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Agnosia

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For the Spanish film, see Agnosía.
Agnosia
SpecialtyNeurology, neuropsychology, psychiatry, neuropsychiatry Edit this on Wikidata

Agnosia (a-gnosis, or loss of knowledge) is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective nor is there any significant memory loss.[1] It is usually associated with brain injury or neurological illness, particularly after damage to the occipitotemporal border, which is part of the ventral stream.[2]. Agnosia usually affects a single modality [3] for example vision or hearing may be affected [4].


Visual Agnosia

Visual agnosia is a broad category that refers to a deficiency in the ability to recognize visual objects. Visual agnosia can be further subdivided into two different subtypes: appreceptive agnosia and associative agnosia.[5] Individuals with appreceptive agnosia display the ability to see contours and outlines when shown an object, but they experience difficulty if asked to categorize objects. Appreceptive agnosia is associated with damage to one hemisphere, specifically damage to the posterior sections of the right hemisphere. [5] In contrast, individuals with associative agnosia experience difficulty when asked to name objects. Associative agnosia is associated with damage to both the right and left hemispheres at the occipitotemporal border. [5]. A specific form of associative agnosia is known as prosopagnosia. Prosopagnosia is the inability to recognize faces. For example, these individuals have difficulty recognizing friends, family and coworkers [5]. However, individuals with prosopagnosia can recognize all other types of visual stimuli[6].

Early Ideas about Agnosia

The first ideas about agnosia came from Wernicke who theorized about sensory aphasia in 1874. He believed that sensory aphasia was due to lesions of the posterior third of the left superior temporal gyrus. He noted that individuals with sensory aphasia did not possess the ability to understand speech or repeat words. Wernicke's explanation for sensory aphasia was that individuals with sensory aphasia had a limited deafness for certain sounds and frequencies in speech [7].

After Wernicke, came Kussmaul in 1877 who attempted to explain word deafness. Contrary to Wernicke's explanations, Kussmaul explained word deafness as the result of major destruction of the first left temporal gyrus. Kussmaul also attempted to explain word blindness as the result of lesions of the left angular and supramarginal gyri [8].

Heinrich Lissauer was one of the first theorists of agnosia, after Wernicke and Kussmaul [9] . In 1890, he theorized that there were two ways in which an object recognition impairment could occur. One way in which impairment could occur was if there was damage to early perceptual processing or if there was damage to the actual object representation. If the actual object representation was damaged, this would not allow the object to be stored in visual memory, and therefore the individual would not be able to recognize the object [10]. Originally when Lissauer first theorized about agnosia, there was little known about the cerebral cortex. Today with new neuroimaging techniques we have been able to expand our knowledge of agnosias greatly [11].

Cases of Famous Patients

Patient DF

Patient DF suffered from bilateral damage to the ventral stream [12]. However DF's dorsal stream was intact. This damage to the ventral stream caused Patient DF to develop visual form agnosia. DF struggled with visual recognition and was unable to recognize simple shapes, or distinguish between them. Additionally, DF could not tell the orientation of an object, or the width of an object. However, DF was able to make copies of the orientation of a line when given an unlimited amount of time. In another task DF was presented with a square and an oblong object. DF was then asked to indicate which of the objects was a square and which of the objects was oblong. When DF was able to pick up the objects she was able to determine which of the objects was a square and which was oblong, but when she was required to answer only verbally she could not correctly determine the shape [13].

Dr. P

Oliver Sacks, a neurologist tells the story of his fascinating patient Dr. P. Dr. P was an average man who taught music at the university level and is commonly known as the man who mistook his wife for a hat. He had issues recognizing students as they approached him, but once they spoke who could identify who the student was. Dr. P was unable to see whole pictures and could only focus on the features of the picture or small pieces of it. For example in a picture depicting a lake, mountains and forests, he would only be able to focus on the mountains. After one appointment with Dr. Sacks, Dr. P got up and tried to lift his wife's head because he thought that her head was his hat. Dr. P suffered from a form of visual agnosia, specifically prosopagnosia. He also suffered from a form of neglect syndrome. When asked to visualize himself walking down a hallway, he would only describe the right side of the hallway and neglect the left side [14].

