Neurosurgery notes/Anatomy/Higher function/Reading

Reading

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Higher function

Alexia

  • Defects in ability to read
  • With regard to perception, language may be accessed through
    • Visual modality: reading
    • Auditory modality: speech
  • Can be due to
    • Peripheral: Difficulty in transmitting the visual percept to the intact language centres
      • Impaired visual acuity as a result of ocular problems,
      • Visual field defect, even if this does not involve central fixation.
      • Impaired ability to coordinate eye movements such as
        • Ocular motor apraxia
        • Saccadic intrusions
      • Alexia without agraphia
        • Disconnection syndrome
        • Pathology
          • Left medial occipital lobe
      • Neglect dyslexia
        • Difficulty with left side of words or page
        • Unable to read the left hand side of words—for example, for SISTER, the patient will only perceive -TER.
        • Pathology
          • Right hemisphere
    • Central: due to an impaired language system
      • Surface dyslexia:
        • Loss of semantic knowledge
        • Difficulty with irregular words
        • Pathology
          • Left temporal lobe
      • Deep dyslexia
        • Only able to read via meaning, not be letter by letter
        • Unable to read non-words (eg: Chog, Lave)
        • Pathology
          • Left hemisphere

Alexia without agraphia

  • This syndrome is rare and more often overlooked
  • A high level visual deficit resulting in inability to read
  • Characteristics
    • Inability to comprehend written material.
    • Can write what he has seen
      • Pathways from primary visual cortex to pre-motor and motor cortex involved in control of writing movements are preserved.
    • But is then unable to read back what he has written.
    • The patient can recognise words spelled aloud, showing that this is an access problem rather than a primary language deficit.
  • It is a sort of category-specific form of visual agnosia for words, in some ways similar to prosopagnosia.
  • Due to
    • Disconnection between visual (Occipital lobe) and language areas (left angular gyrus)
      • Lesions affecting the left occipital lobe and the posterior fibres of the corpus callosum.
        • Lt PCA stroke
            • notion image
      • White matter tracts damaged
          • Left occipital temporal pathway-ILF
          • Ventral indirect subpathway-ILF/UF
          Proposal of a dual-stream model of the ventral amodal semantic route, with incorporation of anatomic constraints, elaborated on the basis of structural-functional correlations provided by intraoperative DES.
          Proposal of a dual-stream model of the ventral amodal semantic route, with incorporation of anatomic constraints, elaborated on the basis of structural-functional correlations provided by intraoperative DES.
  • Often associated with
    • Right homonymous hemianopia
    • Colour anomia
    • Achromatopsia