B455 Intro to Sensory Systems

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  1. 1. What are sensory systems?
    2. What leads to perception?
    3. What is perception?
    4. What do sensory systems do?
    • 1. Neurobiological substrates
    • 2. Activity of sensory systems
    • 3. Bio/psych phenomenon leading to interpretation of external stimuli - not necessarily coupled with awareness.
    • 4. They filter, extract, and distort external info in order to provide a USEFUL (not necessarily accurate picture of the world) - extraction of relevant features
  2. 1. What is lateral inhibition? - get def from book
    2. What is categorical perception? - get diff from book
    3. What is McGerk Effect? - get def from book
  3. 1. Why doesn't all stimuli become perception?
    2. What does magnitude of potential change in receptor cell depend upon? When is the signal passed on?
    3. What is spike potential?
    1. Because we don't have receptors. If a sensory receptor in periphery (not neuron)  is capable of responding to stimuli, the signal will be translated into neural signal (changes in membrane potential) --> action potential.

    2. Depends on magnitude of stimulus, meaning this is a graded response. When signal doesn't translate into a strong enough potential to reach spike potential.

    3. Spike potential - true action potential - when stimulus crosses threshold
  4. 1. How does sensory adaptation work and what does it lead to?
    2. Why is sensory adaptation useful?  2
    3. Difference between tonic and phasic cells?
    1. After an initial intense response --> adapatation - reduction in sensory by ignoring stimulus. Basically, a gradual shift away from what stimulus really is.

    2. To prevent sensory overload and to promote response to changes rather than to constants.

    3. Tonic cells adapt slowly - take much longer to drop off, while phasic cells adapt rapidly.
  5. What is the reasoning behind illusions?
    Computational process of selecting "important" stimuli over others.
  6. Receptive fields: Look this up in book too.
    1. What happens when you have a stimulus within a receptive field?
    2. What happens if you have a stimulus outside a receptive field?

    pg. 22
    • 1. Will affect firing rate no matter what - can have either an excitatory or inhibitory effect.
    • 2. No stimulus (sensory filtering)
  7. 1. How do labeled lines help nervous system? Example?

    2. What are labeled lines used for? (2)
    3. What else must you have to retain and process information from labeled lines?
    1. Labeled lines enable nervous system to distinguish stimuli as signals ascend through nervous system. For example, brain knows difference between vibration and heat because those information tracks are kept separate

    2. To distinguish location (i.e., touch on fingers vs. back), type of stimulus, etc.

    3. Lots of cortical neurons to keep location and stimuli separated. For example, you would have a ton of cortical neurons dedicated to finger and lips lines since these have high acuity touch.
  8. What are three ways that nervous system codes  (represents) information?
    1. Labeled lines (location, modality)

    • 2. Firing rate (location - in systems w/o labeled lines i.e., auditory, stimulus magnitude)
    • - Auditory system, olfactory system, stimuli will be stronger in one ear/nostril vs. the other.

    • 3. Timing of stimulus onset/offset (detecting changes and decoding location)
    • - Auditory system compares onset of stimulus to determine location.

    Cells must be phasic
  9. 1. What is firing rate useful for?
    2. Max firing potential?
    3. How does nervous system get around max firing potential to get the most information?
    4. Onset/offset of stimulus - what kind of cells are needed?
    • 1. Representing stimulus magnitude/intensity (increased intensity --> increased firing rate)
    • 2. 1200 action potentials/s
    • 3. Range fractionation - cells are designated to respond to low, medium, or high intensity stimuli. Then, nervous system extracts actual stimulus intensity from range fractionation by examining population of cells.
    • 4. Fast-acting phasic cells.
  10. Compare and contrast the def of population (ensemble) coding vs. grandmother neuron - sparse coding.

    Can ensemble coding detect grandmother's face?

    Can you only have grandmother neurons? Why or why not? (2) What will you see in most cells?
    • 1. Population coding:
    • - Def: using network of neurons (though single cell can participate in more than one network) to integrate incoming information

    • 2. Grandmother neuron
    • Def - start w/ extracting features of environment and building on them until you have a single cell - when it's active you perceive something very specific (i.e., grandmother's face)

    Not individually, but when fired together, can.

    No, bc not enough space to contain one cell for each/concept ever and if neuron dies, can't detect grandmother anymore.

    Will see combination of the two.
  11. 1. What is parallel processing?
    2. What is an important map that shows this?
    3. What are two other specific maps that are perfect for this concept?
    4. What is serial processing? Where does it begin and end? Name parts of pathway (4)
    • 1. Individual pathways traveling to brain are separate from each other (labeled lines)
    • 2. Homunculus (topographic organization of the somatosensory)
    • 3. Retinoic map (different parts of retina mapped in different parts of brain) and tonotopic map (auditory)
    • 4. Combines simple features to create more complex processing. Periphery (simple) --> cortex (complex)

