Lateral geniculate nucleus
The lateral geniculate nucleus is a relay centre on the visual pathway from the eyeball to the brain. It receives sensory input from the retina via the axons of ganglion cells.
The thalamus which houses the lateral geniculate nucleus is a small structure within the brain, located just above the brain stem between the cerebral cortex and the midbrain with extensive nerve connections to both.
The lateral geniculate nucleus is the central connection for the optic nerve to the occipital lobe of the brain, particularly the primary visual cortex.
Both the left and right hemispheres of the brain have a lateral geniculate nucleus.
There are three major cell types in the lateral geniculate nucleus which connect to three distinct types of ganglion cells:
- P ganglion cells send axons to the parvocellular layer of the lateral geniculate nucleus.
- M ganglion cells send axons to the magnocellular layer.
- K ganglion cells send axons to a koniocellular layer.
The lateral geniculate nucleus specialises in calculations based on the information it receives from both the eyes and from the brain. Calculations include resolving temporal and spatial correlations between different inputs. This means that things can be organised in terms of the sequence of events over time and the spatial relationship of things within the overall field of view.
Some of the correlations deal with signals received from one eye but not the other. Some deal with the left and right semi-fields of view captured by both eyes. As a result, they help to produce a three-dimensional representation of the field of view of an observer.
- The outputs of the lateral geniculate nucleus serve several functions. Some are directed towards the eyes, others are directed towards the brain.
- A signal is provided to control the vergence of the two eyes so they converge at the principal plane of interest in object-space at any particular moment.
- Computations within the lateral geniculate nucleus determine the position of every major element in object-space relative to the observer. The motion of the eyes enables a larger stereoscopic mapping of the visual field to be achieved.
- A tag is provided for each major element in the central field of view of object-space. The accumulated tags are attached to the features in the merged visual fields and are forwarded to the primary visual cortex.
- Another tag is provided for each major element in the visual field describing the velocity of the major elements based on changes in position over time. The velocity tags (particularly those associated with the peripheral field of view) are also used to determine the direction the organism is moving relative to object-space.