Strokes and Effects on Neural Function

Question 1

Stroke

Answer 1

• Disruption of blood supply and subsequent damage to brain

Question 2

Types of strokes

Answer 2

• Ischemic strokes (clots): affect oxygen supply to brain
  
  • Thrombotic stroke: Clot in brain’s blood vessels
  • Embolic stroke: Clot forms elsewhere
• Haemorrhagic stroke: rupture of blood vessels (blood is toxic for cells)

Question 3

Consequences of strokes

Answer 3

• Functional disturbance of surrounding neurons (transient symptoms)
• Primary cell death (apoptosis)
• Secondary cell death (increased intracranial pressure due to swelling response to injury)
• Stroke can cause a wide range of impairment (e.g. cognitive, motor)
• Sometimes these impairments are very severe but recovery of function does occur

⇒ Recovery after stroke demonstrates that the brain is plastic and can reorganise itself

Question 4

Rehabilitation of motor functions

Answer 4

• Most recovery after stroke occurs over the first 3 months (Ward et al., 2003)→ Rehabilitation is most important during this time period
• Even after serious strokes, motor function can recover nearly completely within the first few months

Question 5

Rehabilitation of cognitive functions

Answer 5

• Most common impairments are in psychomotor speed (34%) and executive function (27%)
• Particularly over the first 6 months, some recovery of function is often seen (Turunen et al., 2018)

Question 6

Language deficits after stroke

Answer 6

• Aphasia: common consequence of stroke - Problems producing speech
• Agraphia: problems with spelling and writing
• Alexia (word blindness/visual aphasia): damage to visual/temporal regions in left hemisphere → Problems with reading

Question 7

Dual-route theory of reading

Answer 7

• Coltheart et al., 2001
• The dorsal (phonological) route connects the visual–parietal–frontal areas. Used for when phonetically decoding words: understanding words by mapping them onto sounds.
• The ventral route connects visual to semantic areas in the temporal lobe. Direct mapping of words onto their meaning

Question 8

Alexia

Answer 8

• Some patients cannot read non-words aloud, or recognise rhymes ⇒ dorsal (phonological) route impaired: they can’t turn words into sounds
• But can still show good reading ability – particularly for ‘concrete’ words (e.g. objects)
• Often poor at reading ‘function’ words (e.g., to, and, how)
• Mechanism?
  
  • These patients have to read via meaning using the ventral route (directly matching letter-strings to meanings)
  • Or - reliance on right hemisphere: Right hemisphere is unable to perform letter-sound conversion but does contain an imprecise (‘coarse grain’) route to meaning

Question 9

What do strokes tell us about neural function?

Answer 9

• Effects and recovery from stroke tells us that the brain is plastic (particularly for recovery of motor skills)
• By linking damage to the pattern of impairment, It can also offer clues as to how the brain is organised