Summary
Science Daily Article - Associative Learning in Drosophilia
Sept. 17, 2006

"Association is a connection between the representations of two events (two stimuli or a stimulus and a response) such that the occurence of one of the events activates the representation of the other" (Domjan, 26). This is why researchers from the Schroll et. al. team (as cited in the September 17, 2006 issue of Science Daily) define associative learning as a time when, "animals learn to change their behavior in response to a particular stimulus that would otherwise have a neutral influence on behavior".
 
The study done by Schroll et. al (as cited in the September 17, 2006 issue of Science Daily), actived sets of neurons in Drosophilia. The researchers "fooled" the neurons into thinking that this activation was a positive or negative experience in order to determine which neurons associate the attractive or repulsive value to the neutral stimuli during associative learning. Drosophilia was an attractive choice for researchers because it has a simple system of neurons and its genes are easily manipulated.

Past studies have shown that "neurons expressing dopamine are required for aversive learning whereas neurons expressing another neurotransmitter, octopamine, are required for appetitive learning". In the study done by Schroll et. al., the researchers targeted nerve cells in the ion-channel called channelrhodopsin-2 because the activity is light-sensitive, so all the research team would need to do in order to activate the neurons which have channelrhodopsin-2 would be to shine blue light on Drosophilia larvae. This allowed the researchers to see if the blue light could take the place of an external stimulus in an associative-learning experiment. If an odor was presented concurrently with the activation of the dopamine releasing neurons, the larvae avoided the odor in a later experiment even thought they were then subjected to the odor without a negative stimulus. The researchers also found that if an odor was presented concurrently with the activation of octopamine or tyramine releasing neurons, the larvae later found the odor to be attractive. These results suggest that it is the type of groups of neurons that determine if an odor stimuli is found appealing or repulsive to the organism. This has not yet been tested on more complex nervous systems, such as those found in mammals.



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