2016). Inputs to prefrontal cortex support visual recognition in the aging brain. Scientific Reports, 6, [319643].

Predictive coding models of brain function propose that top-down cortical signals promote efficient neural codes by carrying predictions of upcoming sensory events. We hypothesized that older brains would employ these codes more prominently given their longer repertoire of sensory experience. We measured the connectivity underlying stimulus-evoked responses in cortical visual networks using electroencephalography and dynamic causal modeling and found that in young adults with reported normal or corrected-to-normal vision, signals propagated from early visual regions and reverberated along reciprocal connections to temporal, parietal and frontal cortices, while in contrast, the network was driven by both early visual and prefrontal inputs in older adults with reported normal or corrected-to-normal vision. Previously thought of as exceptions to the rule of bottom-up signal propagation, our results demonstrate a prominent role for prefrontal inputs in driving vision in aged brains in line with lifespan-dependent predictive neural codes. In Bayesian theories of neural function, our brain’s internal generative model of the world is constantly updated through alterations in neural connections and driven by consistent, repeated inputs from the sensorium 1–3 . According to predictive coding accounts of these model updates, learned environmental statistics are encoded by top-down connections as ‘priors’ and serve to constrain bottom-up signal propagation which carry prediction errors 4,5 . While alterations in neuronal activations and connectivity consistent with these effects have been observed during single-session perceptual learning tasks 1,6 , human aging represents a natural ecological extension where predictive coding theories remain to be tested. The predominant view of cortical visual processing posits that perceptions are formed following bottom-up hierarchical signaling of successively complex features of a visual scene. This view has been challenged by recent evidence of a dual-route network in object recognition 7,8 where presumed magnocellular projections to frontal cortex have been shown to exert early top-down effects on signals from bottom-up visual pathways 8 . Several recent studies have highlighted the importance of top-down signaling from higher to lower levels of the visual system to enhance task-relevant information 9,10 , and the idea of top-down influences in visual perception can be traced to the Gestalt school of psychology. This top-down functional pathway may arise anatomically from the mediodorsal thalamic nucleus, which has strong reciprocal connectivity with the frontal cortex and has recently been shown to receive direct inputs from the retina 11 . This prefrontal route carries visual information at low spatial frequencies, offering a ‘gist’ of the visual scene to be filled-in with representational details carried through bottom-up hierarchical processing. This route may accommodate predictive deployments to the visual network and participate in our hypothesized age-related reorganization of perceptual circuitry. Repetition priming, which varies the familiarity of a stimulus