5. Magnocellular pathway
• Parasol ganglion cells project from the retina
via the optic nerve to the two most ventral
layers of the lateral geniculate nucleus of
the thalamus, to the magnocellular cells.
• From the LGN, the M pathway continues by
sending information to the interblob regions
of the 4Cα layer of the V1 region of the visual
cortex, also called the "striate cortex"
6. Parasol ganglion cells (M cells)
• the first step in the magnocellular
pathway.
• They are a type of retinal ganglion
cell
• make up roughly 10% of all retinal
ganglion cells.
• Large cell bodies
• Large branching dendrite
networks
• thick, heavily myelinated axons.
• Fast conduction velocities
• Innervated by large receptive
fields
• Receive NO information about
color
• Contribute information about
motion and depth of objects
7. Magnocellular cells (M-cells)
• Neurons located within the
Adina magnocellular layer
(layer 1 and 2 ) of the lateral
geniculate nucleus.
• broadband because their
field center and surround
receive input from the same
mixture of cone types
• Part of the visual system
• Termed magnocellular
because they have a
relatively larger size than
parvocellular cells
8. Function
• provide useful static, depth, and motion
information.
• have high light/dark contrast detection, and are
more sensitive at low spatial frequencies than
high spatial frequencies
• detecting changes in luminance, and thus
provide useful information for performing visual
search tasks and detecting edges.
• providing information about the location of
objects.
9. Function
• detect quick changes in the position of an
object.This is the basis for detecting motion. The
information sent to the intraparietal sulcus (IPS)
of the posterior parietal cortex allows the
magnocellular pathway to direct attention and
guide saccadic eye movements to follow
important moving objects in the visual field.
• IPS sends information to parts of the frontal
lobe that allows the hands and arms to adjust
their movements to correctly grasp objects based
on their size, position, and location
10.
11.
12. Parvocellular pathway
• Midget cells originate in the ganglion cell layer of
the retina, and project to the parvocellular
layers of the lateral geniculate nucleus (LGN). The
axons of midget cells travel through the optic
nerve and optic tract, ultimately synapsing
with parvocellular cells in the LGN
• The electrically-encoded visual information
leaves the parvocellular cells via relay cells in
the optic radiations, traveling to the primary
visual cortex layer 4A and 4C-β.
13. Midget cells
• small size dendritic trees and cell bodies
• 80% of retinal ganglion cells
• receive inputs from relatively few rods and cones
• slow conduction velocity
• respond to changes in color but respond only
weakly to changes in contrast unless the change
is great
• simple center-surround receptive fields, where
the center may be either ON or OFF while the
surround is the opposite.
14. Parvocellular cells
• are neurons located within the four dorsal
parvocellular layers of the lateral geniculate
nucleus (LGN) of the thalamus (layer 3,4,5 and 6).
• Most parvo cells have color-opponent center
surround receptive fields, e.g., a red on-center
and a green off-surround.
• small size of the cell compared to the larger
magnocellular cells.
• sensitive to colour
• capable of discriminating fine details
15.
16. Parasol vs. Midget cells
Parasol Cell (M cells)
Midget Cell (P cells)
RGC Type
Magnocellular Pathway
Parvocellular Pathway
Pathway it's involved in
Large
Small
Cell body size
Complex
Less complex
Dendritic tree
~1.6 ms
~2 ms
Conduction rate
"Where" objects are;
"How" to grasp the
objects
"What" objects are
according to fine detail
Function in visual system
Low
Medium to high
Sensitivity to spatial
frequency
High
Low
Temporal frequency
Achromatic
Red-green opponency
Color opponency
Ventral Pathway:Retinal P cells → Parvo LGN → V1 (4Cb) → V2 → V4 → IT (Inferior Temporal Cortex)2.
Dorsal Pathway:Retinal M cells → Magno LGN → V1 (4Ca) → V2 → MT (Medial Temporal Cortex) → Posterior Parietal cortex
These cells can detect the orientation and position of objects in space,information that will eventually be sent through the dorsal stream. This information is also useful for detecting the difference in positions of objects on the retina of each eye, an important tool in binocular depth perception.
. This ability has led some neuroscientists to hypothesize that the purpose of the magnocellular pathway is not to detect spatial locations, but to guide actions related to the position and motion of objects.
Parvocellular Cells Parvocellular cells, also called P-cells, are neurons located within the parvocellular layers of the lateral geniculate nucleus (LGN) of the thalamus. "Parvus" means "small" in Latin, and the name "parvocellular" refers to the small size of the cell compared to the larger magnocellular cells. The parvocellular neurons are sensitive to color, and are more capable of discriminating fine details than their magnocellular counterparts. Parvocellular cells have greater spatial resolution, but lower temporal resolution, than the magnocellular cells.
