Lecture 11

Question 1

Receptive fields

Answer 1

is the area of visual space where the presence of light influences the firing rate of the neuron

To find it, animal focuses on a point then shine light on areas near and far to the fixation point and see where in visual space a change alters the spiking activity of the neuron

Question 2

Receptive fields and moving through the visual network

Answer 2

Outside the fovea, many photoreceptors go to one bipolar cell and many bipolar cells go to one ganglion cell
So the receptive fields get bigger

This happens to all visual information at deeper parts of the brain. At the deepest levels it is all of visual space and looks for patterns such as moms face

Question 3

Fist cell in pathway

Answer 3

When correct wavelength of light is presented in a photoreceptors cell the photoreceptor hyperpolarizes and becomes less active - releases less glutamate

Question 4

Second cell in pathway

Answer 4

ON/OFF bipolar cells

Respond differently because they have different glutamate receptors. ON only have inhibitory receptors, off have excitatory

Question 5

ON bipolar cell

Answer 5

When light is presented in ON bipolar cells they depolarize and release glutamate

Question 6

OFF bipolar cells

Answer 6

Hyperpolarize when light is presented to their visual fields. Less glutamate

Question 7

Third cell in the pathway

Types of cells

Implication of all light or all dark

Mechanism of contrast detection

Answer 7

Retinal ganglion cells integrate info from many on/off bipolar cells

Their receptive fields have an CENTER SURROUND organizations.

ON CELL
Have activity when light is in the middle and inhibition when light is in the periphery.

OFF CELL
Have inhibition when light is in the middle and activity when light is in the periphery.

If all area has light or all area has darkness - not much change in firing.

BUT of there is a change in the visual input within this field like a line or an edge, then light from this will enter one part and not the other. This will hugely change neuronal activity.

And so these cells are particularly good at edges and contrast

Question 8

Color vision in ganglion cells

Answer 8

Yellow on/blue off
Blue on/yellow off

Red on/Green off
Green on/Red off

So fire in distinct ways with specific color combinations greatly helping color vision.

Question 9

What do Retinal Ganglion Cells (RGCs) do

Answer 9

Processing for color and edges

Question 10

Path from ganglion to V1

Answer 10

Goes to the lateral geniculate nucleus LGN to V1

Question 11

Receptive fields of V1

Answer 11

Are the sum of many RGCs.

Question 12

Simple cells in V1

Answer 12

Are sensitive to the orientation of light

Can be understood as the sums of the afferent fibers

Also has center/surround orientation
If light is just off from its desired orientation, it fires less

There are cells sensitive for all orientations

Organized into columns with all orientations

Helps to ID edges etc. Downstream neurons will organise this

Question 13

Visual association cortex

Answer 13

25% or cortex is for visual input

The part of the occp lobe that surrounds V1 is the visual association cortex

Each part recognises particular features of the visual environment such as shapes, movement etc

Question 14

Striate/Extrastriate

Answer 14

V1=striate

V2+ = extrastriate

Question 15

Where pathway

Deficit

Answer 15

Dorsal stream

Post parietal pathway

Spatial info

Deficit - Akinetopsia

Question 16

What pathway

Answer 16

Ventral stream

Inferior temporal cortex

Identifies form, what the object is and its color

Deficit - cerebral achromatopsia
No color vision
Deny having it
Everything is shades f grey
Were not born with it, regular achromatopsia do not say  this as it is not news for them, they were born with it

When color aspects of association cortex go, you also lose the memories of those colors

Question 17

Depth perception

Answer 17

Monocular vision
Some V1 neurons respond to monocular depth cues and visual input from just one eye

Binocular vision
MOST respond to input from both

Depth perception - many monocular cues. Relative size, amount of detail, relative movement as we move eyes etc

Question 18

Stereopsis

Answer 18

The perception of depth that emerges from the fusion of two slightly different projections of an image in the two retinas. Difference between the two is called retinal disparity

Improves depth perception

Question 19

Agnosia

Answer 19

A deficit in ability to recognize or understand sensory information

Relates to a problem in an association cortex, or to problems with the sensory neurons themselves or to the primary areas

Question 20

Predictive coding theory of perception

Answer 20

Most pathways in vision are bidirectional. Descending neural activity based on previous experience cancels out upward info so you only have the novel, differences left.

Every level except lowest makes these predictions via feedback connections. What propagates this is the prediction error signal which is used to improve future predictions.

Question 21

Everyone agrees on what they see

Answer 21

Which implies that perception happens THEN cognition.

Not everyone agrees, some say it is all done together and thus how you see the world shapes what you see.

