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Inhibitory Cerebello-Olivary Projections and Blocking Effect in Classical Conditioning

Inhibitory Cerebello-Olivary Projections and Blocking Effect in Classical Conditioning. J J Kim, D J Krupa, R F Thompson Science, vol. 279, 570-573 (1998). Test A alone Normal CR Test B alone Very little or no CR. CS A. CR. CS B. Blocking: Observed data. CS A. UR (A-US). US.

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Inhibitory Cerebello-Olivary Projections and Blocking Effect in Classical Conditioning

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  1. Inhibitory Cerebello-Olivary Projections and Blocking Effect in Classical Conditioning J J Kim, D J Krupa, R F Thompson Science, vol. 279, 570-573 (1998)

  2. Test A alone • Normal CR • Test B alone • Very little or no CR CS A CR CS B Blocking: Observed data CS A UR (A-US) US • First CS (A) paired with US • A-US • First CS (A) and second CS (B) paired with US • Compound conditioning • AB-US CS A CS B UR (AB-US) US

  3. Blocking: Interpretation • If US is fully predicted by A (A-US), then adding B does not provide new information • Save on unnecessary computation • Weaker pre-conditioning of A-US causes a stronger effect of B-US • Inverse proportionality of A-US and B-US CS A CR CS A CS B CR Redundant CS B

  4. Eyeblink Conditioning NMR = nictitating membrane response Eyelid movement measurement device Speaker (CS A) Light (CS B) Eyelid closes (UR, CR) Thread to eyelid Air nozzle (US)

  5. Postulated eyeblink conditioning circuit CS-US association (Purkinje cells in HVI spike when CR is learned) Interpositus nucleus Blocking inhibition GABA antagonists (eg. Picrotoxin [PTX]) prevent blocking The question: Is this circuit correct?

  6. Experiment 1: Procedure • Standard classical conditioning • Tone CS • Airpuff US • Eye closing UR becomes CR during training • 54 Purkinje cells recorded during conditioning • 31 in lobule HVI <--- most likely activity site for eyeblink conditioning • 12 in anterior lobe HV, 6 in HVIIA, 5 in paramedian lobule

  7. Experiment 1: Eyelid & Cell Responses CR UR CS-US trials No purkinje cell response Purkinje cell spikes UR UR US only trials Naïve animals (5 cells) Trained animals (11 cells)

  8. Experiment 1:Control, Conclusions, Comments • Control case: strictly unpaired tone and airpuff trials • 20 out of 45 cells responded to the airpuff with complex spikes • Indicates that tone and airpuff must be paired for spike suppression • Conclusion: as eyeblink conditioning occurs the inferior olive’s ability to convey US information to the cerebellum is suppressed • This is not really shown - just the involvement of Purkinje cells • Comments • UR amplitude in response to US-only trials is higher for trained animals: why?

  9. UR US only Trained eyelid response to picrotoxin (PTX) Purkinje cell spikes • 3 cells recorded • Well-trained rabbits • how many? • PTX injected into inferior olive CS + US before PTX infusion CR No purkinje cell spikes CS + US after PTX infusion CR Purkinje cell spikes

  10. Phase I: Tone-airpuff conditioning • 7 sessions, 1 per day (10 blocks x 10 trials) CS A UR (A-US) US • Phase II: Tone-light-airpuff conditioning • Simultaneously introduce one of two fluids: • GABA antagonist: picrotoxin (PTX) • Placebo: artificial cerebrospinal fluid (ACSF) • 5 sessions, 1 per day (10 blocks x 10 trials) CS A CS B UR (AB-US) US • Light-airpuff test • Light CS + airpuff US testing (B-US) • 5 sessions, 1 per day (10 blocks x 10 trials) CS B ??? US Experiment 2: Procedure • Preparation • Rabbits implanted with guide cannulae above contralateral inferior olive

  11. Experiment 2: Test groups • Main group • ACSF: 6 rabbits • PTX: 12 rabbits • Control group • 5 rabbits Phase I Phase II Light-airpuff Phase II Light-airpuff

  12. Normal acquisition ACSF/PTX maintain response Experiment 2: Results Phase I Tone CS Phase II Tone + light CS Light-airpuff test Light CS US-only Partial response Control case acquisition Blocking • Control case similar to PTX • ACSF shows blocking, then re-learning • PTX does not affect UR amplitude

  13. Is the circuit correct? • Experiment 1 --> something stops Purkinje cell spiking • Purkinje cell spiking correlated with CR • PTX infusion in inferior olive restores Purkinje cell spiking • Inferior olive and GABA are involved • Experiment 2 --> PTX infusion prevents blocking • PTX seems to prevent GABA inhibition of inferior olive Interpositus nucleus Blocking inhibition

  14. Specific Comments • Mechanism for inverse relationship between strength of A-US and B-US is not explained • Slow acquisition during Experiment 2 light-airpuff test (compared to Phase I) not explained • Decrease of blocking over time is not explained • Due to simultaneous extinction of A-US and acquisition of B-US?

  15. The End

  16. Cerebellar Cortex Parallel fibres Molecular layer Stellate cell Basket cell Purkinje cell layer Granule-cell layer Golgi cell Purkinje cell Granule cell Mossy fibre Climbing fibre Purkinje cell axon (Ghez & Tach, 2000)

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