Tag Archives: pharmacology

In-depth perception: notes from the lab of Michael Silver

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Most people who look at the above figure will perceive the symbols as “THE CAT”, when in reality the middle character in each word can be perceived as either an “H” or an “A”. This effect is an example of top-down processing, a mode of brain function in which previous knowledge and contextual information drive our cognition of the world. Bottom-up processing, on the other hand, occurs when information from the physical stimulus, rather than the general context, is used to process sensory input. “Perception” is an integration of both top-down and bottom-up processing.

Recently, scientists discovered that the neurotransmitter acetylcholine modulates brain activity by shifting cortical processing towards a more bottom-up mode. Though the mechanisms remain somewhat obscure, it is known that acetylcholine suppresses intracortical connections that connect neurons within a cortical area to each other, thereby increasing the focus on physical properties of the stimulus. Because the balance between bottom-up and top-down processing is so important, damage to cholinergic cells can have profound consequences on behavior and cognition.