Biopsych Exam #2 (Research Methods and Vision)

scientific method

review what is known

propose study hypotheses

decide upon appropriate methods

conduct study

analyze results

draw conclusions

lesion methods

radio frequency/electrical current, chemical lesions, local anesthetic, sham lesions

chemical (excitotoxic) lesions

kills cell bodies, spares axon

local anesthetic

temporary lesion, brings brain offline temporarily

microelectrodes

single-unit recording, requires amplifiers, way to detect something individual/specific

macroelectrodes

more often used in humans (EEG), records postsynaptic potentials of thousands/millions of neurons

how do you stimulate brain activity?

electrical stimulation, optogenetics

optogenetics

uses light to stimulate activity in the brain

human brain methods

structure vs function

human brain methods (structure)

computerized tomography, structural MRI, diffusion tensor imaging

human brain methods (function)

functional MRI, EEG, MEG, PET

structural MRI

brain’s anatomy, detects energy emitted from hydrogen atoms

atoms are present in different concentrations in different tissues

scanner uses information to prepare pictures of slices of the brain

functional MRI

BOLD signal (blood oxygenation level dependent)

looking at increases in oxygenated blood

oxygen delivered to neurons by hemoglobin in capillaries

when neural activity increases, need for oxygen increases, blood flow increases

Ex. to test the amygdala, scare the person and see if they amygdala is activated

Positron Emission Tomography (PET)

ring of detectors absorb photon energy

PET scanner creates 3D images by computer reconstruction that shows how the radioactivity is distributed

areas where large amount of glucose accumulates are “hot spots”

problems: exposure to radiation, expensive, cannot detect changes < 30 seconds

EEG

technique for measuring electrical activity generated in the brain

measures summation of postsynaptic potentials

MEG

measures magnetic fields

tiny signals, need amplifiers

How does stimulating neural activity work?

TMS/transcranial magnetic stimulation

electromagnetic coil placed against scalp, takes advantage of the fact that you use magnetic fields to affect electrical fields

Ex. video where it affects man’s ability to sing a nursery rhyme

What methods could be used for studying human brain structure?

structural MRI

What are 3 methods for studying brain activity?

functional MRI

EEG

MEG

What method can be used to stimulate the human brain?

TMS (transcranial magnetic stimulation)

where does visual processing begin?

retina

2 types of photoreceptors

rods and cones

rods

low-light

cones

color; provide 90% of input

fovea

central region at back of eye, has dense concentration of cones not obstructed by other cells (clearest view)

blood vessels

midget ganglion cells

blind spot

where the optic nerve leaves the eye, no retina

photopigments

rods and cones have them

embedded in lamellae

when light hits these, split into component parts which producer receptor potential

opsin

protein

retinal

lipid, synthesized from vitamin A

receptive fields

depend on location of photoreceptors providing information

periphery

many receptors converge on single ganglion cell

fovea

almost one-to-one photoreceptor to neuron relationship; called midget ganglion cells

trichromatic theory

cones have different wavelengths

ever color you see is a combo of these 3 cones

color depends on frequency of response in each cell compared to others (long = red, medium = green, short = blue)

opponent process theory

opponent ganglion cells receive input from 2-3 different kinds of cones (ex. afterimage)

retinex theory

cortex compares info from various parts of the retina to determine color and brightness (ex. color constancy)

red-green color deficiency

variants of genes for medium and long pigments more likely in males (on X chromosome)

where does the crossover between the eyes occur?

optic chiasm (processed in contralateral hemisphere)

lateral geniculate nucleus

part of thalamus (has 6 layers)

V1 (striate) cortex

has retinotopic mapping, patterns reflect image

3 types of cells in V1

simple cells, complex cells, hypercomplex cells

simple cells

organized in opponent fashion

respond to edges, bars with particular width, location, and orientation in the visual field

complex cells

movement detectors; do not show inhibitory surround

hypercomplex cells

respond to lines of particular orientation

inhibitory region’s on edges

low frequency

large areas of light/dark and gradual transitions

high frequency

small details and sharp contrasts (ex. Einstein and Marilyn Monroe (low frequency, no sharp details)

retinal disparity

stimulus produces images on slightly different parts of retina

brain makes calculation to how far stimulus is

stereoscopic vision

neurons in striate cortex are binocular

respond to stimulation from either eye

sensitive periods

during which exposure/experience can have long-lasting effects (ex. strabismus aka lazy eye)

2 visual streams

ventral and dorsal

ventral

(what?) terminate in inferior temporal cortex

dorsal

(How? where? moving?) terminates in posterior parietal cortex

includes movement processing, guides navigation and skilled movements

Area V2

receives most outputs of V1 neurons that are sensitive to orientation and spacial frequency

increased level of complexity

inferior temporal lobe

recognition of visual patterns, analyses of form and color together; end of ventral stream

(FFA, EBA, PPA - specialized regions for form perception)

visual agnosia

inability to recognize objects caused by damage to ventral stream

prosopagnosia

face blindness

developmental = reduced activation of fusiform gyrus, reduced white matter connectivity in ventral occipitotemporal cortex

acquired = damage to fusiform gyrus

dorsal stream

area MT (middle temporal cortex, V5)

detects speed, acceleration, deceleration, photographs that imply movement

damage = difficulty to perceive movement; aka become motion blind (akinetopsia), can see objects but can’t see whether they are moving or in what direction

MST (medial superior temporal cortex)

processes complex patterns of movement

what is the center of the retina (where we get the most clear vision?)

fovea

what is the blind spot?

where the optic nerve leaves the eye

what is opponent-process coding? Where does this occur (which type of cell)?

opponent ganglion cells receive input from 2-3 different kinds of cones

ganglion cells

what is the part of the thalamus that receives projections from the optic tract?

Lateral geniculate nucleus (LGN)

Where is the visual/striate cortex?

occipital lobe

what are the 3 types of cells in the striate cortex (V1) that detect visual features?

simple, complex, hyper-complex

what is 1 way that we perceive depth?

retinal disparity

which visual stream answers the question of “what?” or “where?”

ventral

What is prosopagnosia?

face blindness

what brain area is responsible for motion detection?

dorsal stream