Characterizing Olfactory Perceptual Similarity Using Carbon Chain Discrimination in Fischer 344 Rats

Abstract

Performance on olfactory tests can be influenced by a number of stimulus characteristics including chemical structure, concentration, perceptual similarity, and previous experience with the test odorants. Few of these parameters have been extensively characterized in the Fischer 344 rat strain. To investigate how odor quality affects perception in this rat strain, we measured how graded perceptual similarity, created by varying carbon chain length across a series of homologous alcohol pairs, influenced odor discrimination using a liquid-motivated go/no-go task. We employed an automated, liquid-dilution olfactometer to train Fischer 344 rats (N = 8) on a 2-odor discrimination task. Six odorants (1-propanol, 1-butanol, 1-pentanol, 1-hexanol, 1-heptanol, and 1-octanol) were arranged to produce 15 novel odorant pairs differing between 1 and 5 carbon atoms; testing sessions included presentation of only 1 pseudorandomly assigned pair daily (200 trials). Results show that although rats can learn to discriminate between any 2 odorant pairs, performance declines systematically as the pairs become more structurally similar and, therefore, more perceptually confusing. As such, the easier discrimination pairs produced reliable ceiling effects across all rats, whereas performance for the difficult discrimination pairs was consistently worse, even after repeated testing. These data emphasize the importance of considering odorant stimulus dimensions in experimental designs employing olfactory stimuli. Moreover, establishing baseline olfactory performance in Fischer 344 rats may be particularly useful for predicting age-related cognitive decline in this model.

Interaction between age and perceptual similarity in olfactory discrimination learning in F344 rats: relationships with spatial learning

“…The behavioral apparatus and methods employed in this study are identical to those used in our previous work (Yoder et al, 2014, 2015), and detailed descriptions of the training and testing techniques can be found in those previous publications. The olfactometer was connected to a 21-cm deep, 30.5-cm wide, and 24.1-cm tall, ventilated Plexiglas operant chamber.…”

“…Shaping procedures followed those described by Yoder et al (2014). Briefly, rats were initially rewarded for contacting the lick tube with their tongue, followed by nose pokes into the sampling port, and finally for remaining in the sampling port during odorant presentation.…”

“…Thus, by varying carbon chain length between odorants, olfactory stimulus sets can be designed in which perceptual similarity is systematically varied (Cleland et al, 2002; Ho et al, 2006; Weeden et al, 2014). Previously, our laboratory has used a series of aliphatic alcohols to demonstrate that decreasing the difference in carbon chain length between 2 odorants from 5 to 1 produces systematic decrements in discriminability in young rats (Yoder et al, 2014). It remains unknown, however, whether performance across such perceptual gradients is sensitive to alterations in aging, and in particular, may have utility for identifying cognitive vulnerability.…”

“…Young and aged F344 rats were cross-characterized on a hippocampal-dependent water maze task and a go/no-go olfactory learning task (Eichenbaum et al, 1983) in which they discriminated between pairs of odors from homologous chemical series of aliphatic compounds (alcohols, aldehydes, or acids, Yoder et al, 2014). Within a chemical class, the difference in the length of the carbon chain between odorants (i.e., the difference in chemical structure) was varied across discrimination problems to systemically manipulate perceptual similarity.…”

Testing odorant-receptor interaction theories in humans through discrimination of isotopomers

“…Although most of the scientific evidence on odour reception collected in different species is well in agreement with this model, [10][11][12][13] it does not provide satisfactory explanation for the existence of many molecules of completely different chemical properties, i.e. size, shape, and functional groups, resulting in identical odours.…”