Question

Answer all fully please

What is an orientation column? An ocular dominance column? A Hypercolumn? Describe the information present in the Magno, Parvo, Non-m/Non-p (blob) ganglion cells from the retina. Describe the pathway of that information for each from the retina to extrastriate cortex?

Answer 1

Orientation coloum :-

Orientation columns are organized regions of neurons that are excited by visual line stimuli of varying angle.

Orientation columns are located in the primary visual cortex also known as the striate cortex.

The orientation columns are not cylindrical in shape as the word column implies but are flat slabs that are parallel to each other. The slabs are perpendicular to the surface of the visual cortex and are lined up similar to slices of bread. These neurons are highly discriminatory for visual orientations and their motion.

Ocular dominance coloum :-

Ocular dominance columns are stripes of neurons in the visual cortex of mammals including humans.

It isrespond preferentially to input from one eye or the other.The columns span multiple cortical layers, and are laid out in a striped pattern across the surface of the striate cortex (V1).

These stripes lie perpendicular to the orientation columns.

Ocular dominance columns were important in cortical plasticity, as it was found that monocular deprivation causes the columns to degrade, with the non-deprived eye assuming control of more of the cortical cells.

ocular dominance columns is important in binocular vision.

many squirrel monkeys either lack or partially lack ocular dominance columns, which would not be expected if they are useful.

Hypercoloum :-

A cortical column is called as hypercolumn,or cortical module.

It is a group of neurons in the cortex of the brain that can be successively penetrated by a probe inserted perpendicularly to the cortical surface, and which have nearly identical receptive fields.

Neurons within a minicolumn encode similar features, whereas a hypercolumn denotes a unit containing a full set of values for any given set of receptive field parameters.

Information present in Mango,Parvo ganglion cells from retina :-

The information generated by cone of photoreceptors in the retina is compressed and transferred to higher processing centers through two distinct types of ganglion cells known as magno, parvo cells.

These ganglion cells, which travel from the retina to the lateral geniculate nucleus (LGN) and then to the primary visual cortex, have different structural and functional characteristics, and are organized in distinct layers in the LGN and the primary visual cortex.

About 1 million retinal ganglion cells leave the retina as the optic nerve. About 80% of these cells are parvo type cells, and about 20% are magno cells.

The parvo and magno cells get their names from the layers of a nucleus in in the brain to which the majority of them project. Parvo cells project to the 4 dorsal (upper) parvocellular layers of the LGN. The magno cells go to the 2 ventral magnocellular layers of the LGN.

Magno cells are large, have thick axons and usually collect input from many retinal cells.

Parvo cells are smaller, with fine axons and less myelin than mango cells.

Magno cells respond rapidly to changing stimuli, while parvo cells need time to respond.

The distinct patterns of structure and function in these cells have provided an opportunity for clinical assessment of their function.

Functional assessment of these cells is currently used in the field of ophthalmology where frequency-doubling technology perimetry selectively assesses the function of magno cells.

Pathway of information from each Retina to the extrastriate cortex.

cornea and lens comes together to refract light into a small image and shine it on the retina. The retina transcribes this image into electrical pulses using rods and cones.

The optic nerve then carries these pulses through the optic canal. Upon reaching the optic chiasm the nerve fibers decussate (left becomes right). The fibers then branch and terminate in three place.

Most end in the lateral geniculate nucleus (LGN). Before the LGN forwards the pulses to V1 of the visual cortex (primary) it gauges the range of objects and tags every major object with a velocity tag. These tags predict object of movement.

The LGN also sends some fibers to V2 and V3.

In that V1 performs edge-detection to understand spatial organization initially, 40 milliseconds in, focusing on even small spatial and color changes. Then, 100 milliseconds in, upon receiving the translated LGN, V2, and V3 info, also begins focusing on global organization.

V2 forwards pulses to V1 and receives them. Pulvinar is responsible for saccade and visual attention.

V2 serves much the same function as V1, however, it also handles illusory contours, determining depth by comparing left and right pulses . and foreground distinguishment. V2 connects to V1 - V5.

V3 helps process direction and speed of objects. V3 connects to V1 ,V2, and the inferior temporal cortex.

V4 recognizes simple shapes, gets input from V1 (strong), V2, V3, LGN, and pulvinar.

V5’s outputs include V4 and its surrounding area, and eye-movement motor cortices

V5’s functionality is similar to that of the other V’s, however, it integrates local object motion into global motion on a complex level.

V6 works in conjunction with V5 on motion analysis. V5 analyzes self-motion, whereas V6 analyzes motion of objects relative to the background.

V6’s primary input is V1, with V5 additions. V6 houses the topographical map for vision. V6 outputs to the region directly around it . V6A has direct connections to arm-moving cortices, including the premotor cortex.

The inferior temporal gyrus recognizes complex shapes, objects, and faces or, in conjunction with the hippocampus, creates new memories.

The visual association cortex extends anteriorly from the extrastriate cortex to encompass adjacent areas of the posterior parietal lobe and much of the posterior temporal lobe . these areas receive visual input via the extrastriate cortex, which sends color, shape/form, location and motion information to different areas of the visual association cortex