Visual Pathway Overview and Decussation

The point where nerve fibers from each eye cross over to project to the opposite hemisphere of the brain.

The pathway that carries visual information from the eye to the brain.

The part of the thalamus that receives visual input from the optic tract.

A map of the retina onto the LGN, where adjacent areas of the retina are represented in adjacent regions of the LGN.

The crossing of nerve fibers, particularly in the optic chiasm, which ensures that the right hemisphere of the brain processes visual information from the left visual field, and vice versa.

The layers of the Lateral Geniculate Nucleus which receive input from magnocellular cells. Magnocellular cells are bigger.

The layers of the Lateral Geniculate Nucleus which receive input from parvocellular cells, smaller cells.

The way the visual field is divided. The right visual field is processed inthe left hemisphere and vice versa.

Cells in the visual cortex that are specifically activated by the motion of a stimulus in one direction, but not the opposite direction.

A column of cells in the visual cortex where all cells share the same orientation preference and ocular dominance preference.

A group of adjacent orientation columns, covering all possible orientations and both eyes. Each hypercolumn contains the neural machinery to analyze different aspects of a visual stimulus, such as size, orientation, color, and motion direction.

A layer of the visual cortex characterized by a dense arrangement of neuron columns, each column containing cells with similar properties. This arrangement ensures efficient communication and processing of visual information.

The arrangement of orientation columns and hypercolumns within the visual cortex. It allows for efficient processing of visual information, including size, orientation, color, and motion direction.

LGN cells receive input from retinal ganglion cells (RGCs) and have circular receptive fields with a center-surround configuration. These fields respond to light and dark contrast, with two opposing types: "ON" cells that fire when light hits the center of their field, and "OFF" cells that fire when light hits the surrounding area. The inhibitory influence of the surround is stronger in LGN cells compared to RGCs, enhancing the contrast between adjacent RGC regions.

LGN layers are separated into two types: magnocellular (M) and parvocellular (P). This distinction reflects a separation of visual functions, suggesting that different layers process different aspects of visual information.

P cells in the LGN are color-sensitive, meaning they respond differently to various colors. This allows for the perception of color differences. Their small receptive field size makes them responsible for high spatial resolution, which is important for fine detail perception.

M cells in the LGN are not sensitive to color, but respond to all colors equally. They have larger receptive fields, resulting in lower spatial resolution, important for general shape and movement detection. They are also quick to respond to changes in light intensity, making them ideal for detecting motion.

The primary visual cortex (V1) is the first stage of cortical processing of visual information. It receives input from the LGN and contains millions of neurons organized into layers. Layer 4 is the main input layer from the LGN, with the magnocellular pathway projecting to the upper part of layer 4 and the parvocellular pathway projecting to the lower part.

Ocular dominance columns are a pattern in the visual cortex where cells respond preferentially to input from one eye. This pattern is organized in blocks, alternating between left-eye-dominant and right-eye-dominant cells.

Retinotopy refers to the organization of the visual cortex where neighboring regions of the retina are mapped onto neighboring regions of the cortex. This maintains the spatial organization of the visual field. However, the distribution of cells devoted to different retinal areas is not uniform, resulting in a distorted representation.

Cortical magnification is a phenomenon where a disproportionate amount of cortical processing power is devoted to the central part of the visual field, the fovea. This means that the fovea is represented by a larger area in the visual cortex compared to peripheral regions. This is because the fovea has higher visual acuity, requiring more processing to decode fine details.

Cortical cells, unlike RGC or LGN cells, are sensitive to specific orientations. They have elongated receptive fields that respond best to lines or bars oriented at a particular angle. This selectivity allows for the processing of shape information.

Cortical adaptation is a process where prolonged exposure to a specific orientation of a visual stimulus reduces the sensitivity of neurons tuned to that orientation. This can lead to aftereffects where static stimuli appear to be oriented in the opposite direction.

Pinwheels are a visual representation of the orientation preferences of cells in the visual cortex. They reveal a systematic organization of orientation preferences across different areas of the cortex. Each pinwheel represents a cluster of cells with similar orientation preferences, forming a rotating pattern.

Simple cells in the visual cortex respond best to appropriately oriented stimuli within a specific location in their receptive field. They are also 'phase sensitive,' meaning the response is dependent on the position of the stimulus within the field.

Complex cells in the visual cortex are similar to simple cells in their preference for orientation, but they are 'phase insensitive.' This means that they respond regardless of the specific location of the stimulus within their receptive field, as long as it is within the field.

Hypercomplex cells, also known as end-stopped cells, are sensitive to both orientation and contour length. They respond best to a stimulus when its length closely matches the width of their receptive field. They inhibit their response when the stimulus extends beyond the receptive field.

Binocular cells in the visual cortex integrate input from both eyes. These cells have two receptive fields, one for each eye, that are matched in terms of their preferred orientation, location, and direction of motion. This allows for depth perception and fine motor control.

Color-sensitive cells in the visual cortex are found in areas called cortical blobs. These blobs are clustered around ocular dominance columns and contain cells with either red/green or blue/yellow opponency. This arrangement reflects the color opponency found in retinal ganglion cells.