Long-term cocaine use made rats more impulsive, in particular, by making them choose smaller rewards now over larger rewards later. The researchers found this when they were studying the link between impulsivity and cocaine addiction. Interestingly, they did not find evidence that more impulsive individuals were at higher risk of addiction, as previous studies had suggested. The researchers presented their findings published in the journal eNeuro.
First, the researchers divided the rats into three groups: low, medium, and high impulsivity. They did this using the so-called marshmallow test, in which the rats were offered a smaller reward immediately or a larger one later. The tendency to choose the smaller reward in this test is called a sign of impulsive behavior.
After that, the rats were allowed to self-administer cocaine to see if they would develop an addiction, that is, if they would take it regularly. As it turned out, rats from all three groups chose to take a new dose of cocaine with the same frequency. However, there was a correlation between its use and impulsivity: even rats from the low-impulsivity group became more impulsive after prolonged cocaine use.
This was confirmed by their brain activity: before cocaine use, the midbrain, thalamus, and frontal cortex of the rats actively exchanged signals, but after - the connections between them decreased. Scientists associate such changes in the brain with a violation of signal transmission involving the neurotransmitter dopamine, which is often observed during addiction. They suggest that the increase in impulsivity due to cocaine use may push people to consume even more of this drug or other psychoactive substances.
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