Helped or hurt by smart drugs? Insights from cognitive neuroscience Cognitive control
The ability to adapt flexibly to the constant changes in our environment in a goal-directed manner
Cognitive control Dopamine (DA) systems in the human brain
DA
Stefan et al Smart pills Disorders that implicate dopamine
neurobiologie & psychiatrie
Attention deficit hyperactivity disorder
Parkinson’s disease
Drug addiction
Food addiction (obesity)
Behavioural addictions Dopamine-enhancing drugs neurobiologie & psychiatrie
More impulsive Less impulsive
How can dopaminergic drugs have such different effects in different individuals? On the paradox of dopamine neurobiologie & psychiatrie
Drug effects vary as a function of
• Individual (genetic) differences in personality
• Baseline levels of dopamine
• Task demands and associated neural systems Principle 1
Inter-individual variability of drug effects
Drugs can have contrasting effects as a function of (healthy) personality traits
This likely reflects individual (genetic) variability in baseline levels of dopamine Rate-dependency neurobiologie & psychiatrie
placebo
psychostimulant Performance Low impulsive High impulsive
Dews 1958; Robbins and Sahakian, 1979; Lyon and Robbins 1975 Predicting drug effects from trait impulsivity neurobiologie & psychiatrie
• Stratification by impulsive personality – Putative link with variability in the DA system
• > 1200 subjects were prescreened on the self-report Barratt Impulsiveness Scale
• High- and low-impulsive subjects were selected from the tail ends
• Scanned using fMRI once on placebo and once following the dopamine D2 receptor agonist bromocriptine
11
The paradigm
… 13
Interim conclusion neurobiologie & psychiatrie
• Bromocriptine enhanced cognitive flexibility in high-impulsive subjects, but (if anything) reduced it in low-impulsive subjects.
• These effects were accompanied opposite effects on activity in the striatum Next question neurobiologie & psychiatrie
• Why do dopaminergic drugs have opposite effects as a function of trait impulsivity? The danger of pharmacological enhancement - going beyond optimal neurobiologie & psychiatrie
80% 60% DELAYED DELAYED
ALTERNATION 40% SCH SAL SCH SKF +SKF Zahrt et al., 1997
Increasing levels of D1 receptor stimulation
There is an optimal level of neuromodulation, with both excessive as well as insufficient levels being associated with poor performance Individual differences in striatal dopamine synthesis capacity in healthy volunteers
High FMT uptake Low FMT uptake
A PET study with the tracer 6-[18F]fluoro-L-m-tyrosine (FMT) In collaboration with Bill Jagust and Mark D’Esposito
Cools et al., J Neurosci 2009 Individual differences in the efficacyIndividual differencesbromocriptine the in of
Drug-effect on shifting Cools Cools J et al., Neurosci 2009 Interim Conclusion neurobiologie & psychiatrie
• Dopaminergic drugs like bromocriptine have opposite effects on cognition in high- and low-impulsive subjects
• Similar contrasting effects are seen as a function of individual variability in baseline levels of dopamine
• This variability likely reflects individual differences in genetic predisposition Principle 2
Intra-individual variability of drug effects, in healthy subjects
Drugs can have opposite effects even within the same individual by modulating distinct functions with different ‘chemical needs’ Measuring multiple working memory functions Opposite drug effects on ignoring and updating
100 PPlaceboLC MMethylphenidatePH 90 ( % ) 80
A c u r a y 70
60 Ignore Update
Fallon and Cools, in prep Opposite drug effects on ignoring and updating
0.2 PLPlaceboC MMethylphenidatePH 0.1 ( S E D )
g e 0
C h a n −0.1
S i g n a l −0.2 % Ignore Update
Fallon and Cools, in prep Thus
• Ritalin (methylphenidate) can have contrasting effects, even within the same individual, depending on specific task demands
• Specifically, ritalin enhances distractor-resistance while impairing updating of working memory
• Thus high levels of dopamine in the PFC might be beneficial for cognitive stability but detrimental for cognitive flexibility On the paradox of dopamine neurobiologie & psychiatrie
Drug effects vary as a function of
• Individual (genetic) differences in personality
• Baseline levels of dopamine
• Task demands and associated neural systems Conclusion
Cognitive processing can be selectively modified by psychopharmacological interventions
Such interventions almost certainly involve trade-offs between enhancement of some and impairment of other processing
This is not to say that research on psychopharmacological enhancement should be banned. Instead, blurry boundaries between mental health and disease might be recognized & focus should move away from predicting efficacy in ill-defined spectrum disorders towards predicting effects on isolated neurocognitive processes in both ‘health’ and ‘disease’
Progress will depend on the degree to which drugs can be tailored to individuals, component processes and specific molecular events (receptors)
This highlights how societal/ethical discussions about human enhancement should take into account knowledge gained from neuroscience
Thank you Esther Aarts (postdoc) Marieke van der Schaaf (PhD student) Martine van Schouwenburg (PhD student) Sean Fallon (postdoc) Trevor Robbins Mark D’Esposito Bill Jagust
Funding James McDonnell Scholar Award Human Frontiers Research Program Netherlands Organization for Science Dutch Brain Foundation The Royal Society of London National Institute of Health