Problem 2
Yantis & Blake
2 principles that characterize how pathways and networks in the brain are organized
- Functional specialization: different neural pathways and different areas of the brain are
specialized to represent different types of information (such as shape, color motion etc.)
- Retinotopic mapping: vision is spatial, neural signals from retinal ganglion cells travel to
neurons in each visual area in the brain, this way the spatial location of visual features is
reflected in the spatial arrangement of activated neurons in the brain
From eye to the brain
- The 2 optic nerves from each eye travel and meet at the optic chiasm: here the optic
nerves split in half
o The left visual field strikes the right side of each retina, axons from the right side of
both eyes combine into the right optic tract, which continues to the right
hemisphere
o The right visual field strikes the left side of each retina, axons from left side of both
eyes combine into the left optic tract, which continues into the left hemisphere
o Contralateral representation of visual space: an example of contralateral
organization (opposite-side organization as opposed to ipsilateral same-side
organization)
- In each hemisphere, 90% of the axons in the optic tracks go to the lateral geniculate
nucleus, which sends signals to the primary visual cortex via the optic radiations
Lateral Geniculate Nucleus
- A peanut sized structure, one in each hemisphere, it is part of the thalamus
- The thalamus a large structure containing several other nuclei that serve for different
sensory systems
- LGN has many folded layers so the layers curve
, - Cell bodies in layers 1 and 2 are larger so they are
called magnocellular layers
- The magnocellular layers receive signals from
parasol retinal ganglion cells – M cells
- Layers 3 – 6 are called parvocellular layers
- The parvocellular layers receive signals from
midget retinal ganglion cells – P cells
- The thinner layers between are called
koniocellular layers
- The koniocellular layers receive signals from
bistratified retinal ganglion cells
Pathways from the retina to the LGN
- The left LGN receives signals from the right
visual field
- The right LGN receives signals from the left
visual field
- Layers 1,4, and 6 (and corresponding
koniocellular layers) receive signals from the
contralateral eye (on the opposite side)
- Layers 2, 3 and 5 (and corresponding
koniocellular layers) receive signals from the
ipsilateral eye (on the same side)
- Each of the 6 layers contain their own
retinotopic map, and the layers are stacked in
a way that comparable regions of separate
maps are aligned with each other
Information Flow in the LGN
- Information encoded in signals from LGN can
be modified to some degree by top-down
feedback from brain structures (primary visual
cortex and higher cortical areas)
- LGN works as a gateway from the eyes to the rest of the brain by providing control of flow
of incoming information
- Layers of LGN differ functionally too:
o Magnocellular layers: specialized for
carrying information like motion and flicker
(dynamic visual properties)
o Parvocellular layers: specialized for
information like color, texture, form and
depth (static visual properties)
o Less is known about koniocellular layers
Yantis & Blake
2 principles that characterize how pathways and networks in the brain are organized
- Functional specialization: different neural pathways and different areas of the brain are
specialized to represent different types of information (such as shape, color motion etc.)
- Retinotopic mapping: vision is spatial, neural signals from retinal ganglion cells travel to
neurons in each visual area in the brain, this way the spatial location of visual features is
reflected in the spatial arrangement of activated neurons in the brain
From eye to the brain
- The 2 optic nerves from each eye travel and meet at the optic chiasm: here the optic
nerves split in half
o The left visual field strikes the right side of each retina, axons from the right side of
both eyes combine into the right optic tract, which continues to the right
hemisphere
o The right visual field strikes the left side of each retina, axons from left side of both
eyes combine into the left optic tract, which continues into the left hemisphere
o Contralateral representation of visual space: an example of contralateral
organization (opposite-side organization as opposed to ipsilateral same-side
organization)
- In each hemisphere, 90% of the axons in the optic tracks go to the lateral geniculate
nucleus, which sends signals to the primary visual cortex via the optic radiations
Lateral Geniculate Nucleus
- A peanut sized structure, one in each hemisphere, it is part of the thalamus
- The thalamus a large structure containing several other nuclei that serve for different
sensory systems
- LGN has many folded layers so the layers curve
, - Cell bodies in layers 1 and 2 are larger so they are
called magnocellular layers
- The magnocellular layers receive signals from
parasol retinal ganglion cells – M cells
- Layers 3 – 6 are called parvocellular layers
- The parvocellular layers receive signals from
midget retinal ganglion cells – P cells
- The thinner layers between are called
koniocellular layers
- The koniocellular layers receive signals from
bistratified retinal ganglion cells
Pathways from the retina to the LGN
- The left LGN receives signals from the right
visual field
- The right LGN receives signals from the left
visual field
- Layers 1,4, and 6 (and corresponding
koniocellular layers) receive signals from the
contralateral eye (on the opposite side)
- Layers 2, 3 and 5 (and corresponding
koniocellular layers) receive signals from the
ipsilateral eye (on the same side)
- Each of the 6 layers contain their own
retinotopic map, and the layers are stacked in
a way that comparable regions of separate
maps are aligned with each other
Information Flow in the LGN
- Information encoded in signals from LGN can
be modified to some degree by top-down
feedback from brain structures (primary visual
cortex and higher cortical areas)
- LGN works as a gateway from the eyes to the rest of the brain by providing control of flow
of incoming information
- Layers of LGN differ functionally too:
o Magnocellular layers: specialized for
carrying information like motion and flicker
(dynamic visual properties)
o Parvocellular layers: specialized for
information like color, texture, form and
depth (static visual properties)
o Less is known about koniocellular layers
