Some questions that arise in Machine Learning involve the prospect of using feedback from Higher-order areas (downstream) to Lower-order areas (upstream), and using Global Knowledge for Local Processing. A desire to gain insight into those issues from Neuroscience ("how does the brain do it?") led me to some fascinating investigations into the Microcircuits of the Cerebral Cortex. This blog entry is a broad review of the field, in the context of the original motivating questions from Machine Learning. Starting out with a quote from the “bible of Neuroscience”: From Principles of Neural Science, 5th edn (Online book location 1435.3 / 5867). Emphasis and note added by me: Sensory pathways are not exclusively serial; in each functional pathway higher-order areas project back to the lower-order areas from which they receive input. In this way neurons in higher-order areas, sensitive to the global pattern of sensory input, can modulate the activity of neurons in lowe