Behavioral Neuroscience Exam 2

Exam 2 SG

what is a receptive field?

• specific region of sensory space where a stimulus triggers a response in a particular sensory neuron (either excites or inhibits a cell in the visual system of the brain)

• a receptive field is the section of your vision that a certain neuron keeps track of; the point in space from which light strikes it.

  • ex. ganglion cells converge to form the receptive field of the next level of cells

photoreceptors

• specialized cells in the retina that detect light & convert it into electrical signals

• contribute to the formation of receptive fields by providing input to neurons

  • Rods & Cones are photoreceptors

Rods v.s Cones

rods: most abundant in periphery of the eye.

responds to faint light (120 million/retina)

monochromatic perception & sensitive to movement

cones: most abundant in and around the fovea (6 million/retina)

essential for color vision & more useful in bright light

cones provide about 90% of brains input

color vision

• visible light is a portion of the electromagnetic spectrum

• perception of color is dependent upon the species’ wavelength of light

• humans perceive wavelengths btw 400-700 nanometers (nm)

bipolar cells (retina)

-receive messages from visual receptors at the back of the eye

-send messages to ganglion cells that are closer to center of the eye

amacrine cells (retina)

• cells get information from bipolar & ganglion cells, enabling certain ones to respond mainly to particular shapes, direction of movement, changes in lighting, color, or other visual features/stimuli.

the Fovea

• central portion of the retina & allows for acute and detailed vision

• each receptor attaches to a bipolar cell and a single ganglion cell known as a “midget ganglion cell”

• each cone has a direct line to the brain, which allows the registering of the exact location of input

  • our vision is dominated by what we see in the fovea

what is an afterimage?

perceiving the opposite color after staring at a color for a prolonged period of time

Opponent-process color vision theory

• we perceive color through pairs of oppsoing colors

  • red ←→ green

  • blue ←→ yellow

  • separate black ←→ white channel

• some retinal neurons, including bipolar and ganglion cells, are excited by one range of wavelengths and inhibited by another.

• after staring at one color for a long time, the neural response to that stimulus adapts/decreases

Trichromatic theory/Young-Helmholtz color vision theory

• color perception occurs through the relative rates of response by 3 kinds of cones

  • short-wavelength

  • medium-wavelength

  • long-wavelength

• explains color detection by cones

what is photopigment?

chemicals contained in rods AND cones that release energy when struck by light

what is the visual path in the eye

• receptors send messages to BIPOLAR & HORIZONTAL cells, in turn, they send messages to amacrine & ganglion cells.

• axons of the ganglion cells form the optic nerve, which exits the eye at the blind spot and goes to the brain

processing in the retina

the cortex and thalamus constantly feed information back and forth to each other.

• lateral geniculate nucleus

  • specialized for visual perception

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

what are horizontal cells?

• type of cell that receives input from receptors and delivers inhibitory input to bipolar cells

  • rods and cones of the retina make synapses with these cells.

ventral pathway (visual information processing)

• perception path, or the “WHAT” pathway, because of its importance for identifying and recognizing objects (temporal cortex)

• damage to this pathway:

  • people can use vision to guide their actions, but cannot identify what the objects are.

dorsal pathway (visual information processing)

• action path or “HOW” pathway, because of its importance for visually guided movements (parietal cortex)

• Damage to this pathway:

  • prevents people from integrating vision well with arm and leg movements (vision control issues with certain movements).

  • can read, recognize faces, and describe objects in detail, but cannot accurately reach out to grasp an object

secondary visual cortex (V2)

• areas of the brain that process info. from the primary visual cortex (V1) and transmit it to additional areas

• connections in the visual cortex are reciprocal

  • ex. V1 sends info to V2, & V2 returns info to V1. from V2, info. branches out in several directions for specialized processing.

• damage to this pathway:

  • difficulties recognizing objects, impaired motion perception, and challenges in visual attention.

