Vision & Somatosensation

Question 1

Define prosopagnosia

Answer 1

inability to identify faces (face blindness)

bilateral damage to fusiform gyrus (FFA) in the rental stream but more commonly congenital

visual system functions but one cannot recognize faces

Question 2

Describe Capgras Syndrome

Answer 2

belief that a familiar person has been replaced with an exact duplicate
dislocation between face recognition processing in the FFA (fusiform face area) and emotional evaluation processing in the amygdala

Question 3

Roughly describe the routes of the dorsal and ventral streams of visual processing

Answer 3

ventral (what) occipital-temporal, bottom v4

transfers visual information from occipital lobe to temporal lobe, to tell us what it is we saw (and how we should categorize it)
cones in retina —> parvocellular cells in lateral geniculate nucleus (LGN) —> V1 —> V2 —> V4 —> temporal lobe (bottom)
position and size invariance

dorsal stream (where), occipital-parietal, top v5

transfers visual information from occipital lobe to parietal lobe, to tell us where it is we saw (and how we should interact)
rods in retina —> magnocellular cells in lateral geniculate nucleus (LGN) —> V1 —> V2 —> V5 —> parietal lobe (top)

Question 4

Describe what motion blindness is and which brain area is typically damaged

Answer 4

inability to detect motion in visual stimuli though the stimuli itself can still be seen
caused by damage to V5 (dorsal stream)

Question 5

Describe hemispatial neglect: what are some of the symptoms, the brain areas affected,
what fMRI of people with hemispatial neglect reveals about their visual processing, etc.

Answer 5

caused by damage to the right parietal lobe, total neglect to right side of world
nothing wrong with visual system, problem is purely placing attention on left side of world
fMRI while person with hemineglect is presented with an object in their left visual field —> patient reports being unaware of stimulus —> fMRI detects activation in primary and secondary visual cortices

Question 6

Define what a multistable percept is. Give an example and describe how people tend to
process these ambiguous stimuli. Describe some phenomena associated with
multistable percepts, i.e., how do young children typically process them?

Answer 6

multistable precept
brain actively interprets ambiguous stimuli

ex: old woman and young woman

Question 7

Describe the Ebbinghaus illusion and how not everyone is as susceptible to it.

Answer 7

children aged 10 and under and a sample of university students, the illusion was found more often to cause relative-size deception in adults, who have high context-sensitivity, than deception in young children, who possess low context-sensitivity

Question 8

Define the two types of somatosensation

Answer 8

1. cutaneous/subcutaneous system: touch, vibration, pressure, skin tension
2. nociceptive system: pain and temperature

Question 9

You don’t need to know the different types of receptors, (e.g., Pacinian corpuscle, Ruffini’s corpuscle), but have a sense of how there are different receptors sensing
different types of sensations and how these are located in different places and lead to
different levels of sensitivity

Answer 9

different receptors

have a sense of how there are different receptors sensing different types of sensations and how these are located in different places and lead to different levels of sensitivity

the skin is packed with receptors that respond to different sensations — some have smaller receptive fields (near skin’s surface) to pick up more acute sensations, others have large receptive fields (usually in deeper layers of skin) that respond to greater pressures

Question 10

Be able to trace the somatosensory pathway and locate its components

Answer 10

C -> S -> Md -> Mb -> VNP of thalamus -> S1

skin receptor cells —> spinal cord —> medulla —> midbrain —> ventral posterior nucleus of the thalamus —> primary somatosensory cortex

mechanoreceptors and nocireceptors receive stimuli —> neurons innervating a specific area come together to form a dorsal root, or bundle of fibers entering the spinal cord in the same place —> somatosensory input enters spinal cord via dorsal root ganglion —> information crosses the midline of the body at the medulla —> goes through midbrain to the ventral posterior nucleus of the thalamus —> and enters into the primary somatosensory cortex (S1)

Question 11

Identify where along this pathway somatosensory information crosses to the other side.

Answer 11

information crosses the midline of the body at the medulla

Question 12

Be able to locate the primary and secondary somatosensory cortices

Answer 12

primary = big bar
secondly = small spot on bottom right

Question 13

Describe what a nociceptor is

Answer 13

sensory receptors that mediate pain, detect noxious stimuli from environment

myelinated nocireceptors: fast, sharp pain
unmyelinated nocireceptors: dull, lasting pain

Question 14

Be able to trace the pain pathway and locate its components

Answer 14

Sc -> Md -> Mb -> Forebrain

spinal cord —> medulla —> midbrain —> forebrain

injury is signaled by nocireceptors and sent to spinal cord —> input crosses to other side in medulla —> information then travels through midbrain to the thalamus —> thalamus relays info to the somatosensory and insular cortex, and cingulate cortex

Question 15

• Describe the two components of pain and the different brain regions associated with
  each component

Answer 15

emotional and cognitive components of pain

thalamus: receives pain signals and relays them to other brain regions — cognitive component—memory of previous pain experience

prefrontal cortex: focuses attention on or away from pain

amygdala: modulates degree of pain received, depending on context — emotional component—unpleasantness and suffering
insula: encodes degree of pain and responds to pain of others

