New research provides some preliminary evidence that the stimulant methamphetamine alters the neural response to visual stimuli. The findings have been published in the journal Psychopharmacology.

“Amphetamines are thought to increase an organism’s interest in the surrounding environment,” said study author Harriet de Wit, a professor and head of the Human Behavioral Pharmacology Laboratory at the University of Chicago.

“One way they could do this is by increasing reactions to sensory input, and this increased reaction, or sensitivity, may depend on the level of complexity or salience of visual objects.”

In the double-blind study, 18 healthy adults completed two fMRI scanning sessions after consuming 20mg of methamphetamine or a placebo.

During the brain scans, the participants passively viewed various images of nature, which varied in the number of curved or fragmented edges. In other words, the images varied in their visual complexity.

“Our study suggested that methamphetamine differentially increases brain activation the visual cortex, depending on the stimuli,” de Wit told PsyPost.

“We found that more complex stimuli produced greater activation in the visual cortex without the drug, but pretreatment with a low dose of this amphetamine specifically increased activation in response to the simpler images. Thus, drugs can modulate how we see the world.”

But there is still much to learn about how amphetamines impact the brain.

“Many questions remain about how stimulant drugs change people’s’ reactions to the world around them, including sensory stimuli, emotional and cognitive events. This was a small study, with a single dose, in a highly selected sample of healthy young adults,” de Wit said.

“Follow-up studies are needed to determine how and why the drug preferentially affects reactions to certain sensory input more than others, and how this affects the person’s behavior in the natural, non-laboratory world.”

The study, “Effects of methamphetamine on neural responses to visual stimuli“, was authored by Kathryne Van Hedger, Sarah K. Keedy, Kathryn E. Schertz, Marc G. Berman, and Harriet de Wit.