6/3- Higher Cortical Function

Question 1

What is sensation (def)?

Answer 1

Detecting a stimulus e.g. photoreceptor capturing photon

Question 2

What is perception (def)?

Answer 2

Understanding the stimulus; construction of the brain (requires higher cortical function)

Question 3

Examples of how perception differs from visual sensation?

Answer 3

• Gradients
• Moving sticks
• Subjective contours

Question 4

Examples of higher cortical function processes (pt cases)?

Answer 4

• Can only see 1 thing at a time; cannot perceive 2 objects simultaneously
• Deaf man loses ability to sign with his fingers, even though his muscles are fine
• Paralyzed but completely denies it
• Can copy a drawing but cannot name what it is
• Can understand language but has lost the ability to read or write

Question 5

What makes a cortex area “primary”?

Answer 5

Input mainly from thalamic relay nuclei e.g. striate cortex receives input from LGN

Question 6

What makes a cortex area “secondary”?

Answer 6

Input mainly from primary cortex within the sensory system

Question 7

What makes a cortex area “tertiary” (or higher- association cortex)

Answer 7

Input from 1+ sensory system, usually from 2ndary sensory cortex

Question 8

3 principles guiding the interactions of sensory cortex?

Answer 8

• Hierarchical organization (specificity and complexity increases with each level)
• Functional segregation (some groups care about color, edges, angles, movement…)
• Parallel processing

Question 9

Damage results in difference due to hierarchical organization. What happens when you damage receptors?

Answer 9

Complete loss of ability to perceive in that modality

(e.g. deafness, blindness)

Question 10

Damage results in difference due to hierarchical organization. What happens when you damage ‘higher’ areas?

Answer 10

Complex and specific deficits

(e.g. man who mistook his wife for a hat)

Question 11

Where are the primary, secondary, and tertiary cortices located for vision?

Answer 11

Primary (V1)- posterior occipital lobe

Secondary (V2):

• Prestriate cortex- a band of tissue surrounding V1
• Inferotemporal cortex

Tertiary (V3)- various areas, largest single area is in posterior parietal cortex

Question 12

What is a scotoma?

Answer 12

Area of bindness resulting from damage to V1

• Blind in corresponding contralateral visual field of both eyes
• Deficit may not be readily detected due to phenomenon of completion (ex of physiological scotoma (although not from V1 damage) everyone filling in background over area of optic disc)

Question 13

What results from damage to secondary visual cortex?

Answer 13

Visual agnosias- failure of recognition

• Visual agnosia: visual capacities intact, but unable to recognize (recall man who mistook wife for hat); many subtypes (object, motion/akinetopsia, color/acrhomatopsia)
• These result from damage to specific areas of 2ndary visual cortex

Question 14

2 examples of visual agnosias (broad types)?

Answer 14

Associative agnosia- cannot associate visually-presented objects with their semantic meaning, or organize objects into semantic categories

Apperceptive agnosia- fail tests such as visual matching, comparing similar figures and copying drawings

These match to the dorsal and ventral streams

Question 15

What is the dorsal stream in charge of? Where does it go?

Answer 15

• “Where”/control of behavior
• V1 to dorsal; V2 to posterior parietal

Question 16

What is the ventral stream in charge of? Where does it go?

Answer 16

• “What”/conscious perception
• V1 to ventral; V2 to inferotemporal cortex

Question 17

Where is the lesion in a pt who can’t see objects but can grasp them correctly (can’t tell you orientation, but can interact to put something in slot just fine)

Answer 17

Ventral stream

Question 18

Where is the lesion in a pt who can see but cannot grasp correctly?

Answer 18

Dorsal stream

Question 19

What is the inferotemporal cortex?

Answer 19

Final destination (?) cortex of the ventral “what” pathway

• Higher areas in inferotemporal cortex are specific to faces, bodies, animals, houses, tools, etc.
• Moving up the pathway: features -> feature conjunctions -> objects

Question 20

What does each level of the visual pathway process/recognize?

Answer 20

Anterior inferotemporal: objects, categories

Posterior inferotemporal: complex forms

V4: complex geometric shapes

V2: figures, contours

V1: orientation

LGN: luminance, contrast…

Retina: luminance, contrast

Question 21

What is prosopagnosia?

Answer 21

Inability to recognize faces (face blindness)

Question 22

Is prosopagnosia a problem with the ventral or dorsal stream? Where is the lesion?

Answer 22

• Problem with the ventral stream
• Lesion in inferotemporal lobe (bilateral damage to the face area in the ventral what/conscious perception stream)

Question 23

T/F: in prosopagnosia, unconscious face recognition is no longer possible

Answer 23

False.

