The mammalian auditory cortex undergoes continuous plasticity following auditory experience. This study demonstrates the instructive roles of sound frequency and amplitude in representational plasticity in the primary auditory cortex of the mouse. Electrical stimulation of the basal forebrain paired with a tone led to a pronounced shift in the receptive field of the cortical neurons in both frequency and amplitude domains, the shift being towards the frequency and amplitude of the tone. Importantly, the plasticity in the frequency tuning of cortical neurons appeared to be largely dependent upon frequency-specific decreases in the response threshold. The minimum threshold of cortical neurons could be reduced only if the amplitude of the presented tone was lower than the minimum threshold. This finding suggests that training with low-intensity sound can increase the sensitivity of cortical neurons. Furthermore, all of these effects evoked by basal forebrain activation could be eliminated by cortical application of atropine, the acetylcholine muscarinic receptor antagonist. The data suggest that cortical plasticity is guided by both sound frequency and amplitude. The basal forebrain promotes sound-guided cortical plasticity by facilitating neural mechanisms intrinsic to the auditory system.