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March 20, 2014



Before and After Methamphetamine



Text description of Figure 1

The graph shows a flow chart depicting the four stages of a reversal trial, which measures an animal’s mental flexibility. A piece of fruit (a banana) is placed as a reward into one of three boxes labeled with different symbols on their lids (a red cross, green triangle, or yellow sphere). During the acquisition and retention phases (shown on first and second lines from the top) an animal learns to retrieve the fruit reward from one of the boxes marked with a specific symbol (i.e., the red cross). In the reversal and second retention phases (third and fourth lines from the top), the animal has to learn that the fruit reward is no longer available from the box with the cross symbol, but in a box with a different symbol (i.e., the yellow sphere). The number of trials it takes the animal to successfully associate the fruit reward with the new symbol during the second retention phase is recorded to measure the animal’s ability to adapt to a new reward cue.




Text description of Figure 2

The figure shows a scatter plot indicating the relationship between the number of reversal trials, i.e., the number of attempts a vervet monkey made to obtain a food reward after it had been switched to a new visual cue, and a change in gray matter in the monkeys’ brains after exposure to methamphetamine or to saline (an inactive control). The vertical (y)-axis shows the change in the number of reversal trials, which was calculated by subtracting the number of trials before each exposure from the number of trials after the exposure. A positive number for the change indicates that an animal needed a greater number of trials to obtain the food reward after being exposed to methamphetamine or saline and a negative number that it needed fewer trials. The horizontal (x)-axis shows the change in gray matter, which was measured by comparing signal intensities in magnetic resonance imaging scans before and after the monkeys were exposed to the drug or saline. As shown in the graph, after methamphetamine exposure (blue circles), most monkeys needed more trials to obtain the food reward than the monkeys exposed to saline (red circles); most saline-exposed monkeys required fewer trials than before the exposure. The worsening performance of the methamphetamine-exposed monkeys was correlated (indicated by the solid blue line) with increased gray matter in their right putamen.




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