Methamphetamine (MA) abuse has been linked to psychological problems, such as depression, anxiety, and psychosis. It also has been linked to problems in everyday functioning (eg, impulsivity), and neurocognitive deficits in attention, memory, learning, executive function, and fine motor speed. But researchers from Capital Medical University in Beijing and Fujian Medical University in Fuzhou, both in China, say current understanding is limited about the impact of MA abuse in spatial processing, which affects, among other things, alertness.
The researchers conducted a study with 40 MA abusers and 40 nonusers. Participants performed 3 tasks randomly. During the Simple Reaction Task, they pressed a mouse key as quickly and accurately as possible, discriminating between hand and foot pictures. The Spatial Orientation Task asked them to gauge the direction of fingers or toes shown in pictures. The Mental Rotation Task randomly showed hands and feet in 2 different views (dorsum, palm/plantar) and oriented in 1 of 6 clockwise angles. It also assessed 2 different mental rotation strategies: object based and egocentric based, or the ability to judge which side a body part belongs to in the picture and in the participant’s own body. In this test, the researchers say, the transformation of visuospatial mental image is crucial to action, navigation, and reasoning.
The researchers found no significant difference in either accuracy or reaction time between the 2 groups in the first task. In the second, MA users performed less well on reaction time but not accuracy. The results of that task suggested that MA abuse may induce a deficit in spatial orientation ability, mainly on horizontal surface.
On the third task, however, MA abusers performed worse and committed more errors than did the nonusers. They had worse results at every orientation angle and took longer to judge the orientation of leftward but not rightward foot pictures. Such phenomena likely relate to MA damage to cortical gray and white matter, the researchers say. They note that MA users also have shown less activation in the right hemisphere when performing a facial-affect matching task. MA abuse may mainly target the right hemisphere, the researchers add, but the findings may support other research that has found poor decision-making performance in MA abusers that is related to inadequate activation of many brain areas.
The study confirmed “considerably poor visuospatial ability” in MA users. The Mental Rotation Task findings also showed MA abuse of longer duration had more negative effect on spatial process speed. Because both cognitive speed and accuracy were affected on the Mental Rotation Task, but only cognitive speed on Spatial Orientation, MA abuse may affect visuospatial ability more seriously than spatial orientation ability, the researchers say.