Behavioral Neuro 2

Law of specific nerve energies states that

speciifc nerves always convey the same information to the brain

what cell has axons that form the optic nerve and recieve messages from bipolar cells in the retina?

ganglian cells

Which Cells are located closer to the center of the eye- that receive messages from visual receptors at the back of the eye? They are located in the retina

bipolar cells

Which cells are additional cells that recieve information from bipolar cells and send it to other bipolar, ganglion, or amacrine cells? They control the ability of the ganglian cells to respond to shapes, movement, and other specific aspects of visual stimuli.

Amacrine cells

Consists of the axons of ganglion cells that band together and exit through the

back of the eye and travel to the brain

Leaves the back of the eye; the point at which it leaves is called the blind spot because

it contains no receptors

The optic nerve

Which part of the eye is the central portion of the retina

and allows for acute and detailed vision

• Packed tightly with cone receptors

• Nearly free of ganglion axons and blood vessels

Our vision is dominated by what we see in it

The fovea

Each receptor (almost exclusively cones) in the fovea attaches to a single bipolar

cell and a single ganglion cell known as a _______________________

“midget ganglion cell”

Theres a greater number of recpetors (rods)that connverge into ganglion and bipolar cells in this area of the retina which allows for perception of much fainter light.

periphery of the retina

The Arrangement of Visual Receptors are highly ________

like eagles have a higher density of receptors in the top of the eye, and rats have greater density on the bottom of the eye

adaptive to the environment and survival needs

foveal receptors are _______ and reacts well to ________ light and ________ detail whereas peripheal receptors are _______

and reacts well to ______ light and ________ detail

foveal receptors are cones and react well to bright light and good detail (essential for color vision) whereas

peripheral receptors are many rods and react well to dim light and poor detail. (they are also monochromatic perception and sensitive to movement)

_______ are contained by both rods and cones that release

energy when struck by light’

Consist of 11-cis-retinal bound to proteins called opsins

• Light energy converts 11-cis-retinal quickly into all-trans-

retinal

• Light is thus absorbed and energy is released that activates

second messengers within the cell

photopigments

In the electromagnetic spectrum, the perception is dependent on the wavelength of light.

Humans perceive wavelengths between ____ and _____.

400 and 700 nanometers

Two major interpretations of color vision

Trichromatic theory and the opponent-process theory

What is Trichromatic theory?

Color perception occurs through three kinds of cones

-Short-wavelength which is blue

-medium-wavelength which is green

-long-wavelength which is red

the ratio of activity across them determines the color

What is the opponent-process theory?

• We perceive color through pairs of opposing color channels: red ↔

green and blue ↔ yellow (with a separate black ↔ white lightness

channel).

• Possible mechanism: Some retinal neurons, including bipolar and

ganglion cells, are excited by one range of wavelengths and inhibited

by another. For example, a neuron may be excited by red wavelengths

and inhibited by green wavelengths.

• Prolonged exposure: If you stare at one color for a long time, the

neural response to that stimulus adapts/decreases.

• Afterimage: When you look away at a neutral/white surface, the opponent

channel is relatively stronger, so you perceive the opposite color as an

afterimage.

Both the opponent-process and trichromatic theory can't easily explain:

Color constancy: we perceive an object's color as relatively stable even when the lighting changes.

Brightness Constancy: we perceive an object's brightness/lightness as relatively stable despite changes in illumination.

Color Vision Deficiency

An impairment in perceiving color differences

Gene responsible is contained on the X chromosome

Caused by either the lack of a type of cone or a cone that has

abnormal properties

Most common form is difficulty distinguishing between red

and green

Results from the long- and medium-wavelength cones having the

same photopigment

The Mammalian Visual System

Rods and cones of the retina make synaptic contact with horizontal cells and bipolar cells

Horizontal cells are cells in the eye that make inhibitory contact onto bipolar cells

Bipolar cells make synapses onto amacrine cells and ganglion cells

Different cells are specialized for different visual functions

is the place in the mammalian visual system where the two optic nerves leaving the eye meet

