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Study identifies the brain cells regulating the Pavlovian response.

In his famous experiment, Ivan Pavlov rang a bell each time he fed his dogs,  which resulted in the animals drooling in anticipation every time they heard the bell, even before food appeared.  This response process is known as Pavlovian conditioning which refers to a learning procedure where a biological stimulus, in this case, food, is paired with a previously neutral stimulus, such as a sound. The first study to note manual body regulation of diet and eating via the brain, it is highly desirable to map the neuronal-based mechanisms of classical conditioning. Now, a study from researchers at UCLA traces the Pavlovian response to a small cluster of brain cells, namely, striatal parvalbumin (PV)-positive interneurons, known to go awry in Huntington’s disease, Parkinson’s disease, and Tourette’s syndrome.  The team states their research could one day help the global medical community to find new approaches to diagnosing and treating these disorders.  The study is published in the journal Neuron.

Previous studies show Pavlovian conditioning is a learning process where neutral stimulus comes to elicit a response, such as salivation, similar to the one elicited by a dominant or biological stimulus such as food.  It is known species survive because they’ve learned how to link these neutral stimuli or sensory cues including specific sounds, smells, and sights to a dominant stimulus or rewards like food and water. The current study focuses on cellular activity in the striatum, a part of the brain associated with reward, movement, and decision-making to investigate the brain circuitry encoding reward-based learning and behavior.

The current study repeatedly exposes mice to the unfamiliar scent of banana or lemon, followed by a drop of condensed milk. Results show eventually, the mice learn these smells predict the arrival of a reward and began fervently licking the air in anticipation.  Data findings show the mice learned to associate the new scent with food, just like Pavlov’s dogs, as shown in the video provided.

The lab uncovers what happens to the Pavlovian response when support cells are silenced in the striatum.  Results show striatal parvalbumin (PV)-positive interneuron’s influence appears stronger when the mice are first learning to pair the unfamiliar scents with a reward.  Data findings show these cells cause spontaneous medium spiny projection neuron (MSN) activity in conditioning, which diminishes the more the animal is conditioned.

The team surmises their study demonstrates dorsolateral striatal PV interneurons and MSNs influence the initial expression of Pavlovian reward-conditioned responses whose contribution to performance declines with experience.  For the future, the researchers state their findings suggest malfunctioning support cells could lead to neurological disorders, and restoring the cells’ function could eventually help people with these diseases.

Source: UCLA

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