JClub: Hosking et al., 2015

Reference: Hosking, J. G., Floresco, S. B. and Winstanley, C. A. (2015) ‘Dopamine antagonism decreases willingness to expend physical, but not cognitive, effort: A comparison of two rodent cost/benefit decision-making tasks’, Neuropsychopharmacology. Nature Publishing Group, 40(4), pp. 1005–1015. doi: 10.1038/npp.2014.285.

Species: Rat

Key Questions:

  • Does willingness to work hard in mental effort correspond to willingness to work hard in physical effort?
  • What are dopaminergic and noradrenergic contributions to effort?
  • Goal: to compare animals’ behavior on rCET and wettl-established physical effort task, and examine DA and NE contribution to cognitive vs. physical effort

Task Design:

  • rat cognitive effort task (rCET): animals can choose to allocate greater visuospatial attention for greater reward
    • 5-hole operant chamber. animals presented 1 or 2 levers (Low reward or High reward), and following stimulus lights they had to nosepok with previously illuminated aperture for a rerward
    • Trials were unrewarded if rat 1) failed to make a lever response within 10s (choice omission), 2) nosepoked during ITI (premature), poked wrong aperture (incorrectly response), or failed to nosepke at array within 5s (response omission). behaviors were punished with 5s time-out
    • Behavioral measurement: percent choice. two groups of animals, workers (n=40) and slackers (n=15)
  • physical effort-discounting task (EDT)
    • 40 free-choice trials per 32 min session, divided into 4 blocks
    • LR lever: both levers retraced and animal immediately received 2 sugar pellets
    • HR lever: LR lever retracted and animals given 25 seconds to complete a higher number of presses for 4 sugar pellets
    • Animals did not receive reward if they did not make a choice within 25s of lever insertion (choice omision), or if they fialed complete required number of lever presses for HR trial (incomplete HR response)
    • Beahvioral measurement: Percent choice
  • Pharmacological challenge
    • D2 antagonist eticlopride
    • D1 antagonist SCH23390
    • adrenic receptor antagonist yohimbine
    • selective norepinephrine reuptake inhibitor atomoxetine

Key Results:

  • rCET Eticlopride Admin
    • animals chose HR trials more than LR tirlas following saline injection. D2 receptor antagonist eticlopride had not effect on animals choice
    • Animals more accurate on LR vs HR trials (saline). Ectriclopride had no effect on accuracy
    • Etic increase correct response latencies, response and choice omissions, decreased number of completed trials
  • rCET SCH23390 Admin
    • no effect
  • rCET Yohimbine Admin
    • no effect on choice
    • yohimbine dose-dependently decreased accuracy (at highest dose)
    • at low and intermediate doses, speeding effect on all latencies, decreased response omission, increased completed trials
    • highest doest increased response and choice omissions, decreased trials
  • rCET Atomoxetine
    • no effect on choice, accuracy, trending to decreased performance on LR trials
    • increased choice latency and choice omissions, decreased number of completed trials
  • EDT vs rCET
    • all animals demonstrated sensitivity to physical effort costs, choice of HR decreased across blocks as costs increased
  • EDT Eticlopride
    • decreased all animals choice of HR trial across blocks
    • increased latency to complete HR trials, modest increase of choice omissions
  • EDT SCH23390
    • decreased choice at highest effort block
    • modestly increased choice latencies and choice omissions
  • EDT Yohimbine
    • decreasing choice of HR lever during first two blocks but effect not robust
    • lengthened latency to complete HR trials for each block
  • EDT Atomoxetine
    • No effects

Bottom Line:

  • Dopamine is minimally involved in cost/benefit decision-making with cognitive effort costs

Additional Comments:

  • It is interesting that they use 1.0s vs 0.2s stimuli for Low effort and High effort, respectively. I wonder to what extend these differences may more reflect perceptual difficulty, than cognitive effort, per se
  • Observed differences may be due to differences in task design?
  • reward learning and motor learning may be more functionally and anatomically integrated than previously suggested? (Kratviz et al 2012)
  • mental and physical effort differ in systemic cateholamine profiles – interesting. (Fibiger et al 1984)
  • sustained attention and acetycholine? (Passetti et al, 200, Dalley et al., 2001)

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