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Impulsivity and Deep Brain Stimulation

Impulsivity and Deep Brain Stimulation. “Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism” Michael J. Frank, Johan Samanta , Ahmed A. Moustafa , Scott Sherman Reviewed by XXXXX. Hypotheses. Patients will show lack of reinforcement learning.

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Impulsivity and Deep Brain Stimulation

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  1. Impulsivity and Deep Brain Stimulation “Hold Your Horses: Impulsivity, Deep Brain Stimulation, and Medication in Parkinsonism” Michael J. Frank, Johan Samanta, Ahmed A. Moustafa, Scott Sherman Reviewed by XXXXX

  2. Hypotheses • Patients will show lack of reinforcement learning. • Medication will impair negative feedback learning. • DBS will impair high conflict slowing response.

  3. Definitions • Reinforcement Learning – Learning with positive or negative feedback • Negative Feedback Learning – Learning after making error • High Conflict Slowing Response – Pause before making win/win or lose/lose decisions • “Should you vacation in Montreal or Rome?” • “Should you eat chocolate fondue or tiramisu?” • Neither option crosses “critical decision threshold” (STN)

  4. Participants Demographics

  5. Exclusion Criteria • Significant medical history • Concurrent illness (Schizophrenia, Manic Depression) • History of drug abuse/alcoholism • Advanced symptoms (stage V) • MMSE<24 (to screen for dementia) • Additional medications thought to confound findings

  6. Methods • Four Groups of Participants • On/Off medication • On/Off DBS (stimulating in the STN) • Probabilistic Selection Task • Training • AB (A=80%), CD (C=70%), EF (E=60%) • Training (AB=65%, CD=60%, EF=50%) • Test • Novel test pairs • Measured number of correct responses and response times • *non-specific keys for response

  7. Example of Training

  8. Training B A 80% 20%

  9. Correct!

  10. Incorrect

  11. No response detected

  12. Measurements • Positive Feedback Learning – Choosing “A” in novel test pairs • Negative Feedback Learning – Avoiding “B” in novel test pairs • Compared to positive feedback learning • Conflict Effects – Reaction times of novel test pairs with similar reinforcement values as compared to those with dissimilar values

  13. Testing for Negative Feedback Learning Impairment

  14. Testing for High-Conflict Slowing Response Impairment

  15. Results • Feedback learning unaffected in on/off DBS groups • On DBS group differed from off DBS group in conflict effects • On DBS seemed to even speed up with high conflict pairs • No change in high-conflict slowing response in on/off medication groups • On medication group was impaired at negative feedback learning.

  16. Results (cont.) • In on DBS group, the more severe the impairment of high-conflict slowing response, the more errors • On DBS responded faster to high-conflict win/win pairs as opposed to lose/lose pairs

  17. Impairment of Negative Reinforcement for On Medication Group

  18. Impairment of High-Conflict Slowing Response for On DBS Group

  19. Confirmation of Results • “Retrograde DBS procedure” • Off DBS retested with stimulators turned on • Same results found as with on DBS group • Control group also retested with same time delay • No change in conflict-induced slowing response • Off Medication group retested with different time delay • No change in conflict-induced slowing response

  20. Applications • Two roles of Basal Ganglia in decision making • One area of striatum is composed of “Go” neurons (D1 receptors) • Seek reinforcement • Dopamine increases with reinforcement • Another area of the striatum is composed of “No Go” neurons (D2 receptors) • Avoid non-reinforcing stimuli • Dopamine decreases without reinforcement • Medications prevent decrease in dopamine necessary for negative feedback learning

  21. Applications (cont.) • STN provides “Hold Your Horses” response when decision-conflict is high • Two theories of how DBS works • DBS acts as lesion • DBS over-activates STN • Neurons in the STN are firing all the time instead of selectively during high-conflict decision making • With impairment in negative feedback learning and lack of high-conflict slowing response it is easy to understand how one could begin to gamble

  22. Critique of Study • Pros • Controlled for age and education • Controlled for motor deficiencies • Control group • Control group retested • Cons • Attrition • DBS groups had more years diagnosed • No random assignment

  23. Additional Research • Contarino et al. found that hypersexuality and hypomania may be caused by DBS • Desbonnet et al. found premature responding in rats with STN stimulation • Uslaner and Robinson found that STN lesions in rats increased impulsive action • Smeding et al. conducted case study of patient who began DBS and acquired gambling addiction

  24. Thanks!

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