Impulsivity and Deep Brain Stimulation

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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

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Hypotheses

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

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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)

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Participants

• Demographics

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Exclusion Criteria

• Significant medical history
• Concurrent illness (Schizophrenia, Manic
  Depression)
• History of drug abuse/alcoholism
• Advanced symptoms (stage V)
• MMSElt24 (to screen for dementia)
• Additional medications thought to confound
  findings

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Methods

• Four Groups of Participants
• On/Off medication
• On/Off DBS (stimulating in the STN)
• Probabilistic Selection Task
• Training
• AB (A80), CD (C70), EF (E60)
• Training (AB65, CD60, EF50)
• Test
• Novel test pairs
• Measured number of correct responses and response
  times
• non-specific keys for response

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Example of Training
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Training
B
A
80
20
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• Correct!

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• Incorrect

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• No response detected

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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

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Testing for Negative Feedback Learning Impairment
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Testing for High-Conflict Slowing Response
Impairment
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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.

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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

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Impairment of Negative Reinforcement for On
Medication Group
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Impairment of High-Conflict Slowing Response for
On DBS Group
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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

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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

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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

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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

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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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Thanks!