Sensory Aphasia vs. Motor Aphasia - MBBS 1st Year Physiology Notes

What is Aphasia?

Quick Overview Table

Motor (Broca's) Aphasia - In Detail

Definition

Lesion

• Broca's area: Inferior frontal gyrus, posterior part (pars triangularis + pars opercularis), left hemisphere
• Brodmann areas 44 and 45
• Caused by infarct in territory of left MCA superior division

Speech Pattern

• Nonfluent - short phrases, effortful, slow
• Agrammatism (telegraphic speech): patient uses only content words (nouns, verbs), dropping prepositions, conjunctions, and grammatical morphemes
  • Example: "Wife...come...hospital" instead of "My wife came to the hospital"
• May be mute in acute phase
• Dysarthria and apraxia of speech may be present
• Phonemic (literal) paraphasias - substitutes similar-sounding phonemes (e.g., "p" for "b")

Comprehension

• Relatively preserved for everyday conversation
• Difficulty with complex syntax (embedded clauses, prepositional relationships)
  • e.g., "The rug that Bill gave to Betty tripped the visitor" - causes difficulty

Associated Signs

• Right-sided hemiparesis (face and arm predominantly) - because lesion is near the motor cortex
• Right hemisensory loss
• Apraxia of the oral apparatus and left (non-paralyzed) limbs
• Depression is common (patient is aware of their deficit and is frustrated by it)

Sensory (Wernicke's) Aphasia - In Detail

Definition

Lesion

• Wernicke's area: Posterior superior temporal gyrus, left hemisphere
• Brodmann area 22 (extends into inferior parietal lobule and middle temporal gyrus)
• Caused by infarct in territory of left MCA inferior division

Speech Pattern

• Fluent - normal rate, rhythm (prosody), and grammatical structure
• Speech is empty of meaning
• Paraphasias:
  • Verbal (semantic) paraphasia: substituting a related word - e.g., "ink" for "pen"
  • Literal (phonemic) paraphasia: substituting a similar-sounding word part - e.g., "pish" for "fish"
• Neologisms: made-up words
• Jargon aphasia: fluent but largely incomprehensible speech
• Logorrhea (excessive talking) may occur

Comprehension

• Severely impaired - patient does not respond appropriately to questions
• Cannot follow commands (except a few axial commands like "close your eyes")

Associated Signs

• No hemiparesis (motor cortex not involved)
• Right upper quadrant visual field defect (right superior quadrantanopia) - due to involvement of the lower optic radiation (temporal lobe)
• Anosognosia - patient is unaware of their deficit
• May behave angrily or paranoid - can be mistaken for a psychiatric disorder
• Examining Wernicke's aphasia can be frustrating for the examiner (vs. frustrating for the patient in Broca's)

Anatomical Basis

FRONTAL LOBE          TEMPORAL LOBE
  |                        |
Broca's area  ←-- Arcuate fasciculus --→  Wernicke's area
(BA 44, 45)                                   (BA 22)
  |                                               |
Motor aphasia                            Sensory aphasia
(nonfluent, can understand)              (fluent, cannot understand)

Mnemonic

"BROCA = BROKEN speech" - can't speak well, but understands
"WERNICKE = WORDY nonsense" - speaks fluently, but it's meaningless

• Motor (Broca's) = Makes effort, Motor cortex nearby → hemiparesis
• Sensory (Wernicke's) = Speaks fluently, Superior temporal gyrus → no weakness

Clinical Examination of Aphasia (Benson & Geschwind, 6-step bedside test)

1. Fluency - is speech effortless or labored?
2. Comprehension - can they follow commands?
3. Repetition - can they repeat "no ifs, ands, or buts"?
4. Naming - can they name objects shown?
5. Reading
6. Writing

Global Aphasia (for completeness)

• Nonfluent speech + severely impaired comprehension
• Associated with hemiplegia
• Worst prognosis for recovery

Summary in One Line

Motor aphasia (Broca's) = patient knows what they want to say but cannot say it. Sensory aphasia (Wernicke's) = patient speaks freely but produces meaningless language and cannot understand what is said to them.