Question 16

Locate the anterior cingulate cortex and role

Answer 16

involved in encoding the intensity of a pain stimulus, as well as the emotional component of pain

back collar

Question 17

Explain how different brain areas are thought to process aspects of pain, e.g., the periaqueductal gray, amygdala, insula, prefrontal cortex, thalamus, and primary somatosensory cortex

Answer 17

regions are not selectively or exclusively activated by nociception or restricted solely to pain perception. Rather, regions serving several neurological functions including cognition, emotion, motivation and sensation are functionally connected in the context of nociception and give rise to the experience of pain

periaqueductal gray matter: important for endogenous pain relief

endogenous component—endogenous responses like respiratory and blood pressure changes

amygdala: modulates degree of pain received, depending on context
emotional component—unpleasantness and suffering

insula: encodes degree of pain and responds to pain in others
motor component which includes the motor reflexes

prefrontal cortex: focuses attention on or away from pain
distraction/catastrophizing component — various behavioral and psychological responses that depend on social environment and personality

thalamus: receives pain signals and relays them to other brain regions
cognitive component—memory of previous pain experience

primary somatosensory cortex: localizes pain on map of body
sensory-discriminative component—localization and intensity of pain

supports gate control theory — the idea that pain results from nocireceptive and nonnocireceptive pain pathways

Question 18

Broadly explain how pain modulation pathways work and how this modulation seems to
go awry in cases of chronic pain

Answer 18

pain lasting 3 months or more

what causes it? failure of pain modulation system to inhibit pain

Question 19

Explain the idea of hierarchical processing in vision, what this looks like in terms of which areas process which types of information and how damage at particular points in the hierarchy would lead to different symptoms

Answer 19

eyes —> V1 —> V2 —> secondary and tertiary visual and association cortices

specific, signal-oriented responses to more abstract, object-oriented responses

Question 20

Explain the phenomenon of blindsight and what it reveals about visual processing

Answer 20

ability of people who are cortically blind due to V1 lesions to see without conscious awareness

suggests visual information goes to other places besides V1

stimulus presented to blind side —> can “guess” what it was with higher rate than probability even if they don’t report seeing any stimulus

Question 21

Cognitive behavioral therapy (CBT)

Answer 21

is a short-term, goal-oriented psychotherapy treatment that takes a hands-on, practical approach to problem-solving. Its goal is to change patterns of thinking or behavior that are behind people’s difficulties, and so change the way they feel.

Question 22

Locate the FFA

Answer 22

fusiform face area is located inside the fusiform gyrus (on bottom of brain)

responsible for face recognition

Question 23

super recognizer

Answer 23

people who never forget a face

Question 24

Explain how the basic hierarchical model of sensory processing isn’t quite accurate and describe what a more realistic model might look like. Explain how with perception we’re often building an internal model and then checking to see whether and where what we’re seeing comports with that model

Answer 24

we enjoy a unified picture of the world instead of having a separate visual world, auditory world, etc.
the brain produces a unified picture of the world given its specialized processing streams

interconnectivity forces cortical neurons to “come to agreement”

not a basic hierarchical model, but instead an interconnected web of crosstalk and feedback

We build an internal model, which we constantly
update based on prediction errors

———————-

—> what are prediction errors and how do we learn from them in regard to sensory processing?

rewards produce learning 

  —> why? 

keeping the body alive is not an easy task —> the necessary ingredients for survival are seldom readily available (food, water, etc.) —> to stay alive, animals must do more than wander around randomly looking for resources —> they must learn to PREDICT how to find them —>

—————> DONE THROUGH PREDICTION ERROR: the difference between expected outcome and actual outcome

RPE = actual outcome - expected outcome

across most animal species, involves the same midbrain dopamine neurons and their targets in the striatum

Question 25

somatosensory mapping

Answer 25

the body is topographically mapped on the somatosensory cortex

somatotopic: represent adjacent body parts

sensory homunculus: proportioned representation

Question 26

Dr. Ramachandran could touch the patient’s cheek with a Q-tip, and the patient would feel a sensation in his phantom limb

Answer 26

changes to the body plan—such as missing limb—lead to massive cortical reorganization

perceptual confusion — ex: cortex that previously formerly responded to touch on arm now responds to touch on face

important implications —> ALTHOUGH PAIN, WARMTH, AND TOUCH FEEL EMBODIED IN OUR LIMBS, THE FACT IS THAT THEY ARISE IN THE BRAIN

//therefore you can lose a limb without losing sensation in it // and alternatively you can lose sensation without losing the actual limb

Question 27

two-point threshold

how is greater density established?

Answer 27

resolution of touch: 2-point threshold procedure
the smallest separation at which two points applied simultaneously to the skin can be distinguished from one

—>small distance in highly sensitive areas, large distance in less sensitive areas (fingers < 5 mm, upper arm > 45 mm)

—>greater sensitivity in the fingers is due to the greater density of receptors & smaller receptive fields of the receptors in the fingers relative to the arm

SMALLER RECEPTIVE FEILDS + GREATER DENSITY OF RECEPTORS ===> +SENSITIVITY