Dorsal stream is still intact; large skin conductance responses to familiar vs. unfamiliar faces has proved that unconscious face recognition is still possible

Question 24

What is apraxia?

Answer 24

Deficit in executing or carrying out learned purposeful movements, despite desire and physical ability

Question 25

Is **apraxia** a problem with the ventral or dorsal stream?

Answer 25

- Problem with the **dorsal** stream

Question 26

Broader damage to **dorsal** stream can lead to what?

Answer 26

Problems with **attention**; we have the illusion that we pay attention to everything but we can't (e. g. Where's Waldo picture) (e. g. flashing changing pictures)

Question 27

What is the purpose of **selective attention**?

Answer 27

**Improves perception** of what is attended to and interferes with that which is not. Selective attention acts as a controller to i**ncrease the efficiency of all the basic sensorimotor systems**

Question 28

What are the two types of attentive processes? Both are \_\_\_?

Answer 28

**- Internal cognitive processes** (endogenous attention) **- External events** (exogenous attention) focus attention Both of these are **spatial**

Question 29

What is **hemi-neglect**?

Answer 29

Aka **"hemi-attention"** - Neglect most often occurs following damage to the **R parietal** - Pts behave as though one half of the world does not exist, but are completely **unaware** of the missing half; they do not miss it - Only dress/shave one side, only eat half dinner, bump into doors, ignore/transpose sounds and sights from left side, reading errors - **NOT caused by a visual deficit** (can still see something scary in other hemisphere) (- Pt can see perfectly fine, but left half of visual field is ignored) **TESTS**: only draw half of a picture, 12 digits of clock all put on right side, deviated midline when told to bisect, read only words on the right side, copy only right side of a picture

Question 30

Can attentional systems be broken?

Answer 30

Yes; damage to the **dorsal stream** (involved with localizing objects in space) e.g. damage to **parietal** **lobe**

Question 31

What causes **Balint's syndrome**?

Answer 31

**Bilateral** damage to the **posterior parietal** lobes (as opposed to just R damage as in hemi-neglect); damage to **dorsal stream**

Question 32

What is Balint's syndrome? Examples?

Answer 32

Can't see visual field as a whole

Question 33

What is **simultanagnosia**?

Answer 33

**Inability to see visual field as a whole** (result of Balint's?) - Difficulty in copying/drawing/writing because they are unable to see both the end of the pen and what is on the paper at the same time - Unable to describe complex scene - Test with overlapped drawings

Question 34

Where does the ventral stream run? Damage to the path causes what deficits?

Answer 34

**Occipito-temporal** - Visual object agnosias (e.g. prosopagnosia) - Achromatopsia (loss of color vision)

Question 35

Where does the dorsal stream run? Damage to the path causes what deficits?

Answer 35

**Occipito-parietal** - Apraxia - Optic ataxia (deficit in reaching under visual guidance) - Akinetopsia (motion blindness) - Disorders of spatial cognition (hemi-neglect, Balint's, simultagnosia)

Question 36

Where is the primary somatosensory cortex? Organization? Is input uni or bilateral?

Answer 36

- **Postcentral** **gyrus** - **Somatotopic** organization - Input is largely **contralateral**

Question 37

What determines sensitivity?

Answer 37

Amount of somatosensory cortex devoted to it

Question 38

What is the input for SII? Organization? uni or bilateral?

Answer 38

- Mainly input from S1 - Somatotopic - Input from both sides of body

Question 39

Where does output from SI and SII go?

Answer 39

**Association** cortex in **posterior parietal** lobe

Question 40

What is **astereognosia**?

Answer 40

Inabiilty to recognize objects by touch

Question 41

What is **asomatognosia**?

Answer 41

Failure to recognize parts of one's own body e.g. man who tries to throw his own leg out of the bed because he thinks it's not his

Question 42

What often accompanies asomatognosia?

Answer 42

**Anosagnosia**- failure of the pt to recognize his symptoms (e.g. not recognizing that he was paralyzed)

Question 43

Pathway of sound input?

Answer 43

- Eardrum - Ossicles - Oval window - Fluid of cochlea - Auditory nerve axons - Ipsilateral cochlear nucleus - Superior olives - Inferior colliculi - Medial geniculate nucleus - Primary auditory cortex

Question 44

How is the auditory cortex organized?

Answer 44

- **Functional columns** (cells of a columm respond to the same frequency) - **Tonotopic** organization

Question 45

What does the primary auditory cortex sense? Secondary? Tertiary?

Answer 45

**Primary**: pure tones **Secondary**: respond to more complex stimuli such as monkey calls (do not respond well to pure tones) **Tertiary**: language comprehension