Types

Name Description
Alexia Inability to recognize text.[15] Patients with alexia often have damage to their corpus collosum, as well as damage to the left visual association areas [16]. Pure alexia involves not being able to read printed material, but these individuals still have the ability to write. Individuals with pure alexia usually read words letter by letter. However, individuals with pure alexia show a frequency effect. They are able read high frequency words better and faster than they can read low frequency words [17].
Alexithymia While not strictly a form of agnosia, Alexithymia may be difficult to distinguish from or co-occur with social-emotional agnosia. Alexithymia is deficiency in understanding, processing, or describing emotions. It is common to around 85% of people on the autism spectrum. Alexithymia is believed to be due to an information processing delay in the combined processing of information in the left and right hemispheres, resulting in poor differentiation between body messages and emotions.[18] An individual suffering from alexithymia experiences difficulty in emotional self regulation and alexithymia is a possible risk factor for certain psychiatric disorders. There are five major defining factors of alexithymia: a reduced ability or incapability to experience emotions, verbalize emotions or fantasize. Additional characteristics of alexithymia involve an absence in reflection and thought about one's emotions and difficulty in identifying emotions. Alexithymia can be divided into two different types: axis I alexithymia and axis II alexithymia. Axis I alexithymia involves the inability to experience emotion, as well as the absence of the cognitive aspects that accompany emotions. Axis II alexithymia is a selective deficit. Only the cognitive aspects associated with emotions are affected, while the ability to have emotional experiences remains intact [19].
Akinetopsia The loss of motion perception.[20]
Amusia or Receptive amusia Is agnosia for music. It involves loss of the ability to recognize musical notes, rhythms, and intervals and the inability to experience music as musical.
Anosognosia This is the inability to gain feedback about one's own condition and can be confused with lack of insight but is caused by problems in the feedback mechanisms in the brain. It is caused by neurological damage and can occur in connection with a range of neurological impairments but is most commonly referred to in cases of paralysis following stroke. Those with Anosognosia with multiple impairments may even be aware of some of their impairments but completely unable to perceive others.
Apperceptive agnosia Patients are unable to distinguish visual shapes and so have trouble recognizing, copying, or discriminating between different visual stimuli. Unlike patients suffering from associative agnosia, those with apperceptive agnosia are unable to copy images.[21]
Apraxia Is a form of motor (body) agnosia involving the neurological loss of ability to map out physical actions in order to repeat them in functional activities. It is a form of body-disconnectedness and takes several different forms; Speech-Apraxia in which ability to speak is impaired, Limb-Kinetic Apraxia in which there is a loss of hand or finger dexterity and can extend to the voluntary use of limbs, Ideomotor Apraxia in which the gestures of others can't be easily replicated and can't execute goal-directed movements, Ideational Apraxia in which one can't work out which actions to initiate and struggles to plan and discriminate between potential gestures, Apraxia of Gait in which co-ordination of leg actions is problematic such as kicking a ball, Constructional Apraxia in which a person can't co-ordinate the construction of objects or draw pictures or follow a design, Oculomotor Apraxia in which the ability to control visual tracking is impaired and Buccofacial Apraxia in which skilled use of the lips, mouth and tongue is impaired.[citation needed]
Associative agnosia Patients can describe visual scenes and classes of objects but still fail to recognize them. They may, for example, know that a fork is something you eat with but may mistake it for a spoon. Patients suffering from associative agnosia are still able to reproduce an image through copying.
Astereognosis Or Somatosensory agnosia is connected to tactile sense - that is, touch. Patient finds it difficult to recognize objects by touch based on its texture, size and weight. However, they may be able to describe it verbally or recognize same kind of objects from pictures or draw pictures of them. Thought to be connected to lesions or damage in somatosensory cortex.[22]
Auditory agnosia Auditory agnosia has been recognized since 1877 [23]. With Auditory Agnosia there is difficulty distinguishing environmental and non-verbal auditory cues including difficulty distinguishing speech from non-speech sounds even though hearing is usually normal.[22] There are two types of auditory agnosia: semantic associative and discriminative agnosia. Semantic associative agnosia is associated with lesions to the left hemisphere, where as discriminative agnosia is associated with lesions to the right hemisphere [24].
Autotopagnosia Is associated with the inability to orient parts of the body, and is often caused by a lesion in the parietal part of the posterior thalmic radiations.[25]
Cerebral Akinetopsia Cerebral akinetopsia is associated with the inability to perceive visual motion. One cause of cerebral akinetopsia is lesions outside the striate cortex [26].
