Rhythm sequence through the olfactory bulb layers during the time window of a respiratory cycle Buonviso, N., Amat, C., Litaudon, P., Roux, S., Royet,

Rhythm sequence through the olfactory bulb layers during the

time window of a respiratory cycleBuonviso, N., Amat, C., Litaudon, P., Roux, S., Royet, J.P., Farget, V.

and Sicard, G. (2003), Eur. J. Neurosci.,17, 1811–1819

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The Olfactory Bulb

Olfaction & RespirationOlfaction & Respiration

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DiscussionDiscussion

Olfactory CodingOlfactory Coding

Modulation OriginModulation Origin

Functional RoleFunctional Role

IntroductionIntroduction

Temporal RelationshipsTemporal Relationships

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The Main Olfactory Bulb


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Respiration affects on Bulbar Activity

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Attempt to show how respiratory Attempt to show how respiratory dynamics can influence bulbar dynamics can influence bulbar and cortical activity.and cortical activity.

The olfactory sense is intimately The olfactory sense is intimately related to respiration. related to respiration.

Their close relationship occurs Their close relationship occurs because the respiration cycle because the respiration cycle itself provides the mechanism itself provides the mechanism for sampling of odor stimuli.for sampling of odor stimuli.

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Respiration affects on Bulbar Activity

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The mammalian olfactory bulb is The mammalian olfactory bulb is characterized by prominent characterized by prominent oscillatory activity of its local oscillatory activity of its local field potentials.field potentials.

Breathing imposes the most Breathing imposes the most important rhythm.important rhythm.

The authors recorded unitary activities The authors recorded unitary activities in different bulbar layers in different bulbar layers simultaneously with local field simultaneously with local field potentials in order to examine the potentials in order to examine the different relationships existing between:different relationships existing between: (i) breathing and field potential oscillations(i) breathing and field potential oscillations and and (ii) breathing and spiking activity of different (ii) breathing and spiking activity of different cell typescell types Lets Lets

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Recordings in the different OB layers


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The relationship between olfaction The relationship between olfaction and respiration appears to be and respiration appears to be reciprocalreciprocal

This has been nicely shown by a This has been nicely shown by a series of experimentsseries of experiments

Identification of such stimuli Identification of such stimuli induces a discriminative respiratory induces a discriminative respiratory responseresponse

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Reciprocal nature of the

Olfaction & Respiration

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Peripheral Level

The first consequence of periodic The first consequence of periodic sampling during nasal inhalation sampling during nasal inhalation is at the peripheral level where is at the peripheral level where it it induces rhythmical activity in induces rhythmical activity in olfactory receptor neuronsolfactory receptor neurons

This is seen in This is seen in electroolfactogram recordings electroolfactogram recordings showing changes in potential showing changes in potential that are coupled to respirationthat are coupled to respirationLets Lets

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Electrophysiological Activity of the

Olfactory System

Since the earliest Since the earliest electrophysiological studies, the electrophysiological studies, the powerful influence of breathing powerful influence of breathing has been noticed in the OB and has been noticed in the OB and cortex. cortex.

Then followed the ‘‘Freeman Then followed the ‘‘Freeman years’’, administrating a series years’’, administrating a series of experiments to study EEG and of experiments to study EEG and then LFP signalsthen LFP signals

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Temporal Relationships

However, the aim of all these However, the aim of all these experiments was not the study of experiments was not the study of the temporal relationships per se the temporal relationships per se between respiratory and LFP between respiratory and LFP signals. In this paper such signals. In this paper such relationships were examined in the relationships were examined in the anesthetized ratanesthetized rat

Odor stimulation induced oscillatory Odor stimulation induced oscillatory bursts in bulbar LFPs modulated by bursts in bulbar LFPs modulated by high-amplitude respiratory waves.high-amplitude respiratory waves.

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LFP Oscillations

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Temporal Relationships

The most accurate study showed The most accurate study showed that bursts of γ activity were that bursts of γ activity were initiated by inspiration and that initiated by inspiration and that correlation between bulbar and correlation between bulbar and cortical activities was higher during cortical activities was higher during this period.this period.

Appearance of β and γ OB bursts Appearance of β and γ OB bursts depending on the respiratory phase depending on the respiratory phase might indicate that the function might indicate that the function and/or the target of the information and/or the target of the information conveyed by bulbar output neurons conveyed by bulbar output neurons changes according to the epoch of the changes according to the epoch of the respiratory cyclerespiratory cycle during which the during which the stimulus is delivered.stimulus is delivered.

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Olfactory Coding

Hypothesis: The I/E γ period could Hypothesis: The I/E γ period could be devoted to information be devoted to information transmission and communication transmission and communication towards cortex, while β epoch towards cortex, while β epoch would be devoted to feedback would be devoted to feedback controls.controls.

