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Synopsis: Overview Perception Retina Central Projections We emphasize these points from Kandel in Bi/CNS 150 Bi/CNS/NB 150: Neuroscience Read Lecture Vision I Overview of the visual system Oct. 28 Anatomy: The retina, LGN, V1 (today) Perception: What is seeing? David Marr’s three levels of analysis October 28, 2015 Vision I Chapter 26 & 27 Vision is ubiquitous, but many different types of eyes evolved (Adolphs) Visual processing streams originate in the retina Ralph Adolphs Topography: there are maps of visual space in the brain RGCs have center-surround receptive fields Phototransduction Oct. 30 The brain can detect a single photon: amplification Vision II Visual transduction is slow: second messenger pathways Chapter 26 (Lester) Rods and cones hyperpolarize in response to light Retinal ganglion cells send action potentials from retina to brain There is adaptation to bright and dark light levels Midterm Review Nov. 1 Discussion section High-level vision and object recognition Nov. 2 Maps of visual space are topographic but distorted Vision III Chapter 25 & 28 Higher regions synthesize more complex visual representations (Adolphs) There are two broad visual processing streams: ventral and dorsal Higher-level visual cortex has functionally specialized regions 1 2 Synopsis: Synopsis: Overview Friday: Perception Overview Retina Perception More Cortex Central projections Retina Beyond V1 LGN Central projections Human neuroimaging (Visual Cortex) LGN High-level vision (Visual Cortex) 3 4 The Challenge: Stimulus Behavior Subjective experience X Key advances: -electrophysiology Stimulus Mind Behavior -neuropsychology -neuroimaging -modeling Stimulus Behavior 5 6 Sherrington (1948): senses classified as VISION --teloreceptive (vision, hearing) What is seeing? --proprioceptive (limb position) --exteroceptive (touch) To know what is where by looking --chemoreceptive (smell and taste) --interoceptive (visceral) 1. vision involves object identification ! 2. vision involves localization in visual space 3. vision is active 7 8 Vision as a computational problem Cues available for vision • Vision is the process of discovering from images what retinal location visual field location is present in the world, and where it is. luminance brightness wavelength ratios hue change over space contrast/spatial frequency/texture change overNeuron time motion Computational theory Representation and Hardware Goal of the algorithm implementation binocular disparityReviewdepth computation? Why surround/context color, illusions is it appropriate and Implementation? How can representation what is the logic of Representation of the and algorithm be the strategy by input and output? realized physically? synapses and interneurons while layers II and III contain the which it can be Algorithm for the cell bodies of PCs (Neville and Haberly, 2004). Individual PCs carried out? transformation? receive input from MTs scattered throughout the olfactory bulb (Apicella et al., 2010; Davison and Ehlers, 2011; Miyamichi et al., 2011; Wilson, 2001) and the axons of individual MTs branch extensively throughout piriform cortex (Ghosh et al., 2011; Sosulski et al., 2011). Given this connectivity, PCs receive D. Marr, 1980 input from a diverse population of odorant receptors and there- fore could function as combinatorial sensors (Haberly, 2001; 9 Mori10 et al., 1999; Wilson and Sullivan, 2011) that integrate activity resulting from activation of broad swaths of molecularly defined OSNs. Consistent with this hypothesis, cross-habituation studies suggest that PCs respond to combinations of odor molecular features, and not single molecular features as do MT cells (Wilson et al., 2000; Wilson and Rennaker, 2010). Further, activation of MT cells across a wide area of the olfactory bulb is required to drive PCs to spike (Arenkiel et al., 2007; Davison Figure 3. Current Understanding of the Basic Properties of the and Ehlers, 2011). Finally, significant sparsening of odor Olfactory Bulb and Retina Left panel: correlation structure of input to the retina (top) and olfactory bulb responses is thought to occur between bulb and cortex (Poo (bottom). Red indicates the degree of correlated input relative to the indicated and Isaacson, 2009), suggesting that in addition to integrating Stages of Processing point (asterisk). In the retina, neighboring circuits of neurons receive similar input from multiple glomeruli, mechanisms are in place to filter information, allowing for center surround inhibition and other local computa- incoming bulbar input onto PCs. Importantly, piriform cortex, Taskstions to be performed. The olfactory bulb, due to the high number of different receptor types, cannot map its input onto a two-dimensional surface, and so particularly posterior piriform cortex, receives significant input 