  • damage to V1 may cause blindness in part(s) of visual field

mammalian visual systems

• ganglion cell axons form the optic nerve

• optic chiasm is the place where the 2 optic nerves leaving the eyes meet

• half the axons from each eye cross to the other side of the brain

  • bipolar cells make synapses onto amacrine cells and ganglion cells

stereoscopic depth perception

-method of perceiving distance in which the brain compares slightly different inputs from both eyes.

-relies on retinal disparity or the discrepancy between what the left and right eyes see.

-the ability of cortical neurons to adjust their connections to detect retinal disparity is shaped through experience.

blindsight

ability to respond in limited ways to visual information, without perceiving it consciously

• in damaged area, people are unaware of visual input, unable to distinguish btw light and darkness

astigmatation

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

visual agnosia

inability to recognize objects, despite satisfactory vision

• caused by damage to the pattern pathway, usually in temporal cortex

• can be easier to draw from memory than trying to copy an image/drawing of something in front of them

prosopagnosia

impaired ability to recognize faces

occurs after damage to the fusiform gyrus of the inferior temporal cortex

• fusiform gyrus responds much more strongly to faces than anything else

motion perception

• involves a variety of brain areas in all 4 lobes of cerebral cortex

• 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 in[put from magnocellular path; color-sensitive

motion blindness

inability to determine direction, speed, and whether an object is moving

saccades

• do not smoothly track movement, eyes rapidly switch from focusing on one target to another with little/no visual perception of the gap.

  • to prevent confusion/blurring of images during eye movements; saccades are a decrease in activity of visual cortex during quick movements

  • neural activity and blood flow decrease 75 milliseconds before & during eye movements

how does sound travel in hearing?

• sound waves: the periodic compression of air, water, or other media

  • vary in amplitudes & frequency

what is amplitude?

refers to the intensity of the sound waves

what is frequency?

number of compressions per second and is measured in hertz (Hz)

what is timbre?

tone quality or complexity, dependent on the harmonics of the tone

The Outer Ear

pinna: structure of flesh & cartilage attached to each side of the head

• funnels the reflection of sound waves into the middle ear from outer ear

• helps us to locate the source of a sound

The Middle Ear to Inner Ear

contains the tympanic membrane (eardrum)

• vibrates at the same rate when struck by sound waves

• connects to 3 tiny bones (malleus, incus, & stapes) that transform waves into stronger waves to the oval window

  • oval window; transmits waves through the viscous fluid of inner ear

The Inner Ear

the cochlea contains auditory receptors: hair cells (sensory receptors) convert sound vibrations into electrical signals. lie btw the basilar membrane and the tectorial membrane in the cochlea.

Place Theory

• areas along the basilar membrane have hair cells sensitive to only one specific frequency of sound waves

  • limitation: basilar membrane not long enough to accommodate lower frequencies

  • High pitch = BASE (entrance of cochlea)

  • Low pitch = APEX (towards tip of cochlea)

Frequency Theory

basilar membrane vibrates in synchrony with sound and causes auditory nerve axons to produce action potentials at the same frequency

• ex. if frequency is 50 hz→50 action potentials per second in auditory nerve

  • limitation: the refractory period decreases maximum firing rate too much for high frequencies

Volley Principle

auditory nerve produces volleys of impulses (for sounds up to about 4000/sec.)

• multiple neurons alternate their firing

The Current Pitch Theory

• low frequency sounds best explained by frequency theory

• high frequency sounds best explained by place theory

sound localization

depends on comparing the response of the 2 ears through 3 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

high-frequency sounds (2000 to 3000 Hz) create a “sound shadow”

• phase difference btw the ears provides cues to sound locaization with frequencies up to 1500 Hz

what are the 2 categories of hearing loss?

