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Marijuana influences visual development

Marijuana influences visual development

Media Release - University of Auckland - 20 November 2015

Vision science researchers at the University of Auckland have found that prenatal marijuana use benefits a biomarker of visual neurodevelopment in preschool children.

The finding came as a surprise from a study that investigated the impact of prenatal exposure to recreational drugs on the brain’s visual areas. The study was published in Nature: Scientific Reports this week.

“We found that global motion perception*, (a behavioural measure of visual processing), was impaired by prenatal exposure to alcohol, but significantly improved by exposure to marijuana,” says doctoral researcher Arijit Chakraborty. “Children who were exposed to marijuana were almost 50 percent better at the global motion task than those who were not.”

He says that exposure to both alcohol and marijuana prenatally, had no effect – suggesting that the benefits from marijuana cancelled out the harm from alcohol. Prenatal exposure to methamphetamine had no influence on vision.

The study measured global motion perception in 145 four-and-a-half year-old preschool children who had been exposed to different combinations of methamphetamine, alcohol, nicotine and marijuana before birth, and also 25 unexposed children.

Other visual functions, such as measures of visual acuity were not affected by drug exposure.

“Our results show that prenatal drug exposure can influence a behavioural measure of visual development, but that the effects are dependent on the specific drugs used during pregnancy,” says Arijit.

Most studies of prenatal exposure to recreational drugs have investigated how they impair motor and cognitive development in children, but the impact on visual areas of the brain is less well understood.

Participants from the IDEAL study (2014) were recruited into two groups and data collected from the mothers (who were referred to the IDEAL study by midwives and whose prenatal drug use was assessed. Meconium samples were collected from their babies soon after birth for a drug metabolite analysis – carried out in the USA).

“Many mothers of methamphetamine-exposed children were multiple drug users and used two or more types of drugs,” says Arijit. “The control group included children who were also exposed to a range of drug combinations with the exception of methamphetamine, as well as non-drug exposed children.

“Because the mothers’ prenatal drug exposure was verified objectively by meconium analysis, this group of children provided a unique opportunity to study the effects on visual development of prenatal exposure to a range of substances.”

The children studied were made up of 52 percent European, 36.5 percent Maori, and 11 percent from other ethnicities.

The range of drugs they were exposed to was; nicotine 75.2 percent, alcohol 56.4 percent, methamphetamine 44.2 percent and marijuana 40 percent. The majority of children (81.3 percent) had been exposed to multiple drugs. Twenty-five children (15 percent) had no drug exposure and provided a non-drug exposed comparison group.

Only alcohol and marijuana exposure had independent effects on global motion perception (after controlling for the effects of multiple drug exposure, verbal IQ, ethnicity, visual acuity, , and sex).

Children who were exposed prenatally to alcohol had significantly poorer global motion perception than that of children not exposed to alcohol.

“Unexpectedly, children exposed to marijuana had significantly better global motion perception than those of children not exposed to marijuana and there was a significant interaction between the effects of alcohol exposure and marijuana exposure,” says Arijit.

“Exposure to marijuana in the absence of alcohol was associated with improved global motion perception which was significantly better than that of children who had not experienced prenatal drug exposure.”

“Global motion perception for children exposed to both marijuana and alcohol was no different from that of children who had no drug exposure,” he says. “This perhaps has implications for preventing some of the effects of Foetal Alcohol Syndrome.”


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