The optic chiasm

Lateral Inhibition in the Retina *

the reduction of activity in one neuron by activity in neighboring neurons

Sharpens contrasts to emphasize the borders of objects

The response of cells in the visual system depends upon the net

result of excitatory and inhibitory messages it receives

The lateral geniculate nucleus is part of the ________

and is specialized for _______ perception

and is destination for most _______ cell axons

Sends axons to other parts of the thalamus and to the visual areas of the occipital cortex

The cortex and thalamus constantly feed information back and forth to each other

it is part of the thalamus

and is specialized for visual perception

is destination for most ganglion cell axons

What is a Receptive Field?

Receptive field = the specific region of sensory space where a stimulus can affect a particular neuron.

refers to the part of the visual field that either excites or inhibits a cell in the visual system of the

brain

• For a receptor, the receptive field is the point in space from which light strikes it

• For other visual cells, receptive fields are derived from the visual field of cells that either excite or inhibit

• Example: ganglion cells converge to form the receptive field of the next level of cells

Receptive field

the specific region of sensory space where a

stimulus can affect a particular neuron.

The Mammalian

Visual System

Ganglion cell axons form the optic nerve

• The optic chiasm is the place where the

two optic nerves leaving the eye meet

• In humans, half of the axons from each

eye cross to the other side of the brain

• Most ganglion cell axons go to the

lateral geniculate nucleus, a smaller

amount to the superior colliculus, and

fewer to other areas

slides 45-49 **

3 Primate Ganglion Receptive Fields

Ganglion cells of primates

generally fall into three

categories

1. Parvocellular neurons

2. Magnocellular neurons

3. Koniocellular neurons

Neurons Mostly located in or near the fovea

Have smaller cell bodies and small receptive

fields

Highly sensitive to detect color and visual detail

Parvocellular neurons

Neurons

Distributed evenly throughout the retina

Have larger cell bodies and visual fields

Highly sensitive to large overall pattern and moving stimuli

Magnocellular neurons

Neurons that Have small cell bodies

Found throughout the retina

Have several functions, and their axons terminate

in many different places

Koniocellular Neurons

The primary visual cortex (area V1) receives information from

the lateral geniculate nucleus and is the area responsible for

the first stage of visual processing

Some people with damage to V1 show blindsight: an ability to

respond to visual stimuli that they report not seeing

Stereoscopic Depth Perception

A method of percieving distance in which the brain compares slightly different inputs froms the two eyes

Relies on retinal disparity or the

discrepancy between what the left and the

right eye sees

The ability of cortical neurons to adjust

their connections to detect retinal disparity

is shaped through experience

A condition in which the eyes do not point in the

same direction

• Also known as “lazy eye”

• Usually develops in childhood

If two eyes carry unrelated messages, cortical cell

strengthens connections with only one eye

Development of stereoscopic depth perception is

impaired

Strabismus

Early Exposure to a Limited Array of

Patterns

Leads to nearly all of the visual

cortex cells becoming

responsive to only that pattern

_______________ is the blurring of vision for lines in one direction caused by an asymmetric curvature of thee eyes

Astigmatism

Long-Term Consequences of Impaired Infant

Vision

Study of people born with cataracts but had them removed

indicate that

vision can be restored gradually, but problems persist

Difficulty in recognizing objects

Unable to tell that components are part of a whole

Best prognosis is for children whose vision problems are

corrected early in life

The secondary visual cortex (area V2) receives

information from area V1, processes information

further, and sends it to other areas

Information is transferred between area V1 and

V2 in a reciprocal nature

The Ventral and Dorsal Paths

**The Ventral and Dorsal Streams

The ventral stream: path that goes through temporal cortex

(the what path)

