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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

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
Hypotheses

  • Patients will show lack of reinforcement learning.

  • Medication will impair negative feedback learning.

  • DBS will impair high conflict slowing response.


Definitions
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)


Participants
Participants

Demographics


Exclusion criteria
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


Methods
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



  • Training

    B

    A

    80%

    20%





    Measurements
    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




  • Results
    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.


  • Results cont
    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




    Confirmation of results
    Confirmation of Results Group

    • “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


    Applications
    Applications Group

    • 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


    Applications cont
    Applications (cont.) Group

    • 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


    Critique of study
    Critique of Study Group

    • 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


  • Additional research
    Additional Research Group

    • 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


    Thanks
    Thanks! Group


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