  The subcortical sensory pathways are the fundamental channels for mapping the
outside world to our minds. Sensory pathways efficiently transmit information
by adapting neural responses to the local statistics of the sensory input. The
longstanding mechanistic explanation for this adaptive behaviour is that
neuronal habituation scales activity to the local statistics of the stimuli. An
alternative account is that neural coding is directly driven by expectations of
the sensory input. Here we used abstract rules to manipulate expectations
independently of local stimulus statistics. The ultra-high-field functional-MRI
data show that expectations, and not habituation, are the main driver of the
response amplitude to tones in the human auditory pathway. These results
provide first unambiguous evidence of predictive coding and abstract processing
in a subcortical sensory pathway, indicating that the brain only holds
subjective representations of the outside world even at initial points of the
processing hierarchy.
