Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Functional specialization Phrenology Franz Joseph Gall (1757-1828) from Webster’s Academic Dictionary, 1895 Macaque visual areas Flattening the brain Human visual cortical areas IPS2 IPS1 V7 V3A/B V2 IPS2 IPS1 V7 V2 LO2 LO1 MT V1 V3 V4 V3 V3A/B LO1 LO2 MT V4 Functional specialization Match each cortical area to its corresponding function: V1 V2 V3 V3A V3B V4 V5 V7 LO1 IPS1 IPS2 Etc. Motion Stereo Color Texture Segmentation, grouping Recognition Attention Working memory Mental imagery Decision-making Sensorimotor integration Etc. Defining visual cortical areas PhACT Physiology Architecture Connections Physiology Example: direction selectivity in V1 Cytoarchitecture: Brodmann’s areas Korbinian Brodmann (1868-1918) ~50 cytoarchitectural areas defined by cell size, cell density, number of layers, density of myelinated axons. Topography Different stains for different features Golgi stain: small fraction of cell bodies and dendrites Nissel stain: only cell bodies Weigert myelin stain for axons Cortical layers Primary visual cortex slice (Nissl stain) Cytoarchitecture and function layer 4: input layer 5: output Motor cortex: expanded layer 5, reduced layer 4 Primary visual cortex: expanded layer 4 with three sublayers Brodmann areas and functional modalities Brodmann areas correspond coarsely to functional modalities Brodmann areas do not correspond exactly to functional areas Brodmann areas superimposed Functional areas in monkey brain Architecture V2: stripes V1: blobs/puffs MT: dense Example: cytochrome oxidase staining in human visual cortex Connections: white matter bundles Superior longitudinal (arcuate): connects language centers (Broca’s, Wernicke’s). Superior occipitofrontal: dorsal (where) visual pathway. Inferior occipitofrontal: ventral (what) visual pathway. Tracing connections with diffusion tensor imaging Low magnification Tracing connections High magnification Injection site in LGN (rat) Retrograde tracer (horseradish peroxidase) Retina Connections: laminar organization S: supragranular origin I: infragranular origin B: bilaminar origin (no more than 70%-30% split) F: layer 4 termination C: columnar termination (equal density in all layers) M: multilaminar termination (avoids layer 4) Connections: hierarchical organization of visual areas monkey visual cortex Hierarchical organization -$0 6)0 ,)0 -)0 $ 0 0)0 6 6 0/ -34 -4 &34 A 6 340P 340A #)4 !)4 6A 0)4 6 Line thickness represents a loose estimate of connection strength 6 / 4 Topography IPS2 IPS1 V7 V2 V3 V3A/B LO1 LO2 MT+ V4 Each visual brain area contains a map of the visual world and performs a different function. Retinotopy (human V1) Visual Disturbances Following Gunshot Wounds of the Cortical Visual Area Based on observations of the wounded in the recent Japanese wars German edition first published in 1909 Tatsuji Inouye (1880-1976) V1 retinotopy Upper VM HM Lower VM 80 V1 topography & magnification Cortical magnification Retinal image Cortical map Retinotopy (monkey V1) Cortical representation measured with 2-deoxy-glucose stimulus flattened left hemisphere 1 cm 2-deoxyglucose Tootell et al. (1988) Measuring human retinotopic maps non-invasively Radial component Angular component Retinotopy: radial component 1 cm 1 cm Human Monkey Retinotopy: angular component Human 1 cm 1 cm Monkey Visual areas Human 1 cm 1 cm Monkey Flattening the human brain fl act extr face l sur a c i t cor cu t at and te n Cortical segmentation & flattening Retinotopy: angular component dorsal V7 V3A/B V3d V2d medial LO1 LO2 MT lateral V1 V2v V3v V4 ventral Human visual cortical areas IPS2 IPS1 V7 V3A/B V2 IPS2 IPS1 V1 V7 V2 LO2 LO1 MT V3 V4 V3 V3A/B LO1 LO2 MT V4 Monkey visual areas from fMRI V1 V2 V3 V3A V4 MT Topography: columnar architecture in V1 Retinotopic map Columnar architecture 1 mm Columnar architecture Perpendicular electrode penetration: same orientation preferences and ocular dominance. Surface Tangential electrode penetration: orientation preference and/or ocular dominance varies. White matter Ocular dominance columns Optical imaging apparatus Reference image Functional difference image Ocular dominance movie Orientation columns and pinwheels Human ocular dominance columns Amblyopia Columnar architecture in other visual cortical areas Fujita, Tanaka, Ito, Cheng, Nature (1992) Albright, Desimone, Gross, J Neurophysiol (1984) Direction columns in MT Functional specialization “Feature” columns in IT Parallel visual pathways Dorsal & ventral streams: what vs. where Normal observer’s brain Dorsal & ventral streams: action vs. perception Lateral Occipital area (area LO) activation DF’s brain area LO lesion Intact Line Drawings versus scrambled Each image presented for 4 s with 12-s ISI Control DF Increasing receptive field size Increasingly complex selectivity STS MST MT V3A V3 V2 MT Increasing invariance MST STS