Receptive Fields and Visual Pathway (Part 1) Lecture Slides PDF

Receptive fields and the visual pathway (Part I) Dr Tony Redmond PhD MCOptom FHEA Reader in Vision Science School of Optometry & Vision Sciences Cardiff University, UK Lecture contents Retinal Layers (Part I) Receptive Fields (Part I) The visual pathway (Part II) The importance of receptive fields i...

Receptive fields and the visual pathway (Part I) Dr Tony Redmond PhD MCOptom FHEA Reader in Vision Science School of Optometry & Vision Sciences Cardiff University, UK Lecture contents Retinal Layers (Part I) Receptive Fields (Part I) The visual pathway (Part II) The importance of receptive fields in perimetry (Part II) The retina Cross section used for the following slides Cell types in the retina Sclera Cell types in the retina Choroid Choroid Cell types in the retina Neural retina Retinal pigment Epithelium (RPE) Cell types in the retina Nerve fibre layer (NFL) Inner limiting membrane (ILM) Inner plexiform layer (IPL) Ganglion cell layer (GCL) Outer plexiform layer (OPL) Inner nuclear layer (INL; bipolar, horizontal amacrine cell nuclei) Outer limiting Membrane (OLM) Photoreceptor Layer (PL) RPE Choroid Outer nuclear layer (ONL; rod and cone nuclei) LIGHT Cell types in the retina Cell types in the retina Photoreceptors (rods and cones) Cell types in the retina Bipolar cells Bipolar cells Synapse with photoreceptors. Response of bipolars is proportional to amount of glutamate released by photoreceptors (Graded Potential). Some bipolars are excited by the release of glutamate by photoreceptors (OFF-centre bipolars), whilst others are inhibited by it (ON-centre bipolars). **Note: revise Malgorzata’s lectures on phototransduction in photoreceptors ON-centre bipolar cells: depolarising bipolars …depolarised (excited) by an increase in luminance i.e. excited by ↓ glutamate from rods/cones. …hyperpolarised (inhibited) by a decrease in luminance i.e. inhibited by ↑ glutamate from rods/cones Respond strongly to light images on dark backgrounds and onset of light. Increase in light hitting cone Rod/cone hyperpolarised causing decreased glutamate release at synapse ON-bipolar stimulated (depolarised à increased glutmate release) OFF-centre bipolar cells: hyperpolarising bipolars …depolarised (excited) by a reduction in luminance i.e. excited by ↑glutamate from cones …hyperpolarised (inhibited) by an increase in luminance i.e. inhibited by ↓glutamate from cones Respond strongly to dark images on light backgrounds and offset of light. Decrease in light hitting cone Cone depolarised causing increased glutamate release OFF-bipolar stimulated (depolarised) Cell types in the retina Retinal ganglion cells and their axons RGCs fire action potentials when stimulated – the larger the graded potential from the bipolars, the greater the density of action potentials fired by RGCs Retinal Ganglion cells Cell types in the retina Horizontal cell Horizontal cells Carry information horizontally across the retina in the outer plexiform layer Feed information between bipolar cells Feed back information to photoreceptors Communicate with other horizontal cells through gap junctions Receive feedback from inner plexiform layer Horizontal cells Shape receptive fields of bipolar cells. Possible role in colour coding of bipolars Send feedback to photoreceptors, modulating photoreceptor signal under different light levels (Make photoreceptors less sensitive in bright light and more sensitive in dim light) Cell types in the retina Amacrine cells Amacrine cells Interneurones - carry info laterally through inner plexiform layer Synapse with bipolars, amacrines & ganglion cells >25 types in humans, and have various functions Various neurotransmitters and dendritic trees Help ‘sharpen up’ receptive fields of ganglion cells (like horizontal cells do for bipolar cells) Cell types in the retina Optic nerve Sheath Receptive fields For any cell in the visual system, from the retina to the brain, there is an area in the visual field that will produce a change in the response in that cell. This is the cell’s Receptive Field The receptive field of a cell that transmits visual signals is: The area of the retina