The dorsal stream: path in the parietal cortex

The “where” or “how” path

• Important for visually guided

movements

Stream Damage: can see

where objects are but cannot identify

them

ventral stream damage

Dorsal stream damage

Stream Damage:

can identify
objects but not know where they are

Detailed Analysis of Shape

Receptive fields become larger and more specialized as

visual information goes from simple cells to the complex cells

and then to other brain areas

The inferior temporal cortex contains cells that respond

selectively to complex shapes but are insensitive to

distinctions that are critical to other cells

Cells in this cortex respond to identifiable objects

The inability to recognize

objects despite

satisfactory vision

• Caused by damage to the

pattern pathway usually in

the temporal cortex

Visual Agnosia

The fusiform gyrus is knnown for ______________________

face recignition

The impaired ability to

recognize faces

• Occurs after damage to

the fusiform gyrus of the

inferior temporal cortex

• The fusiform gyrus

responds much more

strongly to faces than

anything else

Prosopagnosia

Involves a variety of brain areas in all

four lobes of the cerebral cortex

• The middle-temporal cortex (MT/V5)

responds to a stimulus moving in a

particular direction

• Cells in the dorsal part of the medial

superior temporal cortex (MST)

respond to expansion, contraction, or

rotation of a visual stimulus

• Both receive input from the

magnocellular path; color-insensitive

Motion Perception

The inability to determine the

direction, speed and whether

objects are moving

• Likely caused by damage in area MT

Some people are blind except

for the ability to detect which

direction something is moving

• Area MT probably gets some visual

input despite significant damage to

area V1

Motion Blindness

Rather than smoothly tracking movement, your eyes

can also rapidly switch from focusing on one target to

another with little/no visual perception of the gap

• To prevent confusion or blurring of images during eye

movements:

• They are a decrease in the activity of the

visual cortex during quick eye movements

• Neural activity and blood flow decrease 75

milliseconds before and during eye movements

Saccades

The middle-temporal cortex (MT/V5) is important for:

A. Detecting object color

B. Recognizing familiar faces

C. Processing depth from retinal disparity

D. Responding to motion in a particular direction

D. Responding to motion in a particular direction

The law of specific nerve energies addresses the issue of _____.

how the brain interprets nerve impulses from sense organs

The optic nerve is composed of axons of ____.

ganglion cells

Why is detail vision relatively poor in the periphery?

Many receptors converge on a single ganglion cell there.

The ganglion cells in the fovea of humans and other primates are called ____.

midget ganglion cells

Jaquan has gone outside and forgotten his sunglasses. What will happen to his rods in bright daylight?

they will be bleached

Cones provide about what percentage of the visual input to the brain?

90%

According to the trichromatic theory, which of the following best explains how we discriminate among wavelengths of light?

We use the ratio of activity across the three types of cones.

Which theory posits that we perceive color on a continuum from red to green, another from yellow to blue, and another from white to black?

opponent process theory

Which theory can account for the constancy of color across different lighting conditions?

retinex theory

In mammalian vision, most ganglion cell axons go to the ____.

lateral geniculate nucleus

Scott is looking at a series of grayscale bars. While he stares at a darker bar, it seems as if the border with a lighter bar seems "highlighted." What could explain why he is seeing this visual effect?

lateral inhibition

Which type of ganglion cells are distributed evenly throughout the retina and have relatively large cell bodies and receptive fields?

magnocellular

Elsa has had damage to area V1. As a result, she may experience the ability to respond in limited ways to visual information without perceiving it consciously, a phenomenon called _____.

blindsight

Which type of visual cortex cell has a strong inhibitory area at one end of its large bar-shaped receptive field ?

End-stopped

Terrance was born with congenital cataracts. If the cataracts are not removed until childhood, what are the likely effects?

His motion and depth perception will remain permanently impaired.

Mitsuko is holding an object that he can see is an apple because of the ventral pathway or stream through the temporal cortex. Because it is specialized for identifying and recognizing objects, the pathway is also called the _____.

what pathway

Which part of the facial recognition system responds strongly to a face viewed from any angle, as well as line drawings and anything else that looks like a face?

fusiform gyrus

Oliver has been diagnosed with prosopagnosia. What is his main symptom?

He cannot recognize faces.

Cells in which structure respond selectively when something moves at a particular speed in a particular direction?

