Question

Explain how lateral inhibition works and how it can explain the simple Provide an overview of the basic organization of the visual system from the eye up to the primary visual cortex. Include the three layers of neurons in the retina, circular receptive fields, the lateral geniculate, ocular dominance columns, and simple + complex cells. effect. Include a discussion of brightness effects that are unlikely to be due to lateral inhibition.

Answer 1

Lateral inhibiton is a process whereby application of stimulus to the center of the receptive field excites a neuron, but a stimulus applied near the edge inhibits it, lateral inhibiton increases contrast between strong and weak signals.The primary afferent fiber, whose receptive field is closest to the point of stimulation will produce more action potential then those on the periphery.
Ganglion cells are the first neurons in the retina that respond with action potential , there are two primary types of ganglion cell receptor fields, each receptive field is arranged into a central disk, the center and a concentric ring, the surround, each region responds oppositely to light, light in the center might increase the firing of a particular ganglion cell, where as light on the surround would decrease the firing of that cell, stimulation of the center of an On-center cells receptive field produces depolarization and increases the firing of the ganglion cell, but the stimulation of the surround produces hyperpolarization and decrease in the firing of ganglion cell and stimulation of both center and surround produces only a mild response, in contrast an Off- center cell is stimulated by the activation of the surround and inhibited by stimulation of the center.The center surround receptor field aoganization allows ganglion cells mainly allows transmit information about contrast.

For vison to happen the eye must first form a image on the retina, light energy striking the retina are converted into nerve impulses by photo receptor cells, this process does not start in the brain but in the retina itself and this is than transmitted via the 2nd cranial nerve, the optic nerve, from here the signal is conducted through the geniculate pathway to the occipetal lobe for conscious visual procesing. The visual cortex is subdivided into number of seperate region called visual cortical area, among these the primary visual cortex located on the medial occipetal lobe of the brain is the most important, because LGN send most of the axons there, so this area is the first visual processing area in the cortex this process information arriving from the LGN and passes the output to other visual cortex area. There are three diffrent type of neurons that can be distingushed based on how they respond to visual stimuli, they are called simple cell, complex cells and hyper complex cells. Most neurons of primary visual cortex are orientation selective meaning they respond strongly to lines, bars or edges of particular orientation, but they do not respond to orthogonal orientation ( eg, horrizontak), some neurons of primary visual cortex are direction selective meaning they respond strongly to oriental lines, bars edges moving in a preferd direction eg, vertical lines moving to the right but not vertical lines moving to the left. Simple cells repond best to elongated bar or edges, they are orientation selective, they have separate On and Off subregion.Complex cells are orientation selective, but they have no On and Off subregion. Hyper complex cell respond best to short bar.