NeuroScience Optional Lecture

Get oriented in the brain+

Visual perception and its cortical representation

Part 1

Get oriented in the brain

Brain - the Central Core

• The brain stem– The medulla links the spinal cord to the brain and is involved in

regulating heartbeat, blood pressure and other visceral functions– The reticular formation is a network of neurons running up the center of

the brain stem and into the thalamus that is involved in controlling our different levels of arousal and awareness

• The cerebellum is involved in the coordination of our movements, our sense of balance, and motor and procedural learning

• The thalamus, located at the top of the brain stem, serves as a relay station for incoming sensory information (except smell)

– The basal ganglia are on the outer sides of the thalamus and are concerned mainly with the initiation and execution of physical movements

The Limbic System

Plays a role in our survival, memory, and emotions– The hypothalamus control the pituitary gland, the autonomic

nervous system, and plays a major role in regulating basic drives such as circadian rhythm, eating, thirst, and sex

– The hippocampus is involved in the formation of memories

– The amygdala plays a major role in regulating our emotional experiences, especially fear, anger, and aggression

Processing in the Cerebral Cortex

• The cerebral cortex - information processing center for the nervous system

– Is where perception, language, memory, decision making, and all other higher-level cognitive processing occur

– Consists of two hemispheres connected by a band of neurons called the corpus callosum, allowing the two hemispheres to communicate

Brain Lobes

1. The frontal lobe - the area in the front of each hemisphere and in front of the central fissure and above the lateral fissure

2. The parietal lobe - the area located behind the central fissure and above the lateral fissure

3. The temporal lobe - located beneath the lateral fissure

4. The occipital lobe - located in the lower back of each hemisphere

The Motor Cortex

• The Motor Cortex = frontal lobe strip of cortex, directly in front of the central fissure in each hemisphere, that controls the voluntary movement of different parts of the body– Each hemisphere controls the movement of the opposite

side of the body → a contralateral relationship

– Amount of motor cortex devoted to a specific body part is related to the complexity and precision of movement of which that part is capable - motor homunculus

The Somatosensory Cortex

• The Somatosensory Cortex = parietal lobe strip of cortex, directly behind the central fissure in each hemisphere, is where body sensations of pressure, temperature, limb position, and pain are processed

– Contralateral relationship

– Amount of sensorimotor cortex devoted to a body part is directly proportionate to the sensitivity of that body part – sensory homunculus

Wilder Penfield in 1963, at the age of 73, sketching a cross section of the human brain.(Osler Library of the History of Medicine. McGill University, Photography Collection).

Neural cartography

Homunculi for the Motor Cortex and the Somatosensory Cortex

Visual Cortex and Auditory Cortex

• The visual cortex is located in the occipital lobes at the back of the hemispheres

• The auditory cortex is in the temporal lobes

• These primary areas pass the results of their analyses on to areas in the other lobes to complete the brain’s interpretation of the incoming visual or auditory information

– These secondary cortical processing areas are part of what is termed the association cortex

Association Cortex

• Consists of the other 70% of the cortex not in one of the motor and somatosensory areas

• This is where the higher-level processing such as decision making, reasoning, perception, speech, and language occurs

– All of which require integration of various types of information

Brain structures to function correspondences

http://www.korbinian-brodmann.de/english-article

The regions of the human cerebral cortex as delineated by Brodmann on the basis of cytoarchitecture

Language • Broca’s area, in the left hemisphere’s temporal lobe, is responsible

for fluent speech production– When damaged, people cannot generate fluent speech, but can still

understand speech easily– Singing and musical abilities seem to be housed in the right hemisphere

because damage to Broca’s area does not impair these abilities !

• Wernicke’s area is in the left temporal lobe and is responsible for the comprehension of speech and reading

• Left hemisphere– Language– Math and logic skills– More analytical, analyzing

wholes into pieces

• Right hemisphere– Spatial perception– Solving spatial problems– Drawing– Face recognition

The Two Hemispheres

• When normal people are performing a task, the two hemispheres are constantly interacting and sharing information• The differences in hemispheric performance are for people whose two hemispheres can no longer communicate → it is not very accurate to say someone is “left-brained” or “right-brained”, rather, nearly all of us are “whole brained”

Studying the Two Hemispheres

Studying the Two Hemispheres

• Light waves from the left visual field go to the right half of each eye, and light waves from the right visual field go to the left half of each eye

– The right half of each eye connects with the right hemisphere, and the left half of each eye connects with the left hemisphere

Corpus callosum connects the right and left hemispheres

• With split-brained people, the information cannot transfer between hemispheres because the corpus callosum has been cut

• Split-brain people can only identify information orally when it is presented briefly in the right visual field (and thus processing in the left hemisphere)

– If a spoon was flashed in the left visual field, split-brained people could not say it was a spoon

Case 1: A Landscape Artist

Scenario Neuroanatomy Related Function

Anne the

landscape artist

is standing at

her easel,

painting with

her right hand

as she looks

out the window

at her garden.

She’s listening

to classical

music as she

paints.

