Visual Processing in the Brain
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Visual Processing in the Brain

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Questions and Answers

What role does glutamate play in the visual process?

  • It acts as a signal for the presence of light. (correct)
  • It deactivates the transducin protein.
  • It binds to arrestin to inhibit signal processing.
  • It sustains rhodopsin activation.

    • Which type of ganglion cells processes color, shapes, and details?

  • T cells
  • M cells
  • P cells (correct)
  • K cells

    • What type of cell in the primary visual cortex directly gets information from the LGN?

  • Simple cells (correct)
  • Complex cells
  • Hyper complex cells
  • End-stop cells

    • What is the primary function of the dorsal stream in the visual pathway?

    <p>Determining movement and location.</p> Signup and view all the answers

    Damage to which area can cause a condition known as akinetopsia?

    <p>Dorsal stream</p> Signup and view all the answers

    Which layer in the LGN processes information from M cells?

    <p>Magnocellular layer</p> Signup and view all the answers

    Which type of cells in the visual cortex are sensitive to specific orientations of lines?

    <p>Simple cells</p> Signup and view all the answers

    What does the inferior temporal lobe primarily respond to?

    <p>Complex shapes and faces</p> Signup and view all the answers

    What is the primary function of the cornea in the eye?

    <p>It is responsible for the majority of visual focusing.</p> Signup and view all the answers

    Which part of the retina first receives light before the information is processed?

    <p>Ganglion cells</p> Signup and view all the answers

    What occurs when retinal absorbs light in rod cells?

    <p>Transducin activates phosphodiesterase.</p> Signup and view all the answers

    How does light affect the cGMP levels in rod cells?

    <p>cGMP levels decrease, leading to closure of ion channels.</p> Signup and view all the answers

    What percentage of focusing does the lens of the eye perform?

    <p>20% - 30%</p> Signup and view all the answers

    Which type of cells transmit information from photoreceptors to ganglion cells?

    <p>Bipolar cells</p> Signup and view all the answers

    What is the effect of continuously depolarized rod cells in the dark?

    <p>Continuous release of neurotransmitter glutamate.</p> Signup and view all the answers

    Which structure controls the diameter of the pupil?

    <p>Iris</p> Signup and view all the answers

    What is the primary role of photoreceptor cells in the retina?

    <p>To detect light and convert it into electrical signals</p> Signup and view all the answers

    Which structure in the eye is primarily responsible for bending light onto the retina?

    <p>Lens</p> Signup and view all the answers

    How is the lateral geniculate nucleus (LGN) organized?

    <p>In layers, with each layer processing different types of visual information</p> Signup and view all the answers

    What distinguishes the receptive fields of ganglion cells from those in the primary visual cortex?

    <p>Receptive fields in the primary visual cortex are more complex and can respond to specific shapes</p> Signup and view all the answers

    What is the primary function of the optic chiasm?

    <p>To facilitate the crossing over of visual information from both eyes to opposite hemispheres</p> Signup and view all the answers

    Which areas of the brain process visual information without being involved in conscious perception?

    <p>Optic tectum and hypothalamus</p> Signup and view all the answers

    What is the main reason cones are linked to both color vision and acute vision?

    <p>Their low convergence with ganglion cells</p> Signup and view all the answers

    How does the structure of the fovea contribute to vision?

    <p>It is densely packed with cone cells, providing high acuity vision</p> Signup and view all the answers

    What is the primary role of the eye in the process of vision?

    <p>To capture light.</p> Signup and view all the answers

    Which structure is involved in maintaining the circadian rhythm?

    <p>Superchiasmatic Nucleus</p> Signup and view all the answers

    What happens to rhodopsin in the dark?

    <p>It turns off light sensitivity.</p> Signup and view all the answers

    How do ganglion cells contribute to the process of vision?

    <p>They generate action potentials.</p> Signup and view all the answers

    Which retinal configuration results in contralateral processing of visual stimuli?

    <p>Lateral retina input crosses at the optic chiasm.</p> Signup and view all the answers

    What is the result of increased light exposure on the dark current in rods?

    <p>Decreased production of Cmp.</p> Signup and view all the answers

    What aspect of vision does parallel processing allow for?

    <p>Simultaneous perception of shape, color, and movement.</p> Signup and view all the answers

    What is the effect of light on bipolar cells in relation to rod activity?

    <p>Bipolar cells depolarize with rod hyperpolarization.</p> Signup and view all the answers

    Study Notes

    Transduction & Converting outside Stimuli into neuron activity.

    • Perception: Subjective interpretation of what we sense.
    • Receptors release specific odorants into the air that affects receptors in the nose → ↓AP affect areas of the limbic system.
    • Vision: Most essential sense.

