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V1 Dynamics and Sparsity and Multiple Feature Maps Michael Shelley – Courant Institute/CNS, NYU Collaborators: Bob

V1 Dynamics and Sparsity and Multiple Feature Maps Michael Shelley – Courant Institute/CNS, NYU Collaborators: Bob Shapley – CNS/CIMS David Cai -- CIMS Dave McLaughlin – CIMS/CNS Louis Tao -- NJIT Wei Zhu -- CNS/CIMS. I. I. E. E. V1. Complex. Simple. LGN.

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V1 Dynamics and Sparsity and Multiple Feature Maps Michael Shelley – Courant Institute/CNS, NYU Collaborators: Bob

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  1. V1 Dynamics and Sparsity and Multiple Feature Maps Michael Shelley – Courant Institute/CNS, NYU Collaborators: Bob Shapley – CNS/CIMS David Cai -- CIMS Dave McLaughlin – CIMS/CNS Louis Tao -- NJIT Wei Zhu -- CNS/CIMS

  2. I I E E V1 Complex Simple LGN Excitatory Inhibitory • Important Features: • Nonspecific and Isotropic (egalitarian) cortical coupling (I&II) • (monosynaptic inhibition of shorter length-scale) • Fitzpatrick et al 85, Lund 87, Callaway & Wiser 96 • LGN imparts random preferred spatial phase (I&II) • De Angelis et al (1999) • Combined AMPA and NMDA excitation (II) • Total (LGN + cortical) excitation on a cell is (approx) constant (II) • Miller 96, Royer & Pare 02 NYU V1 models I & II

  3. Drifting Grating Stimulus and S/C characterization Drifting Grating & Modulation Ratio m Simple F1/F0= 1.7 m Complex F1/F0= 0.05 • Isotropic coupling & random phase: (DG) cortical conductances unmodulated • Standard Characterization of Responses: Modulation Ratio F1/F0

  4. Complex Simple extracellular modulation ratio Ringach, Shapley & Hawken JNS 2002 intracellular modulation ratio Priebe et al, Nat. Neuro. 2004

  5. But … • complex cells poorly tuned • increasing self-excitation led to bistability & high firing rates • marked near/far from pinwheel tuning differences • (Sur’s lab: intracellular differences, but little extracellular) • Our previous work suggested that recurrent excitation could be • stabilized and graded by intrinsic fluctuations in the local circuit. • Cai et al, PNAS 2004 • Approach here: Probabilistically sparsify the network and • simultaneously boost efficacy of active connections • (psp’s are fewer and bigger). • Numerology: Mason, Nicoll, Stratford 1991 • Thomson et al 2002 • suggests O(102) presynaptic cortical cells give drive

  6. tuned complex cells small near/far diffs experiment Shapley et al statistically contrast invariant

  7. near pinwheel center iso-orientation domain simple simple complex simple complex complex intracellular conductances somewhat more broadly tuned or diverse at p.w. centers Well-tuned complex cells both near and far from p.w. centers.

  8. What underlies the tuning and the stability? Fluctuations. Simple, homogeneously coupled model network fashioned after V1 model. 50% receive external excitatory drive (simple) 50% receive strong cortical excitation (complex) Existence of critical gain point we call fluctuation controlled criticality hysteric loop critical gain graded response Firing Rate In V1 model, histogram of diff. in spike count on increment and decrement of slowly modulated contrast. Hysteresis in excitatory complex cell network Ex.C. Ex.C.

  9. s.f. firing rate or or 0.1 1 10 0 2π How about “functional” sparsity? Many visual neurons are silent except when driven by near-optimal stimuli, e.g. optimal orientation & spatial frequency (w. Shapley & W. Zhu) tuning curves for orientation and spatial frequency. Xing, Ringach, Shapley, Hawken ‘04  cycles/deg • No observed relation between preferred orientation and • spatial frequency. • In our previous models, LGN drive has single preferred s.f.

  10. 89 cells layer 4Ca But, strong relation between degree of selectivity for orientation and s.f. peak s.f.

  11. orientation map of high spatial freq. response orientation map of low spatial freq. response high low Spatial frequency mapping remains contentious … Hubener, Shoham, Grinvald, Bonhoeffer ’97 Everson et al 1998 Issa, Trepel, Stryker 2000 Sirovich & Uglesich 2004 Suggests the spatial frequency is not a well-structured map, consistent with electrophysiology.

  12. Modification of NYU-II: • Add diversity in preferred spatial frequency of LGN drive to V1. • Keep # of LGN cells independent of pref. s.f. • 50% “even”, 50% “odd” structure. odd or or even

  13. Some results # of cells % of cells preferred s.f. F1/F0

  14. s.f. orientation As with expt., find correlation between tuning of orientation and tuning of s.f. CV[firing rate] LSFV still working on complex cell tuning … Two sample cells

  15. Thanks & Thanks to Jerry

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