Acetylcholine-dependent potentiation of temporal frequency representation in the barrel cortex does not depend on response magnitude during conditioning

The response properties of neurons of the postero-medial barrel sub-field of the somatosensory cortex (the cortical structure receiving information from the mystacial vibrissae can be modified as a consequence of peripheral manipulations of the afferent activity. This plasticity depends on the integrity of the cortical cholinergic innervation, which originates at the nucleus basalis magnocellularis (NBM). The activity of the NBM is related to the behavioral state of the animal and the putative cholinergic neurons are activated by specific events, such as reward-related signals, during behavioral learning. Experimental studies on acetylcholine (ACh)-dependent cortical plasticity have shown that ACh is needed for both the induction and the expression of plastic modifications induced by sensory-cholinergic pairings. Here we review and discuss ACh-dependent plasticity and activity-dependent plasticity and ask whether these two mechanisms are linked. To address this question, we analyzed our data and tested whether changes mediated by ACh were activity-dependent. We show that ACh-dependent potentiation of response in the barrel cortex of rats observed after sensory-cholinergic pairing was not correlated to the changes in activity induced during pairing. Since these results suggest that the effect of ACh during pairing is not exerted through a direct control of the post-synaptic activity, we propose that ACh might induce its effect either pre- or post-synaptically through activation of second messenger cascades.