Role of the Basal Forebrain Neurons in Cortical Activation and Behavioural State Regulation

Re^2: Attention vs. "Arousal" or Cortical Activation

Doug Rasmusson

Re: area-specificity
I think the clearest experiments date back to the dark ages, i.e. pre-microdialysis. Collier & Mitchell (J. Physiol, 1966) put cortical cups over visual and non-visual cortices of rabbits. Visual or LGN electrical stimulation produced 3-4 fold increase in ACh release from visual area and only a doubling from non-visual cortex. Hemsworth and Mitchell (Brit. J. Pharm 1969) did essentially the same with auditory stimulation, getting a 6 fold increase from auditory cortex and 2 fold from other areas. My interpretation of these data has always been that there is a "global", non-specific increase throughout all cortex and an additional, more specific increase that is restricted to the sensory modality that is being turned on. This might be through anatomical specificity (it is still not clear to me how specific the inputs or outputs of individual basal forebrain neurons are) or to presynaptic modulation within the cortex. One possibility that seems to be ignored is that LGN stimulation (in Collier's experiment) may be antidromically firing basal forebrain neurons that are also projecting to visual cortex, or antidromically firing brainstem neurons that are also projecting to the basal forebrain. Do the anatomists have any suggestions about the likelihood of such collaterals contributing to the ACh release findings?
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