Altered perceptual and emotional processing might bind impaired cognitive mechanisms during aging; however the nature of these sensory perception modifications is still unknown. In the present experiment we analyzed in rats, from early to mature life (2 to 11 months old), the response to unattended auditory evoked stimulation (Auditory evoked potential, AEP) and the power spectrum of spontaneous electroencephalogram (EEG), with the aim of unraveling the onset and target functional effects of aging. Somatosensory and cingulate cortex, mediodorsal thalamus and CA3 hippocampus were chosen for examination based on their involvement in sensory processing and age-related deficits. The main finding of this study is the early onset of age-related changes in adult rats as can be established with both AEP's and frequency analyses, and its diversity between brain regions during normal aging.