Mode of [14C] 2-deoxy-D-glucose uptake into retrosplenial cortex and other memory-related structures of the monkey during a delayed response.

Physiological studies on the monkey retrosplenial (RS) cortex have been few, and its functional role remains to be investigated. In the present study, activity of the RS cortex was investigated using radioactive 2-DG while the monkey was performing a visual tracking task with a delay (a delayed-response task) for 45 minutes. A remarkable increase in 2-DG uptake was observed equally in the left as well as in the right RS cortex. The anterior nucleus of the thalamus also showed increased 2-DG uptake. In addition, other memory-related structures (prefrontal cortex, dorsomedial nucleus of the thalamus, amygdala and hippocampus) showed a similar increase in 2-DG uptake compared to control monkeys, though their respective absolute values were different from one another. Since the RS cortex receives afferents from the anterior nucleus of the thalamus, which is one of the main nuclei of the Papez circuit, it is assumed that the RS cortex is important in memory function. Therefore, the remarkable increase in 2-DG uptake in the present study could reflect some aspects of memory or learning processes required to perform the delayed response.