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One of the early discoveries in neuroscience that helped to rekindle the field’s interest in habit came from a 1990s study that separated habit learning in humans from conscious understanding. Twenty participants had Parkinson’s disease, which attacks motor control systems in the basal ganglia, especially the putamen, and impedes the ability to learn new habits (even non-motor ones) and to activate old ones. Twelve participants were patients with amnesia who had dysfunction in a different brain area (the hippocampus), one that interfered with their ability to remember recent events. Parkinson’s patients could explain the task and the instructions. They knew consciously what to do. But it didn’t matter how much they practiced. They could not learn the connections between cues (cards) and rewarded responses (rain/sun forecast). They could not form a habit. In contrast, the amnesiacs acquired habits more readily as they practiced the task. After taking fifty chances at predicting the weather, they could make accurate forecasts based on the cards. But when they were asked about what they were doing, they could not remember the instructions or details of what they had seen. This research provided some of the first insights into the neural mechanics of habit formation. It suggested that, in humans, habit learning isn’t superseded or subordinated by more thoughtful learning systems, as assumed by many researchers during the cognitive revolution. Habits live in resilient, deep-seated neural structures—ones that are fundamental to mammalian life.
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Wendy Wood (Good Habits, Bad Habits: The Science of Making Positive Changes That Stick)