Task 4 on columns and pathways Flashcards
Lateral Geniculate Nucleus
o The axons of retinal ganglion cell synapses in the two LGNs, one in each cerebral hemisphere
o Important for connections on the way to the brain, so it can modulate input from the eyes
Organisation of LGN
The left LGN receives input from the left side of both eyes ad the right LGN receives input from the right site of both eyes, second each layer of the LGNs receive from one or the other eye
Layers 1, 4, and 6 of the right LGN receive input from the left eye (contralateral=referring to the opposite site of the body)
Layers 2, 3, and 5 of the right LGN receive input from the right eye, ipsilateral
Topographical mapping/Retinal topic map
The right side of the world falls on the left side of the retina, whose ganglion cells project it to the right. Cells that are close to each other in the LGN are close to each other in the Visual cortex
o Six layered structure
Magnocellular layers
(bottom two layers), large, receive input from M ganglion cells in the retina
• Respond to large, fast-moving objects
Parvocellular layers
(top four layers), small, receive input from the P ganglion cells in the retina
• Responsible for processing details of stationary objects
Koniocellular cell
A neuron located between the magnocellular and the parvocellular layers, involved in different aspects of processing
The striate Cortex
(primary visual cortex) receives direct input from the LGN, as well as the feedback from other brain areas
Consists of 6 major layers, some of which have sublayers, LGN projects mainly but not exclusively to the 4th layer, with magnocellular axons coming in to the upper part of Layer 4c (known as 4cα) and pavorcellular axons project to the lower part of layer 4c (known as 4cβ)
Cortical magnification
The amount of cortical area devoted to a specific region in the optical field (fovea is dedicated to a bigger part in the striate cortex than the periphery
Receptive fields in the striate cortex
respond more to bares, line, edges than to round spots
Orientational tuning
The tendency of neurons in the striate cortex to respond optimally to certain orientations and less to others, more response to horizontal and vertical targets
Ocular dominance
the property of the receptive fields int the striate cortex that they respond more rapidly to stimuli in the one eye than in the other eye
Simple cells
A cortical neuron whose receptive fields have a clearly defined excitatory and inhibitory region
Edge detector: is most highly exited when there is light on one site and darkness on the other site
Stripe detectors: reacts best to light that has a particular width, surrounded with darkness on both sides
Complex cells
A cortical neuron whose receptive fields does not have clearly defined excitatory and inhibitory regions, it will respond regardless where the stripe is presented
End stopping
The process by which a cell in the cortex first increase firing as the bar length increases to fill up it receptive field. And then decreases when the bar goes further than the receptive field
Important to detect luminance boundaries and discontinuities, responds more when contrast is higher
Column
: A vertical arrangement of neurons. Neurons within a single column tend to have similar receptor fields and similar orientation preferences, arises as a consequence of statistical wiring mechanisms combined with evenly spread mosaics of On and Off centre retinal ganglion cells
Hypercolumn
A 1-mm block of striate cortex containing two sets of columns, each covering every possible orientation (0-180 degrees) with one set preferring input from the right eye and one set preferring input from the left eye
Retinal topic map
Cells that are close to each other in the LGN are close to each other in the Visual cortex
Ventral pathway
(what pathway) from the striate cortex to the temporal lobe
o Responsible for determining an objects identity
o Neurons with high-resolution selectivity & sensitivity to form, pattern & colour
o Some cells respond selectively to faces, to hands … and ignore change in detail after optical & viewpoint transformation (can’t generalise recognition across viewing conditions)
Dorsal pathway
(where/how pathway) from striate cortex to the parietal lobe, how to direct action/movement
o Strongly linked with the premotor regions in frontal cortex
o Form information: from V3 and or V4, both of which project to MT (V5)
o Motion information: inputs pass through MT and MST, both of which contain cells selective for object motion in different directions (including rotation in motion in depth)
o Receives movement information from the magnocellular cells
Optic ataxia
damage to the posterior parietal region results in difficulties in accurate reaching toward objects but not in recognition-problems (dorsal pathway)
Visual agnosia
damage in occipitotemporal regions that causes inability to recognise/ describe common objects although they can easily navigate through the everyday world (ventral pathway)
o Scale grip to dimensions of the objects that were about to be picked up even though they can’t “perceive” those dimensions
Fusiform face area (FFA)
specialised to respond to faces
Inferior temporal cortex
Parahippocampal place area (PPA)
specialised for places & spatial layout
Inferior temporal cortex
Extrastriate body area (EBA)
specialised for (parts of) bodies Inferior temporal cortex
