Researchers from the National Institutes of Health (NIH), the National Institute of Standards and Technology (NIST), and the Chinese University of Hong Kong (CUHK) taught a particular species of moth, Manduca sexta, to extend its proboscis in anticipation of a dollop of sucrose after being given a scent cue.
The researchers have revealed that they had attached electrodes to the insects' mushroom bodies, a structure in their brains known to be integral to learning and memory, in order to observe the mental representation of the scent through spikes in activity across groups of neurons called Kenyon cells.
NIST/NIH researcher Baranidharan Raman says that the objective behind that process was to characterize how odours are represented by this neural population, and how this representation gets associated with the reward.
The study showed that most of the odour-elicited spiking in the Kenyon cells occurred during the beginning and end of an odour pulse, with little to no spiking in between, the researcher adds.
According to the research group, the interval between the odour stimulus onset and sucrose reward was crucial to whether or not the insect learnt to link the representations.
If the sucrose was presented during the onset of spiking, the insect did not learn as well. If the researchers used a long odour stimulus and administered the sucrose just after the offset signal (long after the onset), the insect would not learn to expect it.
The researchers say that learning occurs when reward was presented a few seconds after the onset of neural activity.
Raman believes that the study of biological olfactory systems can offer significant insights into how to build artificial systems to discriminate odours with sensor arrays.
A research article on the study has been published in the journal Nature Neuroscience.