Study identifies the brain cells which regulate the Pavlovian response.

In his famous experiment, Ivan Pavlov rang a bell each time he fed his dogs. Soon, the dogs began drooling in anticipation when they heard the bell, even before food appeared.  This response process is known as Pavlovian conditioning, and refers to a learning procedure in which a biological stimulus, for instance food, is paired with a previously neutral stimulus, the bell or 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, the same neurons that go awry during Huntington’s disease, Parkinson’s disease and Tourette’s syndrome.  The team state that 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 through which neutral stimulus comes to illicit a response, such as salivation, that is usually similar to the one elicited by a dominant or biological stimulus such as food.  It is known that species survive because they’ve learned how to link these neutral stimuli or sensory cues like specific sounds, smells and sights to 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 which encodes reward-based learning and behaviour.

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

The lab uncover what happens to the Pavlovian response when support cells are silenced in the striatum.  Results show that support cells’ influence appear stronger when the mice are first learning to pair the unfamiliar scents with a reward; the change is less dramatic in mice who have already mastered the connection.  Data findings show that these cells were most essential to inexperienced mice who haven’t yet mastered the Pavlovian response.

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

Source: UCLA


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