However, recent findings clearly show that neurons of the primary auditory system are still responsive during sleep , suggesting that the thalamus might not be as effective in gating sensory information as previously believed. Astonishingly, in a study by Issa and Wang (2008) neurons in the primary auditory cortex as well in secondary auditory
cortical areas displayed on average even similar discharge patterns during sleep as compared to wakefulness. With regards to olfactory processing, cortical odor-evoked activity is reduced with regards to the wake state but not eliminated during SWS . Accordingly, the sleeping brain responds to external input,at least to some extent.