Medial temporal cortex

Humans experience hearing by detecting

sound waves

_________ waves are periodic compressions of air, water, or other media

• these waves vary in amplitude and frequency

sound waves

The structure of flesh and cartilage attached to each side of the head

Funnels the reflection of sound waves into the middle ear from the outer ear

Helps us to locate the source of a sound

Pinna

The ____________ contains the tympanic membrane (ear drum):

o Vibrates at the same rate when struck by sound waves

o Connects to three tiny bones (malleus, incus, & stapes) that

transform waves into stronger waves to the oval window

• Oval window is a membrane in the inner ear:

o Transmits waves through the viscous fluid of the inner ear

The middle ear

The ________ contains three fluid-filled tunnels (scala vestibuli, scala media, & the scale tympani

-transduction of sound waves to electrical signals

The cochlea

Place Theory

Areas along the basilar membrane has hair cells sensitive to only one specific frequency of sound wave

• Limitation: basilar membrane not long enough to accommodate lower frequencies so it doesn’t account for the lower frequencies

**better at explaining high frequencies

High pitch → BASE

Near the entrance to the cochlea.

Low pitch → APEX

Farther along the cochlea, toward its tip.

Frequency Theory:

The basilar membrane vibrates in synchrony with the sound and

causes auditory nerve axons to produce action potentials at the

same frequency

• If the frequency is 50 Hz 50 action potentials per second in the

auditory nerve

** better at explaining low frequencies

• Limitation: refractory period decreases maximum firing rate too

much for high frequencies

Low pitch = slow firing

higher pitch = faster firing

The Volley Principle

• The auditory nerve produces volleys of impulses (for sounds up to about 4,000 per second)

• No individual axon solely approaches that frequency, so multiple neurons alternate their firing

• Hearing of higher frequencies not well understood

The __________theory combines modified versions of

both the place theory and frequency theory:

• Low frequency sounds best explained by the frequency theory

• High frequency sounds best explained by place theory

The Current pitch theory

Which theories: Perception of a low tone is to ____ as perception of a high tone is to ____.

frequency theory; place theory

__________ Auditory Cortex (A1): Processes basic sound features such as pitch and volume.

-in which cells respond more to changes in sound than to prolonged sounds

and the ________ Auditory cortex is Involved in higher-level processing, such as speech

comprehension and the recognition of more

complex sounds

** slide 15

The Primary Auditory Cortex

The secondary Auditory Cortex

Functions of the Auditory Cortex

Not necessary for hearing, but for processing the information

Provides a tonotopic map in which cells in the primary auditory cortex are more responsive to preferred tones

Some cells respond better to complex sounds than pure tones

• Damage to A1 does not necessarily

cause deafness unless damage extends

to the subcortical areas

sound localization

Sound localization depends upon comparing the responses of the

two ears

Three cues:

1. Sound shadow

2. Time of arrival

3. Phase difference

Humans localize low frequency sound by phase difference and high

frequency sound by loudness differences

Sound Localization: High frequencys sounds create a __________

Difference in time of arrival at the two ears most useful for localizing sounds with sudden onset

Phase difference between the ears provides cues to sound localization with frequencies up to 1500 Hz

