Cortical Modulation of Synaptic Efficacies through Norepinephrine

Abstract

I propose a norepinephrine- (NE-) neuromodulatory system, which I call “enhanced-excitatory and enhanced-inhibitory (E- E/E-I) system”. The E-E/E-I system enhanced excitatory and inhibitory synaptic connections between cortical cells, modified their ongoing background activity, and influenced subsequent cognitive neuronal processing. When stimulated with sensory features, cognitive performance of neurons, signal-to-noise (S/N) ratio, was greatly enhanced, for which one of the three possible S/N enhancement schemes operated under the E-E/E-I system, namely; i) signal enhancement more than noise increase, ii) signal enhancement and noise reduction, and iii) noise reduction more than signal decrease. When a weaker (or subthreshold) stimulus was presented, the scheme (ii) effectively enhanced S/N ratio, whereas the scheme (iii) was effective for enhancing stronger stimuli. I suggest that a release of NE into cortical areas may modify their background neuronal activity, whereby cortical neurons can effectively respond to a variety of external sensory stimuli.