A pivotal role is played by the acetylcholine system in working memory, holding information in mind temporarily. Despite this it appears to act by influencing the processing of information rather than through memory.
Imaging studies suggest that visual working memory performance can be enhanced by modulating acetylcholine-induced activity in the brain's visual processing area, called the visual cortex, when processing information that is important to the task. Since working memory performance can predict response to conventional antidepressants and ketamine, Furey and colleagues turned to a working memory task and imaging visual cortex activity as potential tools to identify a biomarker for scopolamine response.
Depressed patients have a well-known tendency to process and remember negative emotional information. The researchers propose that this bias stems from dysregulated acetylcholine systems in some patients. They reasoned that such patients would show aberrant visual cortex activity in response to negative emotional features of a working memory task. They also expected to find that patients with more dysfunctional acetylcholine systems would respond better to scopolamine treatment.
Before receiving scopolamine, participants performed a working memory task while their brain activity was monitored via fMRI. For some trials, it required that they pay attention to, and remember, the emotional expression (sad, happy, etc.) of faces flashing on a computer monitor. For other trials, they had to pay attention to only the identity, or non-emotional feature, of the faces. After scanning, and over the following several weeks, 15 patients with depression and 21 healthy participants randomly received infusions of a placebo (salt solution) and/or scopolamine. Mood changes were monitored with depression rating scales.