Color agnosia Color agnosia involves having difficulty categorizing colours, as well as recognizing colours. Colour agnosia is usually caused by neurological damage [27]. There are two regions of the brain which specialize for color recognition, areas V4 and V8. If there is a unilateral lesion to area V4, a loss of color perception will result known as hemiachromatopsia [28].
Congenital Amusia Congenital amusia refers to a deficit in musical processing. One of the deficits involved in congenital amusia is the inability to recognize familiar songs. Congenital amusia occurs without brain damage [29] and affects about 4% of the population [30].
Cortical deafness Refers to people who do not perceive any auditory information but whose hearing is intact.
Dorsal Simultanagnosia Simultanagnosia broadly refers to being unable to recognize more than one thing at once. For example a patient for dorsal simultanagnosia may report seeing only one of four objects that are lined up in front of them. Individuals with dorsal simultanagnosia often use parts of an object to make inferences about an object as a whole. These individuals also have difficulty with reading and counting because it involves more than one object at a time. Dorsal simultanagnosia is commonly caused by bilateral damage to the bilateral parieto-occipito region [31].
Environmental Agnosia It is the inability to locate a specific room or building that one is familiar with, as well as the inability to be able to provide a directions of how to arrive at a particular location. These individuals experience difficulty with learning routes. This form of agnosia is often associated with lesions to the bilateral or right hemisphere posterior regions. It is also associated with prosopagnosia and Parkinson's disease [32].
Finger agnosia Is the inability to distinguish the fingers on the hand. It is present in lesions of the dominant parietal lobe, and is a component of Gerstmann syndrome.[33]
Form agnosia Patients perceive only parts of details, not the whole object.
Integrative agnosia Usually a patient has a form of associative agnosia or appreceptive agnosia. However, in the case of integrative agnosia a patient falls in between a form of associative and appreceptive agnosia [34]. This is where one has the ability to recognize elements of something but yet be unable to integrate these elements together into comprehensible perceptual wholes[35]
Mirror agnosia One of the symptoms of Hemispatial neglect. Patients with Hemispatial neglect were placed so that an object was in their neglected visual field but a mirror reflecting that object was visible in their non-neglected field. Patients could not acknowledge the existence of objects in the neglected field and so attempted to reach into the mirror to grasp the object.[36] Commonly due to a right parietal lesion [37].
Motion agnosia where an individual loses the ability to perceive motion.
Pain agnosia Also referred to as Analgesia, this is the difficulty perceiving and processing pain; thought to underpin some forms of self injury.[38]
Phonagnosia Is the inability to recognize familiar voices, even though the hearer can understand the words used.[39]
Prosopagnosia Also known as faceblindness and facial agnosia: Patients cannot consciously recognize familiar faces, sometimes even including their own. This is often misperceived as an inability to remember names.
Semantic agnosia Those with this form of agnosia are effectively 'object blind' until they use non-visual sensory systems to recognise the object. For example, feeling, tapping, smelling, rocking or flicking the object, may trigger realisation of its semantics (meaning).[40]
Simultanagnosia Patients can recognize objects or details in their visual field, but only one at a time. They cannot make out the scene they belong to or make out a whole image out of the details. They literally "cannot see the forest for the trees." Simultanagnosia is a common symptom of Balint's syndrome.
Social-Emotional Agnosia Sometimes referred to as Expressive Agnosia, this is a form of agnosia in which the person is unable to perceive facial expression, body language and intonation, rendering them unable to non-verbally perceive people's emotions and limiting that aspect of social interaction.
Tactile agnosia Impaired ability to recognize or identify objects by touch alone.[41]
Time agnosia Is the loss of comprehension of the succession and duration of events.[42]
Topographical agnosia This is a form of visual agnosia in which a person cannot rely on visual cues to guide them directionally due to the inability to recognize objects. Nevertheless, they may still have an excellent capacity to describe the visual layout of the same place[43]Patients with topographical agnosia have the ability to read maps, but become lost in familiar environments [44].
Ventral Simultanagnosia Individuals with ventral simultanagnosia are unable to identify more than one object at a time. However, they can see more than one object at a time. These individuals also experience difficulty reading and describing pictures with multiple features. Ventral simultanagnosia is commonly caused by damage to the left inferior tempero-occipital regions of the brain [45].
Verbal auditory agnosia This presents as a form of meaning 'deafness' in which hearing is intact but there is significant difficulty recognising spoken words as semantically meaningful.[46]
Visual agnosia Is associated with lesions of the left occipital lobe and temporal lobes. Many types of visual agnosia involve the inability to recognize objects.
Visual verbal agnosia Difficulty comprehending the meaning of written words. The capacity to read is usually intact but comprehension is impaired.[47]

