Podcast
Questions and Answers
What characterizes blob cells in the visual cortex?
What characterizes blob cells in the visual cortex?
What is the primary role of motion sensitive cells in the visual cortex?
What is the primary role of motion sensitive cells in the visual cortex?
What is a hypercolumn in the visual cortex?
What is a hypercolumn in the visual cortex?
What advantage does the columnar system in the visual cortex provide?
What advantage does the columnar system in the visual cortex provide?
Signup and view all the answers
What do complex cells in the visual cortex respond to?
What do complex cells in the visual cortex respond to?
Signup and view all the answers
What is the purpose of decussation in the visual pathway?
What is the purpose of decussation in the visual pathway?
Signup and view all the answers
Which layers of the Lateral Geniculate Nucleus (LGN) receive input from M cells?
Which layers of the Lateral Geniculate Nucleus (LGN) receive input from M cells?
Signup and view all the answers
In the optic tract, how are the nerve fibers organized in relation to visual hemifields?
In the optic tract, how are the nerve fibers organized in relation to visual hemifields?
Signup and view all the answers
How is the Lateral Geniculate Nucleus (LGN) organized?
How is the Lateral Geniculate Nucleus (LGN) organized?
Signup and view all the answers
What percentage of RGC axons project to the Lateral Geniculate Nucleus (LGN)?
What percentage of RGC axons project to the Lateral Geniculate Nucleus (LGN)?
Signup and view all the answers
What types of cells input into the magnocellular layers of the LGN?
What types of cells input into the magnocellular layers of the LGN?
Signup and view all the answers
Which layer of the LGN receives contralateral input from the left visual hemifield?
Which layer of the LGN receives contralateral input from the left visual hemifield?
Signup and view all the answers
What other brain structures receive RGC axons apart from the LGN?
What other brain structures receive RGC axons apart from the LGN?
Signup and view all the answers
What type of cells are known for their sensitivity to motion and respond well to rapid changes in light intensity?
What type of cells are known for their sensitivity to motion and respond well to rapid changes in light intensity?
Signup and view all the answers
Which layer of the primary visual cortex (V1) primarily receives inputs from the LGN?
Which layer of the primary visual cortex (V1) primarily receives inputs from the LGN?
Signup and view all the answers
What type of cells are concentrated in the cortical blobs and display color opponency?
What type of cells are concentrated in the cortical blobs and display color opponency?
Signup and view all the answers
What phenomenon is described by the adaption stage, in which obliquely oriented gratings create an illusion of orientation in cortical cells?
What phenomenon is described by the adaption stage, in which obliquely oriented gratings create an illusion of orientation in cortical cells?
Signup and view all the answers
Which cells are characterized as monocular in layer 4 of the primary visual cortex?
Which cells are characterized as monocular in layer 4 of the primary visual cortex?
Signup and view all the answers
What type of cell requires a stimulus to be in a specific position within its receptive field for maximum response?
What type of cell requires a stimulus to be in a specific position within its receptive field for maximum response?
Signup and view all the answers
What kind of sensitivity do hyper-complex cells exhibit, particularly with respect to bar length?
What kind of sensitivity do hyper-complex cells exhibit, particularly with respect to bar length?
Signup and view all the answers
What type of spatial distribution does the retinotopic map in the visual cortex exhibit?
What type of spatial distribution does the retinotopic map in the visual cortex exhibit?
Signup and view all the answers
Which type of cell responds to stimuli presented anywhere within its receptive field and is phase insensitive?
Which type of cell responds to stimuli presented anywhere within its receptive field and is phase insensitive?
Signup and view all the answers
What characteristic is unique to the receptive fields of cortical cells compared to LGN receptive fields?
What characteristic is unique to the receptive fields of cortical cells compared to LGN receptive fields?
Signup and view all the answers
Which statement regarding the properties of P cells is accurate?
Which statement regarding the properties of P cells is accurate?
Signup and view all the answers
What is the main function of binocular cells in V1?
What is the main function of binocular cells in V1?
Signup and view all the answers
Which cortical layer does not receive input directly from the LGN?
Which cortical layer does not receive input directly from the LGN?
Signup and view all the answers
What is the primary role of the inhibitory influence of the surround in the receptive fields of LGN cells?
What is the primary role of the inhibitory influence of the surround in the receptive fields of LGN cells?
Signup and view all the answers
Study Notes
Visual Pathway Overview
- Retinal ganglion cells (RGCs) generate action potentials (APs).
- Visual information is transmitted through the optic nerve (cranial nerve II).
- Projections from the contralateral visual hemifield cross at the optic chiasm (decussation).
- The optic tract projects to the lateral geniculate nucleus (LGN) in the thalamus.
- Optic radiations project to the visual cortex.
- This sequence is: RGCs -> AP -> optic nerve -> contralateral -> optic chiasm -> decussation -> optic tract -> thalamus -> LGN -> Optic radiations -> visual cortex.
Decussation Purpose
- Decussation, the crossing of nerve fibers, allows for hemifield-specific processing.
