Simultaneous mnemonic and predictive representations in the auditory cortex

Recent studies have shown that stimulus history can be decoded via the use of broadband sensory impulses to reactivate mnemonic representations.^1-4. However, memories of previous stimuli can also be used to form sensory predictions about upcoming stimuli.^5,6 Predictive mechanisms allow the brain to create a probable model of the outside world, which can be updated when errors are detected between the model predictions and external inputs. ^7-10 Direct recordings in the auditory cortex of awake mice established neural mechanisms for how encoding mechanisms might handle working memory and predictive processes without "overwriting" recent sensory events in instances where predictive mechanisms are triggered by oddballs within a sequence.¹¹ However, it remains unclear whether mnemonic and predictive information can be decoded from cortical activity simultaneously during passive, implicit sequence processing, even in anesthetized models. Here, we recorded neural activity elicited by repeated stimulus sequences using electrocorticography (ECoG) in the auditory cortex of anesthetized rats, where events within the sequence (referred to henceforth as "vowels," for simplicity) were occasionally replaced with a broadband noise burst or omitted entirely. We show that both stimulus history and predicted stimuli can be decoded from neural responses to broadband impulses, at overlapping latencies but based on independent and uncorrelated data features. We also demonstrate that predictive representations are dynamically updated over the course of stimulation.