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Connectivity patterns in the auditory cortex

Connectivity patterns in the auditory cortex. Stanislav S. Zakharenko Department of Developmental Neurobiology, St. Jude Children’s Research Hospital. Allyn and Bacon, 2004. Tonotopic maps in the auditory cortex. Cruikshank, Rose, Metherate, 2002. Peterson and Winer, 1993.

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Connectivity patterns in the auditory cortex

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  1. Connectivity patterns in the auditory cortex Stanislav S. Zakharenko Department of Developmental Neurobiology, St. Jude Children’s Research Hospital

  2. Allyn and Bacon, 2004

  3. Tonotopic maps in the auditory cortex

  4. Cruikshank, Rose, Metherate, 2002 Peterson and Winer, 1993 Schofield and Coomes, 2005 Lima, Hromadka, Zador, A

  5. Two-photon microscopy Utrafast laser vs. cw laser (high peak power, low average power) Pulsewidth (t): 100-200 fsec Pulse frequency (f): 80 MHz Absorption rate increase: 0.56 (1/tf) ~ 35,000 Decrease in average power: 100-1000 times

  6. 1-photon microscopy • Advantages of • multi-photon excitation: • Focal excitation • 2) Longer wavelengths: • Less photobleaching, photodamage –better cell viability • Less light scattering, greater tissue penetration (up to 1 mm, compared to ~50 mm for 1-photon microscopy) 2-photon microscopy

  7. Mystery of thalamocortical reliability • A disconnect between functional and morphological data: • Thalamic projections reliably deliver information to cortical neurons and are considered the most powerful projection system in the mammalian brain (Gil et al., 1999; Stratford et al., 1996). • Thalamic projections comprise only 20% of all projections received by cortical neurons (Benshalom and White, 1986).

  8. Possible explanations Thalamic afferents: • are larger and stronger(Nahmani and Erisir, 2005; Gil et al, 1999; Stratford et al, 1996); • require additional cortical amplification(Lubke et al, 2000); • are better synchronized(Bruno and Sakmann, 2006).

  9. Hypothesis Thalamic afferents occupy advantageous dendritic locations on cortical neurons: • Distance from the cell body; • Dendritic spine morphology.

  10. GFP GFP + calcium indicator Cruikshank, Rose, Metherate, 2002

  11. Conclusion I • Thalamic inputs cluster within 100 mm from the cell body; • Intracortical inputs distributed throughout dendritic trees of cortical neurons.

  12. Conclusion II • Thalamic inputs target short stubby dendritic spines; • Intracortical inputs target both stubby and mushroom dendritic spines .

  13. Conclusion Dendritic locations and dendritic spine morphology determine effectiveness of thalamocortical pathways in the auditory cortex

  14. Acknowledgements Ildar Bayazitov Jay Blundon Chris Calabrese Laurie Earls Robert Fricke Melissa Johnson Robert Richardson Margaret Sperow Jing Yu Funding: ALSAC, NIMH, NCI, Whitehall Foundation, Searle Scholars Program

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