Stimulants are known to enhance attention and memory — which is why many people cannot start their day without a cup of coffee. Despite this, the brain mechanisms that underlie this effect are not well understood. A study published in Human Brain Mapping seeks to address this gap and better understand how stimulants affect the brain and memory.
Different substances that people can ingest can have varying effects on the human brain, both positive and negative. Stimulants are a class of substances that can increase energy and enhance cognition. This is the reason why many people drink coffee or energy drinks when they have an important day ahead of them, and why people who are prescribed medicinal stimulants may take them before an exam or meeting.
Despite this, the biological factors, such as brain structure and chemistry, that contribute to different types of stimulants having this enhancing effect are not well understood. This topic is what this paper seeks to expand upon and address.
For their study, Maxi Becker and colleagues utilized 48 healthy, male participants to serve as their sample. Participants were all recruited from the internet. Exclusion criteria included mental illness, excessive coffee consumption, heavy smoking, prescription stimulant usage, or illicit hard drug use within the past year.
Participants were separated into four groups: methylphenidate, modafinil, caffeine, and placebo. Each participant was given one stimulant as a white pill that they ingested on two separate days approximately a week apart. Participants were given an fMRI brain scan and completed measures on memory of visual material, implicit memory, and memory of auditory material/ false memory.
Results showed that participants who were given stimulants showed stronger performance on memory tasks than participants who were given the placebo treatment. Implicit memory was improved, not only shortly following the ingestion, but also 24 hours later. False memory was lower in the stimulant group after encoding, but not after delayed recall.
Functional connectivity between the frontoparietal network and default mode network was contributed to by the ingestion of stimulants as opposed to placebo. Additionally, there was a decrease in negative connectivity between the right prefrontal cortex and the medial parietal cortex that occurred for the stimulant group. The reduction of negative connectivity was related to enhanced performance on memory tasks.
This study took important steps into better understanding stimulants effects on the brain. Despite this, there are limitations to be aware of. One limitation is that this study only used male participants. Although this was a deliberate decision on the researcher’s part in an attempt to avoid menstrual cycles and their hormone changes, it limits generalizability significantly. Another limitation is that the sample size per different group is low; future research could expand the sample.
The study, “Cognitive enhancement: Effects of methylphenidate, modafinil, and caffeine on latent memory and resting state functional connectivity in healthy adults“, was authored by Maxi Becker, Dimitris Repantis, Martin Dresler, and Simone Kühn.