Left motor cortex

Left frontal lobe

Visual cortex

Both occipital lobes

Auditory cortexes

Both temporal lobes

Right hemisphere

Thalamus

Frontal lobes

Left sensory cortex

Left parietal lobe

Cerebellum

Controls right hand

Contains motor cortex

Used for vision

Contain visual cortex

Used to hear music

Contain auditory cortexes

Spatial ability for painting

Relays sensory information

Deciding what to paint

Feeling the paintbrush

Contains sensory cortex

Coordinates moving arm

Case 2: A Professional Wrestler

Scenario Neuroanatomy Related Function

Crazy Eddie, the

professional

wrestler, is in the

ring wrestling. The

crowd is yelling

and his is taunting

him. Eddie yells

back at his

opponent. The two

of them are out of

breath and

sweating profusely.

They continue their

well-orchestrated

series of wrestling

moves.

Both motor cortexes Frontal lobes Both sensory cortexes Parietal lobes Visual cortexes Both occipital lobes Right hemisphere Wernicke’s area Left temporal lobe Broca’s area Left frontal lobe Thalamus Frontal lobes Medulla Amygdala Reticular formation Cerebellum Hypothalamus Hippocampus

Move muscles Contain motor cortexes Needed for sense of touch Contain sensory cortexes Used for vision Contain visual cortexes Spatial ability for wrestling Understanding taunts Contains Wernicke’s area Produces speech (yells) Contains Broca’s area Sensory relay Decision making & attention Regulates heart and breathing Aggression and fear Controls arousal Balance and coordination Regulates temperature Memory for moves

Case 3: A Student

Scenario Neuroanatomy Related Function

Jill is a law

student

studying for her

exam. She is

reading about

violent rape and

murder cases.

She is snacking

on popcorn and

drinking coffee.

Hippocampus

Wernicke’s area

Left temporal lobe

Amygdala

Frontal lobes

Hypothalamus

Angular gyrus

Remembering and learning

Language comprehension

Contains Wernicke’s area

Anger and fear about cases

Decision making & attention

Regulates hunger and thirst

Needed for reading

Source: Sheldon, J. P. (2000). A neuroanatomy teaching activity using case studies and collaboration.

Teaching of Psychology, 27, 126-128.

Part 2

Visual perception and its

cortical representation

• Visual perception = the psychological process of visual

information; its lack = blindness

• Non-image forming visual functions, independent of

visual perception, include the pupillary light reflex (PLR)

and circadian photoentrainment.

Principles in sensory systems

• Transduction. Detection of outside energy

• Sensory encoding

• Neural pathways

• Receptive fields

• Topographic maps

image representation

object recognition

action movement

visual memory

• The eye, especially the retina

• The optic nerve

• The optic chiasma

• The optic tract

• The lateral geniculate body

• The optic radiation

• The visual cortex

• The visual association cortex.

Good vision requires a focused image on the back of the retina

Transduction

• physical stimulus energy converted into a neural signal

• range of intensities encoded

• respond to changes in intensity

• central processing = code is local potential and action potential

Transduction

• Outer segments stacks

filled with photopigment

• photochemicals turn light

→ electrical signal

Wide range of sensitivity to light intensity

Sensory encoding

• changes in light and dark over time

shape

color

movement

depth

object recognition

action-movement

visual memory

• vision proceeds by transfer of electrical signals from rods

and cones to other cells in the retina

• the transfer of information proceeds in parallel and serially

Neural pathways

transformation of visual signals

- retina, sensory thalamus (LGN)

image components, position

- primary visual cortex

object recognition, face recognition

-prestriate cortex, fusiform gyrus

integrate visual memory and motor plan

- prefrontal and premotor cortex

Five different populations of ganglion cells that

send visual (image-forming and non-image-

forming) information to the brain:

1. M cells, with large center-surround receptive fields that are sensitive to depth, indifferent to color, and rapidly adapt to a stimulus;

2. P cells, with smaller center-surround receptive fields that are sensitive to color and shape;

3. K cells, with very large center-only receptive fields that are sensitive to color and indifferent to shape or depth;

4. another population that is intrinsically photosensitive

5. a final population that is used for eye movements

Neural pathways

• retino-hypothalamic → SCN circadian rhythm

• retino-collicular→ eye movements

• retino-geniculo-cortical → objects and motion visual

awareness

Receptive fields

Hermann grid

www.pc.rhul.ac.uk

Macular projections synapse in the occipital pole

and occupy approximately one‐half the entire

surface area of striate cortex. The occipital tip is

devoted to foveal vision.

The Visual Cortex.

• The early visual cortex consists of visual areas – V1, V2, V4, MT

(V3, MST) – which are determined by anatomical and

electrophysiological measurements. All these areas have a rough

retinotopic organization,and are organized hierarchically. There are

two main pathways:

• (I) The ventral stream consisting of V1, V2, V4,2 and then to the

infero- temporal areas of extrastriate cortex which performs object

detection and scene understanding.

• (II) The second pathway goes from V1, MT to the parietal cortex

and is used for analysis of movements and positions of objects. The

ventral stream puts most emphasis on the central visual field while

the motion analysis concentrates more on the periphery

Where

LGN

What

V1

Retina

what - ventral system

V1-V2-V4-IT

associated with form

recognition and object

representation

where - dorsal system

V1-V5(MT)-MST

associated with motion,

representation of object

locations, and control of the

eyes and arms

Visual association cortex

Other types of visual perception

• Synesthesia is an extraordinary perceptual phenomenon, in which the world is experienced in unusual ways: a particular stimulation in a given sensory modality (e.g., smell) or cognitive process (e.g., computing) automatically triggers additional experiences in one or several other unstimulated domains (e.g., vision, emotion)