Watching Viswanathan Anand taking time to make his move when he plays against Magnus Carlsen reminds us about the famous theory of speed-accuracy trade-off. This idea has been challenged and debated in the field of olfaction research – forming two schools of thought, one supporting a causal link between the accuracy and speed of decision-making and other uncoupling these.
In this Cell Reports article, the research group of Dr. Nixon Abraham from IISER Pune, in collaboration with researchers from Heidelberg University and University of Geneva, responds to this debate by performing behavior experiments and in vivo imaging in rodents.
For this study, the team first trained mice to distinguish rewarded and non-rewarded odors of varying complexities; observing the behavioral read-outs such as sniffing followed by the presence or absence of a lick formed the basis for inferring how fast and how well the mice were able to distinguish odors.
Through these studies, the researchers report decision times specific for each odor pair. They also find a consistent increase in the decision time for complex stimuli of two-odor mixtures compared to the corresponding simple monomolecular odors, for all chemical classes tested.
“When we smell a new perfume, we tend to take a deep breath to collect maximum fragrance molecules. But, rodents breathe with higher frequencies when they smell the odorant molecules. We tested an important and related question of how rodents sample the smell stimuli of varying complexities while they are challenged with decision-making tasks,” says Dr. Abraham.
The team allowed the mice to develop a sniffing strategy to sample the stimuli— a strategy that is not governed by the rules set by the experimenters. This enabled the researchers to study how the decision times were modulated by the sniffing and how the sampling strategies developed over the course of learning.
To their surprise, the team observed the occurrence of a synchronized and enhanced sniffing during the decision-making time for simple stimuli and this enhanced sampling preceded the decisions by few tens of milliseconds for complex odor pairs.
The team also studied the specific spatial activity patterns at the level of glomeruli in the olfactory bulb, the first relay station in the olfactory pathway of rodents, in response to different smell stimuli.
Through this, the team probed the relationship between decision times and the evoked spatial activity for many odor pairs. They calculated the Euclidian distances, a similarity measurement for quantifying the spatial organization of evoked activities. They found a strong anti-correlation between similarity index of odorant activity patterns and the time needed for decisions, providing a strong evidence for the dependence of decision times on the complexity of stimuli in decision contexts.
Describing the implications of the study, Dr. Abraham says, ”This study demonstrates the additional processing time needed for accurate complex decisions and thereby bringing a consensus on the long-standing debate of why speed-accuracy trade-off theory could be applicable in processing the information related to different smells.”
“These findings also open further research questions on how our sampling strategies can influence us in making accurate decisions”, Dr. Abraham adds.
This work received funding from Wellcome Trust – DBT India Alliance, IISER Pune and UGC NET for researchers from IISER Pune.
Article Citation: Similarity and strength of glomerular odor representations define a neural metric of sniff-invariant discrimination time. Anindya S. Bhattacharjee, Sasank Konakamchi, Dmitrij Turaev, Roberto Vincis, Daniel Nunes, Atharva A. Dingankar, Hartwig Spors, Alan Carleton, Thomas Kuner, and Nixon M. Abraham (2019). Cell Reports 28(11): P2966-2978.E5.
– With inputs from Nixon Abraham; news article edited by Shanti Kalipatnapu; graphic by Rafeeque Mavoor