sound shadow

What is Amusia vs Absolute pitch

tone deafness

• The impaired detection of frequency changes associated with

thicker than average auditory cortex in the right hemisphere,

• Fewer connections from auditory cortex to frontal cortex

Absolute pitch: Ability to hear a note and identify it

• Genetic predisposition may contribute to it

• Early and extensive musical training

• More common in people who speak Vietnamese

Two categories of hearing impairment/loss

1. Conductive or middle ear deafness

2. Nerve deafness or inner ear deafness

Occurs if bones of the middle ear fail to transmit sound waves

properly to the cochlea

Can be caused by disease, infections, or tumorous bone

growth

Normal cochlea and auditory nerve allow people to hear their

own voice clearly

Can be corrected by surgery or hearing aids that amplify the

stimulus

Conductive/Middle Ear Deafness

Results from damage to the cochlea, the hair cells, or the auditory

nerve

Can vary in degree

Can be confined to one part of the cochlea

• People can hear only certain frequencies

Can be inherited or caused by prenatal problems or early childhood

disorders

Nerve or Inner-Ear Deafness

Frequent or constant ringing in the ears

• Experienced by many people with nerve deafness

Sometimes occurs after damage to the cochlea

• Axons representing other parts of the brain previously

responsive to sound

• Similar to the mechanisms of phantom limb

Tinnitus

system that detects the position and

movement of the head

Directs compensatory

movements of the eye and

helps to maintain balance

is in the

ear and is adjacent to the

cochlea

The vestibular sense

_________ organ comprises two otolith organs (the

saccule and utricle) and three semicircular canals

Otoliths are calcium carbonate particles that push

against different hair cells and excite them when

the head tilts

Semicircular canals

Are filled with a jellylike substance and hair cells

that are activated when the head moves

Action potentials travel to the brain stem and

cerebellum

Vestibular organ

The 4 touch receptors

Touch receptors may be:

1. Meissner corpuscles

2. Pacinian corpuscles

3. Ruffini endings

4. Merkel discs

Stimulation of these opens sodium channels to trigger an action potential

Touch receptor that detects light touch

• These help you detect gentle

touch and movement across

your skin.

Meissner corpuscles

Touch receptor that detects deep pressure and high-

frequency vibration.

• Resists gradual or constant pressure

• Chemicals can stimulate receptors for

heat and cold: e.g., capsaicin &

menthol

• They're located deeper in the skin and

other tissues.

The Pacinian Corpuscle

Touch recpetor that detects Fine detail and sustained pressure

These help you detect steady, gentle pressure, edges, shapes, and fine details. They are

especially useful for distinguishing textures and forms.

Merkel Disks

Touch recpetor that detects skin stretch

These respond to stretching of the skin

and help provide information about

sustained deformation of the skin and

hand position.

Ruffini Endings

Somatosensation in the Central Nervous System (CNS)

Information from touch receptors

in the head enters the CNS

through ___________________

Information from receptors below the head enters through _________________________

Information from touch receptors

in the head enters the CNS

through the cranial nerves

Information from receptors below

the head enters the spinal cord

and travel through the spinal cord and spinal

nerves to the brain

***** Mild pain causes the release of

the neurotransmitter ___________.

• Stronger pain also releases several neuropeptides including __________ and ____________.

glutamate

substance P and CGRP (calcitonin gene-related peptide)

Emotional Pain

Emotional association of pain

• Activate a path that goes through the reticular formation of the medulla

• And then to several of the central nuclei of the thalamus, the amygdala, hippocampus, prefrontal cortex, and cingulate cortex

Experimenters monitored people’s brain activity and found hurt feelings activate the same pathway

Relieving Pain

Opioid mechanisms are systems that are sensitive to

opioid drugs and similar chemicals

Opiates bind to receptors found mostly in the spinal cord

and the periaqueductal gray area of the midbrain

Capsaicin

• Produces a temporary burning sensation followed by a longer period of decreased pain

_______ theory proposes that the spinal cord areas that receive messages from

pain receptors also receive input from touch receptors and from

axons descending from the brain

These other areas that provide input can close the “gates” by

releasing endorphins and decrease pain perception

Non-pain stimuli around it can modify the intensity of the pain

**women in labor and hair combs

Gate Theory

Mechanisms of the body to increase sensitivity to pain

• Damaged or inflamed tissue releases histamine, nerve growth factor, and other

chemicals that increase the responses of nearby pain receptors

Certain receptors become potentiated after an intense barrage of

painful stimuli

• Leads to increased sensitivity or chronic pain later

sensitization to pain

****Nonsteroidal anti-inflammatory drugs decrease pain by

by reducing the release of chemicals from damaged tissue (aspirin)

Chemical Coding:

Labeled-line principle:

Each touch/pain receptor responds to a limited

range of stimuli and sends a direct

line to the brain

-labeled line = direct line to brain, limited range of stimuli