Assessing Agnosia

In order to assess an individual for agnosia, it must be verified that the individual is not suffering from a loss of sensation, and that both their language abilities and intelligence are intact. In order for an individual to be diagnosed with agnosia, they must only be experiencing a sensory deficit in a single modality. To make a diagnosis, the distinction between appreceptive and associative agnosia must be made. This distinction can be made by having the individual complete copying and matching tasks. If the individual is suffering from a form of appreceptive agnosia they will not be able to match two stimuli that are identical in appearance. In contrast, if an individual is suffering from a form of associative agnosia, they will not be able to match different examples of a stimulus. For example, an individual who has been diagnosed with associative agnosia in the visual modality would not be able to match pictures of a laptop that is open with a laptop that is closed [48].

Testing for Agnosia

Alexia: Individuals with alexia usually have difficulty reading words as well as difficulty with identifying letters. In order to assess whether an individual has alexia, tests of copying and recognition must be performed. An individual with alexia should be able to copy a set of words, and should be able to recognize letters [49].

Congenital Amusia: A test known as the Montreal Battery for the Evaluation of Amusia (MBEA) can be administered to an individual to test for congenital amusia. The MBEA consists of seven subtests that test for music perception and memory, time dimension and incidental memory [50].

Prosopagnosia: Individuals are usually shown pictures of human faces that may be familiar to them such as famous actors, singers, politicians or family members. The pictures shown to the patient are selected to be age and culture appropriate. The task involves the examiner asking the individual to name each face. If the individual cannot name whose face appears in the picture, the examiner may ask a question that would help to the face in the picture. An example of a possible question for a picture of Madonna would be "Who sang the song Borderline?" [51].

Causes

Agnosia can result from strokes, dementia, or other neurological disorders. It may also be trauma-induced by a head injury, brain infection, or hereditary. Some forms of agnosia have been found to be genetic.[52] A study in 2011 linked Phonagnosia to Dyslexia. [53] Additionally, some forms of agnosia may be the result of developmental disorders [54]. Damage causing agnosia usually occurs in either the occipital or parietal lobes of the brain. Although one modality may be affected, cognitive abilities in other areas are preserved [55].

Patients who experience dramatic recovery from blindness experience significant to total Agnosia.[56]

Treatment

For all practical purposes, there is no direct cure. Patients may improve if information is presented in other modalities than the damaged one. Different types of therapies can help to reverse the effects of Agnosia. In some cases, occupational therapy or speech therapy can improve agnosia, depending on its etiology.

Initially many individuals with a form of agnosia are unaware of the extent to which they have either a perceptual or recognition deficit. This may be caused by anosognosia which is the lack of awareness of a deficit. This lack of awareness usually leads to a form of denial and resistance to any form of help or treatment. There are various methods that can be used which can help the individual recognize the impairment in perception or recognition that they may have. A patient can be presented with a stimulus to the impaired modality only to help increase their awareness of their deficit. Alternatively, a task can be broken down into it's component parts so that the individual can see each part of the problem caused by the deficit. Once the individual acknowledges their perceptual or recognition deficit, a form of treatment may be recommended. There are various forms of treatment such as compensatory strategies with alternate modalities, verbal strategies, alternate cues and organizational strategies [57].

