Lateral geniculate nucleus - Research Paper Example

? Lateral geniculate nucleus The lateral geniculate nucleus is transmission center for visual data that is received from the retina. It happens to both eyes and it takes place in the hemisphere of the brain (Goodale and Milner, 2005). In relation to the following definition, this paper will cover the historical view of the system, based on research and followed by the findings compared to how the system is viewed in the modern world. There have been arguments based on the findings, for example arguments on whether the lateral geniculate nucleus has layers, and if it really has, then how many layers are there and does the number of layers affect the specific species that is being researched? The most important aspect, therefore, is to understand what lateral geniculate nucleus is, how its findings have evolved examples of species sampled and the actual findings in the difference between the historic view and modern view. Lateral Geniculate Nucleus Studies carried out show that in nonhuman primates visual deprivation commencing at different ages have different effects on cells in the magnocellular and pervocellular laminae of the lateral geniculate nucleus (LGN). According to Goodale and Milner (2005), lateral geniculate nucleus is a primary system where visual information is sent to the eye from the retina. All this activity happens in the hemisphere of the brain. The LGN acts as the site where ganglion cell axons synapse with neurons which in turn form optic radiations. The visual pathways are mainly described by ophthalmoscopic findings, distinct papillary and visual fields. Such findings make it possible and easy for a person to understand and locate the accurate area where the visual pathway is (Fulton, 2004). Within the LGN there is the thalamus which plays an important role in deciding the sensory information that is transmitted to the cortex. It assists in the encoding the receptive fields which carry out more advanced duties like orientation and direction selectivity. It is important to note that there have been recent findings that have shown that there are other set of retinal ganglion cells projected to the Lateral geniculate nucleus. The LGN of a human and old primate contains six layers, these layers are numbered from number one to six ventrally. There are other primates which have two pairs of a LGN with two layers of pervocellular, whereby one layer receiving information from ipsilateral eye and the other receives retinal input from contra lateral eye. Magnocellular layers are numbers 1 and 2, then number 3 to number 6 we get the parvocellular layers (Heckenlively and Arden, 2006). The retinal ganglions are the LGN receptive field properties; they are determined by their imputs. Magnocellular are much bigger compared to the pervocellular. Their main function is to process visual information related to low spatial frequencies, high temporal frequencies, low contrast and luminance (Heckenlively and Arden, 2006). Manocellular are fast in conducting information, it is through optic radiations that they are capable of receiving information which they get from parasol cells. After receiving the information it is edited by the visual cortex, magnocellular transmit mainly parietal cortices where there is the dorsal cortex. They opt to operate fast without concern for the detail transmitted. On the other hand, pervocellular is concerned with the processing of visual information concerned with high contrast, color, low temporal frequencies and high spatial frequencies. It is believed that as evolution took place, the pervocellular continued developing more than the magnocellular. There are midget cells that transmit input to the parvocellular, the midget cells are a type of retinal ganglion cells whose axons leaving the optic tract. The transmissions take place in one of the four dorsal parvocellular layers of the LGN. The separation of information that goes to the different eyes is done at this point, which later continues in the visual cortex. The pervocellular are more accurate when it comes to color and they are more detailed compared to magnocellular (Goodale and Milner, 2005). In an experiment where color was used to see the difference between the functions of the pervocellular and magnocellular functions, in relation to amblyopic eyes, with differences in age, it was found that color and luminance were lower in the amblyopic eyes unlike in their counterparts the amblyopes. Luminance is being low was due to the reduction in the sensitivity of the amblyopic eye and an increase to the amblyopes due to increase in sensitivity. There was reduction in color too and after comparing the reduction in color to the luminance it was found that the reduction was much greater in eyes with late rather than early onset (Fulton, 2004). The patterns of cell size changes in magnocellular and pervocellular of a non human differ showing the differences in sensitivity between an early and later set which proves the changes that take place in the pathway considering the two periods that marked the development in sensitivity. A possible explanation to the difference in the pathway between the magnocellular and the pervocellular is that the magnocellular pathways continued to mature and lost their plasticity earlier compared to the pervocellular. It is important to note that the pervocellular has a peak in sensitivity at the age of 6 months and 9 months. It can be related to the increase in sensitivity between the ages that are equal to early and late onset groups. In conclusion it is evident that there has been continuous development in the magnocellular and pervocellular laminae of the lateral geniculate nucleus from the ancient time to modern times. The lateral geniculate nucleus has six layers that are divided into the magnocellular and the pervocelluar lamniae. The two have different functions as the magnocellular works faster than the pervocellular while the pervocellular is more detailed in its functions than the magnocellular. In comparison the magnocellular are larger than the pervocellular, but the pervocellular are more modern compared to the magnocellular. As human being and animal undergo change in the environment and life, change takes place in all parts of the human body, with slight changes in the eye of a person, there is a definite change in the way transmission of information across the eye as an organ is done. The two key components of information transformation have developed separately in time. However, the pervocellular has been faster in its development than the magnocellular. We have seen the difference in functions between the pervocellular and the magnocellular, and as much as the functions should be consistent with change, the magnocellular and the pervocellular can fail to carry out their functions. This faillure can affect the visual transmission of information across the human and animal eye. The functions of the two are differently affected in relation to the amblyopic and fellow eyes. There is a significant difference however in the late onset than in the early onset. References Heckenlively, R. and Geofrey, B. (2006). Principles and Practice of clinical Electrophysiology of vision.. Cambridge: The MIT press Fulton, J. (2004) Processes in Biological Vision. Vision Concepts 1(949) p.759-0630. Goodale, M. & Milner, D. (2004) Sight unseen.Oxford University Press, Inc.: New York. Read More