Neuroanatomical Basis of Three Disorders: Aphasia, Agnosia, and Apraxia

Introduction

• Speaker: Dr. Adel Bandock
• Institution: Mansoura University, Egypt
• Topics: Aphasia, Agnosia, Apraxia

Language Areas in the Dominant Hemisphere

• Dominant hemisphere: Left in 95% of right-handed, 85% of left-handed people
• Four language areas:
  1. Motor Speech Area (Broca's Area) (Area 44 & 45)
  • Location: Posterior part of inferior frontal gyrus
  • Function: Formulation of words
  2. Sensory Speech Areas:
  • Area 22 (Wernicke's Area): Posterior part of superior temporal gyrus, understanding spoken language
  • Area 39 (Angular Gyrus): Understanding written language
  • Area 40 (Supramarginal Gyrus): Understanding sizes, shapes, textures, body part recognition, left/right distinction
• Connections: Sensory speech areas connected to motor speech area by arcuate fasciculus (superior longitudinal fasciculus)

Aphasia

• Definition: Language disability causing:
  • Difficulty understanding
  • Difficulty speaking
  • Difficulty reading
  • Difficulty writing
• Types of Aphasia and site of lesion:
  1. Broca's Aphasia (Expressive/Motor/Non-Fluent Aphasia)
  • Lesion: Broca's area
  • Features: Difficulty speaking, normal comprehension, ability to write
  2. Wernicke's Aphasia (Sensory/Receptive/Fluent Aphasia)
  • Lesion: Wernicke's area
  • Features: Fluent but meaningless speech, impaired comprehension
  3. Global Aphasia
  • Lesion: Broca's area + Wernicke's area
  • Features: Cannot read, write, repeat sentences, or name objects
  4. Conduction Aphasia
  • Lesion: Arcuate fasciculus
  • Features: Normal comprehension, fluent but meaningless speech
  5. Anomic Aphasia
  • Lesion: Angular gyrus
  • Features: Alexia (inability to read), Agraphia (inability to write)

Agnosia

• Definition: Inability to recognize a sensory modality despite intact sense
• Types of Agnosia:
  1. Auditory Agnosia
     • Lesion: Wernicke's area of dominant hemisphere
     • Feature: Inability to recognize familiar sounds despite normal hearing
  2. Tactile Agnosia (Astereognosis)
     • Lesion: Somatosensory association area (Area 5, 7, 40)
     • Feature: Inability to recognize objects by touch with eyes closed
  3. Visual Agnosia
     • Lesion: Visual association area (Area 18, 19)
     • Feature: Inability to recognize seen objects, normal vision
  4. Color Agnosia
     • Feature: Absence of color vision
  5. Prosopagnosia (Face Blindness)
     • Lesion: Posterior fusiform gyrus (Area 37)
     • Feature: Inability to recognize familiar faces, relies on sounds
  6. Unilateral Neglect & Finger Agnosia
     • Lesion: Right supramarginal gyrus (non-dominant hemisphere)
     • Feature: Neglects left space, left space processed only by right hemisphere
     • Examples: May shave/apply makeup to only right side

Apraxia

• Definition: Motor disorder, inability to perform learned/familiar movements on command, absence of paralysis
• Types of Apraxia:
  1. Motor Apraxia
     • Lesion: Premotor area (Area 6), inferior parietal lobule, arcuate fasciculus (dominant hemisphere)
     • Feature: Cannot perform motor activity on command but can do spontaneously
  2. Callosal Apraxia (Split Brain/Callosal Disconnection Syndrome)
     • Lesion: Corpus callosum infarction
     • Feature: Confined to left hand, disconnects dominant and non-dominant hemispheres
  3. Constructional Apraxia
     • Lesion: Inferior parietal lobule (non-dominant hemisphere)
     • Feature: Inability to draw shapes or copy diagrams

Conclusion

• Summary of key points on aphasia, agnosia, and apraxia.
• Emphasized the neuroanatomical basis of various higher brain function disorders.
• Best wishes and good luck.