Brain Disorder Unit 2 Study Guide Key Terms

X-ray

2D structural image created by differential radiation absorption. Useful for imaging skull fractures and foreign objects

CT Scan

Computed tomography - acquires series of 2D X-ray images to create 3D image. Best for quickly viewing skull fractures, stroke, bleeding, and brain swelling

MRI - T1

Structural MRI where gray matter is darker than white matter (and water appears dark). This is the more 'normal' brain image. Good for examining detailed anatomical structures (and tumors with contrast dye)

MRI - T2

Structural MRI where water appears bright and white matter is darker than gray matter. This is also called a 'diffusion-weighted' image, as it is measuring fluid content/motion in the tissues. Good for viewing brain swelling, stroke, bleeding, MS lesions (loss of myelin = increased CSF), and infection (swelling from immune system)

DTI

Diffusion Tensor Imaging - MRI technique that images white matter tracts and connectivity by a computer analyzing many diffusion-weighted scans to track water/fluid movement along major axon bundles

EEG

Electroencephalogram - functional measurement that records electrical activity of the brain using scalp electrodes. Temporal resolution is similar to neural activity timing, but spatial resolution is not so good. Useful for seizures, arousal level, and brain death

ECoG

Electrocorticography - functional measurement that uses invasive recording of electrical activity directly from brain surface. Better spatial resolution than EEG as the electrical activity does not have to travel first through the meninges, skull, and scalp

PET scan

Positron Emission Tomography - functional measurement that measures brain metabolism using radioactive tracers. Good for dementia, stroke, and tumors

fMRI

Functional MRI - measures blood oxygenation changes (BOLD signal) to detect when neurons are active. This is a very good but indirect measure of neural activity. Excellent for cognitive disorders and research

Visual Field

The entire area that can be seen when an eye is fixed straight at a point in space

Vertical Meridian

Line dividing field into left/right halves

Horizontal Meridian

Line dividing field into top/bottom halves

Hemifield

Half the visual field (typically left/right)

Quarterfield

One quadrant of the visual field

Optic Nerve - visual pathway

Axons of retinal ganglion cells

carrying visual information from eye to the optic chiasm

axons continue on as the optic tract to synapse in the lateral geniculate nucleus of the thalamus on vision's path to the brain

Optic Chiasm - visual pathway

Where nasal (inner) fibers cross

allows left visual field information from both eyes to go to right hemisphere and vice versa

Optic Tract - visual pathway

After chiasm

GN (Lateral Geniculate Nucleus) - visual pathway

Relay in thalamus

Optic Radiations - visual pathway

Pathway to cortex

Primary Visual Cortex (V1) - visual pathway

Occipital lobe

Midget RGCs → Parvocellular Pathway

Small receptive fields

Specialized for: COLOR, fine detail, high spatial resolution

Sustained response

Parasol RGCs → Magnocellular Pathway

Large receptive fields

Specialized for: MOTION, low spatial resolution

Transient response

Small Bistratified RGCs → Koniocellular Pathway

S-cone pathway inputs (blue)

Low acuity visual information

Support

Three Opponent Channels

Red vs. Green: L (red) cones vs. M (green) cones

Blue vs. Yellow: S (blue) cones vs. combined L+M (yellow)

Dark vs. Bright (Luminance): Combined L+M+S

Primary Visual Cortex (V1) Function

First cortical area to receive visual input; processes basic features like edges and orientation

Cortical Magnification

Disproportionately large representation of fovea in V1 → higher acuity in central vision

more brain area is devoted to parts of the body or visual field that is needed for high precision

Dorsal Visual Pathway ("Where/How" - Perception for Action)

V1 → Parietal regions

Spatial awareness, guiding actions

Motion processing

perception for action: motion & spatial location

Ventral Visual Pathway ("What" - Perception for Recognition)

V1 → Temporal regions

perception for recognition: objects, faces, color

Object recognition

Face processing

Color processing

Cataract

Opacity (clouding) in the LENS that blocks light from reaching retina

Often age-related due to UV exposure

Surgical lens replacement needed

Scotoma

Area of impaired or lost vision in visual field

Can result from damage anywhere from: Retina → Optic nerve → V1

Brain often "fills in" missing region, so patient may not see black spot unless in center

MONOCHROMACY: Rod Monochromacy

All cones non-functional; vision relies entirely on rods

Complete color blindness

Low visual acuity (no functional fovea, only periphery working)

Sees in black and white only

MONOCHROMACY: Blue-Cone Monochromacy

Only rods & S (blue) cones functional

Can see ~100 colors (vs. normal 10 million)

Sex-linked; men most likely to have it

DICHROMACY (Two Cone Types): Protanopia

Missing: L (red) cones

Red-green (X-linked)

