University of British Columbia
New research from the University of British Columbia suggests there
may be some truth to the belief that marijuana use causes laziness-- at
least in rats.
The study, published today in the Journal of Psychiatry and Neuroscience,
found that tetrahydrocannabinol (THC), the main psychoactive ingredient
in marijuana, makes rats less willing to try a cognitively demanding
task.
"Perhaps unsurprisingly, we found that when we gave THC to these
rats, they basically became cognitively lazy," said Mason Silveira, the
study's lead author and a PhD candidate in UBC's department of
psychology. "What's interesting, however, is that their ability to do
the difficult challenge was unaffected by THC. The rats could still do
the task-- they just didn't want to."
For the study, researchers looked at the effects of both THC and
cannabidiol (CBD) on rats' willingness to exert cognitive effort.
They trained 29 rats to perform a behavioural experiment in which the
animals had to choose whether they wanted an easy or difficult
challenge to earn sugary treats.
Under normal circumstances, most rats preferred the harder challenge
to earn a bigger reward. But when the rats were given THC, the animals
switched to the easier option, despite earning a smaller reward.
When they looked at the effect of CBD, an ingredient in marijuana
that does not result in a high, researchers found the chemical did not
have any effect on rats' decision-making or attention. CBD, which is
believed to be beneficial in treating pain, epilepsy and even cancer,
also didn't block the negative effects of THC.
"This was surprising, as it had been suggested that high
concentrations of CBD could modulate or reduce the negative effects of
THC," said Catharine Winstanley, senior author of the study and an
associate professor in UBC's department of psychology. "Unfortunately,
that did not appear to be the case."
Given how essential willingness to exert cognitive effort is for
people to achieve success, Winstanley said the findings underscore the
importance of realizing the possible effect of cannabis use on impairing
willingness to engage in harder tasks.
While some people view marijuana as a panacea that can cure all
ailments, the findings also highlight a need for more research to
determine what THC does to the human brain to alter decision-making.
That could eventually allow scientists to block these effects of THC,
allowing those who use medical marijuana to enjoy the possible benefits
of cannabis without the less desirable cognitive effects.
METHOD
At the beginning of each behavioural experiment, rats chose between
two levers to signal whether they wanted an easy or hard challenge.
Choosing the easy challenge resulted in a light turning on for one
second, which the rats could easily detect and respond to by poking it
with their nose, receiving one sugar pellet as a reward. In the more
difficult challenge, the light turned on for only 0.2 seconds, rewarding
the rat with two sugar pellets if they responded with a nose poke.
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