Anatomy of Striate Cortex and Visual Pathway

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Questions and Answers

What are the three types of cortical neurones discovered by Hubel and Wiesel through single cell recording using microelectrodes?

Simple cortical cells, Complex cortical cells, and End-stopped cells (also known as 'hypercomplex' cells)

In the Striate Cortex, which layer do fibres from M- and P-cells of LGN enter, and how are they further divided?

Layer IVc, with M-cells entering IVcα and P-cells entering IVcβ

What is the characteristic of Simple Cortical Cells in terms of their response to bar-like stimuli?

They have excitatory and inhibitory regions arranged side by side, and respond best to a bar of light aligned along the length of their receptive field.

What are the 'BLOBS' and 'INTERBLOBS' observed in the Striate Cortex after introducing cytochrome oxidase?

Areas of staining are referred to as 'BLOBS', while areas of no staining are referred to as 'INTERBLOBS'. Signup and view all the answers

What is the role of the Lateral Geniculate Nucleus (LGN) in the visual pathway, and which type of fibres originate from it?

The LGN acts as a relay station between the retina and the Striate Cortex, and fibres from M-, P-, and K-cells originate from it. Signup and view all the answers

What is the significance of the Striate Cortex in the visual pathway, and how many layers does it consist of?

The Striate Cortex is the primary visual cortex, and it consists of 6 Brodmann layers. Signup and view all the answers

What type of information is processed in the thick stripes of the extrastriate area V2?

Magno information, sensitive to disparity, orientation, and movement. Signup and view all the answers

What is the significance of the interstripes in the extrastriate area V2?

They contain parvocellular information, are orientation sensitive, but not colour coded. Signup and view all the answers

What is the function of the ventral stream in the visual cortex?

It is the WHAT pathway, involved in object recognition and identification. Signup and view all the answers

What is the organization of the retinotopic map in the extrastriate area V2?

It consists of 3 interleaved maps. Signup and view all the answers

What is the role of the superior colliculus in the visual pathway?

Eye movement control Signup and view all the answers

What is the role of the striate cortex in the visual pathway?

It receives input from the lateral geniculate nucleus and sends output to the extrastriate area V2. Signup and view all the answers

What are the two main layers of the Lateral Geniculate Nucleus (LGN)?

Magnocellular layer (layers 1-2) and Parvocellular layer (layers 3-6) Signup and view all the answers

What is the significance of the CO staining in the extrastriate area V2?

It reveals thin stripes, thick stripes, and interstripes. Signup and view all the answers

What type of receptive fields are found in the Lateral Geniculate Nucleus (LGN)?

Centre-surround receptive fields Signup and view all the answers

What is the primary role of the Geniculocortical pathway?

To transmit visual information from the LGN to the striate cortex Signup and view all the answers

What is another name for the Striate Cortex?

Primary Visual Cortex or V1 or Brodmann Area 17 Signup and view all the answers

What is the function of the Lateral Geniculate Nucleus (LGN) in regulating visual information?

To regulate signal transmission to prevent over-stimulation of the visual cortex Signup and view all the answers

Study Notes

The Visual Pathway

The visual pathway consists of the retina, optic nerve, optic chiasm, LGN (lateral geniculate nucleus), optic tract, and superior colliculus.
90% of the optic nerve originates from the retina, while 10% originates from the superior colliculus.

Lateral Geniculate Nucleus (LGN)

Located in the thalamus, in the forebrain.
Contains 6 layers, with layers 1-2 being magnocellular and layers 3-6 being parvocellular.
Koniocellular cells are found between layers.
Layers 2, 3, and 5 receive input from the ipsilateral eye, while layers 1, 4, and 6 receive input from the contralateral eye.
The LGN is the first extra-retinal synapse in the visual pathway and contains centre-surround receptive fields and a retinotopic map in each layer.

Striate Cortex (Primary Visual Cortex)

Also known as V1 or Brodmann Area 17.
Located in the occipital lobe of the brain.
Consists of 6 Brodmann layers with numerous subdivisions.
Magnocellular, parvocellular, and koniocellular fibres from the LGN enter different layers of the striate cortex.
Areas of high cytochrome oxidase staining are known as "blobs", while areas of no staining are known as "interblobs".

Receptive Fields

Hubel and Wiesel (1959, 1962, 1968) discovered 3 types of cortical neurones: simple, complex, and end-stopped cells.
All respond best to bar-like stimuli with specific orientation and are orientation-specific.
Simple cortical cells have excitatory and inhibitory regions arranged side by side, acting as edge detectors.

Organisation of Pathways

The two major pathways from the retina to the visual cortex are the magnocellular and parvocellular pathways.
The magnocellular pathway is involved in low-contrast, flicker, movement, spatial location of objects, and achromatic vision with poor spatial resolution.
The parvocellular pathway is involved in chromatic, high-contrast, high spatial resolution vision.
Streaming of information into pathways continues into the striate cortex and beyond.

Visual Areas of the Brain

Extrastriate area V2 receives the bulk of input from the striate cortex.
V2 has thin stripes (colour-coded), thick stripes (magno information), and interstripes (parvocellular information).
Each set of stripes contains a retinotopic map, with information segregated into ventral (WHAT?) and dorsal (WHERE?) streams from V2.

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Description

Explore the structure and function of the striate cortex, including its layers, subdivisions, and fibre pathways involved in visual processing.