1. Transduction olfactory input is necessarily fragmented acrossDisorders the olfactory bulb (Cleland from the rest of the brain (Illig, 2005; Maier et al., 2012). and Sethupathy, 2006), and nearby glomeruli do not receive correlated input 2. Perception (early) Detection(Soucy et al., 2009). Right panel: basic circuit diagrams of modular networks Sensation within the retina (top, after GollischApperceptive and Meister, 2010) andAgnosia olfactory bulb Feedforward Inhibition and Coincidence Detection 3. Recognition (late perception) Discrimination(bottom). Excitation is marked by closed circles and inhibition by open in Piriform Cortex Knowledge diamonds. Recent work suggests thatAssociative transmission through Agnosia the olfactory bulb Piriform cortex exhibits strong sensory-evoked inhibition (Poo 4. Memory (association) Categorizationmay be more similar to the retina than previously thought, with external tufted Belief and Isaacson, 2009), which serves to narrow the temporal 5. Judgment (valuation, preference) Recognition(ET) cells acting as intermediaries between receptorAmnesia neuron input (R) and mitral Decision cell (MC) output, much as bipolar cells (B) functionAnomia between photoreceptors (P) window during which MT input can be effectively integrated 6. Planning (goal formation) Conceptual andknowledge retinal ganglion cells (G), although weak connections between the olfac- (Luna and Schoppa, 2008; Stokes and Isaacson, 2010). Di- tory receptor neurons and MCs are also thought to exist (dashed line); synaptic feedforward inhibition acts on PCs in as little as 2 ms 7. Action Namingunderstanding the relative functional contributions of these two pathways will require future work in awake animals. Periglomerular (PG) and granule cells following MT cell spike input. This inhibition is well suited to trun- (GC) provide inhibitory feedback onto ETs and MCs, functioning somewhat like cate sensory input, as it occurs in the distal dendritic arbor, horizontal (H) and amacrine (A) cells, although gap junctions have not been where MT axons terminate (Stokes and Isaacson, 2010). physiologically demonstrated between inhibitory and excitatory neurons in the olfactory bulb. Red cells are glutamatergic and blue GABAergic in the lower Disynaptic inhibition onto PC dendrites is mediated by layer 1a panel. Tufted cells, which share some properties with both MCs and ETs, are interneurons (neurogliaform and horizontal cells; see Suzuki not shown. and Bekkers, 2012), which are reliably activated by MT cell axons due to a larger number of axons targeting these cells as well as a olfactory-motor coupling (Xu and Wilson, 2012). Indeed, under- higher release probability for MT to interneuron synapses in standing this input to hippocampus will likely be useful for future contrast to MT to PC connections (Stokes and Isaacson, 2010). 11 understanding of signal processing in this structure. During12 a burst of action potentials from MT cells, disynaptic Since a majority of work on postsynaptic processing of MT feedforward inhibition to the dendrites depresses, and polysyn- output has been conducted in the piriform cortex, we will focus aptic feedback inhibition targeted to the PC soma begins to here on the mechanisms of MT communication from the olfac- dominate during later spikes in the train. This form of inhibition tory bulb to the piriform cortex. We will address olfactory bulb is short latency following MT cell input (5–10 ms; Luna and to piriform projections in enough detail to provide adequate Schoppa, 2008), and has been suggested to originate primarily context for an understanding of the temporal processing of from interneurons driven by PC cell spikes (Stokes and Isaacson, olfactory signals. We suggest the reader consult recent reviews 2010). for a comprehensive discussion of the piriform cortex (Isaacson, Although PCs have active dendritic conductances (Bathellier 2010; Wilson and Sullivan, 2011) and signal processing and input et al., 2009), inhibition by interneurons sets a short temporal to the glomerular layer of the olfactory bulb (Cleland, 2010; window for integration of MT input by PCs. Indeed, elimination Linster and Cleland, 2009; Mori and Sakano, 2011; Wachowiak of inhibition greatly expands temporal integration in PCs, such and Shipley, 2006), as well as a general discussion of olfactory that integration is then only limited by the membrane time con- temporal coding (Bathellier et al., 2010). stant of the PC (Luna and Schoppa, 2008). Further, MT input is The piriform cortex is composed of three layers. Input from MT broadly spread across the distal dendritic arbor of each neuron cell axons terminates on the distal dendrites of piriform cortex and does not appear capable of causing dendritic spikes (Bath- pyramidal cells (PCs) in layer Ia.
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