This study extends previous work measuring the time course of rapid odor adaptation in humans to mice using a novel psychophysical paradigm. The researchers measured odor detection thresholds in mice under baseline conditions and after exposure to an adapting odorant at different onset delays and concentrations. They found that adaptation increased thresholds for the target odorant and that asymptotic adaptation levels were similar for higher and lower adapting odorant concentrations, though the rate of adaptation was faster at the higher concentration. Comparing the results to human data, adaptation-induced threshold increases were observed in mice starting around 100-200 ms of exposure to the adapting odorant, slightly later than the 50 ms onset seen in humans. This paradigm can be used to further characterize the mechanisms underlying odor adaptation in animal

1. Perceptual odor adaptation
A technique for characterizing the time course of adaptation in mice
Olivia Munizza1  Wendy M Yoder2  Michelle Lyman1  Leslie Gaynor2,3  Barry Setlow2,4,6  Jennifer L Bizon3,4,5,6  David W Smith2,5
1Program in Interdisciplinary Studies, Neurobiological Sciences  2Program in Behavioral and Cognitive Neuroscience, Department of Psychology  3Department of English  4Department of Psychiatry  5Center for Smell and Taste  6Department of Neuroscience, University of Florida College of Medicine, Gainesville, Florida
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Paradigm and behavioral methodology
Baseline thresholds are estimated first Time course of rapid adaptation│Humans
Acknowledgments
References
Time course of rapid adaptation │Mice
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24:637–645.
3. Kelliher K, Ziesmann J, Munger S, Reed R, Zufall F. 2003. Importance of the CNGA4 channel gene for odor discrimination and adaption in behaving
mice. PNAS 100:4299-4304.
4. Li W, Howard JD, Gottfried JA. 2010. Disruption of odour quality coding in piriform cortex mediates olfactory deficits in Alzheimer’s disease. Brain
133:2714-2726.
5. Smith D, Gamble K, Heil T. 2010. A novel psychophysical method for estimating the time course of olfactory rapid adaptation in humans. Chemical
Senses 35: 717-725.
6. Zufall F, Leinders-Zufall T. 2000. The cellular and molecular basis of odor adaptation. Chemical Senses 25: 473-481.
Much is
known about
the mechanisms
and temporal
characteristics
underlying odor
adaptation.
wendyyoder@ufl.edu
Figure 1: General Method. Licking in the
presence of the target odorant (S+) results
in 5 µl of liquid reinforcement (Ensure).
Conversely, incorrectly licking in the
presence of the control odorant (S-) results
in a 5 second time-out; the rat cannot
initiate new trials during this interval.4
Go No/Go Discrimination Task
1 block
20 pseudorandomized trials
Reinforcement
5-s Time-out
+
-
Figure 3: Stimulus conditions.
Baseline thresholds were estimated in
the presence of a null, adapting
background. Then adaptation was
measured by varying both time (onset
delays) and concentration: (AO=1x
threshold) and (AO=2x threshold).
Figure 3: Time course of adaptation, plotted as
changes in threshold at different adapting odorant
(AO) concentrations. A 2000-ms null stimulus (DH2O)
served as the AO in the baseline condition (black
circles). Mean detection thresholds are plotted for
thresholds measured alone and in the presence of the
AO. AO concentrations were set relative to each
animal’s threshold (1x threshold concentration, grey
squares; 2x threshold concentration, grey circles.
Asymptotic levels of adaptation were similar for both
concentrations, though the rate of adaptation was
faster for the 2x threshold AO condition.
Figure 5: Mean change in
threshold as a function of
AO concentration. Increases
in threshold stimulus
concentration were evident
even at 100-ms and
increased to an asymptotic
level of 100% (v/v) with
onset delays longer than
600-ms (solid line). Error
bars represent standard
deviations. Dashed lines
represent a fitted, two-
component sigmoidal curve
for the 1x AO concentration
and a fitted, two-component
exponential for the 2x AO
concentration.
Our laboratory has previously
shown that rapid odor adaptation
can be measured in human
subjects using a novel paradigm.
The present study extends
our technique to measure
the time course of
adaptation in mice.
Figure 4: Individual (n=4) baseline thresholds. Initial
thresholds were estimated in the presence of DH2O (as the
adapting odorant). Mice were tested in incremental steps
using serial dilutions. Threshold was defined as the lowest
concentration the mouse received ≥85% accuracy. The
odor sampling duration was gradually increased from 0 ms
to 1000 ms delays at threshold.
Figure 6: Time course of adaptation, plotted
as changes in threshold. To more directly
compare adaptation in humans and mice, the group
mean contour from the present study can be
compared with human psychophysical estimates
collected with the same odorant and simultaneous
odorant paradigm. For humans, measurable
differences in threshold were evident following a 50-
ms AO exposure, whereas observable differences in
mice were not evident until 100 or 200-ms. Although
the smaller group size (n=4 mice) could potentially
account for this disparity, systematic, adaptation-
induced threshold increases were routinely observed
for all mice. This suggests that while initial, baseline
thresholds may vary across mice (and humans), the
general adaptation trend remains relatively consistent.
Discussion and translational applications
This psychophysical paradigm can be
adapted in animal models, where
experimental and genetic manipulations
can be used to characterize the different
mechanisms underlying odor adaptation.
These data further establish a critical
temporal link between perceptual
adaptation and olfactory receptor
mechanisms at the periphery and set the
groundwork for future research seeking to
establish a link between olfactory adaptation
impairments and pathological progression
in certain neurodegenerative diseases.1
We thank Dr. Barry Ache, Center for
Smell and Taste, University of Florida,
for conference travel funding.
1
Our olfactory environments are
characterized by rapidly changing
chemical fluctuations.
Adaptation is a
complex, time
dependent process
that functions to
limit receptor
saturation.
It suppresses
neural responses
to sustained
stimulation and
enhances the
detection of new
chemical stimuli
But behavioral
measures are
still needed to
determine how
adaptation affects
perception.
Figure 2: Schematic presentation of odor adaptation. The
premise of this technique is that extended presentation of an
odorant will produce odor adaptation, decreasing the sensitivity of
the receptor and increasing thresholds for a brief, “simultaneous”
target odorant presented at different temporal points after the
adapting stimulus-onset.
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