Lateral geniculate nucleus

At its most fundamental level, the circadian cycle rests on the influence of so-called clock genes . These genes have been studied most extensively in insects but they have also been found in humans. Their protein products enter the cell nucleus and regulate their own transcription. This feedback process is linked to exposure to light and so it is not surprising that visual inputs are important for maintenance of circadian rhythms. However, it is not the reception of specific visual information, transmitted in the optic nerve to the lateral geniculate nucleus (LGN) and visual cortex (i.e. visual discrimination), that is responsible for the rhythm but the more simple, almost subconscious, reception of light. 

Figure 22.3 Possible links in the induction of circadian rhythm between daylight, the suprachiasmatic nucleus and melatonin release from the pineal gland. Some fibres in the optic nerve, projecting from the eye to the lateral geniculate nucleus (LGN) in the thalamus, innervate the suprachiasmatic nucleus (SCN) in the anterior hypothalamus, via the retinohypothalamic tract (RHT). Others project to the SCN from the LGN in the geniculohypothalamic tract (GHT). The release of melatonin into the circulation from the pineal gland (PG) is maximal at night and appears to be controlled partly by noradrenaline released from sympathetic nerves originating in the superior cervical ganglion (SCG). Melatonin receptors are found in the SCN, the removal of which dampens melatonin secretion...

The second cluster of neurons lies more caudally, near the pons, in the pedunculo-pontine (PPT) and laterodorsal tegmental (LDT) nuclei (see Fig. 22.6) and could be regarded as part of the ARAS (see McCormick 1992). It innervates the non-specific thalamic nuclei as well as some more specific ones like the lateral geniculate nucleus (visual pathway), the pontine reticular formation and occipital cortex. Because long... 

Albrecht D., Quaschling U., Zippel U., Davidowa H. (1996). Effects of dopamine on neurons of the lateral geniculate nucleus an iontophoretic study. Synapse. 23, 70-8. 

Govindaiah G., Cox C. (2006). Depression of retinogeniculate synaptic transmission by presynaptic D(2)-like dopamine receptors in rat lateral geniculate nucleus. Eur. J. Neurosci. 23, 423-34. 

C.K. Tong and M. Chesler, Activity-evoked extracellular pH shifts in slices of rat dorsal lateral geniculate nucleus. Brain Res. 815, 373-381 (1999). 

Uhlrich, D. J., Manning, K. A. and Xue, J. T. Effects of activation of the histaminergic tuberomammiUary nucleus on visual responses of neurons in the dorsal lateral geniculate nucleus. /. Neurosci. 22 1098-1107, 2002. 

The mechanisms of flashbacks are probably mixed. Some cases may be similar to post-traumatic stress disorder induced by a bad trip (Paton et al., 1973). Abraham (1983) suggested that some of the visual phenomena, such as trailing and after-images, were due to failure of inhibition in visual pathways, possibly mediated in the lateral geniculate nucleus which (in the macaque monkey) contains on-off colour neurons with receptor fields similar to those described in flashbacks. The neurochemical causes of such flashbacks, which can be very disturbing, remains elusive and attempts at treatment are usually ineffective. 

Upton AL, Ravary A, Salichon N, Moessner R, Lesch KP, Hen R, Seif 1, Gaspar P (2002) Lack of 5-HT(lB) receptor and of serotonin transporter have different effects on the segregation of retinal axons in the lateral geniculate nucleus compared to the superior colliculus. Neuroscience 111 597-610... 

Figure 2.9 Path from the retina to the visual cortex. On its way to the lateral geniculate nucleus, some axons cross at the optic chiasm. Information from the right half of the visual field is processed inside the left hemisphere of the brain. Information from the left half of the visual field is processed inside the right hemisphere. (Reproduced from Semir Zeki. A Vision of the Brain. Blackwell Science, Oxford, 1993, by permission of Blackwell Science, UK.)...

Figure 2.11 A simple cell responds to lines or edges oriented at a particular orientation. It may be constructed by receiving input from several of the center-surround neurons found in the lateral geniculate nucleus. (Reproduced from D. H. Hubei and T. N. Wiesel. Receptive fields, binocular interaction and functional architecture in the cat s visual cortex. Journal of Physiology, Vol. 160, pp. 106-154, 1962, by permission of Blackwell Publishing, UK.)...

De Valois RL and Pease PL 1971 Contours and contrast responses of monkey lateral geniculate nucleus cells to luminance and color figures. Science 171, 694-696. 

Davidson C, Stamford JA. Serotonin efflux in the rat ventral lateral geniculate nucleus assessed by fast cyclic voltammetry is modulated by 5-HT1B and 5-HTm autoreceptors. Neuropharmacology 1996 35 1627-1634. 

Heggelund P, Hartveit E. 1990. Neurotransmitter receptors mediating excitatory input to cells in the cat lateral geniculate nucleus. I Lagged cells. J Neurophysiol 63 1347-1360. 

Kwon YH, Esguerra M, Sur M. 1991. NMDA and non-NMDA receptors mediate visual responses of neurons in the cat s lateral geniculate nucleus. J Neurophysiol 66 414-428. 

List of Abbreviations ISI, interstimulus interval LGN, lateral geniculate nucleus M, magnocellular MST, medial superior temporal area MT, medial temporal area NMDA, N-methyl-D-aspartate P, parvocellular ssVEP, steady-state visual evoked potential TE, temporal lobe TEO, temporal occipital area tVEP, transient visual evoked potential YEP, visual evoked potential VI, primary visual cortex... 

Kwon YH, Nelson SB, Toth LJ, Sur M. 1992. Effect of stimulus contrast and size on NMDA receptor activity in cat lateral geniculate nucleus. J Neurophysiol 68 182-196. 

Selemon LD, Begovic A. 2007. Stereologic analysis of the lateral geniculate nucleus of the thalamus in normal and schizophrenic subjects. Psychiatry Res 151 1-10. 

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