over which a light stimulus can change the activity of that cell. Receptive fields Retinal ganglion cells and their axons Receptive fields For Example: RF DF The Dendritic Field (DF) of a ganglion cell is the physical area of the dendritic arbour. The Receptive field (RF) of a ganglion cell describes the area of photoreceptors that will ultimately contribute to the response of the ganglion cells (after relay by bipolar cells) Receptive fields: Bipolar cells Each bipolar cell receives a direct input from a group of photoreceptors. ON-centre bipolars are excited by light hitting these photoreceptors, OFF-centre bipolars are inhibited BUT surrounding photoreceptors also synapse with bipolar cell indirectly via horizontal cell H-cells add an opponent signal to receptive field and introduce centresurround antagonism ON OFF OR OFF ON CONES BIPOLAR HORIZONTAL HORIZONTAL CENTRE SURROUND Horizontal and amacrine cells contribute to the formation of receptive field configuration RF centres have a positive response to its preferred stimulus RF surrounds have a negative response to the same stimulus Combine to give a centresurround or ‘Mexican Hat’ configuration From Zapp et al, Trends Neurosci 2022;45(6):430-445 Receptive fields: Retinal Ganglion cells Centre-surround organisation of bipolar cell receptive fields is passed on to ganglion cells. RGC receptive fields modified by amacrine cells. There are ON-centre RGCs (respond strongly to light on centre of receptive field and dark on surround)… …and OFF-centre RGCs (respond strongly to dark on centre of receptive field and light on surround). Consequences of centre-surround organisation 1) Centre-surround organisation manifests as spatial antagonism (or lateral inhibition). 2) Visual system responds strongly to luminance boundaries i.e. local contrast, and less strongly to even, unchanging areas of luminance. 3) Ganglion cells are spatially tuned to spots of different sizes (different RGCs are tuned to different sized spots of light). ON OFF Figure 2.7 (p.28) redrawn from Tovee: An Introduction to the Visual System. Centre-surround organisation leads to spatial tuning - +++ - + RECEPTIVE FIELD Cell Response RGC response Spatial tuning curve of a single ganglion cell glion cell ponse Decreasing Spatial frequency stimulus size Spatial tuning Ganglion cell will respond most strongly to a stimulus of a certain size – any larger or smaller and response is reduced (increasing spatial frequency) RGC response Retina contains numerous ganglion cells with differently sized receptive fields Decreasing stimulus size Which of the following would be the best stimulus for an ON-centre bipolar cell? 1. A black spot (of the same size as the receptive field centre) against a light background. 2. Diffuse light across the receptive field 3. A light spot (of the same size as the receptive field centre) against a dark background. 4. Diffuse dark across the receptive field ON and OFF pathways Bipolar & ganglion receptive fields can be ON- centre or OFF- centre. ON-centre respond to light pattern on dark or light ONSET. OFF-centre respond to dark pattern on light or light OFFSET. Distinct ON- and OFF- pathways through the retina. + - + + - + ON- CENTRE RECEPTIVE FIELD On Off Stim. + + - - + -+ + + OFF-CENTRE RECEPTIVE FIELD Chromatic and achromatic pathways Also have separate achromatic and chromatic pathways to visual cortex… Achromatic pathways = compare brightness of image across the retina (local contrast between light and dark). L-cones and M–cones are responsible for achromatic pathway through retina. Chromatic pathways = compare wavelength of light across the retina (simultaneous colour contrast). L-cones , M-cones and S-cones responsible for colour pathways through retina. Chromatic receptive fields Some retinal receptive fields are chromatic… The cells with L-cone centres receive antagonistic signals from M-cones in the surround of their receptive field and vice versa. Blue ON- pathway receives antagonistic input from yellow light (combined response from L-cones and M-cones) feeding into the receptive field (Note: GC receptive fields for blue/yellow pathway don’t have a concentric centresurround