A controlled human experiment found changes between selected resting brain networks after methamphetamine, while within-network connectivity did not significantly change. The observed network changes were not significantly associated with subjective drug-effect ratings.
Malina and colleagues studied 22 healthy young adults in two double-blind sessions. Participants received 20 mg oral methamphetamine or placebo in counterbalanced order, with sessions separated by at least four days. The investigators measured resting-state functional MRI and subjective and cardiovascular responses.
Networks were identified using an independent-component approach based on placebo data. The analysis distinguished synchronization among regions within a network from synchronization between different networks. These are different quantities, even though both are described as functional connectivity.
The drug did not significantly alter within-network connectivity. Between networks, it increased connectivity of thalamic and cerebellar networks with selected sensorimotor and temporal networks, while reducing connectivity between sensorimotor and middle temporal networks.
Methamphetamine also produced expected subjective and cardiovascular effects. However, correlations did not establish that the significant connectivity changes tracked subjective responses. The imaging findings therefore should not be presented as a direct neural readout of how strongly an individual felt the drug.
The sample was small and relatively homogeneous. The authors could not entirely exclude residual motion effects, and they did not include a perfusion measurement to assess global blood-flow effects. The data were collected at rest; task-related connectivity could follow a different pattern.
Functional MRI measures changes in a blood-oxygenation-related signal. It is not a methamphetamine or amphetamine assay, and the study established no concentration threshold or individual impairment classifier. Increased connectivity is also not inherently beneficial, while decreased connectivity is not inherently harmful. The result is a specific pharmacological network effect whose behavioral significance requires additional evidence.
Read our analysis of network integrity and segregation after amphetamine and other drugs.
Effects of Methamphetamine on Within- and Between-Network Connectivity in Healthy Adults. doi:10.1093/texcom/tgab063.