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Profound context-dependent plasticity of mitral cell responses in olfactory bulb.

Doucette W, Restrepo D - PLoS Biol. (2008)

Bottom Line: The response changes occur in a manner that increases the ability of the circuit to convey information necessary to discriminate among closely related odors.Remarkably, a switch between which of the two odors is rewarded causes mitral cells to switch the polarity of their divergent responses.Taken together these results redefine the function of the OB as a transiently modifiable (active) filter, shaping early odor representations in behaviorally meaningful ways.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Neuroscience Program, Rocky Mountain Taste and Smell Center, University of Colorado Denver Anschutz Medical Campus, Aurora, Colorado, United States of America.

ABSTRACT
On the basis of its primary circuit it has been postulated that the olfactory bulb (OB) is analogous to the retina in mammals. In retina, repeated exposure to the same visual stimulus results in a neural representation that remains relatively stable over time, even as the meaning of that stimulus to the animal changes. Stability of stimulus representation at early stages of processing allows for unbiased interpretation of incoming stimuli by higher order cortical centers. The alternative is that early stimulus representation is shaped by previously derived meaning, which could allow more efficient sampling of odor space providing a simplified yet biased interpretation of incoming stimuli. This study helps place the olfactory system on this continuum of subjective versus objective early sensory representation. Here we show that odor responses of the output cells of the OB, mitral cells, change transiently during a go-no-go odor discrimination task. The response changes occur in a manner that increases the ability of the circuit to convey information necessary to discriminate among closely related odors. Remarkably, a switch between which of the two odors is rewarded causes mitral cells to switch the polarity of their divergent responses. Taken together these results redefine the function of the OB as a transiently modifiable (active) filter, shaping early odor representations in behaviorally meaningful ways.

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Related in: MedlinePlus

Behavioral Decision and Unit Divergence Times(A) This figure shows the p-value of the difference between the lick responses in rewarded and unrewarded trials calculated for each block for the data shown in Figure 5A using a rank sum test at each 0.15-s bin through the trial. As shown in Figure 5A each bin is allocated a value of 1 if the mouse licked at least once or a value of zero if the mouse did not lick. The rank sum test is performed on all zeros and ones in each bin within each block. The vertical red lines indicate when the p-value drops below 0.05. The horizontal red lines indicate the 0.05 level. The blocks are shown from top (first block) to bottom (last block).(B) Percent cumulative probability plot summarizing the decision times for the 19 go–no-go experiments where at least one unit diverged when the response to the reinforced and unreinforced odors were compared (the experiments contributing to the green wedge in the pie charts in Figure 4B). The decision time becomes smaller as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.(C) Plot of the p-value of the difference between firing rates between odor A trials and odor AB trials compared at different times throughout the trial for the unit shown in Figure 3A. p-Values were calculated by using a rank sum test applied to the firing rate calculated in each block in each 0.15-s bin. The horizontal red line is drawn at a p-value of 0.05. The vertical blue lines indicate the time at which the difference in firing rate between odor A and AB dropped below 0.05 for two or more consecutive points. Because of multiple comparisons, the p-value falls below 0.05 occasionally for a single point as seen by the few single data points that fall below the red line in the period before odor responses (−2 to 0 s). We found that two adjacent data points fall below 0.05 only rarely in this prestimulus period (4% of the time) allowing us to use the criterion of two adjacent points below 0.05 as the time when the two rates differ. The vertical red lines are taken form (B) and allow for a comparison of timing between divergent lick behavior and divergent MC firing.(D) Distribution of the difference between unit divergence times and their corresponding behavioral decision times during the best block. The majority of unit divergence occurs after the animal has begun divergent licking behavior (positive values). Only 20% of the units diverge in their firing rate responses to the rewarded and unrewarded odor prior to behavioral divergence of licking.
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pbio-0060258-g008: Behavioral Decision and Unit Divergence Times(A) This figure shows the p-value of the difference between the lick responses in rewarded and unrewarded trials calculated for each block for the data shown in Figure 5A using a rank sum test at each 0.15-s bin through the trial. As shown in Figure 5A each bin is allocated a value of 1 if the mouse licked at least once or a value of zero if the mouse did not lick. The rank sum test is performed on all zeros and ones in each bin within each block. The vertical red lines indicate when the p-value drops below 0.05. The horizontal red lines indicate the 0.05 level. The blocks are shown from top (first block) to bottom (last block).(B) Percent cumulative probability plot summarizing the decision times for the 19 go–no-go experiments where at least one unit diverged when the response to the reinforced and unreinforced odors were compared (the experiments contributing to the green wedge in the pie charts in Figure 4B). The decision time becomes smaller as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.(C) Plot of the p-value of the difference between firing rates between odor A trials and odor AB trials compared at different times throughout the trial for the unit shown in Figure 3A. p-Values were calculated by using a rank sum test applied to the firing rate calculated in each block in each 0.15-s bin. The horizontal red line is drawn at a p-value of 0.05. The vertical blue lines indicate the time at which the difference in firing rate between odor A and AB dropped below 0.05 for two or more consecutive points. Because of multiple comparisons, the p-value falls below 0.05 occasionally for a single point as seen by the few single data points that fall below the red line in the period before odor responses (−2 to 0 s). We found that two adjacent data points fall below 0.05 only rarely in this prestimulus period (4% of the time) allowing us to use the criterion of two adjacent points below 0.05 as the time when the two rates differ. The vertical red lines are taken form (B) and allow for a comparison of timing between divergent lick behavior and divergent MC firing.(D) Distribution of the difference between unit divergence times and their corresponding behavioral decision times during the best block. The majority of unit divergence occurs after the animal has begun divergent licking behavior (positive values). Only 20% of the units diverge in their firing rate responses to the rewarded and unrewarded odor prior to behavioral divergence of licking.