However, a second hypothesis However, a second hypothesis might might be advanced that the respiratory be advanced that the respiratory modulation itself could carry some modulation itself could carry some information about the odor.information about the odor. Lets Lets

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Olfactory Coding

During odorant stimulationDuring odorant stimulation

The respiratory synchronization of The respiratory synchronization of M/T cells becomes quite obviousM/T cells becomes quite obvious

For the first time, (1972): a change in For the first time, (1972): a change in firing frequency of M/T cell dischargesfiring frequency of M/T cell discharges

was not a sufficient measure of was not a sufficient measure of responsivenessresponsiveness


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Olfactory Coding

have a single increase in firing have a single increase in firing activity at some point in the activity at some point in the

respiratory cyclerespiratory cycle‘‘‘‘suppressive simple synchronized suppressive simple synchronized

patterns’’ patterns’’ display a single decrease or cessation of display a single decrease or cessation of firing activity at some point in the respiratory firing activity at some point in the respiratory cyclecycle

‘‘‘‘complex synchronized patterns’’ complex synchronized patterns’’


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exhibit multiple firing frequency exhibit multiple firing frequency changes along the respiratory cyclechanges along the respiratory cycle

‘‘‘‘Excitatory simple synchronized Excitatory simple synchronized patterns’’patterns’’






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Phase Relationships relative to Respiration

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Phase Relationships relative to Respiration


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Respiration Modulation Origin

Respiratory modulation of bulbar and Respiratory modulation of bulbar and cortical activities has multiple origins, and it cortical activities has multiple origins, and it is probably the combination of all of them is probably the combination of all of them that makes it’s influence so robust. that makes it’s influence so robust.

First of all, the peripheral rhythmic effect of First of all, the peripheral rhythmic effect of sampling drives bulbar activity.sampling drives bulbar activity.

Then, glomeruli and bulbar cells seem to be Then, glomeruli and bulbar cells seem to be intrinsically pretuned to a frequency close to intrinsically pretuned to a frequency close to respiratory frequency; respiratory frequency;

this intrinsic frequency can be entrained by this intrinsic frequency can be entrained by the natural rhythmic sensory input. the natural rhythmic sensory input.

Finally, centrifugal controls originating both Finally, centrifugal controls originating both in olfactory cortices and respiratory centers in olfactory cortices and respiratory centers could themselves act phasically.could themselves act phasically.

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Functional role of respiratory modulation

I.I. By triggering the activity into the By triggering the activity into the bulbar network, the early inspiratory bulbar network, the early inspiratory patterns of glomerular cells could be patterns of glomerular cells could be dedicated to a priming function; dedicated to a priming function;

II.II. Mitral and tufted cell discharges Mitral and tufted cell discharges occurring during the occurring during the γγ episodes around episodes around transition I/E epoch would serve a transition I/E epoch would serve a gating function,gating function,

III.III. The late and slow expiratory patterns of The late and slow expiratory patterns of deeper cells could serve a tuning deeper cells could serve a tuning function, modulating the bulbar function, modulating the bulbar message during β oscillatory episodes.message during β oscillatory episodes. Lets Lets

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Functional role of respiratory modulation


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Functional role of respiratory cycle

In such a hypothesis, the different In such a hypothesis, the different epochs of a respiratory cycle would epochs of a respiratory cycle would not be equivalent in function. not be equivalent in function.

However, these assumptions are However, these assumptions are mainly drawn from results acquired in mainly drawn from results acquired in the anesthetized animal. the anesthetized animal.

Now, the crucial point is to know to Now, the crucial point is to know to what extent those assumptions might what extent those assumptions might hold during sniffing in the awake hold during sniffing in the awake animal.animal.

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Future Thoughts

Besides its phase, the frequency of Besides its phase, the frequency of respiratory cycles could also have an respiratory cycles could also have an important role. important role.

One can hypothesize that an ‘‘optimal’’ One can hypothesize that an ‘‘optimal’’ frequency might exist which could, frequency might exist which could, facilitate an odor molecule’s access to facilitate an odor molecule’s access to the nasal mucosa and, tune optimally the nasal mucosa and, tune optimally the duration of the temporal unit for the duration of the temporal unit for information processing.information processing.

However, the nature of such a However, the nature of such a ‘‘ ‘‘supervisor’’ center, capable of supervisor’’ center, capable of synchronizing respiratory, olfactory, synchronizing respiratory, olfactory, and limbic structures, is a fascinating and limbic structures, is a fascinating issue which still needs to be elucidated.issue which still needs to be elucidated.

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The End

Thank YouThank You


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Documents

Rhythm sequence through the olfactory bulb layers during the time window of a respiratory cycle Buonviso, N., Amat, C., Litaudon, P., Roux, S., Royet,