Vision & Somatosensation Flashcards
Define prosopagnosia
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
Describe Capgras Syndrome
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
Roughly describe the routes of the dorsal and ventral streams of visual processing
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)
Describe what motion blindness is and which brain area is typically damaged
inability to detect motion in visual stimuli though the stimuli itself can still be seen
caused by damage to V5 (dorsal stream)
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.
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
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?
multistable precept
brain actively interprets ambiguous stimuli
ex: old woman and young woman
Describe the Ebbinghaus illusion and how not everyone is as susceptible to it.
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
Define the two types of somatosensation
- cutaneous/subcutaneous system: touch, vibration, pressure, skin tension
- nociceptive system: pain and temperature
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
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
Be able to trace the somatosensory pathway and locate its components
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)
Identify where along this pathway somatosensory information crosses to the other side.
information crosses the midline of the body at the medulla
Be able to locate the primary and secondary somatosensory cortices
primary = big bar secondly = small spot on bottom right
Describe what a nociceptor is
sensory receptors that mediate pain, detect noxious stimuli from environment
myelinated nocireceptors: fast, sharp pain
unmyelinated nocireceptors: dull, lasting pain
Be able to trace the pain pathway and locate its components
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
- Describe the two components of pain and the different brain regions associated with
each component
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
Locate the anterior cingulate cortex and role
involved in encoding the intensity of a pain stimulus, as well as the emotional component of pain
back collar
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
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
Broadly explain how pain modulation pathways work and how this modulation seems to
go awry in cases of chronic pain
pain lasting 3 months or more
what causes it? failure of pain modulation system to inhibit pain
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
eyes —> V1 —> V2 —> secondary and tertiary visual and association cortices
specific, signal-oriented responses to more abstract, object-oriented responses
Explain the phenomenon of blindsight and what it reveals about visual processing
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
Cognitive behavioral therapy (CBT)
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.
Locate the FFA
fusiform face area is located inside the fusiform gyrus (on bottom of brain)
responsible for face recognition
super recognizer
people who never forget a face
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
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
somatosensory mapping
the body is topographically mapped on the somatosensory cortex
somatotopic: represent adjacent body parts
sensory homunculus: proportioned representation
Dr. Ramachandran could touch the patient’s cheek with a Q-tip, and the patient would feel a sensation in his phantom limb
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
two-point threshold
how is greater density established?
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