Mentions: Figures 3A and 4A showed examples when an SMC's firing rate diverged between the reinforced and unreinforced odor trials, but how does the time of onset of firing rate divergence compare to the time when the animal makes its decision about the difference in odor identity? In order to examine this question we determined when the licking of the tube that is required for reinforcement with water differed between reinforced and unreinforced odor trials by performing a rank sum test for differences in licking at every 0.15-s bin. Figure 5A shows the licking patterns and Figure 8A illustrates the time course for the p-value for the test of lick divergence. The red vertical bars indicate where the p-value drops below 0.05 (the time when the licking pattern diverges between unrewarded and rewarded odors). Figure 8B shows the cumulative percent probability for decision times measured in the eight animals in 19 sessions where at least one unit diverged in firing between the two odors. As shown, the decision time becomes quicker as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is not at time zero, but is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.


Profound context-dependent plasticity of mitral cell responses in olfactory bulb.

Doucette W, Restrepo D - PLoS Biol. (2008)

Behavioral Decision and Unit Divergence Times(A) This figure shows the p-value of the difference between the lick responses in rewarded and unrewarded trials calculated for each block for the data shown in Figure 5A using a rank sum test at each 0.15-s bin through the trial. As shown in Figure 5A each bin is allocated a value of 1 if the mouse licked at least once or a value of zero if the mouse did not lick. The rank sum test is performed on all zeros and ones in each bin within each block. The vertical red lines indicate when the p-value drops below 0.05. The horizontal red lines indicate the 0.05 level. The blocks are shown from top (first block) to bottom (last block).(B) Percent cumulative probability plot summarizing the decision times for the 19 go–no-go experiments where at least one unit diverged when the response to the reinforced and unreinforced odors were compared (the experiments contributing to the green wedge in the pie charts in Figure 4B). The decision time becomes smaller as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.(C) Plot of the p-value of the difference between firing rates between odor A trials and odor AB trials compared at different times throughout the trial for the unit shown in Figure 3A. p-Values were calculated by using a rank sum test applied to the firing rate calculated in each block in each 0.15-s bin. The horizontal red line is drawn at a p-value of 0.05. The vertical blue lines indicate the time at which the difference in firing rate between odor A and AB dropped below 0.05 for two or more consecutive points. Because of multiple comparisons, the p-value falls below 0.05 occasionally for a single point as seen by the few single data points that fall below the red line in the period before odor responses (−2 to 0 s). We found that two adjacent data points fall below 0.05 only rarely in this prestimulus period (4% of the time) allowing us to use the criterion of two adjacent points below 0.05 as the time when the two rates differ. The vertical red lines are taken form (B) and allow for a comparison of timing between divergent lick behavior and divergent MC firing.(D) Distribution of the difference between unit divergence times and their corresponding behavioral decision times during the best block. The majority of unit divergence occurs after the animal has begun divergent licking behavior (positive values). Only 20% of the units diverge in their firing rate responses to the rewarded and unrewarded odor prior to behavioral divergence of licking.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2573932&req=5

