A small stimulation experiment in people with methamphetamine use disorder reported better visual working-memory capacity without a corresponding change in precision. Remembering more items and remembering each item more exactly are different outcomes.
Sun and colleagues compared intermittent theta-burst stimulation over the left dorsolateral prefrontal cortex with stimulation over the vertex as a control. Participants received five daily sessions. Memory was assessed before stimulation and after the first and fifth sessions.
The task involved remembering orientations of visual patterns and later reproducing a probed orientation. A model of the response errors separated a capacity-related estimate from the precision of remembered orientations. After one participant was excluded for chance-level performance, analyses included nine participants in the active group and eight in the control group.
The researchers reported improved working-memory performance after active stimulation, including an increase in estimated capacity. They did not observe a change in precision. Their conclusion therefore concerns a particular component of visual working memory, rather than an improvement in all memory processes.
That distinction matters because two people can make similar average errors for different reasons: one may fail to retain an item, while another retains it imprecisely. The statistical model helps distinguish those possibilities but remains a model of task responses.
The sample was small, and the authors noted that some statistical findings were marginal. They also lacked a valid craving measurement that would permit testing whether memory changes tracked craving changes. Better task performance consequently cannot be relabeled as reduced craving, reduced drug use, or proven relapse prevention.
Five sessions and a specific visual task do not establish long-term benefit or generalization to complex daily activities. This was an intervention in humans with a use disorder, not methamphetamine dosing and not a roadside impairment validation.
The study provides preliminary evidence for a selective cognitive effect of stimulation. Clinical benefit requires evidence about durability and meaningful functioning as well as test scores. Our discussion of working-memory demands explains why one task cannot stand in for every memory challenge.