Marijuana’s effect on emotion

Stephanie Mason

Volunteer Stephanie Bastidas is measured for the cap before she starts an EEG scan.
Volunteer Stephanie Bastidas is measured for the cap before she starts an EEG scan.

Since the passing of Amendment 64 in 2012, researchers have been active in working to understand marijuana and its effects on the human brain.

Lucy Troup from Colorado State University’s Psychology Department is conducting research on the impact marijuana usage has on an individual’s emotional state.


“The bottom line is it appears that marijuana use does affect the brain’s ability to process emotional information,” Troup said.

Troup uses a brain activity measuring tool called the electroencephalogram to look at brain function. The EEG measures something called the P300, which is associated in the brain with emotional responses.

“The methods I use allow me to look more closely with how behavior is linked to brain mechanism with EEG,” Troup said. “When you make a positive stimulus or a negative stimulus, it changes with the size of that waveform.”

In Troup’s lab, images showing emotional expressions are shown to participants being monitored by the EEG. She looks at how self-reported marijuana users identify with the emotions displayed.

An EEG scan gives levels of P300 activity in the brain. A lower P300 is also called ‘depressed’, which indicates lower levels of emotion recognition.

The tests are done on three groups: people who have never used marijuana, people who have occasionally used and people who are chronic users.

“We have seen really interesting results,” Troup said. “We have a definite deficit for the usage amounts. Those who are chronic users have a very depressed P300, those who have used it once or twice have a P300 that falls in the mid range.”

Troup uses EEG to better understand how emotions are processed in the human brain.

“We look for biomarkers: indicators in brain activity that suggests difference between people who present with emotional disorders and those that don’t … just looking at what the brain does in regards to emotion and emotion processing,” Troup said.

The Troup lab is working on analyzing which emotions result in a depressed P300 level in the chronic user’s brain.


“We seem to be seeing brain mechanism effects that suggest that marijuana is changing how the brain processes emotional information,” Troup said. “What is less clear, and what we are starting to investigate further, is how that affects behavior.”

According to Troup, there have been a great deal of stories circulating mass media about behavioral changes of marijuana users, which prompted her interest in the study.

Troup also gained initial interest in marijuana research after Amendment 64 was passed.

“There is no such thing as a safe drug,” Troup said. “Caffeine is not safe, any drug or anything you put into your body … has some sort of risk attached to it. The idea that something was completely safe sort of mystified me.”

Marijuana usage is also going to be looked at as a possible depression treatment. Troup is interested in seeing if depression can be treated with marijuana. Her research will soon include EEG scans on a group that uses medical marijuana to treat their depression.

“Marijuana does have some really interesting applications medically,” Troup said. “The reasons people were asking for (marijuana) were not necessarily the ones best treated by endocannabinoids.”

According to Troup, people who use marijuana have varied reactions to the drug’s effects. The research is looking at how individual users can be affected on different levels.

“Some people may be able to cope quite well with these deficits and not have issues with interpreting emotional expressions, but for some people, this may be a problem,” Troup said.

Troup’s lab is not the only marijuana-related research going on at CSU. Kevin Walters is a second year graduate student working with the physical and psychological health that goes along with working in the new marijuana industry.

“As this legalization is occurring we notice this industry of marijuana workers that is just growing rapidly before our eyes,” Walters said. “Essentially what our project is aiming to do is to access potential issues and occupational health and well being in the workplace.”

Stephanie Bastidas is a graduate student who helps with the EEG scanning and research. People fill out questionnaires before the scan to list family history and many other factors that may contribute to the study.

“It is not as bad as it looks,” Bastidas said. “The experiment people are just kind of looking at images and processing them how we tell them.”

The lab is currently looking for volunteers to participate in the research.

“Please come and participate,” Bastidas said. “We want to try and get a wide range.”

Collegian Science and Technology Beat Reporter Stephanie Mason can be reached at or on Twitter @stephersmason.