Localization of Cortical Dysfunction

Question 1

What are the 3 domains of consciousness?

Answer 1

1. alertness
2. attention
3. awareness

Question 2

Level Of Consciousness (4):

Answer 2

awake state on one end of spectrum to coma on the other

1. awake
   
   • one is able to maintain alertness, attention, awareness including awareness of self & environment
2. sleepy
   
   • alertness wanes after short period without stimulation
3. stupor
   
   • alertness severely impaired
   • attention, awareness only maintained with continued stimulation
4. coma
   
   • loss of alertness, attention, awareness
   • unarousable

Question 3

• delirium:
• encephalopathy:

Answer 3

• delirium
  
  • alert and aware, but attention severely impaired
  • confused
• encephalopathy
  
  • all 3 domains affected, but to a lesser degree than in a coma
  • some alertness maintained

Question 4

Where are structural or functional abnormalities that can cause an altered state of consiousness?

Answer 4

• diffuse bilateral cerebral hemispheres
  
  • ​lesion involving half the cerebrum will typically NOT cause altered consciousness
  • although they will have focal deficits
• bilateral thalami
  
  • ​because ARAS projects to brain, which then projects to cerebrum
• brainstem ARAS
  
  • ascending reticular activation system

Question 5

FRONTAL LOBE:
Primary motor cortex

Answer 5

• functions to voluntarily control contralateral movement
• lesion (eg. stroke) ⇒ contralateral hemiparesis
• activation (eg. seizure) ⇒ contralateral clonic movements
• Jacksonian march
  
  • seizures in the primary motor cortex that travels along gyrus
  • activates muscles in an order seen on the motor homunculus

Question 6

FRONTAL LOBE:

Frontal Eye Fields

Answer 6

• contralateral saccades
  
  • voluntary eye movements to contralateral field
• lesion of FEF ⇒ ipsilateral gaze preference
  
  • eg. L FEF stroke ⇒ L gaze preference

Question 7

FRONTAL LOBE:

Broca’s Area

Answer 7

• fluency of language
• inferior frontal lobe in dominant hemisphere
  
  • in most R handed and most L handed people, language is represented in the dominant (L) hemisphere
  • more L handed individuals tend to have bilateral language representation
• loss of function causes a Broca’s aphasia = Non-fluent aphasia
  
  • speech is non-fluent, halting, effortful, composed of few words that usually make sense
  • agrammatic
  • repetition impaired
  • Broca’s area is supplied by MCA
  • lesion could be caused by stroke or tumor

Question 8

FRONTAL LOBE:

Prefrontal Cortex

Answer 8

• provides ORDER
• mediates personality, executive function, ability to sequence & organize tasks, abstract, problem solving

Question 9

FRONTAL LOBE:

Orbitofrontal cortex

Answer 9

• provides RESTRAINT
• inhibits socially inappropriate behavior
• part of limbic system
  
  • plays role in memory & emotions
• 2 most common ways to lesion this region of brain
  
  1. ​​head trauma as orbitofrontal cortex rubs along base of skull with jagged surface
  2. meningioma (tumor of meninges at base of skull)

Question 10

Frontotemporal dementia (Pick’s disease):

Answer 10

• progressive dementia due to neurodegeneration
• affects prefrontal cortex first ⇒ causes personality changes, irritability, mood changes, poor executive function
• eventually affects other regions of frontal cortex such as orbitofrontal cortex & also temporal cortex
• dementia occurs in mid life (50’s), which is much earlier than most cases of Alzheimer’s
• lifespan is shortened

Question 11

FRONTAL LOBE:

Mesiofrontal cortex

Answer 11

• provides INITIATIVE
• mediates motivation, goal-directed behavior
  
  • micturition inhibitory center allows voluntary inhibition of urination
• lesion causes akinetic mutism (patients do not move or talk), abulia (lack of initiative), incontinence as seen in hydrocephalus (ventricles enlarge & stretch fibers travelling medially to spinal cord)

Question 12

PARIETAL LOBE:
Primary somatosensory cortex

Answer 12

mediates contralateral sensation

Question 13

PARIETAL LOBE:

Parietal somatosensory association cortices

Answer 13

• mediates higher order sensation (primary sensation must be intact):
  
  • graphesthesia = ability to discern what is written on skin
  • stereognosis = ability to discern object placed in hand based on sensation

Question 14

Describe the characterstics of a deficit in the parietal somatosensory association cortex on the non-dominant side:

Answer 14

• non-dominant parietal cortex (in most people, the R parietal cortex) drives spatial attention on both hemifields
  
  • R parietal cortex controls spatial attention on L hemifield >> R hemifield
  • L parietal cortex controls spatial attention on R hemifield primarily
• lesion of non-dominant parietal cortex (R) results in contralateral neglect & apraxia
• neglect = not paying attention to contralateral hemifield
  
  • eg. R parietal lesion will cause severe L neglect
  • patient “ignores” the left side of the world
  • they will bump into objects on L side, will ignore the L side of their body

Question 15

Apraxia:

Answer 15

inability to perform a skilled task

• brushing teeth, combing hair, dressing, tying shoe lace

Question 16

Gerstmann syndrome:

