PSyc 6 10/5/16
Popular in Introduction to Neuroscience
Popular in Psychology (PSYC)
This 5 page Class Notes was uploaded by Sabrina Straus on Wednesday October 5, 2016. The Class Notes belongs to PSYC 6 at Dartmouth College taught by Catherine Cramer in Fall 2016. Since its upload, it has received 2 views. For similar materials see Introduction to Neuroscience in Psychology (PSYC) at Dartmouth College.
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Date Created: 10/05/16
5. 10-4-16 Intro to Neuro class notes Vision II: Central Processing I. Visual pathways Nasal decussates and temporal does not } decussation is based on visual field Overlap helps with binocular vision A. Primary visual pathway optic nerve -> chiasm -> tract lateral geniculate nucleus (of the thalamus) occipital cortex B. Pretectal pathway C. Tectal pathway: branch off and go to midbrain/ reflect evolutionary history+allows you to adjust the lens superior colliculus II. Laminar arrangement of the lateral geniculate } 6 layers Ipsilateral and contralateral layers Parvocelular P-type ganglion cells } outer layers } coding shape Magnocellular M-type ganglion cells } coding motion Koniocellular nonM-nonP ganglion cells } k1-k6 ventral to each principal layer } coding color Blob pathway III. Initial cortical processing A. Recordings from V1 (aka primary visual cortex) layer 4 pyramidal cells} 1st place visual info gets to cortex Light stimulus: bar that produces maximum firing simple cells: most responsive to a vertical bar of light complex cells: sensitive to orientation and movement and direction B. Functional organization V1 occular dominance columns: dominant to one eye orientation columns: diagonal bar in square receptive field } along a different axis C. Hierarchical model } things add up done by cortical cell ganglion cells -> simple cells -> complex cells hypercomplex cells: sensitive to 2 lines in a particular direction and orientation "grandmother" cells?: higher order cell that is used for a complex but specific time of stimulus } challenging flaw allow you to build an image based on lines IV. Visual cortex beyond V1: initial processing A. Functions of extrastriate cortex (aka secondary visual cortex) V2- contours filling in image V4 - gratings and "swirling" stimuli, color IT - objects (inferior temporal) } neurons form columns in temporal lobe that respond to categories of shapes V5 - motion B. A working hypothesis: two general streams of information 1. ventral stream into the temporal lobe (V1 -> V2 -> V4 -> IT) recognition of objects 2. dorsal stream into the parietal lobe (V1 -> V5) } movement and location visually-guided action based on their characteristics Chapter Notes Chapter 10: Central Visual System ~retina extracts info about differences in brightness and color ~pathway serving conscious visual perception: lateral geniculate nucleus and primary visual cortex (striate cortex) -Retinofugal Projection ~neural pathway that leaves the eye beginning w/ optic nerve ● Optic nerve, chiasm, and tract ○ Optic nerve: exit left and right eyes at optic disks->fatty tissue->skull-> combine to form chiasm ○ Chiasm: axons originating in the nasal retinas cross from one side to the other -> optic tracts ○ Decussation: crossing of a fiber bundle from one side of the brain to the other ● Right and left visual hemifields: ○ Visual hemifield: divided left and right by midline ○ Binocular visual field: portion viewed by both retinas ● Targets of optic tract: some form synaptic connections in hypothalamus or midbrain but most innervate the lateral geniculate nucleus ○ LGN: has axons that project to the primary visual cortex } optic radiation ○ Tract: opposite sides ○ Nerve: same sides ○ Non Thalamic targets of the optic tract: ■ Pretectum: direct projections to midbrain to control the size of pupil ■ Superior colliculus: some ganglion cells project to this part of midbrain tectum (called optic tectum for vertebrate groups) } projection = retinotectal projection ● Involved in orienting the eyes esp fovea w/ cones -lateral geniculate nucleus (in dorsal thalamus and targets of optic tracts) ~6 layers of LGN } bend around optic tract ● Segregation of input by eye and ganglion cell type ○ LGN receive from ganglion and project to primary visual cortex thru radiation ○ Different types of info in each of the 6 layers ○ LGN: contralateral ○ Magnocellular LGN layers: ventral ■ M type ○ Parvocellular LGN layers: dorsal ■ Only Ptype ○ Koniocellular: has tiny neurons ● Receptive fields ○ Magnocellular: large field and burst of AP + insensitive to different wavelengths ○ Parvocellular: small fields and sustained increase of AP + color opponency ○ Koniocellular: light/dark or color opponency ● Nonretinal inputs to LGN: LGN receives inputs from