pbio-0060258-g008: Behavioral Decision and Unit Divergence Times(A) This figure shows the p-value of the difference between the lick responses in rewarded and unrewarded trials calculated for each block for the data shown in Figure 5A using a rank sum test at each 0.15-s bin through the trial. As shown in Figure 5A each bin is allocated a value of 1 if the mouse licked at least once or a value of zero if the mouse did not lick. The rank sum test is performed on all zeros and ones in each bin within each block. The vertical red lines indicate when the p-value drops below 0.05. The horizontal red lines indicate the 0.05 level. The blocks are shown from top (first block) to bottom (last block).(B) Percent cumulative probability plot summarizing the decision times for the 19 go–no-go experiments where at least one unit diverged when the response to the reinforced and unreinforced odors were compared (the experiments contributing to the green wedge in the pie charts in Figure 4B). The decision time becomes smaller as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.(C) Plot of the p-value of the difference between firing rates between odor A trials and odor AB trials compared at different times throughout the trial for the unit shown in Figure 3A. p-Values were calculated by using a rank sum test applied to the firing rate calculated in each block in each 0.15-s bin. The horizontal red line is drawn at a p-value of 0.05. The vertical blue lines indicate the time at which the difference in firing rate between odor A and AB dropped below 0.05 for two or more consecutive points. Because of multiple comparisons, the p-value falls below 0.05 occasionally for a single point as seen by the few single data points that fall below the red line in the period before odor responses (−2 to 0 s). We found that two adjacent data points fall below 0.05 only rarely in this prestimulus period (4% of the time) allowing us to use the criterion of two adjacent points below 0.05 as the time when the two rates differ. The vertical red lines are taken form (B) and allow for a comparison of timing between divergent lick behavior and divergent MC firing.(D) Distribution of the difference between unit divergence times and their corresponding behavioral decision times during the best block. The majority of unit divergence occurs after the animal has begun divergent licking behavior (positive values). Only 20% of the units diverge in their firing rate responses to the rewarded and unrewarded odor prior to behavioral divergence of licking.
Mentions: Figures 3A and 4A showed examples when an SMC's firing rate diverged between the reinforced and unreinforced odor trials, but how does the time of onset of firing rate divergence compare to the time when the animal makes its decision about the difference in odor identity? In order to examine this question we determined when the licking of the tube that is required for reinforcement with water differed between reinforced and unreinforced odor trials by performing a rank sum test for differences in licking at every 0.15-s bin. Figure 5A shows the licking patterns and Figure 8A illustrates the time course for the p-value for the test of lick divergence. The red vertical bars indicate where the p-value drops below 0.05 (the time when the licking pattern diverges between unrewarded and rewarded odors). Figure 8B shows the cumulative percent probability for decision times measured in the eight animals in 19 sessions where at least one unit diverged in firing between the two odors. As shown, the decision time becomes quicker as the animal progresses through the session as evidenced by a shift of the median decision time from 2.5 s for the first block, to 1.0 s for the best block, and 0.95 s for the last block. It is important to state that as explained in the Materials and Methods the actual time of arrival of the odor is not at time zero, but is delayed ∼300 ms, and therefore what is important in this experiment is not the absolute value of the decision times but rather the relative values.

Bottom Line: The response changes occur in a manner that increases the ability of the circuit to convey information necessary to discriminate among closely related odors.Remarkably, a switch between which of the two odors is rewarded causes mitral cells to switch the polarity of their divergent responses.Taken together these results redefine the function of the OB as a transiently modifiable (active) filter, shaping early odor representations in behaviorally meaningful ways.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Neuroscience Program, Rocky Mountain Taste and Smell Center, University of Colorado Denver Anschutz Medical Campus, Aurora, Colorado, United States of America.

ABSTRACT
On the basis of its primary circuit it has been postulated that the olfactory bulb (OB) is analogous to the retina in mammals. In retina, repeated exposure to the same visual stimulus results in a neural representation that remains relatively stable over time, even as the meaning of that stimulus to the animal changes. Stability of stimulus representation at early stages of processing allows for unbiased interpretation of incoming stimuli by higher order cortical centers. The alternative is that early stimulus representation is shaped by previously derived meaning, which could allow more efficient sampling of odor space providing a simplified yet biased interpretation of incoming stimuli. This study helps place the olfactory system on this continuum of subjective versus objective early sensory representation. Here we show that odor responses of the output cells of the OB, mitral cells, change transiently during a go-no-go odor discrimination task. The response changes occur in a manner that increases the ability of the circuit to convey information necessary to discriminate among closely related odors. Remarkably, a switch between which of the two odors is rewarded causes mitral cells to switch the polarity of their divergent responses. Taken together these results redefine the function of the OB as a transiently modifiable (active) filter, shaping early odor representations in behaviorally meaningful ways.

Show MeSH
Related in: MedlinePlus