use of the processes from 2 Measure association between DA- related traits and task performance

A 5-Step Strategy: Steps Develop computational model and simulate task performance - explore effects of varying key DA parameters in model - parameter effects on performance should be **very** strong 5.Attempt direct neurobiological validation of model e.g. by drug studies

An Illustration of Steps 1 to 4 Behavioural data presented later were collected by Rozmin Halari (Institute of Psychiatry University of London)

STEP ONE: CANDIDATE TRAITS

Which Personality Traits Are DA-Related? Extraversion-Introversion (Depue, Rammsayer) Example measures: EPQ-E; Introvertive Anhedonia (IntAnh) Impulsive Antisocial Sensation Seeking: ImpASS (Gray, Cloninger, Zuckerman, Pickering) Example measures: EPQ-P; Novelty Seeking; Sensation Seeking Scale Positive Schizotypy (many) Example measures: Unusual Experiences

Example Questionnaire Items ImpASS: Measure = EPQ-P (25 items) -Have people said that you sometimes act too rashly? -Should people always respect the law? -Would you take drugs which may have strange or dangerous effects? Positive Schizotypy: Measure = Unusual Experiences (30 items) -I have felt that I have special, almost magical powers -Do you ever feel that your thoughts dont belong to you -Sometimes my thoughts are as real as actual events in my life

What Evidence Implicates DA in Personality Traits? Direct evidence for extraversion and ImpASS -Traits correlate with psycho- physiological response to DA drugs -Traits correlate with DA-binding in neuroimaging studies -Traits correlate with DA receptor gene variations No evidence for positive schizotypy but argument by analogy with schizophrenia and schizotypal personality disorder

DA and ImpASS: Sample Evidence Gray, Pickering & Gray (1994) SPET D2-binding in basal ganglia and EPQ-P

STEP TWO: CANDIDATE PROCESSES

What Psychological Processes Might be DA-Related? Several main candidates are widely proposed: 1.Appetitive reinforcement and motivation during learning DA activity has been viewed as provided a reinforcement signal which is required for synaptic plasticity (3-factor learning rule)

DA-Related Processes (cont) 2.Working Memory / Executive Function 3.Input Modulation / Gain Enhancement (selective attention process) Schultz (1998): DA lets only the strongest cortical influences pass to striatal neurons, whereas weaker inputs become ineffective Floresco et al (2001): DA receptor activity serves to strengthen salient inputs while inhibiting weaker ones

STEP THREE: CANDIDATE TASKS (LEARNING)

Evidence for Influence of DA on Learning Neuropsychological Studies with patients with damage to DA-rich striatal brain regions are impaired on specific learning tasks Neurophysiological Studies suggest synaptic plasticity in striatal brain regions require appropriately timed DA signal

Category Learning in Parkinsons Disease Weather task: Knowlton et al, 1996

Category Learning in Parkinsons Disease Main Findings: Knowlton et al, 1996

Category Learning & ImpASS Scores: Early Studies Ball & Zuckerman (1990): positive correlation between Sensation Seeking scores and learning of a concept formation task Pickering (2 studies): positive correlations for Novelty Seeking and EPQ-P scores with learning of a filtration category learning task Suggestive but uninformative about what DA-related processes might be involved

Reinforcement Study Pickering and Halari Within-Ss design using 2 equivalent probabilistic category learning tasks: Weather task and a Symptoms-Disease task Training Task 1:enhanced reinforcement £0.10 per correct response Task 2:paired-associate training meant no reinforcement Testing Categorise each stimulus without reinforcement

Details 40 healthy male participants, mostly students Personality Measures Extraversion: Introvertive Anhedonia (IntAnh) ImpAss:EPQ-P Schizotypy:Unusual Experinces (UnEx) Dependent Variable = Accuracy of responses during test

Results: Correlations RF= reinforcement task score PA= paired-associate task score Pos SZExtraImpASS RFUnExIntAnhEPQ-P PA * RF *0.00 UnEx * IntAnh0.13

Summary of Findings DA-related personality traits correlated with performance on DA- sensitive category learning tasks Extraversion-introversion (but not ImpAss or schizotypal traits) is correlated with learning under appetitive reinforcement

STEP FOUR: MODELLING

Dopaminergic Interpretation Extraversion-Introversion may be associated with functional variation in the DA receptors involved in appetitive reinforcement Possibly post-synaptic D1-like receptors Receptors situated in structures such as striatum which are implicated in category learning tasks

DA Receptors in Striatum After Schultz, 1998 DA receptors: Unfilled rectangles GLU receptors: Filled rectangles

Striatal Connections

Schematic Model