Compensatory strategies with alternate modalities: These strategies elicit the use of an unaffected modality. For example visual agnosics can use tactile information in replacement of visual information. Alternatively, an individual with prosopagnosia can use auditory information in order to replace visual information. They can wait for someone to speak, and will usually recognize the individual from their speech.

Verbal Strategies: Using verbal descriptions may be helpful for individuals with certain types of agnosia. Individuals such as prosopagnosics may find it useful to listen to a description of their friend or family member and recognize them based off of this description more easily than through visual cues.

Alternate cues: Alternate cues may be particularly useful to an individual with environmental agnosia or prosopagnosia. Alternate cues for an individual with environmental agnosia may include color cues or tactile markers to symbolize a new room or to remember an area by. Prosopagnosics may use alternate cues such as a scar on an individual's face or crooked teeth in order to recognize the individual.

Organizational strategies: Organizational strategies may be extremely helpful for an individual with visual agnosia. For example organizing clothes according to different hangers provides tactile cues for the individual, making it easier to identify certain forms of clothing as opposed to relying solely on visual cues.

See also

References

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  2. ^ Kolb & Whishaw: Fundamentals of Human Neuropsychology, 2003
  3. ^ Burns, M (2004). "Clinical Management of Agnosia". Top Stroke Rehabilitation. 11 (1): 1–9.
  4. ^ "NINDS Agnosia Information Page". National Institute of Neurological Disorders and Stroke. Retrieved 28 March 2012.
  5. ^ a b c d al.], Kathleen M. Galotti ... [et (2010). Cognitive psychology : in and out of the laboratory (1st Canadian ed. ed.). Canada: Nelson. ISBN 9780176440657. {{cite book}}: |edition= has extra text (help)
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  15. ^ Welcome to MedLink Neurology
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  20. ^ Christof Koch - The Quest for Consciousness: a Neurobiological Approach, Roberts and Co., 2004, p.218
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  29. ^ Tillmann, Barbara (NaN undefined NaN). "Congenital amusia: A short-term memory deficit for non-verbal, but not verbal sounds". Brain and Cognition. 71 (3): 259–264. doi:10.1016/j.bandc.2009.08.003. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  30. ^ Tillmann, Barbara (NaN undefined NaN). "Congenital amusia: A short-term memory deficit for non-verbal, but not verbal sounds". Brain and Cognition. 71 (3): 259–264. doi:10.1016/j.bandc.2009.08.003. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  31. ^ "Dorsal Simultanagnosia". University of Calgary. Retrieved 28 March 2012.
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  33. ^ Definition: finger agnosia from Online Medical Dictionary
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  35. ^ Integrative Agnosia
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  38. ^ analgesia - Britannica Online Encyclopedia
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  43. ^ Topographical Agnosia
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  50. ^ Tillmann, Barbara (NaN undefined NaN). "Congenital amusia: A short-term memory deficit for non-verbal, but not verbal sounds". Brain and Cognition. 71 (3): 259–264. doi:10.1016/j.bandc.2009.08.003. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  51. ^ Burns, M (2004). "Clinical Management of Agnosia". Top Stroke Rehabilitation. 11 (1): 1–9.
  52. ^ http://72.14.253.104/search? q=cache:8l6tU6ZOKuUJ:visionlab.harvard.edu/Members/Ken/Ken%2520papers%2520for%2520web%2520page/148CognitiveNDuchaine2007.pdf+genetic+agnosia&hl=en&ct=clnk&cd=7&gl=au
  53. ^ Dyslexia makes voices hard to discern, study finds, BBC, 2010-07-29
  54. ^ "NINDS Agnosia Information Page". National Institute of Neurological Disorders and Stroke. Retrieved 28 March 2012.
  55. ^ "NINDS Agnosia Information Page". National Institute of Neurological Disorders and Stroke. Retrieved 28 March 2012.
  56. ^ "The New Yorker: From the Archives: Content". Archived from the original on 2006-08-31. Retrieved 2010-05-05. mentally blind, or agnosic—able to see but not to decipher what he was seeing.
  57. ^ Burns, M (2004). "Clinical Management of Agnosia". Top Stroke Rehabilitation. 11 (1): 1–9.

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