    Receptors in spinal cord/brain stem --> ascending systems --> midbrain (auditory/visual tectum - superior and inferior colliculus) -> thalamus (relay station to cortex) --> cortex (first primary sensory area) --> other cortical areas.
  12. 1. As info ascends, what happens to it before thalamus? Where?
    2. What is the exception? Name pathway (3 parts)
    3. What is serial processing important for?
    • 1. No
    • 2. Because it goes straight through cortex (does not go through thalamus)
    • 3. McGerk Effect (combination of auditory and visual senses) - influenced by multiple modalities
  13. 1. Does olfactory sense go through thalamus?
    2. Why would odors elicit strong emotions?
    • 1. No
    • 2. Because it goes straight through cortex (does not go through thalamus)
  14. 1. Do touch receptors use parallel processing or serial processing?
    2. What receptor is for feeling vibration? Would this receptor be fast/slow? Would receptive fields be large/small? Why?
    • 1. Parallel (labeled lines)
    • 2. Pacinian Corpuscles - fast-adapting (vibration = rapid oscillation) and large (enables single receptor to integrate more info to detect vibration)
  15. 1. What receptor is for feeling fine touch (precision)? Would this receptor be fast/slow? Would receptive fields be large/small? Why?

    2. What receptor is for feeling fine touch (texture)? Would this receptor be fast/slow? Would receptive fields be large/small? Why?

    What does it specifically need to discern between?
    1. Merkel's Disc - slow-adapting (tonic) to recognize precise forms of bumps. Small for higher acuity (increased receptors in field and improve perception of intersection) - reading braille.

    2. Meissner's corpuscle - fine touch (texture) - fast - only needs to determine whether its smooth or bumpy. Small - to distinguish information instead of lumping it all together.

    Whether it's bumpy or smooth - not individual bumps.
  16. 1. What receptor is for feeling stretch? Would this receptor be fast/slow? Would receptive fields be large/small? Why?
    1. Ruffini's ending - slow to get accurate representation about duration of stimulus. Large - don't need to know exactly WHERE stimulus is occurring, just need to know that it is occurring at all.
  17. Name the four touch receptors found in skin, what they're responsible for sensing, whether they employ fast/slow-acting cells and whether they have large/small receptors.
    • 1. Pacinian corpuscles (vibration) - fast, large
    • 2. Merkel's discs (fine touch - precise) - slow, small
    • 3. Meissner's corpuscles (fine touch - texture) - fast, small
    • 4. Ruffini's ending (stretch) - slow - duration of stimulus & large
  18. 1. What happens when touch receptors reach generator potential and transduce stimulus? pathway contains 6 places - where does decussation occur?

    2. What would occur if you got lesion on left somatosensory cortex? Spinal lesion on right side of body?
    1. Release NT onto neurons whose cell bodies are in dorsal horn --< dorsal root ganglion, ascends through dorsal column of spinal cord, projects upon medulla (decussation) --> thalamus --> S1 Cortex

    2. Both --> can't sense touch on right side of body!
  19. 1. On homunculus of somatosensory cortex, what parts are overrepresented/ What is characteristic of these parts and what are they better at doing?

    2. If you record somatosensory cortex from cortical cell, what will you see? (2) What is this a result of?
    1. Lips/fingers - parts of body with greater density of receptor cells - finer acuity.

    2. (1) precise receptive field to determine spatial location and (2) submodality - one aspect of touch (light touch vs. deep pressure)

    This is a result of how labeled lines from receptor cells in periphery converge and interact in projection patterns of cortex.
  20. 1. Very basically, how is somatosensory cortex organized? (3)
    2. What is true about all cells in a column? (2)
    3. What does each column represent? (2)
    4. What types of cells do wide columns receive info from? Narrow columns? What happens to this information?
    • 1. Columns, layers, and areas
    • 2. Columnar cells all compute the same thing
    • 3. Each column is for one receptor type and one location in space
    • 4. Fast-acting; slow-acting. It's integrated into combination.
  21. Somatosensory cortex layers:
    Describe what layers 1-6 do.
    • 1. Few neurons - more pathway projections (axons)
    • 2 & 3 - output: projection to other cortical regions
    • 4 - input (always) from thalamus. This is the first stop then shares info with other layers
    • 5 - shares info with basal ganglia - important for modulating motor systems.
    • 6 - shares info with thalamus
  22. What is so great about somatosensory cortex's layers? (4)
    • 1. Evolutionarily wonderful b/c all cells are close together in proximity so:
    • (1) all aligned and can repeat same types of computations again
    • (2) faster - short axons & dendrites
    • (3) More efficient
    • (4) Saves space - more compact, can fit more computational power)
  23. What do areas do?

    What does area 1 do?
    Area 2?
    Area 3 a and b?

    Why would different parts of cortex have varying thickness?
    Areas combine columns and layers in higher submodality.

    Area 1 produces sensation of texture

    Area 2 produces sensation of size & shape of objects

    Area 3a and 3b divide sensation according to part of skin stimulated (3a = superficial; 3b = deep)

    Different computational power needs
  24. Plasticity:
    1. Can receptive fields be changed by experience?
    2. What happens when a finger is removed?
    What happens when a monkey is trained to keep two fingers on a rotating stimulating disc
    3. Pro musicians?
    4. Man who got new hand?
    • 1. Yes
    • 2. The cortical representations of surrounding finger expand to fill space

    • Two fingers that are stimulated - cortical representations expand
    • 3. Increased cortical representation of left hand
    • 4. After 35 handless years, was able to sense and control hand
Card Set:
B455 Intro to Sensory Systems
2013-03-04 13:48:40

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