Test 3

optic nerve

neurons/nerve bundles closest to retina

• both sides of both eyes collect info from both sides of the visual field

• before optic chiasm

optic chiasm

where criss crossing of visual information occurs

• info from left visual field (collected from both eyes) gets processed in the right hemisphere

optic tract

visual information makes its way to the thalamus

• after the optic chiasm

Lateral Geniculate Nucleus (LGN)

nucleus in the thalamus

• APs make their way to primary visual cortex (V1)

optic radiation

tells us we’ve crossed the thalamus and going to occipital lobe

primary visual cortex

information that is first landing in the occipital lobe (V1)

• first place info lands where processing occurs

• moves information toward higher order processing (visual processing areas 2, 3, 4, 5) → more complexity in processing (higher area, more complex - colour, motion, orientation)

Calcarine sulcus

location of area V1; divides the upper and lower halves of the world (what we’re looking at)

Lingual gyrus

visual cortical regions V2 and VP (ventral posterior area)

• VP is at the posterior area of the temporal lobe, closest to occipital

Fusiform gyrus

area V4; more anterior in the temporal

Occipital cortex

• could have more than 6 layers in the occipital cortex as opposed to everywhere else

  • possibly because V1 does a lot of work

• first cortical area involved in visual processing

• decides where information should be going

  • sends visual info received from LGN to extrastriate cortex areas for higher order processing (colour, motion, orientation)

• receives visual input from the LGN of the thalamus

Area V1

• laminar organization: most distinct of all cortical layers (in layer 4)

  • distinct layers, not uniform across the cortex

  • layer 1: axons, dendrites → layer 3: lots of pyramidal cells

  • layer 1 looks different from layer 3 = laminar organization

  • in this case, layer 4 is the most distinct

• heterogenous

  • has more than one distinct function (since there are different layers)

  • preserved in V2 (and V1)

Striate cortex

• another name for visual cortex, due to its striped appearance in layer 4

• layer 4 also has a striated appearance because different cell types

staining - cytoarchitecture (V1 & V2)

tells us the unique characteristics of the different cells in a particular layer

• Area V1

  • blobs = sensitive to colour

    • more metabolically active than other cells

  • interblobs = sensitive to orientation (found between the cells/blobs)

• Area V2

  • thin stripes = colour perception

  • thick stripes = form (shape) and motion perception

which area has the primary job of colour vision?

Area V4

• but distributed throughout the occipital cortex

• also plays a role in detection of movement, depth, and position (colour can change)

connections of the visual cortex - V1 (primary visual cortex)

• input from LGN

• output to all other levels

connections of the visual cortex - V2 (secondary visual cortex)

• works closely w/ V1 to move info to other areas of the brain

• output to all other levels

connections of the visual cortex - after V2

streams of processing

• output to parietal lobe: dorsal stream

• output to temporal lobe: ventral stream

• output to superior temporal sulcus (STS): STS stream

streams of processing

• dorsal stream: visual guidance of movements (where)

• ventral stream: object perception (what)

• STS stream: visuospatial functions

  • collecting info from both where and what pathways (it lies between them)

  • has access to info from both parietal and inferior temporal

Case study: organization of social perception & cognition within the STS

STS is involved in:

• language (stories vs nonsense speech)

• voices (voices vs environmental sounds)

• faces (moving faces vs moving objects)

• biological motion (point light humans vs point light objects)

• theory of mind (what’s happening in someone else’s mind)

Wernicke’s area = posterior section of the superior temporal gyrus and middle temporal gyrus, and by extension, the cortex in between them in the posterior STS.

