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

kazue semba
semba@is.dal.ca

Thank you very much for your comments and for sharing with us your recent findings on the role of BF in reticular facilitation of visual cortical response. It is interesting that you are finding that midbrain reticular formation (MRF) stimulation most commonly inhibits BF neurons; short-latency excitation has been previously reported (Szymusiak in this symposium; also Szymusiak and McGinty, 1989). It might be due to differences in stimulation/recording sites or cell types (e.g., "wake-active" vs. "sleep-active").

Just to clarify, did I understand you correctly in that single LGN stimulation alone without MRF stimulation can evoke a (relatively weak?) excitatory response in BF neurons? That would be very interesting, and I am wondering which pathways could mediate this response. If this response is mediated through the visual cortex as you have suggested, it has to involve limbic cortical or subcortical region(s) because the visual cortex does not directly project to BF. Also, as you know, the LGN does not project directly to the BF. Alternatively, it might involve antidromic activation of brainstem neurons, which could in turn activate BF neurons via other neurons or through axon collaterals. I am also wondering about the selectivity of BF neurons that respond to LGN stimulation. Do you find such BF neurons to be localized within a certain region of BF?

Hope you get the chance to send us a reply before the symposium ends!

KazueJust