- It enables the right hemisphere of the brain to process information from the left visual field and the left hemisphere from the right visual field.
Lateral Geniculate Nucleus (LGN)
- Part of the thalamus, a crucial relay station in the brain.
- Approximately 80% of RGC axons project to the LGN.
- The remaining axons project to the superior colliculus (eye movements) and hypothalamus (circadian rhythm).
- The LGN has six layers with different cellular properties:
- Layers 1-2 (magnocellular layers): Larger cells, input from M cells.
- Layers 3-6 (parvocellular layers): Smaller cells, input from P cells.
- K cells input is sandwiched between magnocellular and parvocellular layers.
- Each LGN receives both contralateral and ipsilateral input from each eye.
LGN Retinotopy
- Each LGN layer is organized retinotopically, meaning adjacent retinal areas are represented in adjacent LGN regions.
- The spatial relationships of the retina are maintained in the LGN.
- Each layer has a retinotopic map.
- LGN cells are sensitive to specific regions of visual space.
LGN Cell Receptive Fields (RFs)
- LGN cell RFs have a center-surround configuration.
- There are ON and OFF types of cells.
- The inhibitory influence of the surround in LGN cells is stronger than in RGCs, enhancing differences between neighboring retinal regions.
- The subdivision of LGN input (M vs P) suggests a subdivision of visual function.
Cell Type Properties
-
P cells:
- Nearly all are color-sensitive.
- High spatial resolution due to small receptive fields (smallest in fovea).
- Slow response to rapid changes in light intensity.
-
M cells:
- Not color-sensitive.
- Large receptive fields, lower spatial resolution.
- High sensitivity to motion and rapid changes in light intensity.
Visual Cortex Structure
- The LGN projects to the primary visual cortex (V1) via optic radiations.
- V1 (striate cortex) has ~100 million cells per hemisphere.
- LGN input enters V1 at layer 4 (magnocellular in upper L4, parvocellular in lower L4).
- K cells project directly to layers 1-3.
Ocular Dominance Columns
- Cells in layer 4 receive input from one eye only.
- Adjacent cell blocks receive input from the opposite eye.
- This creates a pattern of ocular dominance columns perpendicular to the surface.
Cortex Retinotopy
- Adjacent retina regions are mapped to adjacent cortical regions, maintaining retinotopy.
- The distribution of cells associated with each retinal region is distorted, with greater cortical representation in the fovea.
- Cortical magnification reflects foveal focus (spatial resolution and density of RGCs).
Functional Properties of Cortical Cells
-
Similarities to RGC/LGN cells:
- Maintain retinotopic map.
- Not particularly sensitive to illumination level.
- Respond best to abrupt illuminance changes like lines/bars.
-
Differences from RGC/LGN cells:
- Selectivity to orientation.
- Sensitivity to size, color and direction of motion.
Cortical Cell Differences (V1)
- Cortical cells show a preference for specific orientations.
- Cortical receptive fields are shaped for optimal response to specific orientations.
Orientation Selectivity
- Cortical adaptation demonstrates orientation selectivity.
- Obliquely oriented gratings adapting cells cause static gratings to appear rotated.
- This is caused by changed neuronal sensitivity.
How to see orientation preference?
- Staining reveals orientation preferences, producing pinwheel patterns.
Size and Location Sensitivity
-
Simple cells:
- Optimum response to properly oriented stimuli.
- Stimulus in a specific position within the receptive field.
- Phase-sensitive.
-
Complex cells:
- Optimum response to properly oriented stimuli.
- Stimulus anywhere within the receptive field.
- Phase insensitive.
-
Hyper-complex cells:
- Optimum response depends on orientation and contour length.
- Maximum response to bar lengths matching RF width, showing end-stopping.
Binocularity
- Layer 4 V1 cells are monocular.
- Other V1 cells are binocular, receiving input from both eyes.
- Response to a stimulus is more vigorous with stimulation of both eyes.
- Binocular cells have two receptive fields (one per eye) matching in type and responding to similar orientations/locations/motion.
Color Selectivity
- Color-sensitive cells are concentrated in cortical blobs in each ocular dominance column.
- Cells show red/green or blue/yellow opponency within blobs.
Direction Selectivity
- Many cortical cells show a preference for motion in a particular direction.
- Simple cells react to slow motion, complex cells to faster motion.
Columns and Hypercolumns
- Visual cortex is composed of columns with the same orientation and ocular dominance preferences.
- Hypercolumns contain the neural machinery to analyze multiple image attributes, including size, orientation, color, and direction of motion.
- Foveal hypercolumns cover smaller regions of visual space than peripheral ones.
- Advantages: minimized distance between neurons with similar stimulus properties, efficient communication for faster processing.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Dive into the visual pathway and learn about the crucial roles of retinal ganglion cells, the optic nerve, and the lateral geniculate nucleus. This quiz highlights how visual information is processed and the significance of decussation in visual field perception. Test your knowledge on the intricate steps that lead to visual processing in the brain.
