The third type, the koniocellular-projecting (K) cells , only relatively lately became a focus of attention and their function Lapatinib clinical trial is as yet poorly understood. The studies of Kuffler  pointed out that retinal ganglion cells depict the visual space in a concentric ��on�� and ��off�� manner. Although these studies were not carried out in primates, since then it has been established that the same principle stands for primates as well . An ��on�� zone is defined as the part of the receptive field, which upon stimulation with a suddenly appearing light stimulus, evokes an excitatory response (spike train) in the given cell. An ��off�� zone evokes the same response upon the disappearance of that stimulus.
The direction- and motion-sensitivity of retinal cells were first described by Barlow and Levick  registering the electrical activity of ganglion cells extracellularly.Pathways Inhibitors,Modulators,Libraries originating in retinal ganglion Inhibitors,Modulators,Libraries cells project on the lateral geniculate nucleus (LGN) of the diencephalon, traditionally Inhibitors,Modulators,Libraries considered to be part of the thalamus, while applying more strict anatomical criteria it is part of the metathalamus . As discussed later, in connection with tectal pathways, retinal ganglion cells also project upon the superficial layers of the superior colliculus (SC, optic tectum in lower vertebrates) as monosynaptic afferents. The lateral geniculate body of primates consists of six layers. The concentric on/off receptive field arrangement is to be found here as well. That these cells should be directionally sensitive is quite unlikely, however, they may serve as input to higher order cells exhibiting that sort of sensitivity.
Which LGN cells have a role in movement detection remains an open question. The four dorsal layers comprise the neurons of the parvocellular system. These neurons are color-sensitive, while they exhibit no special sensitivity to luminance Inhibitors,Modulators,Libraries modulation, that is, their contrast-sensitivity is low. The remaining two layers belong to the magnocellular system. Cells here respond to a wide spectrum of light, and they exhibit no color opponency. Cells receiving wide-spectrum chromatic input are highly contrast sensitive . Isoluminant chromatic stimuli have but little effect on motion sensation , which does not support the role of the parvocellular layers in motion perception. Figure/background segmentation in these layers is poor too .
Therefore, the magnocellular cells of LGN layers 5 and 6 are more likely candidates. These cells primarily Carfilzomib respond to transient stimuli.In primates, LGN projects upon V1, the primary selleck chem Perifosine visual cortex. Parvocellular and magnocellular systems bifurcate in V1, where (in primates) directional sensitivity first appears, in the cells of cortical layer 4C . From here, motion information is transmitted toward the dorsal stream, via layers 4B and 6.