configuration. Their ON- and OFF- portions are co-extensive. Red ON / Green OFF Red OFF/ Green ON Blue ON/ Yellow OFF Green ON / Red OFF Green OFF/ Red ON Blue OFF/ Yellow ON Receptive fields: resolution (acuity) vs sensitivity Convergence – determines size of receptive fields Human retina: 126 million photoreceptors : 1 million ganglion cells Rod system has lots of convergence (120:1) – G sensitive but poor resolution. Cone system has little convergence (6:1) – less sensitive but better resolution. Convergence even less in G foveal cones (1:1) Receptive fields: rods G G G High Sensitivity Poor Resolution Receptive fields: cones G G G G G G G G G G G G G Poor sensitivity (compared to that of rods) High resolution General rule of thumb: Large receptive fields = high sensitivity, low resolution Small receptive fields = low sensitivity, high resolution Retinal ganglion cells in cats Classified by physiology as X- Y- and W- cells Classified by morphology (structure) as alpha and beta cells (but now 21 other types known). X-cells (~80%) Small concentric receptive fields (sensitive to high spatial frequencies) Prevalent in central retina Slow conduction rate, so delayed response Strong, sustained response to stationary stimuli Unresponsive to fast-moving stimuli. Beta morphology Retinal ganglion cells in cats Y-cells (~5%) Large concentric receptive fields (sensitive to low spatial frequencies) Poor spatial acuity Prevalent in periphery Transient, weak responses to sustained stimuli Strong response to fast moving stimuli Alpha type morphology W-cells Non-concentric receptive fields (~15%) Retinal ganglion cells in primates P-cells Start of the Parvocellular pathway (~80%) Like cat X cells. Also known as tonic cells. In addition show colour anatagonism Small receptive fields – Most sensitive to high spatial frequencies and have good acuity. Retinal midget cells M-cells Start of the Magnocellular Pathway (~10%) Like cat Y cells. Also known as phasic cells. Big response to transient/fast moving stimuli Most sensitive to low spatial frequencies, poor acuity. Retinal parasol cells Retinal ganglion cells in primates Parasol cells – larger receptive fields than midget cells. Parasol and midget cell dendritic trees (and so receptive fields) get larger towards periphery. Periphery has higher sensitivity, but poorer spatial acuity. Retinal ganglion cells in primates K-cells About 10% of retinal ganglion cells Start of Koniocellular pathway Newly characterised Moderately slow conduction velocity Moderate spatial acuity Carry blue-yellow colour opponent information Retinal bistratified ganglion cells. Retinal ganglion cells in primates Dacey DM, Packer OS. Colour coding in the primate retina: diverse cell types and conespecific circuitry. Curr Opin Neurobiol, 2003;13(4):421-427 Parallel pathways Distinct and separate processing and transmission through visual pathway. e.g. ON vs. OFF / Chromatic vs. achromatic All carried in 3 major channels: parvocellular, magnocellular- and koniocellular. Rod Processing Rods mainly contribute to Magno- pathway. Cones contribute to both Magno- and Parvo- pathways Parasol ganglion cells receive dual input from rods (via AII and A17) and cones. Rod system has larger receptive fields, which are more diffuse (less centre-surround antagonism). Also have no OFF pathway. References and Recommended Reading Recommended reading Schwartz (1999). Visual Perception. A Clinical Orientation. Chapters 2, 12, 13, 14 & 15. Livingstone and Hubel “Segregation of Form, Color, Movement, and Depth: Anatomy, Physiology, and Perception” (PDF on Blackboard) Useful website… http://www.webvision.med.utah.edu/ Other References Hubel & Wiesel (1959). Journal of Physiology, 148, 574-591. Hubel & Wiesel (1962). Journal of Physiology, 160, 106-154. Hubel & Wiesel (1968). Journal of Physiology, 195, 215-243. Hubel & Wiesel (1965). Journal of Neurophysiology, 28, 1041-1059. Hubel & Wiesel (1974). Journal of Comparative Neurology, 177, 361-380. LeVay, Hubel & Wiesel (1975). Journal of Comparative Neurology, 159, 559-575. Bruce, Desimone & Gross (1981). Journal of Neurophysiology, 46, 369-384. Questions? Dr Tony Redmond [email protected] @tony_redmond