Neurology · MU Sofia

18. Gnosis and agnosia

Explains gnosis as the recognition of previously learned sensory information with intact sensation, consciousness, memory and language, and the cortical areas it depends on. Describes visual, auditory and tactile gnosis, then goes through the main agnosias such as visual agnosia, prosopagnosia, colour agnosia, auditory agnosia, astereognosis and autotopagnosia, with their causes and clinical features. Closes with bedside examination methods and a table linking each agnosia to its typical lesion site.

Inside: 1 section · 1 table · 15 flashcards · 2 min

Topic 18 of 88 in the MU Sofia syllabus for Neurology (Medicine, Year 4). The free AceMed note covers it in 1 section, about 314 words (2 min of reading), with 15 flashcards.

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  1. Gnosis and agnosia

Gnosis and agnosia

Gnosis

Gnosis is the ability to recognize, identify, and interpret previously learned sensory information despite intact sensation, consciousness, memory, and language.

It requires:

  • Intact sensory pathways
  • Intact primary sensory cortex
  • Intact association cortical areas (mainly parietal, temporal, and occipital lobes)

Types of Gnosis

1.Visual Gnosis: Recognition of objects, faces, colors, and symbols through vision.

2.Auditory Gnosis: Recognition of sounds, words, and melodies.

3.Tactile Gnosis: Recognition of objects by touch (stereognosis).

Agnosia. "Can Sense but Can't Recognize"

Agnosia is the inability to recognize or identify familiar objects, persons, sounds, or stimuli despite normal sensory function and preserved consciousness.

  • It is usually caused by lesions of the association cortex.

Types of Agnosia

1. Visual Agnosia: Inability to recognize objects by sight despite normal vision.

  • Causes: Occipital lobe lesions. Occipitotemporal lesions
  • Clinical Features: Patient sees the object but cannot identify it. Recognition is possible through touch or sound

2. Prosopagnosia: Inability to recognize familiar faces.

  • Lesion: Occipitotemporal region (usually right hemisphere)
  • Clinical Features: Cannot recognize family members or familiar people by face. May identify them by voice

3. Color Agnosia: Inability to recognize or identify colors despite normal color perception.

4. Auditory Agnosia: Inability to recognize sounds despite normal hearing.

  • Types
  • Inability to recognize environmental sounds
  • Pure word deafness (cannot understand spoken words)

5. Astereognosis (Tactile Agnosia): Inability to identify an object by touch while sensory function is intact.

  • Examination: Place a familiar object in the patient's hand with eyes closed.
  • Causes: Contralateral parietal lobe lesion. Posterior column lesions

6. Autotopagnosia: Inability to identify or localize parts of one's own body.

  • Usually associated with dominant parietal lobe lesions.

Examination of Gnosis

1.Visual Gnosis: Show familiar objects and ask the patient to identify them.

2.Auditory Gnosis: Ask the patient to identify familiar sounds.

3.Stereognosis: Patient identifies a key, coin, pen, etc., by touch with eyes closed.

4.Body Recognition: Ask the patient to point to body parts.

Cortical Localization

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