Neurociencia

Cognitive Neuroscience 1/26/12

Visual System
Retino-geniculate Pathway (90% of optic nerve): optic nerve goes from retina to lateral geniculate nucleus
• In retina there are rodsand cones (photoreceptors) that translate light into action potentials
• Info from retina to LGN; division between right and left visual fields (everything in your left visual field ends up on righthalf of your brain in the right LGN and vice versa)
• Each LGN gets info from one temporal and one nasal hemi-retina.
• Along optic radiation, projected to primary visual cortex (V1, BA 17, striatecortex)
o Left visual field ends up in right hemisphere
o Left and right eye stay separate (ocular dominance columns)
o Retinotopy: keep things separated based on where they are on the retina
oOrientation selectivity: we construct the visual world based on several tiny lines.
Mechanisms for Edge-Detection
• Rods and cones give information to ganglion cells, translate light into actionpotentials either by telling a ganglion cell there is light on me you should fire (excitatory), or there is light so you shouldn’t fire (inhibitory)
• On-Center and Off-Center Ganglion cells. All cellsare looking for light, they only respond to light.
• Increasing size of receptive field from ganglion cells to LGN cells (because LGN receive input from multiple ganglions)
• Cells in V1 areselected based on the orientation of lines.
• LGN cells work to pick up points; V1 cells work to connect lines
• Ocular dominance columns: strips of cortex in V1 just responsible for input from one ofthe eyes
• Within each ocular dominance column, there are perpendicular smaller columns that are responsive to orientation of lines, responsive to different line orientations.
• Blobs are responsiblefor responsive for color, information from cones ends up in blobs which are in the ocular dominance columns.
• Beyond Primary Visual Cortex
o Organizational Principle: higher-level visual areas...