Intranasal insulin improved odor-cued reactivation of spatial memory in young men, according to a study published in the Journal of Clinical Endocrinology & Metabolism.
Lead researcher Yvonne F. Brünner, of RWTH Aachen University, and colleagues found that intranasal insulin improved the delayed but not immediate odor-cued recall of spatial memory.
Insulin receptors make up the hypothalamus, hippocampus and olfactory bulb, and this suggests that brain insulin signaling influences central nervous system (CNS) functions that depend on these brain regions. The olfactory bulb relays odor information to various CNS sites including the hippocampus, which is critical for the conscious recall of memories.
In light of connections between odor and CNS functions, the researchers investigated if a single dose of intranasally-applied insulin would influence the odor-cued recall of newly encoded spatial memory in cognitively healthy men.
In a double blind experiment, each subject participated in two sessions where they received either two puffs of intranasal insulin or a placebo. They were then presented with an odor-place memory task, in which they smelled a randomized odor in conjunction with viewing a green-colored squared field. They were then re-exposed to the odor cues and asked to choose the corresponding square on the screen.
After each choice, the correct answer was shown for 5 seconds to ensure re-encoding. The second task was identical to the first except no feedback was provided.
During the immediate recall task, the accuracy did not differ between the insulin and control groups. However, during the delayed recall (scheduled 10 minutes after the immediate recall), the insulin group had increased accuracy compared with the control group.
These findings indicate that acute intranasal insulin may improve odor-cued reactivation of spatial memory in young men.
The present study aimed at examining if intranasal insulin, which is known to transiently increase brain insulin levels in humans, would improve odor-cued reactivation of spatial memory in young men.
Intranasal insulin improved the delayed (i.e. free) but not immediate odor-cued recall of spatial memory. This effect was independent of odor type and in the absence of systemic side effects (e.g. fasting plasma glucose levels remained unaltered). In contrast, place and odor recognition remained unaffected by the insulin treatment.