We have shown previously that Hebbian modifications are sensitive to phase relations between excitatory synaptic inputs and suprathreshold membrane potential oscillations in layer 2/3 visual cortex pyramidal neurons during cholinergic neuromodulation. During bath application of the cholinergic agonist carbachol (5 microM) pairing trains of extracellularly evoked EPSPs in layer 2/3 at 20 Hz with the peaks of suprathreshold 20 Hz Vm oscillations resulted in LTP, while pairing with the oscillation troughs induced LTD (Wespatat et al., SFN 2000). Here, we further investigate how blockade of cholinergic receptors affects the phase-angle sensitivity of Hebbian modifications during oscillations. Bath application of the muscarinic and nicotinic receptor antagonists scopolamine (10 microM) and hexamethonium (100 microM) resulted in LTD with both peak pairing, where EPSPs coincided with postsynaptic discharges and with trough pairing, where EPSPs were shifted 180° out of phase with postsynaptic discharges. Thus, cho...