but there were naysayers:
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But there were naysayers:. Maybe with high frequency (300cps), square pulse (instant rise) ESB you are giving un-natural activation of CNS pathways. Maybe by activating entire central pathways, you are also doing something that doesn’t happen in nature. Sooooooo……. We did an expewriment:. - PowerPoint PPT PresentationTRANSCRIPT
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But there were naysayers:
• Maybe with high frequency (300cps), square pulse (instant rise) ESB you are giving un-natural activation of CNS pathways.
• Maybe by activating entire central pathways, you are also doing something that doesn’t happen in nature. Sooooooo……
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We did an expewriment:
• Much slower soft starting stimulation at low frequency
• &• We stimulated centrally the same
density of fibers in and outside the descending inhibition.
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This was M & L’s very important theory of descending inhibition…(rather than suppression of higher pathways.
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• Morphine had no effect on the aversive reaction threshold for the “Miss” at left (101% baseline). But it elevated the aversive reaction threshold of the “hit” to 320% baseline.
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Is there a summation of effects…
• ….from 2 or more interacting sites?
• First study was behavioral:
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But where were the summation(s)?
• This required a study of single neuron responses to see if one lower level could be activated to a greater by two higher places than by either alone.
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Studying neurons in NRM presented us with a wrinkle:
• Fields & colleagues at UCSF found that there were 2 kinds of cells in NRM, On Cells and Off Cells.
• On cells turned on by pain, off by opiates.• Off cells ere the other way around: turned
off by pain, on by opiates.• Thus cells had to be On/Off classified
before studying summation effects. Classification done with tail flick in lightly anaesthetized rats, ala Fields.
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So, we showed that different brainstem sites interacted at RM…• But was one site (e.g., PAG)
necessary for the other site (e.g., PGC) to function? This suggested a reversible lesion experiment:
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Naturally naysayers said “nay”…
• “You are comparing a double injection (PGC-M + PAG-T) with a single one (PGC-M). “
• OK so we did the appropriate comparison to get the thing published:
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So of course next, we had to see what the lesions did to on and off
cell responses.
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Moral of the story:
• If you stay away from complex higher cognitive functions and study something simple (like sensory responsiveness, e.g., pain) then you can learn a lot with lesions & ESB