Excellent Network Courses Department of Neurology Affiliated hospital of Jiangsu University
Agnosia
Visual Agnosia Lissauer (1890) described 2 types: a) Apperceptive Cannot see objects b) Associative Does not know what the object is
1. Apperceptive Agnosia classic form ; most severe Visual processing intact; but no ability to distinguish between shapes, cannot copy, cannot match shapes May be due to extensive damage to the occipital lobe as a result of carbon monoxide poisoning, mercury intoxication, cardiac arrest, bilateral strokes, bilateral posterior cortical atrophy
1. Apperceptive Agnosia Case Study Mr. X, 25 years old man with carbon monoxide poisoning blind until he was found navigating the hall with his wheelchair Name colors, follow visual stimuli with his eyes Able to determine relative size, some movement Able to identify objects tactically Memory, speech comprehension, repetition were intact
1. Apperceptive Agnosia Case Study He could not match, copy, recognize objects, photos, body parts, letters, numbers. Apperceptive Agnosia
Types of apperceptive agnosia a) Dorsal simultanagnosia b) Ventral simultanagnosia
Types of apperceptive agnosia a) Dorsal simultanagnosia Wolpert (1924): unable to appreciate the meaning of a whole picture but able to recognize individual parts. Luria: complex, perceptuomotor breakdown of the active feature-by-feature analysis necessary for processing elements of a visual scene. Cannot count objects presented together. Due to bilateral parietooccipital damage.
Types of apperceptive agnosia a) Dorsal simultanagnosia Case Study Ms. S, who was developed visual problems after basal artery occlusion. She could see only one object at a time. She said she could only see bits and fragments. Lost her place easily. Made very few long saccades that relate one part of the picture to another.
Types of apperceptive agnosia a) Dorsal simultanagnosia Case Study
Types of apperceptive agnosia b) Ventral simultanagnosia Due to lesions in the left occipitotemporal junction. Unable to relate small portions of what they see to the remainder of the object. Cannot perceive more than one object at a time. Milder form than dorsal simultanagosia.
Types of apperceptive agnosia b) Ventral simultanagnosia
2. Associative Agnosia Able to group objects and copy drawings. Unable to draw from memory. Cannot appreciate the entire form of a picture or object. Deficits more pronounced if the object becomes degraded. Makes visual similarity errors. Poor at matching novel or complex objects.
2. Associative Agnosia
3. Special Types of Agnosia 1 Prosopagnosia: visual agnosia for faces only ---- Bilateral or right hemispheric damage to fusiform gyrus or occipitotemporal area.
3. Special Types of Agnosia Prosopagnosia informs us of the following for facial processing: Posterior right hemisphere is important Anterior fusiform gyrus and parahippocampal gyrus important for facial identification and retrieval of biographical information Superior temporal sulcus is sensitive to facial gestures and facial orientation Fusiform gyrus can be modified by experience
3. Special Types of Agnosia
3. Special Types of Agnosia 2 Auditory Agnosia: Impaired capacity to recognize sound but adequate hearing. 3 types: a) Verbal auditory agnosia or pure word deafness cannot understand speech sounds b) Nonverbal auditory agnosia cannot understand non-speech sounds c) Mixed auditory agnosia cannot attach meaning to speech and non-speech sounds
Case Study Mr. M, 65 year old seen for nerves and headaches 3 years after stroke. No aphasia but unable to recognize common sounds.
Case Study Somatosensory or Tactile Agnosia Also called astereognosis. Unable to identify objects by touch in the absence of sensory deficits, naming problems, or intellectual deterioration. 2 types proposed: Unable to use tactile information to form a percept. Tactile asymbolia: unable to link percept to symbolic meaning. May be due to damage to left inferior parietal area.