Answer 16

• lesion of dominant (L) parietal cortex (angular gyrus)
• 4 components to clinical syndrome:
  
  1. agraphia
     
     • inability to write
  2. acalculia
     
     • inability to calculate
  3. finger agnosia
     
     • inability to recognize fingers
  4. right/left confusion
     
     • cannot discern between right & left

Question 17

TEMPORAL LOBE:
Wernicke’s area

Answer 17

• comprehension of language
• superior temporal gyrus in dominant hemisphere
• loss of function causes Wernicke’s aphasia = Fluent aphasia
  
  • nonsensical gibberish
  • patient may be partially aware that what is said is not correct despite not comprehending
  • patient cannot follow commands
  • impaired repetition
• Wernicke’s area is supplied by MCA

Question 18

1. Conduction Aphasia:
2. Global Aphasia:

Answer 18

1. Conduction Aphasia:
   
   • ​​inability to repeat
   • mediated by arcuate fasciculus
2. Global Aphasia:
   
   • ​​loss of comprehension, repetition, & fluency
   • these patients usually have no language
   • usually due to complete MCA stroke at its proximal origin (where ICA divides into ACA & MCA)

Question 19

Kluver-Bucy Syndrome:

Answer 19

• due to injury to bilateral anterior temporal poles & bilateral amygdala
• hyperorality (pt explores environment with mouth)
• inappropriate sexual displays (removing clothes, masturbation in public, inappropriate kissing/flirting)
• irritability & aggression
• anterograde amnesia—due to amygdala involvement
• alternating episodes of depression & overactivity

Question 20

What is the Function of the Medial Temporal Lobe? What can disrupt its function?

Answer 20

• memory center of brain
• hippocampal atrophy
  
  • ​neuronal degeneration in the hippocampus occurs early in Alzheimer’s disease
• hippocampal sclerosis
  
  • ​scarring of hippocampus is thought to cause or be the result of uncontrolled complex partial seizures

Question 21

OCCIPITAL LOBE:
Primary visual cortex

Answer 21

• right occipital cortex mediates vision from contralateral hemifield
• optic radiations: originate from lateral geniculate nucleus ⇒ visual cortex
  
  1. LGN ⇒ optic radiations travels into parietal region ⇒ synapses onto superior bank of occipital cortex
     
     • inferior vision
  2. LGN ⇒ optic radiations travel into temporal region (Meyer’s loop) ⇒ synapses onto inferior bank of occipital cortex
     
     • superior vision

Question 22

Describe how lesions in the primary visual cortex affect vision:

Answer 22

1. R occipital cortex lesion ⇒ L homonymous hemianopia (and vice versa)
2. monocular visual field defects ⇒ usually anterior to chiasm
3. binocular visual field defects (ie. homonymous) ⇒ retro-chiasmal
4. lesion of the parietal optic radiations ⇒ contralateral inferior quadrantanopia
5. lesion of Meyer’s loop ⇒ contralateral superior quadrantanopia

Question 23

Define homonymous:

Answer 23

affecting both sides

• R homonymous hemianopia indicates that R field on both eyes are affected
• presence of a homonymous hemianopia indicates that lesion is in cortex/subcortex

Question 24

Homonymous hemianopia with macular sparing:

Answer 24

• may occur due to dual blood supply to occipital pole
• outer tip of calcarine cortex ⇒ macular vision
  
  • highest visual acuity
• inner portions of calcarine cortex ⇒ peripheral vision
• primary blood supply is from PCA
  
  • ​secondary blood supply is from branch of MCA
• PCA stroke may still allow intact macular vision due to blood from MCA branch

Question 25

Balint syndrome:

• Simultanagnosia
• Optic Ataxia
• Ocular Apraxia

Answer 25

• lesion of bilateral occipital-parietal pathways
  
  • ​“where” pathway
  • helps determine spatial relations of objects
  • triad below
• Simultanagnosia
  
  • inability to perceive the visual field a whole
  • Pt focuses on small portions of picture but cannot conceptualize picture as a whole
• Optic ataxia
  
  • inability to point/reach for objects in visual field under visual guidance
• Ocular apraxia
  
  • inability to look at objects in VF using saccades
• can be caused by b/l MCA-PCA watershed infarcts, Alzheimer’s disease

Question 26

What is a watershed infarct?

Answer 26

• due to cerebral hypoperfusion
• vulnerable cortex between main arterial territories are lesioned
• ACA-MCA infarct
• MCA-PCA infarct

Question 27

ACA-MCA infarct:

Answer 27

• lesion of cortex that is not primarily supplied by MCA or ACA
• results in “man in a barrel” syndrome
  
  • ​motor cortex representing torso & shoulder are more vulnerable than hands and legs/feet
  • due to arrangement of motor homunculus
  • results in relative sparing of movement of hands/feet
• caused by stenosis of ICA with superimposed hypoperfusion

Question 28

MCA-PCA infarct:

Answer 28

• lesion of cortex that is not primarily supplied by MCA or PCA
• results in Balint syndrome
• can be caused by systemic hypoperfusion
  
  • cardiac arrest