DICHROMACY (Two Cone Types): Deuteranopia

Missing: M (green) cones

Red-green (X-linked) - MOST COMMON dichromacy

DICHROMACY (Two Cone Types): Tritanopia

Missing: S (blue) cones

Blue-yellow (NOT sex-linked) - VERY RARE

ANOMALOUS TRICHROMACY (MOST COMMON)

All three cone types present BUT shifted sensitivity

ANOMALOUS TRICHROMACY: Protanomaly

red-weakness

ANOMALOUS TRICHROMACY: Deuteranomaly

green-weakness - MOST COMMON colorblindness overall

ANOMALOUS TRICHROMACY: Tritanomaly

blue-weakness

Tetrachromacy

Condition where person has 4 cone types (2 types of L-cones)

Can see ~100 MILLION colors (vs. normal 10 million)

2-3% of women

** Brain circuitry can form normally even with extra cone type!

Visual Field Defects (Hemianopsias): Unilateral Field Loss

Complete blindness in ONE eye

damage: Optic nerve (before chiasm); tumor or trauma

Visual Field Defects (Hemianopsias): Bitemporal Hemianopsia

Outer (temporal) halves (hemifields) of BOTH eyes

damage: Optic chiasm (often tumor)

Visual Field Defects (Hemianopsias): Binasal Hemianopsia

Inner (nasal) halves of (hemifields) BOTH eyes

damage: Uncrossed fibers (calcified carotid arteries); hydrocephalus

Visual Field Defects (Hemianopsias): Homonymous Hemianopsia

SAME half of both eyes (e.g., right half of both)

damage: Opposite V1 or optic tract (e.g., left V1 → right hemianopsia); stroke, trauma

Sensation

First stage of sensory function - information at peripheral sensory receptors

Perception

Process of recognizing, organizing, and interpreting sensory information

Optic Radiation

nerve fibers carrying visual info from thalamus - V1 (primary visual cortex)

Optic Radiation: inferior retina

temporal love (meyer’s loop): carries upper visual field

Optic Radiation: superior retina

occipital lobe: carries lower visual field

Visual Field Mapping: left visual field

right brain

Visual Field Mapping: right visual field

left brain

Blindsight

Phenomenon where people with V1 damage are perceptually BLIND but show some unconscious response to visual stimuli

ability to respond to visual stimuli w/o conscious awareness (blind)

damage to V1

alternative pathways send info directly to motion area (MT)

Visual Agnosia

Inability to recognize objects, scenes, or faces DESPITE intact elementary visual perception

vision intact, but object recognition impair

damage occurs after V1

Visual Agnosia: Apperceptive Agnosia

Cannot name, copy, OR recognize objects (impaired shape perception)

BUT knowledge of objects is intact

Visual Agnosia: Associative Agnosia

Cannot identify OR name the objects (meaning disconnected from perception)

BUT can perceive object shape and copy

Object Agnosia

cannot recognize objects by sigh, but can recognize by touch or sound

Vision neurons: fovea (center vision)

lots of neurson

Vision neurons: peripheral vision

fewer neurons

Gestalt Grouping & Object Recognition

brian uses prior knowledge to organize visual input

Fusion Face Area (FFA)

specialized for face recognition, active in both hemispheres

Prosopagnosia

(face blindness) Inability to recognize FACES despite normal vision and object recognition

Associative:

Prosopagnosia (Apperceptive)

problem with recognizing face vs. other objects (fruit face)

Prosopagnosia (Associative)

able to tell it’s a face, but problem with recognition

Capgras Syndrome

belief that a loved one has been replaced by an identical impostor

face recognition works, but emotional response is disconnected

Rare delusional misidentification syndrome

Fregoli Syndrome

belief that multiple people are actually one person in disguise

over-activation of face familiarity systems

Rare delusional misidentification syndrome

Simultanagnosia

inability to perceive more than one object at a time in a scene

can identify individual items, but cannot understand the whole scene

Simultanagnosia: Dorsal Simultanagnosia

perceives only one stimulus at a time, single word or object, may appear blind

Simultanagnosia: Ventral Simultanagnosia

Can see multiple objects but cannot recognize them, one at a time

Can navigate and count but cannot read

Cerebral Achromatopsia (Cortical Color Blindness)

loss of color in both visual field

caused by cortical lessions: stroke, trauma, dementia

Cerebral Achromatopsia: Hemiachromatopsia

Loss of color in ONE half of visual field

Cerebral Achromatopsia: Transient

Temporary loss (hours) from TIA or transient ischemic attack

Akinetopsia (Motion Blindness)

Inability to perceive MOTION smoothly (which affects temporal processing)

series of still images

damage to V5 and MT

stroke, trauma, antidepressants

Troxler Effect

Visual phenomenon where fixating on one point causes stationary peripheral images to fade