11/20/2011 L. 48 Visual Processing for Motion in Flies and Mammals Fri. November 18, 2011 Carl Hopkins Reading Barlow, H. B. and W. R. Levick (1965) The mechanism of directionally selective units in rabbit’s retina. J. Physiol. 178:477-504. Borst A, Euler T. Seeing things in motion: models, circuits, and mechanisms. Neuron. 2011 Sep 22;71(6):974-94. Kim, I-J, Zhang, Y., Meister, M., and Sanes, J.R. (2010) Laminar restriction of retinal ganglion cell dendrites and axons: subtype specific developmental patterns revealed with transgenic markers. J. Neurosci. 30(4) 1452-1462. 1
11/20/2011 CANNONICAL CIRCUITS (Lecture 6) a) A delay line inhibitory circuit blanks excitation in the null direction b1 b2 null direction preferred direction b1 |||||||| |||||||| |||||| |||||||||| b2 |||||||| output CANNONICAL CIRCUITS (Lecture 6) Delay-line coincidence detector responds to movement direction a b1 b2 b1 b2 null direction preferred direction b1 |||||||| |||||||| |||||| |||||||||| b2 |||||||||| output 2
11/20/2011 The Reichardt (Correlation) Motion Detector 2 1 Photoreceptors Low-pass filters F F 2 create delay 1 A A 1 2 Multiplier Subtractor R(t) A (T)F (T - t) - A (T)F (T - t) 2 1 1 2 Barlow Levick Detector • Barlow and Levick (1965) delay • Identical to Reichardt but with one half of basic Reichardt model • And not (veto) from inhibition 3
11/20/2011 DS Cells are now known from Flies and from Mammals • Lobula plate: third layer of neurons in the optic pathway • (cells in the medulla are too small to study) • Lobula Plate Tangential cells (LPTC) respond to time ordered signals. • Number about 50. Varies by species. HS horizontal sensitive VS vertical sensitive • HS: front to back motion sensitive. Tangential Cell Flies: Tangential Cells in the Lobula Plate The Barlow and Levick DS cells are ON/OFF ganglion cells. They have dendrites that terminate in both the inner part of the IPL and the outer part of the IPL (accounting for the Off response and the On response). Broad tuning to both temporal frequency and spatial frequency, but with a preference for temporal tuning (i.e. Reichardt detector) 4 sub types defined by direction (D V; V D; A P; P A) ON DS ganglion cells. Dendrites only in On sublamina of IPL OFF DS ganglion cells. Dendrites only in the Off sublamina of IPL. Borst and Euler, 2011 4
11/20/2011 Network mechanisms for directional selectivity at the cellular and subcellular level Good evidence that in the INSECT DS Neurons in the lobula plate, there are numerous inputs from Reichardt type detectors all over the visual field, but which cells? i.e. both excitatory and inhibitory inputs, already directional, onto tangential neurons of the lobula plate. 5
11/20/2011 Excitatory inputs to the LPTC is via nAChRs Inhibition to LPTC is via GABA receptors. In Drosophila, both receptor types were colocalized in dendrites of HS and VS neurons. 6
11/20/2011 Barlow and Levick’s (1965) hypothesis for a DS ganglion cell in the Rabbit retina 7
11/20/2011 (a) In principle, directional selectivity may not occur in the retina of some mammals (i.e. primates). Instead, DS may be imparted by combining inputs from a high pass (or transient responding) bipolar cell pathway, and a low pass (sustained) pathway contacting ganglion cells with narrow stratification. These ganglion cells woulod be transmitted via separate channels to the brain. (Masland (2001) Nature Neuroscience 4(9):877) (b) A more broadly stratified ganglion cell receives inputs from both the high pass bipolar cell and the low pass bipolar cell, thereby preserving its broad band responsiveness. Such cells might receive directionally selective permutations from amacrine cells. (Masland (2001) Nature Neuroscience 4(9):877) 8
11/20/2011 DS Ganglion cells receive input from both bipolar on cells and off cells, and Starburst Amacrine Cells. SACs have both excitatory and inhibitory terminals on Ganglion cells OFF responding cells are shown, ON pathway is not shown for clarity. Starburst amacrine cells in retina contribute directionally sensitive inputs to ganglion cells. Ablation of SACs knock out directional sensitivity (Amthor et al, 2002) Gavrikov et al. PNAS 2006;103:18381-18382 9
11/20/2011 • Starburst Amacrine Cells are sensitive to centrifugal light stimulation (Expanding circular wave of light), but not centripital. Expanding light evokes strong calcium response in the distal dendrites of this Starburst Amacrine Cell, while a contracting stimulus does not. • The distal dendrites are where the output synapses on ganglion cells are located. • Each separate arm of the dendritic field is essential ly electrically independent of each other arm. Euler et al., 2002; Borst and Euler(2011) input zones from bipolar cells output to ganglion cells 10
11/20/2011 Apparent motion stimulation of a DS retinal ganglion cell (1 followed by 2, or 1’ by 2’) or single flashes, 1, or 2. The directional selectivity is facilitated by cholinergic input from the Starburst Amacrine Cells Asymmetric synaptic wiring between Starburst Amacrine Cells and Directionally Selective ganglion cells. SAC neuron with output synapses indicated by black dots. The synapses are color coded according to the preferred direction of the post-synaptic ganglion cells. The dendritic field of the ganglion cells are shown as elipses, showing the asymmetry in synaptic inputs. Briggman, K.L., Helmstaedter, M., and Denk, W. (2011). Wiring specificity in the direction- selectivity circuit of the retina. Nature 471, 183 – 188. 11
11/20/2011 12
11/20/2011 Kay et al (2011)’s genetic markers indicate that the patterns of molecular specificity are determined early in embryonic life, before eye opening and are thus experience independent. Also, there are differences amongst the genetically identified cells in the embryonic dendritic patterns and axon projections to the brain. Information about motion in different directions is sent to different destinations in the brain. “The last decade has witnessed much progress in our understanding of the cellular and subcellular mechanisms underlying direction selectivity. To a large extent, this is due to the application of advanced optical as well as genetic methods to this problem….. Borst and Euler (2011) 13
11/20/2011 “The last decade has witnessed much progress in our understanding of the cellular and subcellular mechanisms underlying direction selectivity. To a large extent, this is due to the application of advanced optical as well as genetic methods to this problem….. Optical methods are indispensible whenever different anatomical compartments of a neuron turn out to be electrically separated, operating almost in isolation from the rest of the cell, such as the different dendritic branches of a SAC in the vertebrate retina and the output terminals versus the dendrite of lamina cells or the dendrite of lobula plate tangential cells in the fly. … Borst and Euler (2011) “The last decade has witnessed much progress in our understanding of the cellular and subcellular mechanisms underlying direction selectivity. To a large extent, this is due to the application of advanced optical as well as genetic methods to this problem….. Optical methods are indispensible whenever different anatomical compartments of a neuron turn out to be electrically separated, operating almost in isolation from the rest of the cell, such as the different dendritic branches of a SAC in the vertebrate retina and the output terminals versus the dendrite of lamina cells or the dendrite of lobula plate tangential cells in the fly. … Another amazing fact is how much effort over so many years had to be invested in this one single problem of direction selectivity in order to achieve the current level of understanding, a problem that, in terms of computation and information processing, seems quite modest (telling leftward from rightward), compared to the complex intellectual capabilities of humans. Our hope is that understanding this simple neural computation of direction selectivity in full detail will provide an important stepping stone toward our understanding of more complex functions of the nervous system.” Borst and Euler (2011) 14
11/20/2011 Cajal, c. 1892 15
Recommend
More recommend