Question 22

Visual information pathways (3)

Answer 22

(1) thalamus - LGN goes to V1
Determines what you are looking at. Creates a mental image of the entire visual space

(2) midbrain - Superior Colliculi
Fast, visually guided movements
Doesn’t know what you are looking at but knows where light is moving in visual space

(3) Hypothalamus: Circadian rhythm
Doesn’t know what you are looking at but knows how much light is present in your environment

Question 23

3 parts of somatosensory system

Answer 23

Exteroceptive (cutaneous) responds to external stimuli

Interoceptive (organic senses) provides information about conditions within the body and is responsible for its maintenance (HR, Breathing, Hunger etc)

Proprioceptive system Position of body, posture and movement

Question 24

Cutaneous system (4 senses)

Answer 24

Pressure - mechanical deformation of skin

Vibrations

Temp

Pain

Question 25

Layers of skin

Answer 25

Epidermis - nob blood vessels, get O2 from air

Middle layer - dermis

Hypodermis or subcutaneous

Question 26

Glabrous skin

Answer 26

Hairless. Usually sensitive

Meissner’s corpuscles - only found here, detect very light touch

Question 27

Vibration senseors

Answer 27

Pacinian corpuscles

Question 28

Free nerve endings

Answer 28

Temp and pain

Question 29

Perception of temp

Answer 29

Free nerve endings in skin

2 cats of receptors: warmth and coolness
Poorly localized, unmyelinated, slow (touch before temp)

Some receptors that are sensitive to temp can be activated by ligands (capsaicin for heat, menthol for cold)

Question 30

Thermal grill illusion

Answer 30

4 grills. some heated or cooled, others not

Put hand across all of them

Brain cannot differentiate the two so experiences this ambiguity as pain

Question 31

Pain

Answer 31

Free nerve endings - skin

Many types

High-threshold mechanoreceptors (pressure receptor cells) are free nerve endings that spike in intense pressure like pinching or a strike

Others respond to extreme heat or presence of chemicals that should not be extracellular (like ATP)

Question 32

2 pathways

Answer 32

(1) Spinothalamic tract
Poorly localized (crude touch, pain, temp)
Crosses over immediately in spinal chord and synapses there
Runs up to thalamus in spinothalamic tract

(2) Dorsal column
Highly localized info (fine touch)
Ascends ipsilaterally in dorsal column
First synapse is in medulla
Then crosses over to contralateral thalamus

Both get bundled together in the midbrain and synapse in the thalamus

Both go to somatosensory cortex

Question 33

somatosensory cortex map

Answer 33

Relationship between cortical stimulations and body sensations is soma topic map

Somatosensory homunculus - the dude

Question 34

Tactile agnosis

Answer 34

Cant id objects by touch alone

They an draw the object without looking and then recognize it

Question 35

Phantom limb

Answer 35

Pain after amputation

Report feeling limb still exists and is hurt

Confusion on somatosensory cortex )primary and association). The brain gets nonsense sign als from cut axons and cannot interpret them.

Therapy
Often using mirrors
Re-organise brain

Question 36

Taste

Answer 36

Transduces like synapses
Receptor protein changes membrane potential either directly or via g protein cascades
Tastes are due to activation of different receptor proteins

Taste buds are groups of 30-50 receptor cells which all express the same receptor (so are sensitive tot he same taste).

Replaced every 10 days as mouth is noxious

Question 37

6 tastes

Answer 37

Sweentess (sugar)
unami (Glutamate)
bitterness (many molecules)
saltiness (ions)
Sourness (pH level and carbonation)
Fat (Fatty acids)

Sugar and unami are instinctively rewarding and tasty. Bitter are repulsive instinctively although we can come to like them. Avoid poison

Question 38

Primary Gustatory Cortex

Answer 38

Insula lobe of cerebral cortex

Question 39

Smell

Answer 39

Specialized for identifying specific molecules called odorants
Change membrane potential - metabotropic g protein receptors
400 types
Odorant are volatile with molecular weight of 15-300. Not all molecules that meet this definition have odors

Question 40

Olfaction

Answer 40

The olfactory epithelium is the tissue of the nasal sinus that sits under the skull and has the olfactory receptors. Each olfactory cell has only one type of receptor

All synapse in glomeruli in the olfactory bulb

They pass through the skull all together but are then sorted with each receptor and cell going to one glomerulus

400 receptors, can do 100000 smells based on combinations

Does not go to thalamus, goes to primary cortex the the temporal lobe directs and the amygdala

Nothing is inborne

Kids find all smells curious

Learn by association what is bad.