    The Eye

    • Info passed to the thalamus → decoded in the Primary visual cortex [occipital and temporal lobes].

    Light

    • Electromagnetic spectrum: Energy produced by electrical charges radiated in waves.
    • Light consists of photons (acts chemical substance, Important for Photosynthesis).
    • Blue and purple: ~400nm length
    • Orange and red: ~700nm length
    • Animals transducing light to nerve signals

    The Eye

    • Light rays (70-80% of focusing)
    • Cornea, pupil and lens focus on the retina → converts the rays into impulses → optic nerve → brain where they are recognized as images.
    • Cornea: 70% - 80% of focusing occurs; Protects the eye
    • Pupil: Surrounded by Iris (controls diameter of pupil: larger in dim light and smaller in bright light).
    • Lens: Controls the 20% - 30% of focusing. You get older the lens get stiffer.
    • Optic nerve leaves the retina.

    The Retina

    • Back of the eye = Retina.
    • Made of several cells:
      • Ganglion cells: Light first hits here; gets info from Intermediate and photoreceptor cells. Axons make up optic nerve.
      • Intermediate cells: transmits info from photoreceptor to ganglion
      • Connects ganglion cells to photoreceptors.
        • Bipolar, amacrine and horizontal cells.

    Phototransduction Of Rods

    • In the dark, Dosil Nat flow into rod cells through ion channels that are activated by CGMP [helps to keep depolarizing dark current flowing into the rods]
    • Influx of Na+ = cells are depolarized which leads to continuous release of NT glutamate.
    • Rod rhodopsin is inside the rod cell.
    • Opsin + retinal
    • Capable of absorbing light. When retinal absorbs light, its configuration changes and prompts Opsin to activate a molecule called transducin.
    • Transducin activates an enzyme (phosphodiesterase) which breaks down CGMP.
    • As CGMP levels fall, ion channels that are opened by CGMP begin to close.
    • Sodium enters cell and it becomes more hyperpolarized due to C-1.
    • Glutamate release which acts as a signal that a light stimulus is present.
    • Rod cells return to normal state when activated rhodopsin is deactivated and a protein called arrestin binds to it.
    • Blocks the ability of rhodopsin to activate transducin (clenatures CGMP)
      • A complex process restore retinal to original configuration → ready to absorb light again.

    ### LGN of thalamus

    • Retinotopic map.
    • LGN is a map of the retina.
    • Types of ganglion cells that send signals to the LGN:
      • P cells
        • Gets info from fovea and send projections to layers 3, 4, 5 & 6 in LGN
        • Parvocellular layer gets info from P cells and processes colour, shapes and details.
      • M cells
        • Large ganglion cells found in periphery of retina and projects to the magnocellular layer.
        • Magnocellular layer gets info from M cells and process movement and low-intensity light.
      • K cells

    Visual Coney

    • Cells of the primary Visual Cortex
      • Primary Visual Cortex
        • Also called V1 and striate cortex.
      • Is located in the occipital lobe and gets the first info from LGN.
      • Neuronal tuning (neurons represent a specific stimulus).
      • Discovered by David Hubel and Torsten Wiesel.
      • Types of neurons described by Hubel and Wiesel
        • Simple cells: Rectangular receptive fields; gets info directly from LGN and are sensitive to lines of specific orientation.
        • Complex cells: Gets info from simple cells. Respond selectively to lines of specific orientation that move in specific directions.
        • Hypercomplex cells and end-stop cells: Simple + complex and respond to lines with specific orientation, angles and length.

    Extrastriate pathways.

    • Dorsal stream
      • Starts @ magnocellus to the V1, V2, V3 and V5 and then the parietal lobe.
      • "Where" a "now" stream because it is to movement & location.
      • Akinetopsia (damage to dorsal stream where an individual is unable to see object moving).
    • Ventral stream
      • Parvocellular **V1, V2, V4 **→ inferior temporal.
      • "What" pathway because of V4 processes info.
      • Cerebral achromatopsia (color blindness to V4)
    • Inferior and medial Temporal lobes (outside the V1)
      • Inferior temporal (IT)
        • Responds to complex shapes and faces.
      • Medial temporal (MT)
        • Perception and memory.

