The research team, headed by psychologist Jonathon Crystal, showed that rats "under the influence" had difficulty distinguishing between long and short periods of time during tasks for which they were trained.
"In the real world, this suggests that someone smoking marijuana might well be able to do a task briefly, but over time there could be serious attention problems," said Crystal. The implication is that users of marijuana could be lulled into thinking they are capable of using the motor skills for such actions as driving when in fact there could be serious long-term attention-span problems.
The research was just published online in the journal Behavioural Brain Research and will be published soon in its print version. Co-authors of the paper are Andrea Hohmann and laboratory research coordinator Kenneth Maxwell, both also of UGA. The study was funded by a grant from the National Institute on Drug Abuse.
The study used rats that were placed in a box equipped with a speaker and two retractable levers. A sound was presented to the rats for either a short period or a long period. For example, the rats were required to distinguish between four and 16 seconds. If the duration of the sound was short, the rat had to press one of the levers to obtain a pellet of food. The rat had to press the other lever to receive food if the sound was long.
"Under these circumstances, animals will typically learn to press the correct lever with high accuracy," the authors said.
The research team then played sounds of intermediate length to find a midpoint at which rats were equally likely to respond as if the sound were "short" or "long."
After the rats learned the right levers to press, they were injected with a synthetic cannabinoid, and their sensitivity to time was measured. Cannabinoids produced a substantial decline in sensitivity to time through a specific brain receptor mechanism.
Crystal's team used a synthetic compound rather than tetrahydrocannabinol (THC), the "active" ingredient in marijuana, because the synthetic cannabinoid is more powerful and easier to use in laboratory settings. It is so close chemically to THC, however, that the findings can be equated with the effects of THC.
Using computer models to interpret the data, the scientists found that the general ability to maintain attention was altered by exposure to the cannabinoid. The cannabinoid disrupted performance of the task by producing a disorder of attention.
The raw data from the study are available at http://www.