When my daughter was a few weeks old, I developed a curious compulsion to speak to her every time I passed the playpen and found her alert. A decade later, I find comfort in a recent paper showing that the newborn rat brain does indeed respond to repetitive, albeit passive, acoustic stimulation within a few weeks of birth.Zhang, Bao and Merzenich have studied the onset of several functional properties of neurons in the auditory cortex of the newborn rat [1xPersistent and specific influences of early acoustic environments on primary auditory cortex. Zhang, L.I. et al. Nat. Neurosci. 2001; 4: 1123–1130Crossref | PubMed | Scopus (241)See all References[1]. In adults the neurons are systematically arrayed in tonotopic maps according to their preferred frequencies. The presumptive auditory cortex of young rats is large and responds best to high frequency sounds, but the region gradually shrinks, acquiring low frequency selectivity and good tonotopy, as development proceeds.The authors asked whether this developmental sequence could be altered by experience. Pups were raised in a distorted acoustic environment. From postnatal days 9 to 28, monotonic stimuli were pulsed for 10–16 hours a day at moderate intensities (60–70 dB): about the same levels as conversational speech. The effect on cortical physiology was striking. Within five days of the onset of exposure, precocious responses to low frequency stimuli were apparent in animals exposed to low frequency monotones. This is four to six days ahead of schedule. By postnatal day 22, the region devoted to lower frequencies was larger than that of naive rats. In animals exposed to high frequency monotones, the enlarged region preferred the higher frequencies. The distortion in frequency representation persisted into adulthood.The exposed mothers were unaffected by an acoustic experience that so profoundly affected their pups. This was notable because Merzenich's group had previously shown cortical plasticity in adult rats if the auditory stimulus was paired with electrical stimulation of basal forebrain, a region believed to engender behavioural relevance to sensory input. So the mother's cortex will change if the stimulus matters, but not if it doesn't.Future experiments should address whether cortical plasticity is accompanied by structural modifications. Finally, I am left wondering whether adolescence ushers in a new period of plasticity, accompanied by degradation in the cortical representation of auditory stimuli that have emerged as behaviorally irrelevant. After all, my daughter now seems to have a hard time hearing my repeated requests to clean her room.