Rhythm sequence through the olfactory bulb layers during the time window of a respiratory cycle Buonviso, N., Amat, C., Litaudon, P., Roux, S., Royet, J.P., Farget, V. and Sicard, G. (2003), Eur. J. Neurosci., 17, 1811–1819 LLLL eeee tttt ssss GGGG oooo !!!!

2 The Olfactory Bulb Olfaction & Respiration Olfaction & Respiration The END The END Discussion Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role Introduction Temporal Relationships Temporal Relationships LLLL eeee tttt ssss GGGG oooo !!!!

3 The Main Olfactory Bulb Olfaction & Respiration Olfaction & Respiration The END The END Discussion Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role Introduction Temporal Relationships Temporal Relationships LLLL eeee tttt ssss GGGG oooo !!!!

4 Olfaction & Respiration Olfaction & Respiration Introduction Respiration affects on Bulbar Activity The END The END Discussion  Attempt to show how respiratory dynamics can influence bulbar dynamics can influence bulbar and cortical activity. and cortical activity.  The olfactory sense is intimately related to respiration. related to respiration.  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. LLLL eeee tttt ssss GGGG oooo !!!! Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

5 Olfaction & Respiration Olfaction & Respiration Introduction Respiration affects on Bulbar Activity The END The END Discussion  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 important rhythm. important rhythm.  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 types cell types LLLL eeee tttt ssss GGGG oooo !!!! Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

6 Recordings in the different OB layers Olfaction & Respiration Olfaction & Respiration The END The END Discussion Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role Introduction Temporal Relationships Temporal Relationships LLLL eeee tttt ssss GGGG oooo !!!!

7 Olfaction & Respiration Olfaction & Respiration Introduction  The relationship between olfaction and respiration appears to be and respiration appears to be reciprocal reciprocal  This has been nicely shown by a series of experiments series of experiments  Identification of such stimuli induces a discriminative respiratory induces a discriminative respiratory response response LLLL eeee tttt ssss GGGG oooo !!!! Reciprocal nature of the Olfaction & Respiration The END The END Discussion Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

8 Peripheral Level  The first consequence of periodic sampling during nasal inhalation sampling during nasal inhalation is at the peripheral level where it is at the peripheral level where it induces rhythmical activity in induces rhythmical activity in olfactory receptor neurons olfactory receptor neurons  This is seen in electroolfactogram recordings electroolfactogram recordings showing changes in potential showing changes in potential that are coupled to respiration that are coupled to respiration LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Temporal Relationships Temporal Relationships Olfaction & Respiration Olfaction & Respiration Introduction Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

9 Electrophysiological Activity of the Olfactory System  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 years’’, administrating a series years’’, administrating a series of experiments to study EEG and of experiments to study EEG and then LFP signals then LFP signals LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Temporal Relationships Temporal Relationships Introduction Olfaction & Respiration Olfaction & Respiration Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

10 Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Introduction Temporal Relationships  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 rat anesthetized rat  Odor stimulation induced oscillatory bursts in bulbar LFPs modulated by bursts in bulbar LFPs modulated by high-amplitude respiratory waves. high-amplitude respiratory waves. LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

11 LFP Oscillations LLLL eeee tttt ssss GGGG oooo !!!! Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Introduction The END The END Discussion Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role

12 Temporal Relationships  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 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 cycle during which the respiratory cycle during which the stimulus is delivered. stimulus is delivered. LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Modulation Origin Modulation Origin Functional Role Functional Role Introduction

13 Olfactory Coding Olfactory Coding Introduction Olfactory Coding  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 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. LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role

14 Olfactory Coding During odorant stimulation The respiratory synchronization of M/T cells becomes quite obvious For the first time, (1972): a change in firing frequency of M/T cell discharges was not a sufficient measure of responsiveness Introduction LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role

15 Olfactory Coding have a single increase in firing activity at some point in the respiratory cycle ‘‘suppressive simple synchronized patterns’’ display a single decrease or cessation of firing activity at some point in the respiratory cycle ‘‘complex synchronized patterns’’ Introduction LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion exhibit multiple firing frequency changes along the respiratory cycle ‘‘Excitatory simple synchronized patterns’’ Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role

16 Phase Relationships relative to Respiration LLLL eeee tttt ssss GGGG oooo !!!! Introduction The END The END Discussion Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role

17 Phase Relationships relative to Respiration Introduction The END The END Discussion Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role LLLL eeee tttt ssss GGGG oooo !!!!

18 Introduction Respiration Modulation Origin  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 sampling drives bulbar activity. sampling drives bulbar activity.  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 the natural rhythmic sensory input. the natural rhythmic sensory input.  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. LLLL eeee tttt ssss GGGG oooo !!!! Modulation Origin Modulation Origin The END The END Discussion Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Functional Role Functional Role

19 Introduction Functional role of respiratory modulation I.By triggering the activity into the bulbar network, the early inspiratory patterns of glomerular cells could be dedicated to a priming function; II.Mitral and tufted cell discharges occurring during the γ episodes around transition I/E epoch would serve a gating function, III.The late and slow expiratory patterns of deeper cells could serve a tuning function, modulating the bulbar message during β oscillatory episodes. LLLL eeee tttt ssss GGGG oooo !!!! The END The END Discussion Modulation Origin Modulation Origin Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Functional Role Functional Role

20 Functional role of respiratory modulation Introduction The END The END Discussion Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Modulation Origin Modulation Origin Functional Role Functional Role Olfactory Coding Olfactory Coding LLLL eeee tttt ssss GGGG oooo !!!!

21 Functional role of respiratory cycle  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 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 what extent those assumptions might what extent those assumptions might hold during sniffing in the awake hold during sniffing in the awake animal. animal. LLLL eeee tttt ssss GGGG oooo !!!! Introduction The END The END Discussion Modulation Origin Modulation Origin Olfactory Coding Olfactory Coding Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Functional Role Functional Role

22 Future Thoughts  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’’ 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 ‘‘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. LLLL eeee tttt ssss GGGG oooo !!!! Introduction The END The END Discussion Modulation Origin Modulation Origin Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Functional Role Functional Role

23 The End Thank You Introduction The END The END Discussion Modulation Origin Modulation Origin Olfaction & Respiration Olfaction & Respiration Temporal Relationships Temporal Relationships Olfactory Coding Olfactory Coding Functional Role Functional Role LLLL eeee tttt ssss SSSS tttt oooo pppp !!!!