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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
slide8

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
  • “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
  • 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.)
  • 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
  • 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
  • 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
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