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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

Go–No-Go Odor Discrimination Task.(A) Time course for each trial in the odor discrimination task. The trial is started by a nose poke of the mouse into the odor chamber. When the computer senses the nose poke it turns a valve that diverts the air flow of 2 l/min to the exhaust and it turns on the odor valve that injects odorized air into the main air flow at 40 ml/min. The mouse must remain in the chamber for a time period made up of a variable 0–0.5-s period (variable diverting valve period or vDV) followed by a fixed 1-s interval (fDV). At the end of the fixed diverting valve (fDV) period the odor has mixed thoroughly with the main air flow, and the diverting valve directs the air flow back into the chamber (time 0 s). At this time the mouse must stay for 0.5 s in the chamber (S) and then must lick at least once in each of the 0.5-s response area (RA) segments if the odor is a rewarded odor. If the mouse licks in the four RA segments, the mouse is rewarded with water flowing through the tube it has been licking. A 6-s time out follows the end of the trial. If the odor is an unrewarded odor the mouse does not have to lick, and typically withdraws the head from the odor port shortly after it makes a decision. While the diverting valve is activated at time zero, there is a delay in delivery of the odor that we estimate to be of the order of ∼300 ms.(B) Typical curve for behavioral performance in an odor discrimination session. The percent correct response is shown as a function of block number. Each block includes ten rewarded odor and ten unrewarded odor trials. A correct response is licking of the tube in the four RA segments for a rewarded odor and not licking in at least one RA period for the unrewarded odor (this is the go–no-go criterion). Note that this mouse starts with chance performance (50%) and reaches the arbitrary response criterion of 85% correct by four blocks.
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pbio-0060258-g002: Go–No-Go Odor Discrimination Task.(A) Time course for each trial in the odor discrimination task. The trial is started by a nose poke of the mouse into the odor chamber. When the computer senses the nose poke it turns a valve that diverts the air flow of 2 l/min to the exhaust and it turns on the odor valve that injects odorized air into the main air flow at 40 ml/min. The mouse must remain in the chamber for a time period made up of a variable 0–0.5-s period (variable diverting valve period or vDV) followed by a fixed 1-s interval (fDV). At the end of the fixed diverting valve (fDV) period the odor has mixed thoroughly with the main air flow, and the diverting valve directs the air flow back into the chamber (time 0 s). At this time the mouse must stay for 0.5 s in the chamber (S) and then must lick at least once in each of the 0.5-s response area (RA) segments if the odor is a rewarded odor. If the mouse licks in the four RA segments, the mouse is rewarded with water flowing through the tube it has been licking. A 6-s time out follows the end of the trial. If the odor is an unrewarded odor the mouse does not have to lick, and typically withdraws the head from the odor port shortly after it makes a decision. While the diverting valve is activated at time zero, there is a delay in delivery of the odor that we estimate to be of the order of ∼300 ms.(B) Typical curve for behavioral performance in an odor discrimination session. The percent correct response is shown as a function of block number. Each block includes ten rewarded odor and ten unrewarded odor trials. A correct response is licking of the tube in the four RA segments for a rewarded odor and not licking in at least one RA period for the unrewarded odor (this is the go–no-go criterion). Note that this mouse starts with chance performance (50%) and reaches the arbitrary response criterion of 85% correct by four blocks.

Mentions: We sought to determine whether SMC odor responses would change as the animal learned to discriminate between two odors. We trained mice to perform a go–no-go task in which thirsty animals were rewarded with water when they licked on a response tube in the presence of the correct odor in the pair being tested (described in detail in the Materials and Methods) [37]. Figure 2A shows the events associated with each trial. The trial was initiated by the mouse by poking its nose into an odor port. This initiated a sequence of events. First, the air stream was diverted away from the odor sampling port to an exhaust port by a valve, and the mouse had to wait with its head inside the odor port for a period when odor was not present in the chamber. This diverting flow interval varied randomly from 1 to 1.5 s (this is the interval denoted by vDV + fDV in Figure 2A). After the end of the diverting flow interval the valve shifted the air flow back into the odor port, but this time the air stream carried the odor. The instant when the diverting valve shifts the air stream back into the odor port is time zero in all our trials. Odor reaches the odor sampling chamber a fraction of a second later (we estimate ∼0.3 s, but this time would have to be measured to determine a precise delivery time). Mice were asked to respond to the rewarded (S+) odor by licking on a tube at least once in each of four 0.5-s intervals that span the time from 0.5 to 2.5 s (the response area in Figure 2A). Licking at least once in each of the response area intervals is the go–no-go criterion. Note that the mouse is not required to lick during the unrewarded odor (S- trial) and therefore the mouse is free to leave the port once it makes a decision.


