Effects Of Adaptation On The Response Property Of LGN Cells In Cats

Visual system will produce a self-calibration mechanism in a continuous work, and such a self-calibration mechanism will allow the visual system adapt to the dominated statistics component of the signal input. Adaptation is a common phenomenon in visual system. Since the adaptation phenomenon has been found, it has been studied comprehensively in psychophysics and physiology. Adaptation is of interesting for two reasons: one is that adaptation occurs rapidly enough to contribute to real time sensory information processing; another is that adaptation is a useful tool for studying the plasticity of normal issues. Therefore,adaptation is known as the electrode or probe of psychophysicist.In physiology, the adaptation phenomenon has been found at all levels of visual system. At first, adaptation studying focuses on the primary visual cortex. With the study going on, the adaptation phenomenon has gradually been found in retina, LGN and the advanced visual cortex.In perception, adaptation could bring about various after-effects. For physiology, one task of study is to find the physiological basis of these after-effects and the site of its occurring. Orientation adaptation is thought to be the physiological substrate of the well-known tilt after-effect (TAE). In primary cortex of cat, the observation of the repulsive shift of orientation preference after orientation adaptation leads to the view that the TAE originates from the V1.The LGN is often thought of as a passive relay of visual information to the cortex. However, recent studies have demonstrated that the LGN could play an important role as an early"gatekeeper"for controlling the gain of attentional responses and visual awareness. This suggested that LGN is not only a passive relay of visual information transmitting. Therefore, we studied the effects of adaptation on the responses properties of LGN cells, which include the effects of orientation adaptation on the responses properties of LGN cells with high orientation bias in cats and contrast adaptation has different effects on X and Y cells of the lateral geniculate nucleus.1. The effects of orientation adaptation on the responses properties of LGN cells with high orientation bias in catsAdaptation to stimulus orientation is assumed to have a cortical basis, but few studies have addressed whether it affects the activity of subcortical neurons. Previous studies demonstrated that some LGN neurons exhibited an orientation bias and also showed adaptation phenomena. In the light of these studies, it seems that orientation adaptation could have specific effects on the activities of LGN neurons with high orientation bias.In the central visual system, the properties of neurons at each stage are modulated by feedback from higher structures. For cats and primates, retinal afferents comprise 10% of the inputs to LGN relay cells, whereas corticofugal feedback comprises 30% of their inputs. Previous studies have shown that cortical feedback influences the spatial structure and centre-surround interaction of LGN receptive fields, controls temporal synchronization of LGN spiking activity. Thus, it is possible that corticogeniculate feedback contributes to the orientation adaptation of LGN neurons.Using single-unit recording and inactivating cortex by freezing, we studied the effects of orientation adaptation on the responses of lateral geniculate nucleus (LGN) neurons with high orientation bias in anesthetized and paralyzed cats under with feedback or without feedback condition. Following adaptation to one stimulus orientation, the response at the adapting orientation was decreased and the preferred orientation was shifted away from the adapting orientation. This phenomenon was similar to the effects observed for orientation adaptation in the primary visual cortex, and was obvious when the adapting orientation was at an appropriate location relative to the original preferred orientation. Moreover, when the primary visual cortex was inactivated, the response at the adapting orientation was also decreased but the preferred orientation did not show a systematic shift after orientation adaptation in LGN. This result indicates that cortical feedback contributes to the effect of orientation adaptation on LGN neurons, which have a high orientation bias. These data provide an example of how the corticothalamic loop modulates the processing of visual information, and suggest that the LGN is not only a simply passive relay but also a modulator of visual information.2. Contrast adaptation has different effects on X and Y cells of the lateral geniculate nucleusContrast adaptation is well known psychophysical phenomenon. When we stare at a high contrast stimulus for a time, our subsequent contrast sensitivity will decrease. Contrast adaptation provides two potential benefits: it may protect a cell from saturation by high contrast stimuli and it may ensure that the operating range of a cell spans only the range of contrasts contained in a particular image.In electrophysiology, Contrast adaptation first has been found in primary cortex of cat and primate, and early physiological studies has found little contrast adaptation in the LGN of cat or monkey. These results would place contrast adaptation strictly into early cortex. However, a slow contrast adaptation has been found in the retina of salamander, rabbit, and macaque, and furthermore a reevaluation of adaptation in cortical neurons has concluded that contrast adaptation occurs almost exclusively in that part of the visual pathway which is monocular. These finding suggest contrast adaptation could occur at the level of LGN.Solomon et al have found contrast adaptation affects most on the M cells and little on the P cells in the LGN of macaque. Recently Duong's results have also confirmed contrast adaptation phenomenon exists in LGN of cat from the other side. However, whether contrast adaptation has same effects on X and Y cells of lateral geniculate nucleus (LGN) of cat are not clear documented. Using single-unit recording, we here studied this issue in anesthetized and paralyzed cats. We found that contrast adaptation mostly shifted contrast gain of LGN cells, caused maximum response to change little, and increased the contrast detection threshold of LGN cells. Y cells express stronger contrast adaptation than X cells for contrast gain change. However, there was no significant difference between X and Y cells for the increase of contrast detection threshold. These results indicate contrast adaptation is separated to process by LGN cells and further provide an example of separate processing of visual information.