    Vision and cheomorecoption

    • Memo recordings
      • Single celled organisms = chemical sensations.
        • Olfactory
          • The reason why we smell things is because items are given off volatile chemicals and they go into the nose and attach to mucosa.
        • Visceral
          • Senses in gut
        • Vibration
          • Touch and auditory from a distance.
      • Electromagnetic sensation [energy produced by electrical charges radiated in waves]
        • Vision
          • Images are perceived that have form, movement, color, identity & location.
      • Done simultaneously. Conscious perception. Called parallel processing.
      • The eye is responsible for capturing the light.
        • Blue: sensitive to green → first
        • Red: sensitive to yellow
      • Left visual field crosses to the right visual field and vice versa through the optic chasm.
        • Optic nerve = part between the eye and optic chasm.
        • Part between the optic chasm and LGN is tract.
        • Ipsilateral.
        • Ganglion cells form the medial retina are contralateral while lateral retina is ipsilateral.
        • Optic radiation: fan out.

    The Callosum

    • The brain is mostly used to process finger touch information move.
    • Main sulcus in the center of the medial occipital lobe.
    • Where the center of the visual field.
    • Primary visual cortex/V1/Rodman area #11

    Parallel subcortical Pathways

    • Hypothalamus
      • Superchiasmatic nucleus [keeps track of the day night cycle or circadian rhythm]
    • Midbrain
      • Superior Colliculus [helps detect what is going on]

    Rods and Cones

    • Rods are sensitive to the same photopigment
    • Rhodopsin
      • In the dark, light turns them off. [Every active in the dark]
      • Dark current: depolarization occurs in the dark and light hyperpolarizes it - The brighter the light, the brighter the hyperpolarization - The more rhodopsin is struck, the less the dark current occurs.
      • In the dark, there is production of Cmp which opens Nat channels, producing EPSPs and causes transmitters to be released from the rods. No A.P here.
      • When more light, less Cmp and less transmitters - The brighter the light, the less activity, the darker the light the more activity.
      • Rods influence horizontal cells.
    • Ganglion cells are A.P
    • Cell voltage is depolarized until light hyperpolarizes it.
    • Bipolar cells depolarize when rods hyperpolarize.
    • (+) decreases neurotransmitter. Less glutamate is released during hyper polarization.
    • What makes the cells change the response depends on the channel opened (depolarize or hyperpolize)

    Define/describe the following terms:

    • Transduction: The process of converting one form of energy into another.
    • Receptor cell: Any cell that is specialized to detect a specific type of energy.
    • Distal/proximal stimulus: The distal stimulus is the object in the world that we perceive. The proximal stimulus is the image of the object that is projected onto our retina.
    • Sensation versus perception: Sensation is the process of detecting physical energy from the environment and encoding it as neural signals. Perception is the process of interpreting these neural signals and giving them meaning.
    • Receptive field: The area of the sensory surface that, when stimulated, causes a change in the activity of a neuron.
    • Sensory organ: A specialized organ that is designed to detect a specific type of energy.

    For what reason have the various senses developed? Describe some of the physical energies they are capable of detecting.

    • The various senses have developed to allow organisms to interact with their environment and survive.
    • Vision detects light energy.
    • Hearing detects sound waves.
    • Touch detects pressure, temperature, and pain.
    • Taste detects chemicals dissolved in saliva.
    • Smell detects chemicals in the air.

    Describe how the eye collects and manipulates light. What is the function of the cornea, lens, iris, and retina? What is the physical nature of light (as particles and electromagnetic radiation)?

    • The eye collects light by focusing it onto the retina.
    • The cornea and lens are responsible for focusing light.
    • The cornea is the clear outer layer of the eye that provides most of the focusing power.
    • The lens is a flexible structure that can change shape to fine-tune focusing.
    • The iris is a pigmented muscle that controls the size of the pupil, which is the opening in the iris that allows light to enter the eye.
    • The retina is the light-sensitive layer at the back of the eye that converts light into neural signals.
    • Light is a form of electromagnetic radiation that can be thought of as both waves and particles.
    • As waves, light travels with a specific wavelength that determines its color.
    • As particles, light consists of photons, which are packets of energy.

    Describe the function and structure of the retina.

    • Photoreceptor cells: rods and cones
      • Rods are responsible for vision in dim light and do not provide color information.
      • Cones are responsible for color vision and provide sharp details.
      • The concentration of cone photoreceptors is highest in the fovea.
    • Bipolar cells: Receive input from photoreceptors and transmit information to ganglion cells.
    • Ganglion cells: Receive input from bipolar cells and their axons form the optic nerve, which carries information to the brain.
    • Horizontal and amacrine cells: Modify signals between photoreceptors and bipolar cells or between bipolar cells and ganglion cells.
    • Fovea: A small area of the retina specialized for high acuity vision.
    • Blind spot/optic disk: The point where the optic nerve exits the eye, where there are no photoreceptors.

    Describe the connections of the retina to the rest of the brain.