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

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

Go–No-Go Odor Discrimination Task.(A) Time course for each trial in the odor discrimination task. The trial is started by a nose poke of the mouse into the odor chamber. When the computer senses the nose poke it turns a valve that diverts the air flow of 2 l/min to the exhaust and it turns on the odor valve that injects odorized air into the main air flow at 40 ml/min. The mouse must remain in the chamber for a time period made up of a variable 0–0.5-s period (variable diverting valve period or vDV) followed by a fixed 1-s interval (fDV). At the end of the fixed diverting valve (fDV) period the odor has mixed thoroughly with the main air flow, and the diverting valve directs the air flow back into the chamber (time 0 s). At this time the mouse must stay for 0.5 s in the chamber (S) and then must lick at least once in each of the 0.5-s response area (RA) segments if the odor is a rewarded odor. If the mouse licks in the four RA segments, the mouse is rewarded with water flowing through the tube it has been licking. A 6-s time out follows the end of the trial. If the odor is an unrewarded odor the mouse does not have to lick, and typically withdraws the head from the odor port shortly after it makes a decision. While the diverting valve is activated at time zero, there is a delay in delivery of the odor that we estimate to be of the order of ∼300 ms.(B) Typical curve for behavioral performance in an odor discrimination session. The percent correct response is shown as a function of block number. Each block includes ten rewarded odor and ten unrewarded odor trials. A correct response is licking of the tube in the four RA segments for a rewarded odor and not licking in at least one RA period for the unrewarded odor (this is the go–no-go criterion). Note that this mouse starts with chance performance (50%) and reaches the arbitrary response criterion of 85% correct by four blocks.
© Copyright Policy
Related In: Results  -  Collection

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

pbio-0060258-g002: Go–No-Go Odor Discrimination Task.(A) Time course for each trial in the odor discrimination task. The trial is started by a nose poke of the mouse into the odor chamber. When the computer senses the nose poke it turns a valve that diverts the air flow of 2 l/min to the exhaust and it turns on the odor valve that injects odorized air into the main air flow at 40 ml/min. The mouse must remain in the chamber for a time period made up of a variable 0–0.5-s period (variable diverting valve period or vDV) followed by a fixed 1-s interval (fDV). At the end of the fixed diverting valve (fDV) period the odor has mixed thoroughly with the main air flow, and the diverting valve directs the air flow back into the chamber (time 0 s). At this time the mouse must stay for 0.5 s in the chamber (S) and then must lick at least once in each of the 0.5-s response area (RA) segments if the odor is a rewarded odor. If the mouse licks in the four RA segments, the mouse is rewarded with water flowing through the tube it has been licking. A 6-s time out follows the end of the trial. If the odor is an unrewarded odor the mouse does not have to lick, and typically withdraws the head from the odor port shortly after it makes a decision. While the diverting valve is activated at time zero, there is a delay in delivery of the odor that we estimate to be of the order of ∼300 ms.(B) Typical curve for behavioral performance in an odor discrimination session. The percent correct response is shown as a function of block number. Each block includes ten rewarded odor and ten unrewarded odor trials. A correct response is licking of the tube in the four RA segments for a rewarded odor and not licking in at least one RA period for the unrewarded odor (this is the go–no-go criterion). Note that this mouse starts with chance performance (50%) and reaches the arbitrary response criterion of 85% correct by four blocks.
Mentions: We sought to determine whether SMC odor responses would change as the animal learned to discriminate between two odors. We trained mice to perform a go–no-go task in which thirsty animals were rewarded with water when they licked on a response tube in the presence of the correct odor in the pair being tested (described in detail in the Materials and Methods) [37]. Figure 2A shows the events associated with each trial. The trial was initiated by the mouse by poking its nose into an odor port. This initiated a sequence of events. First, the air stream was diverted away from the odor sampling port to an exhaust port by a valve, and the mouse had to wait with its head inside the odor port for a period when odor was not present in the chamber. This diverting flow interval varied randomly from 1 to 1.5 s (this is the interval denoted by vDV + fDV in Figure 2A). After the end of the diverting flow interval the valve shifted the air flow back into the odor port, but this time the air stream carried the odor. The instant when the diverting valve shifts the air stream back into the odor port is time zero in all our trials. Odor reaches the odor sampling chamber a fraction of a second later (we estimate ∼0.3 s, but this time would have to be measured to determine a precise delivery time). Mice were asked to respond to the rewarded (S+) odor by licking on a tube at least once in each of four 0.5-s intervals that span the time from 0.5 to 2.5 s (the response area in Figure 2A). Licking at least once in each of the response area intervals is the go–no-go criterion. Note that the mouse is not required to lick during the unrewarded odor (S- trial) and therefore the mouse is free to leave the port once it makes a decision.

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