1. Conductive or middle ear deafness

2. nerve deafness or inner ear deafness

explain Conductive or Middle Ear Deafness

• occurs if the bones of middle ear fail to transmit sound waves properly to the cochlea

• can be caused by disease, infections, tumors, or bone growth

  • can be corrected by surgery or hearing aids that amplify the stimulus

explain Nerve or Inner Ear Deafness

• results from damage to the cochlea, hair cells, or auditory nerve

• can vary in degree

• can be confined to one part of the cochlea; and cause people to hear only one frequency

  • can be inherited or caused by prenatal problem or early childhood disorders

major types of somatosensory [touch] receptors (4)

1. Meissner corpuscles

2. Pacinian corpuscles

3. Merkel discs

4. Ruffini endings

*stimulation open sodium channels to trigger an action potential

Meissner corpuscles

detect gentle and light touch & movement across the skin

• respond well to changes in light contact

Pacinian corpuscles

detect deep pressure and high-frequency vibration

• resists gradual and constant pressure

• chemicals can stimulate receptors for heat & cold; menthol & capsacin

• located deeper in the skin and other tissues.

  • ex. feeling phone vibration in your hand or sensing a buzzing electric toothbrush

Merkel discs

fine detail and sustained pressure

• helps you detect steady, gentle pressure, edges, shapes, and other fine details; useful for distinguishing textures and forms

  • ex. feeling ridges of a coin or reading braille with fingertips

Ruffini endings

respond to stretching of the skin and help provide info about sustained deformation of the skin and hand position

• ex. opening your hand wide and feeling your skin stretch/pull

chemical process/reaction to Pain

• mild pain causes the release of neurotransmitter, glutamate

• stronger pain releases several neuropeptides, including substance P and CGRP (calcitonin gene-related peptide)

• prefrontal cortex responds to pain as long as the pain lasts

cannabinoids

• chemicals related to marijuana that block certain kinds of pain

• act mainly in the periphery of the body

capsaicin

produces temporary burning sensation followed by a longer period of decreased pain

Itch [in relation to somatosensory experiences]

• release of histamines by the skin produces itching sensations

• activates a distinct pathway in the spinal cord to the brain

• impulses travel slowly along this pathway (half a meter/second)

  • pain and itch have an inhibitory relationship

  • opiates increases itch

chemical coding; label-line principle v.s across-fiber pattern

labeled-line principle: each receptor responds to a limited range of stimuli and sends a direct line to the brain

across-fiber pattern: each receptor responds to a wider range of stimuli and contributes to the perception of each of them

what is the Suprachiasmatic Nucleus (SCN)?

• control center of the circadian rhythms of sleep & temperature

• light resets the SCN via a small branch in optic nerve,

• located above the optic chiasm and part of the hypothalamus

  • damage to this SCN results in less consistent body rhythms that are no longer synchronized to environmental patterns of light and dark

what does a typical night of sleep look like; progression & cycling of different sleep stages?

There are 6 stages of sleep. After an hour, a person cycles back through the stages from stage 4 to stages 3 and 2, then REM—the sequence repeats, each lasting 90 minutes.

stage 1 sleep (light sleep)

• alpha waves begin a state of relaxation and brain activity declines

• lasts 1-7 minutes

stage 2 sleep (moderate sleep)

• presence of sleep spindles and k-complex

• sleep spindles; 12-14hz waves during burst, lasts ½ second each

• k-complex; sharp wave associated with temporary inhibition of neural firing

• HR slows, body temp drops, brain produces brief bursts of electrical activity (sleep spindles); 50% of total sleep

Slow-wave sleep—stage 3 & 4 (deep/SWS)

• slow HR, BR, and brain activity present

• highly synchronized neural activity

  • deepest, most restorative stage; tissue repair and & growth hormone released

Paradoxial or REM sleep

• REM describes periods of sleep characterized by Rapid Eye Movements, high brain activity, and relaxation of large muscles

How is an EEG used to study sleep?

• the EEG lead to the discovery that sleep happens in stages

• allows for comparison of brain activity at different times during sleep

How brain wave patterns are shown across sleep stages

Stage 1: dominated by irregular, jagged, low-voltage waves

Stage 2: sharp waves & spindles/k-complexes

Stage 3 & 4: slow, large-amplitude waves

Paradoxical & REM: irregular, low-voltage, & fast waves

what are the main functions of sleep?

