OPTM4102 Visual Pathway II PDF

OPTM4102 Visual pathway II LGN to visual cortex Dr. Richa Verma Acknowledgement of country The University of Western Australia acknowledges that its campus is situated on Noongar land, and that Noongar people remain the spiritual and cultural custodians of their la...

OPTM4102 Visual pathway II LGN to visual cortex Dr. Richa Verma Acknowledgement of country The University of Western Australia acknowledges that its campus is situated on Noongar land, and that Noongar people remain the spiritual and cultural custodians of their land, and continue to practise their values, languages, beliefs and knowledge. Artist: Dr Richard Barry Walley OAM Objectives Lateral Geniculate Nucleus ~ Layers-Organisation of nerve fibres ~ Magnocellular versus parvocellular versus koniocellular ~ Spatial relationships to surrounding structures Optic radiations ~ Organisation of nerve fibres-Parietal versus temporal ~ Spatial relationships to surrounding structures Visual cortex-Input from radiations ~ Representation of visual field (retinotopic map)-Spatial relationships to surrounding structures Vascular supply  Visual pathway Retina: Ganglion cell- Optic nerve- Optic Chiasm- Optic tract Lateral Geniculate Nucleus (dLGN) Optic radiations V1- V2-association areas, V3, V4 & V5 Visual pathway http://higheredbcs.wiley.com  Dorsal -LGN - => locatedjust thalamus 0 = Retinal informations does not go here. Conly go to LCN). of information 90-95% before LGN to the goes I primary to the enters cortex- Visual http://cognitiveconsonance.info  Ganglion cell to LGN Three classes of ganglion cells: – Midget ganglion cell – Parasol ganglion cell – S-cone ganglion cells projects to specific layers in dorsal LGN. Within the LGN the fibers are organized for nasal and temporal fibers form contralateral and ipsilateral eyes side same side opposite  Nasal fibers opposite side (contralateral) Cross over to the at the chiasm : optic. and do fibers : Do not cross over , remains on the same side Lipsilateral) not Temporal cross at the optic chiasm. Visual Cortex processed before being sent to the where visual information is. LGN Center in the Thalamus : a relay Contralateral Inputs I receive in put from the nasal fibers of the layers , 6 , 4 Cortains 6 layer - opposite eye. input from the temporal fibers of the Ipsilateral Input : layers 2, 3 , 5 receive same side eye. Left visual field : information from the left visual field of both eyes (which hits the nasal retina ofthe and temporal retina of left eye the right eye) is processed in the right LGN. ( Visual field infiers from right visual field of both eyes Right : nascel retina of the right 2 which hits the temporal retina of the left eyes eyea is processed in the leftLGN LGN layers http://webvision.med.utah.edu/  LGN layers The LGN is organized in layers where the layers 1 and 2 are the magno layers which gets its projections form the achromatic ganglion cell system-parasol ganglion cells and one layer from each eye. Layers 3-6 are the four parvo-cellular layers which gets its projections from the midget and midget-like retinal ganglion ferne cells transmitting signals for“red-green” color vision. Once again two layers for each eye. The S-cone mediating retinal ganglion cells which are involved in “blue-yellow” color vision go to the konio-cellular layers. These are located in between and the literature still shows incomplete understanding of the koniocellular layers in the humans.  > innermost layers of the LGM contain larger neurons (magno large : Magnocellular layers = ,. input from the contralateral eye. L 1: receive Layer 2 : receive input from the ipsilateral eye. Layer a motion borad outlines of objects. involved in processing transient Stimuli · FAST a responsive to (Parro small. LGN , contain smaller : Outer layers of the neurons Parrocellular layers => ipsilateral eye L... : Layer] 4 contralateral eye Layer. :... Layer J :... ipsilateral eye I contralateral eye Layer 6. :... involved in colour fine details & high-solution aspects of Vision processing , to sustained stimuli. SLOWER & responsive  LGN layers formed by the connection of the parasol from the retina ganglion cell Summary - - - to the in the LETN magnocellular layer - Achromatic/Luminance Channel- parasol ganglion cells-Magnocellular layer. formed by > - Red-Green channel-midget ganglion cells- Parvocellular layer. Koniocellular Pathway-S cone ganglion cells- Koniocellular layer  Optic radiation => in are axons LGN to the from the primary neurons visual Cortex , The signal from LGN then goes to the primary visual cortex (V1) via the axons of the neuron in the LGN which forms optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway). Carries information from the superior Visual field (inferior retinal ↑T Fibers from the inferior retina called as Myers Loop Carries information from the inferior visual field (superior retinal. ↑ Fibers from the superior retina called as Baum’s loop Optic radiation http://ophthalmology.stanford.edu  Optic radiation The optic radiation carries information from superior and inferior field of each eye lesions involving of the the optic radiation often gives field defect in one - quadrant. > - visual field half ofthe visual space Superior : upper. images are projected onto the inferior half of the retina. Inferior visual field : lower half of the visual space. Images are projected half of the retina. onto the superior => Meyer's loop lesion : damage here can cause a superior quadrantanopia , where the upper quarter of the visual field is lost. where => Baum's loop lesion : damage here can cause an inferior quadrantanopia , the lower quarter of the visual field is. lost => Complete Optic radiation lesion : damage to the entire optic radiation cause homonymous hemianopia , where the same half of the Visual field both is lost in. eyes  Crossing of fibres The optic radiation carries information from superior and inferior field of each eye lesions involving of the the optic radiation often gives field defect in one quadrant. http://teachmeanatomy.info Retina-LGN-Cortex http://www.nature.com  Receptive field Levine & Schefner, 1991-defined a receptive field as an "area in which stimulation leads to response of a particular sensory neuron”. For sensory neuronal cell, the neuronal response is elicited only when the stimulus is presented within the receptive field. First described by Sherrington, 1906.  