December 26, 2008

Scientists Find Brain Cells Linked to Learning

Thanks to new imaging technology, scientists are able to see neurons that are critical to how people and animals learn from experience.

Researchers at the University of Washington used a new imaging technique to examine the brains of rats that had been subjected to conditioned taste aversion training.  They were able to visualize individual neurons that were activated as a result of the experiment.  

More than a century ago, Russian psychologist Ivan Pavlov conditioned his dog to salivate when it heard the sound of a tone prior to receiving food. Associative, or Pavlovian, conditioning is a fundamental form of learning in mammals, and scientists frequently use it to study plasticity, or how the circuits in the brain can change as a result of experience, according to Ilene Bernstein, UW professor of psychology and the study's senior author.

The UW researchers subjected rats to conditioned taste aversion training. Taste aversions have evolved in many animals to help them avoid toxic substances, researchers said.

For the study, thirsty rats were allowed to drink a saccharine solution for five minutes. After 25 minutes, they were injected with lithium chloride, which caused nausea, and then five minutes later, they were killed.  Scientists then examined slices of the rats' brains under a microscope.

The researchers were able to directly observe the convergent neurons where learning is suspected of taking place.  They found that some neurons were activated by the saccharine -- the conditioned stimulus -- and others were activated by the lithium chloride -- the unconditioned stimulus. Also, a small number of neurons were activated by both stimuli.

When the scientists reversed the order of the stimuli, a procedure known to be ineffective in producing learning, convergent neurons were not activated, even thought the animals were exposed to identical stimuli, according to the study.


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