BOLD fMRI studies linked other cognitive functions (e.g., social cognition and perception to STS)

what was the first cognitive function ascribed to STS?

language comprehension

Hierarchical organization of the occipital lobe

Vision begins in V1 is heterogenous, then moves to more specialized cortical zones

• blobs (V1): Area V4 → colour

• interblobs (V1): Area MT/V5 → motion

• V1 & V2: Area V3 → (dynamic form: shape of objects in different orientations, like during motion)

• selective lesions up the hierarchy produce specific visual deficits

• lesions to V1 are not aware of seeing

  • patients report not seeing anything, but will catch ball thrown at them

vision beyond the occipital lobe

vision-related areas in the brain make up about 55% of the total cortex

• vision is not just in the occipital lobe

• multiple visual regions in temporal, parietal, and frontal lobes

5 categories for vision

1. vision for action

2. action for vision

3. recognition

4. space

5. visual attention/how to not get overwhelmed

vision for action

• parietal visual areas in the dorsal stream

• reflex-based (not using your attention)

  • bottom-up

  • ducking, catching

action for vision

• attention-based (using your attention to visually scan an environment)

• visual scanning → top-down

• eye movements and selective attention

• normal subject: eye movements concentrate on facial features and directed more to left side of photograph (eye movements track shape of stimuli)

• agnosic subject: eye tracking is disorganized, not connected to shape of stimulus

visual recognition

• temporal lobes

  • recognizing object, face, person → temporal lobe processing

• object recognition

• what pathway (ventral)

visual space

• parietal lobes

  • where something is in the environment

  • where pathway (dorsal stream)

• spatial location

  • egocentric space: location of object relative to person

  • allocentric space: location of object relative to another

visual attention

paying attention to important characteristic of an image

• aka: how to not get overwhelmed

  • binding problem

  • brain doesn’t encode everything, lots of things we ignore in our visual system

Milner-Goodale Model

Ventral and Dorsal streams

• there is hierarchical processing in vision

Ventral stream:

• V3: dynamic form (perception of objects/shapes that change over time)

• V4: colour

Dorsal stream:

• V3A: form (shape)

• V4: motion (speed)

what’s the difference between areas V3 and V3A?

• V3: part of ventral stream; detects dynamic form

• V3A: part of dorsal stream; detects form/shape

monocular blindness

loss of sight in one eye

• due to damage to retina or optic nerve

bitemporal hemianopia

loss of vision in both temporal fields

• due to tumour to pituitary gland that puts pressure on the optic chiasm

• preserved nasal vision

right nasal hemianopia

lesion in the lateral chiasm leading to loss of vision in one nasal field

homonymous hemianopia

blindness of one visual field due to damage in either: optic tract, LGN, V1

quadrant-anopia

loss of vision in one-quarter of the visual field

• due to visual cortex lesions, particularly near calcarine sulcus

macular sparing

• differentiates lesions of the optic tract or thalamus from cortical lesions

  • lesions of occipital lobe will often spare the macula

• macular vision is preserved (spared from damage)

  • macula = small specialized area of high visual acuity, near retina

why/when does macular sparring occur?

• likely because the macular part of area V1 might receive double vascular supply from medial and cerebral artery

• lesions of occipital lobe often spare the macular region of the visual field (as opposed to lesions of the optic tract or thalamus)

scotoma

small visual cortex lesions, particularly near the calcarine sulcus

• produces blindspots (scotomas)

monocular blindness

bitemporal hemianopia

right nasal hemianopia

homonymous hemianopia

quadrant-anopia

macular sparing

hemianopia (loss of vision in one visual field)

quadrant-anopia

scotoma

Visual agnosia (definition)

neurological condition that affects person’s ability to recognize or interpret visual information, despite having normal vision

• broad term, need to specify what type of agnosia

types of visual agnosia

Object agnosia

• Apperceptive agnosia

  • Simultagnosia

• Associative agnosia

Other types of agnosia

• Prosopagnosia (facial agnosia)

• Alexia (dyslexia)

• Visuospatial

apperceptive agnosia

difficulty with tasks like matching or identifying objects by shape, size, colour

• due to: gross bilateral damage to occipital lobe

simultagnosia: inability to perceive more than one object at a time

• difficulty with tasks that require processing multiple objects/scenes at once

• e.g., reading, finding objects in cluttered space

associative agnosia

difficulty in recognizing objects due to a problem with connecting visual information with knowledge about the object