retina, thalamus, and brain stem ○ Major input is from primary visual cortex -Anatomy of the striate cortex ~main target: primary visual cortex (Brodmann’s area 17 }occipital lobe) / V1 / striate cortex ● Retinotopic:organization whereby neighboring cells in the retina feed info to neighboring places in their target structures (LGN) ○ Mapping of visual field onto retinotopically organized structure is distorted bc visual space isn’t sampled uniformly (more in fovea) ○ A discrete point of light can activate many cells in retina ○ Perception is based on the brain’s interpretation of distributed patterns of activity ● Lamination of striate cortex ○ Layer I:devoid of neurons and consists almost entirely of axons and dendrites ○ Different layers of cells ■ Spiny stellate cells: small neurons w/ spine dendrites ■ Pyramidal cells: characterized by single thick apical dendrite that branches as it ascends toward the pia mater and by basal dendrites that extend horizontally ● Send axons out to connect to other parts of the brain ■ Inhibitory neurons ● Inputs and outputs of striate cortex: ○ Axons from LGN terminate in IVC mostly ○ Innervation of other cortical layers from layer IVC: perpendicular ○ Ocular dominance columns:layer IVC projects axons radially (info from both eyes begin to mix) } bands of cells extending through the thickness of the striate cortex ○ Striate cortex outputs ■ pyramidal-> white matter ■ 2,3,4 ->coritcal areas ■ 5->superior colliculus+pons ■ 6->back to LGN ● Cytochrome oxidase blobs: mitochondrial enzyme used for cell metabolism ○ Form pilars ○ 2+3:visual processing -physiology of the striate cortex ● Receptive fields ○ IVCa: neurons are insensitive to wavelength ○ IVCB: center-surround color opponency ○ Binocularity: monocular neurons in IV layer receive afferents afferents from LGN ■ Two receptive fields one in the ipsilateral eye and one in the contralateral eye ○ Orientation selectivity } help w/ analysis of object shape ■ Bars perpendicular to optimal orientation generate a weaker response ■ Orientation column ○ Direction selectivity: respond when bar of light moves in one direction (subset of the cells that are orientation selective)} help w/ analysis of object motion ○ Simple and complex receptive fields ■ Binocular: neurons receive afferents from both eyes ■ Orientation-selective: have receptive field elongated along an axis w/ on and off region and an antagonistic surround ■ Simple cell: cortical neurons receive a converging input from LGN cells with receptive fields that are aligned along one axis } segregation of On and Off regions ■ Complex cells: no distinct On Off regions ■ Blob receptive fields: input from koniocellular LGN and magno/prarvo cellular IVC ● Wavelength sensitive ● Monocular ● Lack orientation and direction selectivity ■ Double opponent: color center and color surround ● Parallel pathways and cortical modules ○ Parallel pathways } mix and receptive field properties are not unique ■ Magnocellular pathway: begins w/ M-type ganglion cells of retina} send axons to magnocellular layers of LGN -> IVCa -> IVB ● Analysis of motion and guidance of motor actions ■ Parvo-interblob pathway: P-type-> parvocellular layers-> IVCa-> layer 2 and 3 interblob regions ● Analysis of shape ■ Blob pathway: receives input from nonM-nonP -> koniocellular-> cytochrome oxidase blobs layers 2 and 3 ● Analysis of color ~toward parietal lobe: motion ~toward temporal lobe: color ○ Cortical modules: necessary to see but sufficient enough to analyze that particular point -Beyond the striate cortex ~V1: first area to receive info from the LGN ~extrastriate areas: beyond V1 } large-scale cortical streams of visual processing >dorsal stream: visual motion and action >ventral stream:perception and processing streams ● Dorsal stream ○ Area MT: V5} specialized processing of motion} large receptive fields that respond to movement & direction selective ○ Dorsal areas and motion processing ■ Medial superior temporal: cells selective for linear motion, radial motion, and circular motion ■ Roles: 1. Navigation 2. Directing eye movements 3. Motion perception ● Ventral stream ○ Area V4: receives input from blob and interblob regions ■ Neurons have large receptive fields ■ Orientation & color selective -> shape + color ○ Area IT: output goes to temporal lobe parts involving learning and memory ■ Esp faces -single neurons->perception ~perception: task of identifying and assigning meaning to objects in space ● Receptive field hierarchy + perception\ ○ Patches on retina->photoreceptors v. center-surround->retinal ganglion ○ Facial recognition} grandmother cells } against the idea that perception is based on selective receptive fields ● Parallel processing and perception
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