Oct 212005

A forthcoming article in Nature explains how recent experiments by researchers at MIT have shed some light on why sometimes habits seem to be broken but never truly die. Scientists have discovered that with the proper stimulus a dormant habit can be retrieved from memory and once again influence a subject’s behavior.

It has been known that habitual behavior changes neural activity patterns in the brain, specifically the basal ganglia, the area associated with motor and learning functions. Repeated or continuous stimulation of a neural region can cause a physical change in the synapses, the connections between neurons. This is known as synaptic plasticity, and it is believed to be the key to memory and learning.

Ann Graybiel, a professor of neuroscience at MIT’s Department of Brain and Cognitive Sciences, performed a series of experiments with rats in a maze. The rats were guided through the maze by audible tones and rewarded at the end with a piece of chocolate. Graybiel monitored the neural activity of the rats as they performed and found that while learning the course, neurons in the basal ganglia fired consistently from beginning to end. Once a rat was familiar with the maze, however, neural activity spiked only when starting and finishing and remained essentially inactive during the course itself. She found that if the reward was removed, consistent activity would return. The tones no longer had the same meaning (directing the rat to the reward) so the rat was forced to reevaluate it’s sensory input and re-learn what it meant in terms of navigating the maze. Interestingly, as soon as the piece of chocolate was used again as a reward, the spiked neural activity returned.

Dr. Graybiel has concluded that the spiked patterns she witnessed reflects what happens during habitual behavior. Once the proper stimulation is received and the initial pattern is recalled/fired, the brain essentially goes on autopilot until completing it’s stored sequence of events. Removing the stimulus “breaks the habit” but not permanently since the behavior returns immediately once the stimulus is reintroduced.

This research will be important to understanding and treating addicts and addictive behavior like drinking, over-eating and gambling, but it will also help to understand and treat diseases like Parkinson’s disease and OCD where similar neural patterns are a result of the disease itself and not what is initially voluntary activity.

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