Vision Loss and V1

91 Magnocellular and Parvocellular pathways

Learning Objectives

Know the differences between the magnocellular and parvocellular pathways.

Know how the M and P pathway are organized in the LGN.

There are two visual nuclei in the thalamus: the lateral geniculate nucleus (LGN) and the pulvinar, which we won’t talk about. Neurons in the LGN have receptive fields that are center/surround like the retinal ganglion cells. The LGN has 6 layers, segregating inputs/outputs according to the eye of origin, which eye the information is coming from, on- or off- receptive field, whether the center is excitatory or inhibitory, and magnocellular or parvocellular pathway (more details below). The names of the pathways come from the fact that the retinal ganglion cells have large (magno) or small (parvo) cell bodies. It’s useful to think of two streams of information coming from the eyes to the brain.

 

Fig. 9.7.1. The magno- and parvocellular pathways can be thought of as 2 streams of different information that the brain combines and relates. (Credit: Jarod Davis. Provided by: University of Minnesota. Original image from: Wikipedia Commons. License: CC0)

The magnocellular pathway carries information about large, fast things (low spatial frequency, high temporal frequency) and is colorblind. The parvocellular pathway carries information about small, slow, colorful things (high spatial frequency, low temporal frequency).

 

Magnocellular cells are large and detect motion, depth, and luminance via rods. The response is rapid and transient. They consist of layers 1 and 2. Parvocellular cells are small and detect color and fine details. The response is slow and sustained. This comes from layers 3 through 6. Koniocellular cells are extremely small and receive information from the short-wavelength blue cones. There is much to still be studied about this system. These cells reside between the magnocellular and parvocellular layers.
Figure 9.7.2 In humans the LGN is normally described as having six distinctive layers. The inner two layers (1 and 2) are magnocellular layers, while the outer four layers (3, 4, 5, 6), are parvocellular layers. An additional set of neurons, known as the koniocellular layers, are found ventral to each of the magnocellular and parvocellular layers. (Credit: Wikipedia, https://en.wikipedia.org/wiki/Lateral_geniculate_nucleus, CC-BY-SA 3.0).

 

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Cheryl Olman PSY 3031 Detailed Outline
Provided by: University of Minnesota
Download for free at http://vision.psych.umn.edu/users/caolman/courses/PSY3031/
License of original source: CC Attribution 4.0
Adapted by: Katya Tomlin

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Introduction to Sensation and Perception by Students of PSY 3031 and Edited by Dr. Cheryl Olman is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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