Receptive field - LAN contains neurons Posterior , forea receptive field are near. the IGN the on to anterior , As move location becomes increasingly receptive field the retina - peripheral in LGN - http://jn.physiology.org/content/80/4/2063  Receptive field The arrangement of ganglion cells within the retina is preserved by the spatial organization of the neurons within the LGN layers, nasal temporal organizations from contralateral an ipsilateral eye. This arrangement holds true for central and peripheral retina. Where the posterior LGN contains neurons whose receptive field are near the fovea and the anterior LGN has the receptive field locations for neurons in the peripheral retina (Erwin et al., 1999).  Retinotopic map The retinotopic map is topographical organisation or the visuotopic map of each point in the visual field to its representative neuron in the LGN and the visual cortex. http://www.cns.nyu.edu  Location of V1 In the Occipital lobe called - also -x Primary visual cortex-V1- striate cortex- brodmann area 17 is loacated and identified by the position of calcarine sulcus. It extends rostrally (front) up to lunate sulcus and postero-laterally (at the back and also side) to the inferior occipital sulcus called s V2- extrastriate cortex- brodmann area 18 V3, V4 and V5- extrastriate cortex- association areas - Location of V1 http://thebrain.mcgill.ca Location of V1 https://www.studyblue.com Organization of V1-layers http://www.nature.com  Organization of V1 The basic organizing principles of primate V1: Laminar arrangement – the cortex is arranged in layers and each of the layers have specific in the way neurons are projected. For e.g from LGN goes to layer 4c. Compartments: The regular spacing of anatomical/functional compartments revealed by cytochrome oxidase (CO). These are referred as blobs. Columnar arrangement- along with cells being organized in layers the cortex is also arranged systematically in vertical aspect which we refer as columns. ~ of excitatory and inhibitory neurons (an arrangement shared with other neocortical areas) Organization of V1-layers http://www.zuniv.net/physiology  Organization of V1-columns A cortical column can be defined based on ~anatomical features (e.g. stereotyped patterns of pyramidal cell apical dendrite bundles) ~functional features (e.g. columns of cortical cells all responding to the same stimulus orientation) ~both.  Organization of V1-columns FRI Many types of columns have been proposed including ~ocular dominance ~orientation ~spatial frequency ~color columns https://mcb.berkeley.edu  Ocular dominance column Eye-dominance column represents group of cells which are arranged in vertical direction and get projection from one eye either left or right. The discovery of these columns comes from single cell recordings from monkeys where every time the electrode entered the cortex perpendicular to the surface, cell after cell coarsely arranged, responded to only eye. When the electrodes were moved laterally the cells responded to the other eye and followed the same pattern in vertical direction.  Ocular dominance column The layer 4C, receives input from the dominant eye and respond only to monocular stimulation. - However in layers above or below layer 4c there are cells which respond when the non dominant eye is stimulated assessmen and - referred as binocular cells. Ocular dominance column http://www.cns.nyu.edu  Cells in layer 4C Just to summarize the cells in cortex are arranged in layers and columns. The columns are of different types. 4 - types. Here we have mainly covered the ocular dominance column. # Where the cells in layer 4c has very specific projection from the dominant eye and holds the monopoly.  What happens in amblyopia RAN & Nomal http://www.cns.nyu.edu Retinotopic map http://webvision.med.utah.edu/  Retinotopic map The retinotopic map for right eye from monkey is compared across the folded cortical surface in the gray matter of the Calcarine sulcus. The foveal part is represented at the very back and the peripheral part in the front of the left V1. http://hubel.med.harvard.edu http://mauryillustrates.com/anatomical.html  Blood supply The blood supply to the brain branches from the internal carotid artery ~ which has anterior and posterior branches (PCA) supplying the anterior and posterior parts of the brain respectively. The vertebral artery Both of these blood arteries forms the anastomotic branches at the circle of Willis. Medial surface of the visual cortex receives branches from the posterior cerebral artery (PCA ) Lateral surface receives cortical branches from the middle cerebral artery and its inferior surface from small branches of the posterior temporal and temporo-occipital arteries (100%). Blood supply-Circle of Willis http://www.neuroems.com  Blood supply The understanding of blood supply to the brain is important in localizing the vascular damage caused by stroke or any other obstruction leading to neuro- ophthlmological problems as they affect localized areas of the brain unless it involves the main arteries. Some of the branches penetrate directly the visual cortex whereas few forms a network in pia mater and then into the cortex.  Feedback Direct feedback projections to V1 originate from: V2, V3, V4, V5 or Mid Temporal (MT), Frontal eye field-FEF and infero-temporal cortex to what we know so far there might be more areas. Direct feedback projections from V1 extend to Superior colliculus (SC), LGNd, pulvinar, and pons- major being the dLGN. In this lecture we have mainly covered only feedforward connections to V1 from the LGN.  Reading resources ~Webvision-http://webvision.med.utah.edu ~Visual neuroscience by Chalupa