PMID-6077726[0] The limbic system and behavioral reinforcement
- Can't seem to find Olds 1965, as was a conference proceeding .. this will have to do, despite the lack of figures. images/966_1.pdf
- First reference I can find of chronic (several weeks) (4-9 microelectrodes, single) recording from the rat.
- Basically modern methods: commutator + solid state preamplifiers mounted to a counterbalanced slack-relieving arm.
- If unit responses were observed in recordings from a given probe a week after surgery they were usually recordable indefinitely. 44 years later ...
- Used a primitive but effective analog spike discriminator based on:
- minimum amplitude
- maximum amplitude
- minimum fall time
- maximum fall time.
- Also had a head movement artifact detector, which blanked the recordings (stopped the paper roll) for 2 sec.
- Reinforced on 'bursting', threshold sufficiently high that it only occurred once every 5-15 minutes.
- Food reinforcement or 1/4 second train of brain stimulation (30ua, 60Hz, sine, in hypothalamus).
- Reinforcement was conditioned on an 'acquisition' signal, which is visual (?) Bursting is rewarded for 2 minutes, ignored for 8 minutes.
- Also recorded control neurons.
- (they were looking at these things as though anew!) "The most striking aspect of the records so formed [on sheets of paper] was that all discriminators at one time or another exhibited rate changes that had the appearance of waves with a period of 10 to 20 minutes. Waves between units in the same animal were to some degree synchronized." Then describes a ramp ..
- Longer term variations: FR would vary by a factor of 2-5 over a period of several hours.
- This would make negatively correlated neurons (on a short time scale) appear positively correlated over long time scales (have to fix this in the BMI!)
- As this was a conditional reinforcement task, they unexpectedly found that the acquisition periods were systematically different than extinction periods
- More like pavlovian conditioning, esp in the hippocampus, where a conditioned response was also reflected on a control neuron.
- Even when the light was lit throughout the acquisition period was replaced by a bell at the beginning of the acq. period, there was still a sustained change in FR.
- Then during the extinction period: it appeared from the record of responses that a definite operant behavior was tried several times and then stopped altogether."
- In the pontine nucleus (relay from M1 to cerebellum, v. roughly), judging from the control responses, all were conditioned.
- Pontine responses seem to correspond with movement of the eyes or head that did not set off the movement detector/blanker.
- Saw brief and very fast bursts during the extinction periods of the kind that Evarts found to characterize pyramical neurons during sleep.
- When units shifted from food reward to ICS reward, units became undiffarentiated, and within a day they would be reconditioned.
- Also tried paralyzing the animal to see if it could still generate operant responses; the animal died, results inconclusive.
- Flood lights made it hard for the rats to produce the operant behavior.
____References____
[0] Olds J, The limbic system and behavioral reinforcement.Prog Brain Res 27no Issue
144-64 (1967) |
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