    • Where is the first synapse outside the retina?
    • The first synapse outside the retina occurs between photoreceptor cells and bipolar cells.
    • What purpose does the optic chiasm serve?
    • The optic chiasm serves to cross the axons from the nasal (inside) part of each retina to the opposite hemisphere of the brain.
    • This allows the two hemispheres to receive information from both eyes, which is necessary for depth perception.
    • What is the lateral geniculate nucleus (LGN)? - The LGN is a relay center in the thalamus that receives visual input from the retina.
    • How is it organized and how is this organisation related to function? (hint: parvocellular & magnocellular)
    • The LGN is organized into six layers.
    • The bottom two layers are called the magnocellular layers receive input from M-type ganglion cells (large and fast conducting) and process motion and low-resolution information.
    • The top four layers are called the parvocellular layers and receive input from P-type ganglion cells (small and slow conducting) and process color and details.
    • To where do LGN neuron axons extend,- The axons of neurons in the LGN project to the primary visual cortex (V1) in the occipital lobe.
    • What is striate cortex and where is it located?
      • Striate cortex is another name for the primary visual cortex (V1). It's located in the occipital lobe.

    Describe the various cortical visual areas in the occipital lobe and surrounding area (including extrastriate areas). Pay particular attention to V1 (primary visual cortex), V4, V5, and the inferior temporal ("ventral/inferior stream") and posterior parietal areas ("dorsal stream"). Be familiar with how these functions were discovered (both human brain injury and animal experimental data). What does it mean that the visual cortex is modular (hint: parallel processing)?

    • V1 (primary visual cortex)
      • The first area in the cortex to receive visual input from the LGN.
    • This area is responsible for processing basic features of visual information, such as orientation, color, and movement.
    • V4:
      • Involved in processing more complex visual features, such as color and shape.
    • V5 (also known as MT):
      • Involved in processing motion information.
    • The ventral stream (inferior/temporal stream):
      • Begins in V1 and travels to the temporal lobe. Is thought to be involved in identifying objects
        • Inferior Temporal Cortex (IT):
        • Essential for visual perception, including the perception of faces.
    • The dorsal stream
      • Travels from V1 to the parietal lobe and is thought to be involved in processing spatial information and guiding action.
      • Posterior parietal areas:
      • Area that helps control and guide movement.
      • The visual cortex is modular because it is composed of different areas, or modules, that specialize in processing different types of visual information.
      • This modularity allows for parallel processing, where different aspects of visual information are processed simultaneously.
      • The functions of these areas have been discovered using a variety of methods, including:
        • Human brain injury: examining the behavioral deficits that result from damage to these areas
        • Animal experimental data: using single-cell recordings, lesions, or other techniques to study the functioning of these areas in laboratory animals.
    • Cones provide both color vision and acute vision because they are concentrated in the fovea, which is the central part of the retina.
      • The fovea has a higher density of cones than rods, which allows for greater visual acuity.
      • The fovea is also characterized by a one-to-one convergence of cones to ganglion cells, which means that each cone synapses onto a single ganglion cell.
    • The foveal area is "blown up" or "zoomed" on the visual cortex because it receives a disproportionate amount of representation in the visual cortex.
      • This means that a larger area of the visual cortex is dedicated to processing information from the fovea compared to other areas of the retina.
      • This is due to the fact that the fovea is responsible for our central vision, which is essential for tasks such as reading and recognizing faces.

    What is the receptive field of a sensory neuron and how is it created? Compare and contrast the receptive fields of ganglion cells and neurons in the primary visual cortex. What is the purpose of these receptive fields?

    • The receptive field of a sensory neuron is the area of the sensory surface that, when stimulated, causes a change in the activity of that neuron.
    • The receptive field of a ganglion cell is typically a circular area of the retina.
    • The receptive field of a neuron in the primary visual cortex is more complex, typically consisting of a rectangular area with a specific orientation.
    • Receptive fields are created by the convergence of inputs from multiple sensory receptors onto a single neuron.
    • The organization of receptive fields allows for neurons to encode specific features of the sensory world, such as the location of a stimulus, its orientation, or its movement.

    Describe the functions of subcortical brain areas that are not responsible for perception yet receive "light" input:

    • Optic tectum (superior colliculus):
      • Plays a major role in visual reflexes and attention, including orienting the eyes and head toward a stimulus.
    • Hypothalamus (suprachiasmatic nucleus):
      • Responsible for regulating the sleep-wake cycle and other circadian rhythms, using light input as a cue.
      • Amygdala:
      • Plays a role in emotional learning and processing, including the detection of threats and the generation of fear responses. It can process information about the surrounding environment.

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    Description

    This quiz explores the critical roles of various cells and pathways involved in visual processing, including the functions of glutamate, ganglion cells, and the dorsal stream. Test your knowledge on how the brain interprets visual information and the specific areas responsible for different aspects of vision.

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