Abstract
The cortex constitutes the largest area of the human brain. Yet we have only a basic understanding of how the cortex performs one vital function: the integration of sensory signals (carried by feedforward pathways) with internal representations (carried by feedback pathways). A multi-scale, multi-species approach is essential for understanding the site of integration, computational mechanism and functional role of this processing. To improve our knowledge we must rely on brain imaging with improved spatial and temporal resolution and paradigms which can measure internal processes in the human brain, and on the bridging of disciplines in order to characterize this processing at cellular and circuit levels. We highlight apical amplification as one potential mechanism for integrating feedforward and feedback inputs within pyramidal neurons in the rodent brain. We reflect on the challenges and progress in applying this model neuronal process to the study of human cognition. We conclude that cortical-layer specific measures in humans will be an essential contribution for better understanding the landscape of information in cortical feedback, helping to bridge the explanatory gap.
Highlights
The layered cortexThe integration of feedforward and feedback signals is important for healthy cognition and consciousness
The laminar integration of sensory inputs with feedback signals in human cortex Lucy S
The cortex is deficient in integrating sensory signals with internal representations; during hallucinations, the brain fails to determine thematch between its internal representation and the information it receives from the sensory environment, resulting in a conscious percept of a non-existent sound or sight for example (e.g. Horga, Schatz, Abi-Dargham, & Peterson, 2014)
Summary
The integration of feedforward and feedback signals is important for healthy cognition and consciousness. We need paradigms in which we can access internal (i.e. non-sensory) signals (Chong, Familiar, & Shim, 2015, see Petro & Muckli, 2016) Such paradigms are essential for mapping function to physiological measures, because feedforward and feedback processing have markedly different effects on (population) receptive fields. Predictive processing may be important for guiding cognition and behaviour, and may be the core computation of the cortex upon which reward, attention, expectation and emotion act as modulators Such network systems are central to the question of what is transmitted by top-down signals (Petro, Vizioli, & Muckli, 2014), in addition to sensory-specific feedback signals of complex features. The neuronal implementation of feedforward-feedback integration in cognition remains not fully conceptualized
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