1. Dan D. Stettler and Richard Axel REPRESENTATIONS OF ODOR IN THE PIRIFORM CORTEX Neuron 63, p. 854-864 (2009)

2. THE OLFACTORY BULB IS QUITE ORGANIZED Cortex What about the cortex? ?

3. THE PIRIFORM CORTEX 3-layered structure On the ventral-lateral surface of the cerebral hemisphere Pyramidal cells synapse with mitral cell afferents in layer 1 SL = pyramidal???? http://aups.org.au/Proceedings/38/9-14/ pyramidal 100μm

4. IMAGING METHOD For the calcium imaging the calcium sensitive fluorescent dye Oregon Green 488 BAPTA-1 AM was used. The dye was injected into broad regions of layer 1, causing the labeling of > 90% of the pyramidal cell bodies in layers 2 and 3 across wide regions in the piriform cortex. Imaging was done at multiple sites in more than 100 mice. 50μm Baseline fluorescence (air)

5. STIMULI Stimulation consisted of a 1sec??? puff of odorant at concentrations of 0.5-80ppm in air. 20 different odors were used

6. ODORANT-EVOKED RESPONSES IN MOUSE PIRIFORM USING IN VIVO TWO-PHOTON CALCIUM IMAGING Fluorescence changes were elicited in 3-15% of the piriform neurons (Fox urine) Each odorant activated a unique but dispersed ensemble of cells in layer 2. Behaviorally different odors elicited the same type of response.

7. 50μm Responses of the 5 marked cells to 5 odorants DPG/air Adjacent cells can respond selectively to different odorants

8. ODORANT-EVOKED CALCIUM RESPONSES IN PIRIFORM CORTEX ARE HIGHLY CONSISTENT Odor puff

9. ODORANT-EVOKED CALCIUM RESPONSES IN PIRIFORM CORTEX ARE HIGHLY CONSISTENT Cells responsive to a given odorant within the same imaging field exhibited a range of statistically significant positive responses

10. CONCENTRATION DEPENDENCE OF ODOR-EVOKED RESPONSES

11. ODORANTS EVOKE RESPONSES IN UNIQUE BUT OVERLAPPING ENSEMBLES OF PIRIFORM NEURONS

13. DISTRIBUTED ODORANT REPRESENTATIONS EXTEND ACROSS WIDE REGIONS OF PIRIFORM CORTEX

14. THE RESPONSE OF PIRIFORM CELLS TO A MIX OF ODORANTS EXHIBITS STRONG SUPPRESSION AND WEAK SYNERGY

16. A MODEL OF PIRIFORM RESPONSES BASED UPON RANDOM CONNECTIVITY BETWEEN THE BULB AND PIRIFORM CAN GENERATE THE OBSERVED ODORANT REPRESENTATIONS

18. CONCLUSIONS Unlike visual, auditory or somatosensory cortical sensory areas: The piriform cortex discards the spatial segregation and chemotopy apparent in earlier stages of the olfactory system. The piriform shows a highly distributed organization - different odorants activate unique but dispersed ensembles of cortical neurons. Neurons in the piriform cortex don’t have an apparent continuous receptive fields (chemotopy, ….behavioral What else was checked?) → It should be remembered, though, that a relevant odors space still needs to be defined, while in other senses this step is more straightforward. Caveat – results are dependent on thresholds of imaging

20. GLUTAMATE BLOCKADE DIMINISHES ODORANT- EVOKED RESPONSES

21. MONTE CARLO SIMULATIONS OF RESPONSIVE CELL DISTRIBUTIONS.

22. AUTO- AND CROSS- CORRELATION ANALYSIS REVEALS NO CONSISTENT FINE-SCALE PATTERNING IN ODORANT RESPONSES.

23. MOTIVATION  Measuring the input to neurons.  In electrical measurements one finds: directional selectivity of the firing rate but no directional selectivity under hyperpolarization – indicating a low tuning level of the inputs. POSSIBILITIES OF INPUT TUNING AND ORGANIZATION: Untuned Tuned and clustered Tuned and dispersed Investigating the activity under hyperpolarization

24. HETEROGENEOUS DISTRIBUTION OF PURE- TONE-ACTIVATED SPINES ALONG DENDRITES. Xiaowei Chen, Ulrich Leischner, Nathalie L. Rochefort, Israel Nelken & Arthur Konnerth Functional mapping of single spines in cortical neurons in vivo Nature 475, 501–505

26. http://www.nobelprize.org/nobel_prizes/medicine/lau reates/2004/illpres/2_olfactory.html

28. 2-photon microscope

29. 1.Near simultaneous absorption of the energy of two infrared photons results in excitation of a fluorochrome that would normally be excited by a single photon of twice the energy. 2.The probability of excitation depends on the square of the infrared intensity and decreases rapidly with distance from the focal volume. Practical theory of 2-photon microscopy

30. Advantages of 2-photon microscopy 1.Increased penetration of infrared light allows deeper imaging. 2.No out-of-focus fluorescence. 3.Photo-damage and bleaching are confined to diffraction- limited spot. 4.Multiple fluorochrome excitation allows simultaneous, diffraction- limited, co-localization. 5.Imaging of UV-excited compounds with conventional optics.