• strengthening memories

• reorganizing synapses

• resting muscles

• preforming cellular metienence in neurons

• decreasing metabolism

what neurotransmitters are responsible for sleep/wakefulness?

• acetylcholine (excitatory; increases arousal)

• GABA (essential for sleep)

• histamine (produce widespread excitatory effects in brain)

• norepinephrine (arouse various areas of the cortex)

• orexin (excititory neuropeptide)

what is reticular formation?

structure extends from the medulla into forebrain; controls motor areas of the spinal cord

• needed to stay awake (attention) and aroused

what is GABA important for?

• decreasing temperature and metabolic rate

• decreasing stimulation of neurons

what is dreaming?

• either internal or external stimulation activates parts of the parietal, occipital, and temporal cortex

• lack of sensory input from V1 and no criticism from prefrontal cortex creates the hallucinating perceptions

what is the activation-synthesis hypothesis? (dreaming)

• suggests dreaming begins with spontaneous activity in the pons, activates many parts of the cortex; it synthesizes a story from the pattern of activation. (most common dreaming type)

what is the neurocognitive hypothesis?

• places less emphasis on pons, PGO waves, or even REM sleep

  • suggests dreams are similar to thinking, under unusual circumstances

  • dreams begin with arousing stimuli that are generated in brain

  • (stimulation combined with recent memories from senses)

insomnia

disorder caused by or associated with inadequate sleep

• causes: by noise, stress, pain, diet, and medication

• can be the result of disorders such as epilepsy, Parkinson’s, depression, anxiety, or other conditions

sleep apnea

• disorder characterized by the inability to breathe while sleeping for a prolonged time

• consequences: sleepiness during the day, impaired attention, depression, & sometimes heart problems

  • effects; cognitive impairment might be a result

narcolepsy

• frequent periods of sleepiness

• gradual/sudden attacks of hypnagogic hallucinations; dreamlike experiences of sleepiness

• occasional cataplexy; muscle weakness triggered by strong emotions

• sleep paralysis; inability to move while falling asleep or waking up

• hypnagogic hallucinations; dreamlike experiences

  • cause: lack of hypothalamic cells that produce & release orexin

REM Behavior Disorder

• associated with vigorous movement during REM sleep (associated with acting out dreams)

• research suggests inadequate GABA and other inhibitory neurotransmitters may be the cause

how does timing affect memory and learning?

• increased brain activity occurs in the brain region activated by a newly learned task while someone is asleep

• patterns of activity in the hippocampus during learning were similar to those shown during sleep

  • brain replays daily experiences during sleep

  • sleep spindles increase in # after new learning

4 types of consciousness

coma—an extended period of unconsciousness characterized by low, steady brain activity. little response to stimuli is shown

vegetative state— person alternates between periods of sleep and moderate arousal, but no awareness of surroundings

minimally conscious state— 1 stage higher than a vegetative state marked by occasional brief periods of purposeful action and limited speech comprehension

brain death— no sign of brain activity and no response to any stimulus

how does travel disrupt sleep?

disruption of the circadian rhythm occurs following crossing different time zones.

• traveling west “phase-delays” our circadian rhythm

• traveling east “phase-advances” our circadian rhythm

  • stems from a mismatch between the internal circadian clock and external time

what is taste?

stimulation of the taste buds

• our perception of flavor is the combo of taste & smell

• taste receptors = modified skin cells

what is gate theory?

• proposes non-painful stimuli can help decrease pain perception

  • ex. comb prongs squeezed to help decrease pain of childbirth

what is zeitgeber?

German meaning of “time giver” refers to the stimulus that resets the circadian rhythm

• ex. sunlight, tiles, exercise, meals, arousal of any kind, temp of environment, etc.

what is Melatonin, why is it important?

regulates sleep/wake cycle and maintaining circadian rhythms

• comes from the pineal gland; based on signals from the Suprachiasmatic Nucleus (SCN)