• can perceive objects, but cannot identify them

• due to: lesions of anterior temporal lobe

• e.g., able to copy drawing, but unable to name what they drew

  • semantic problem (intact perception, but cannot understand its meaning)

prosopagnosia

facial agnosia → loss of knowledge associated with faces

• cannot recognize previously known faces

• due to: bilateral damage in temporal cortex

alexia

dyslexia → inability to read

• due to: damage in left fusiform and lingual areas

visuospatial agnosia

• topographic disorganization

• inability to find one’s way

• due to: damage to occipitotemporal regions and medial fusiform and lingual areas

• symptom of dimentias

• other visual deficits can accompany it (facial recognition)

Case study: V1 damage and a scotoma

• MRI with lesion in occipital lobe + showing area of reduced visual acuity

• right infarct (dead tissue) in occipital lobe

• quadrantanopia (evidence from visual acuity)

• experienced blindsight: could perceive a prior location once the light moved into a “visual” quadrant

  • vision without consciousness → occurs if there’s damage to V1

blindsight

• vision without consciousness

• dedicated V1 function

• COME BACK TO THIS TO WATCH THE VIDEO

Case study: symptoms of hemianopia and cortical blindness (blindsight)

• MRI shows an angioma in right calcarine fissure

• symptoms include hemianopia and blindsight

• probably due to damage in V1

Case study: vascular abnormality resulting in damage to V5

• damage to medial temporal area (area MT/V5)

• symptoms include inability to intercept moving objects by using their hand

• therefore, there is loss of movement vision

Case study: bilateral hemorrhages in the occipitoparietal regions

• symptoms include optic ataxia → a deficit in visually guided hand movements

  • visually guiding hand to move in a direction — where pathway (where something is in space)

optic ataxia

impairments in using visually guided hand movements

Case study: right occipitotemporal lesion

• what pathway

• symptoms include prosopagnosia

  • deficit in facial recognition

  • unable to give an identity to someone

Case study: left occipitotemporal lesion

• Left → L → language

• symptoms include alexia

  • inability to read

mental rotation

the cognitive ability to imaginatively turn 2D or 3D objects in one’s mind to determine if they match another object, regardless of orientation

although V1 appears to be anatomically homogenous…

staining it with cytochrome oxidase (enzyme for making energy available to cells), shows it to be heterogenous

what differentiates cat/dog vision from humans?

colour-related info processing enriches our capacity to detect motion, depth, position

• in the absence of colour analysis, dogs/cats have overall reduced visual capacity compared to humans

single-celled organism Euglena

• alters its swim pattern as a function of ambient light in different parts of the pond

• since sunlight helps food production, it follows it to feed

• example of how vision for motion evolved before vision for recogntion

Milner & Goodale

distinguished between ventral and dorsal streams

• blind patient, but still had unconscious vision (dorsal stream intact)

• vs patients with damaged dorsal stream who can’t reach accurately

proposed that dorsal stream = set of systems for visual control of action, based on:

1. visual neurons in posterior parietal regions are unique in that they are only active when the brain acts on visual information

2. visual posterior parietal neurons act as an interface between analysis of the visual world and motor action taken on it

3. most visual impairments associated with lesions to parietal cortex can be characterized as visuomotor or visuospatial

Limitation to the Milner—Goodale model

• it mentions 2 distinct visual streams

  • dorsal: guiding movements

  • ventral: identifying objects

• a third stream of visual processing: STS stream

  • associated with both the parietal and temporal pathways

the STS is part of the multimodal cortex characterized by…

polysensory neurons: neurons responsive to both visual and auditory or both visual and somatosensory input

parietal lobe intro slide

• spatial awareness

• body awareness: where you are located in the room

• proprioception

• attention/sensory attentional control

• mathematical cognition (+, -, x, /)

• numerical cognition: understanding that there are multiple vs one

2 main functions of the parietal lobes

1. process and integrate somatosensory information

2. process and integrate visual information

somatosensory system

comprises the receptors and processing centres to produce the experience of:

• touch

• temperature

• proprioception

• nociception

anterior border of parietal lobe

marked by central fissure (border between frontal and parietal lobe)

• separates precentral and postcentral gyri

ventral border of parietal lobe

marked by Sylvian/lateral fissure

parietal lobe is dorsal to the…

cingulate gyrus

• connects occipital, temporal, parietal lobes to frontal

• mediates attention (prayer, meditation)

posterior border

marked by the parieto-occipital sulcus

postcentral gyrus

main sensory receptive area for the sense of touch

• very specific, could think of it as unimodal (as in only sense of touch)

inferior parietal lobe (what does it contain?)

contains a multimodal associative area that receives auditory, visual, and somatosensory inputs

• where pathway processing

• includes 2 gyri:

  • supramarginal gyrus

  • angular gyrus

• one of the last structures to mature

superior temporal gyrus

includes Wernicke’s area

• as opposed to inferior temporal gyrus, which is the what pathway (ventral)

inferior parietal lobe is involved in…

comprehension of written language

• it’s one of the last structures to mature, which may explain why children typically do not begin to read/write till they’re 5-6

angular gyrus (of the inferior parietal lobe)

• involved in language processing/reading

• converts written words into meaningful information by integrating visual information from eyes w/ language-related processing areas

• reading comprehension, word recognition, semantic processing

word recognition in terms of parietal cortex

organizing words/letters (spatial organization)

word recognition in terms of temporal cortex

giving an identity to the words being read

Vogt and Vogt + Forster

architectonic mapping of the brain

• electrophysiological mapping

• forsees development of modern brain mapping

brodmann subdivided cerebral cortex into numerous areas based on cytoarchitecture

anterior zone: areas 1, 2, 3, 43

• closest to frontal cortex

posterior zone: all other areas of parietal cortex

• closest to occipital cortex

Von Economo’s cytoarchitectonic regions

for the labelling of the posterior zone

• PE, PF, PG

functional zones of the parietal lobe

• anterior zone: somatosensory cortex

• posterior zone: where/how pathway

posterior parietal areas

PE, PF, PG

somatotopic organization

• somatosensory cortex (postcentral gyrus) → anterior zone

• contains the sensory homunculus

• assists with somatosensation:

  • intensity

  • timing

  • location

  • temperature

  • pressure

  • pain

where does somatotopic organization also exist (other than somatosensory cortex)?

in the cerebellum

Area PE

Connections:

• somatosensory cortex (postcentral gyrus)

• motor cortex (precentral gyrus)

• PF

Function:

• somatosensory

• role in guiding movement by providing info about limb position

if someone has difficulty with a sport they have played for years/dancer, and have trouble moving their limbs in that way, what area is most likely damaged?

area PE

Area PF

Connections:

• Somatosensory cortex

• Motor cortex

• Premotor cortex

• PG

Function:

• part of the mirror neuron system

• theory of mind: facilitated by mirror neurons

Area PG

Connections are multimodal:

• receives complex connections (visual, somesthetic, proprioceptive, auditory, vestibular, oculomotor, cingulate)

Function:

• dorsal stream

• parieto-temporo-occipital crossroads

posterior parietal cortex is also closely related to…

the prefrontal cortex and limbic system

• memory

• spatially guided behaviour

• spatial navigation

pathways from posterior parietal regions

• posterio-premotor: “where”/”how” pathway

• posterio-prefrontal: working memory

• posterio-medial temporal: spatial navigation

Theory of parietal frontal lobe function

• anterior zones process somatic sensations and perceptions

• posterior zones integrate vision with multimodal info

viewer-centered object identification

parietal processing → where pathway (orientation, location in space)

• works with temporal processing which helps figure out what we’re looking at (object identity)

• binding problem

3 somatosensory symptoms of parietal lobe lesions

• afferent paresis

• astereognosis

• abnormally high sensory threshold

afferent paresis

clumsy finger movement due to lack of feedback about finger position