Classical conditioning specifically modifies receptive fields in primary and secondary auditory cortical areas to favor the frequency of a tone signal over other frequencies, including tuning shifts toward, or to, this frequency. This plasticity of receptive fields is associative and highly specific, can develop very rapidly, can be expressed under anesthesia and can be maintained indefinitely. Muscarinic receptors in the cortex may be involved. Non-lemniscal thalamic nuclei also develop receptive field plasticity that may contribute to cortical plasticity.