Agnosia Definition: Fundamentally defined as a disorder of recognition and the inability to recognize the meaning of information received via the sensory system, from the external environment to the brain. The inability to recognize sensory stimuli. Agnosia presents as a deficit of one particular sensory channel, such as visual, auditory, or tactile. A neurological disorder, Agnosia is the not having the ability to recognize common objects like an orange or a key, people, aromas, or sound though other senses function normally to visual or auditory stimuli. Agnosia is not an amnesia or memory loss, deficit. Often resulting from brain damage in areas involving spatial integration and processing of visual and motor stimuli, information, and attention. Posterior parietal cortex and occipito-temporal areas included. Can be of sudden onset 1 after a stroke or head injury, may be brought about by gradual degeneration of brain tissue in certain areas of the brain or even due to tumors. Not a speech or language disorder, Agnosia affects a person’s ability to identify objects or phonemes in speech, often present(s) similarly to Anomia or Wernicke’s aphasia. Agnosia auditory deficit, is characterized with difficulty to distinguish phonemes in speech from non-speech sounds though hearing processes are normal. Subject(s) with Wernicke’s aphasia similarly have difficulty understanding phonemes in speech though the catalyst(s) are different from those in agnosia, recognizing the speech sounds. Visual agnosia, subject(s) are impared at identifying common objects. Anomia patients recognize the object, yet find difficulties in naming it. Anomia and Agnosia are not deficits associated with problem(s) of memory. Some types of Agnosia: VISUAL AGNOSIAS Apperceptive Visual Agnosia Associative Visual Agnosia Visual Object Agnosia ventral association processing disruption Prosopagnosia (ventral association processing disruption) Color Agnosia – 3 classes ● Central Achromatopsia loss of color vision due to CNS disease ● Color Anomia success on visual-visual tasks and on verbal-verbal tasks, but cannot name colors ● Specific Color Aphasia Simultanagnosia Balint’s syndrome ● Simultanagnosia Cortical Blindness and Anton’s Syndrome Metamorphopsia AUDITORY AGNOSIAS related disorders Pure word deafness auditory word agnosia Auditory Sound Agnosia Phonagnosia Cortical Deafness Receptive Amusia sensory amusia Auditory affective agnosia TACTILE AGNOSIAS related disorders Apperceptive Variety Associative Variety Tactile Agnosias ● Amorphognosia ● Ahylognosia ● Tactile THEORETICAL PERSPECTIVES Stage Models Lissauer’s two-stage model of perception/recognition Disconnection Models Computational Models Cognitive Neuropsychological Models OTHER AGNOSIA TERMS Autotopagnosia Finger agnosia 2 Static Object Agnosia References Burns M. Clinical management of agnosia. Top Stroke Rehabil. 2004:11(1):1-9. https://www.ncbi.nlm.nih.gov/pubmed/14872395 Kumar & Wroten. Agnosia. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Bookshelf ID: 2019:NBK493156. Osman, S. What is Agnosia. NAA 2020. Agnosia Neuroanatomy: Damage to the parietal, temporal, or occipital lobe of the brain. The areas that store memories of the useful practical manner of importance, familiar objects, sights, and sounds associated with integrated memory, perception, and identification. Agnosia often occurs suddenly after a head injury or stroke. Apperceptive: damage Early in the recognition platform of internal identification, before perception is properly constructed. Subjects do not perceive objects in the normative manner and are unable to recognize them. Associative: 3 fault in later stages of recognition; perception may be intact, but access to memory information is not, a normal percept stripped of its meaning. Agnosia, the rare disorder whereby a person is unable to recognize and identify objects, people, or sounds using one or more of their senses with no direct deficit of normally functioning senses. Unexplainable by memory, attention, language, or stimuli. Sensory modalities are affected. Unable to identify a cup for instance by sight, though color may be identified. Different from Anomia the a naming disorder where a person cannot name an object despite using sensory modalities such as touch and smell. Distinction being subjects who can successfully copy but not identify are associative agnosia. Often those with severe deficits in the visual perception platform can accurately copy things thru crude, line drawing approach. Object agnosia is defined as an object recognition deficit and typically results from lesions of occipito-temporal cortex. Presently, research continues, with much remaining unknown about the cortical re organization of visual representations, information, and specifics. Object representation assessments (s) of agnosia often utilizes fMRI to examine the cortical organization including retinotopy and object-related activations in an agnostic subject(s). Severe deficit(s) in object and face recognition often follows damage of the right hemisphere, standard retinotopic mapping can uncover the organization of visual cortex, helping determine the presence of lesion(s) within this locale of the Retinotopic cortex. Object-selectivity is attributed to the ventral visual cortex using fMRI paradigms. Retinotopic mapping can uncover regular patterns of phase reversal(s) in both hemispheres. 4 Surface analysis can also reveal if a lesion is responsible and identify its vicinity. The posterior part of the medial fusiform gyrus anterior and dorsolateral contrast comparisons between object and blank presentation or difference in activated volume. FMRI-adaptation often reveals differences in activation patterns. Object selective response both laterally and bilaterally in the anatomical location posterior, dorsal, and ventral. Object-selective voxel in the location of a lesion or otherwise damaged vicinity. The left hemisphere is attributed to object selectivity. Right medial fusiform gyrus is involved in object processing, with object processing continuing in the dorsal pathway. References De Renzi E. Agnosia. Recenti Prog Med. 1989 Dec;80(12):633-7. Coslett HB. Sensory Agnosias. In: Gottfried JA, editor. Neurobiology of Sensation and Reward. CRC Press/Taylor & Francis; Boca Raton (FL): 2011. Álvarez R, Masjuan J. Visual agnosia. Rev Clin Esp (Barc). 2016 Mar;216(2):85-91. Martinaud O. Visual agnosia and focal brain injury. Rev Neurol (Paris). 2017 Jul - Aug;173(7-8):451-460. Slevc LR, Shell AR. Auditory agnosia. Handb Clin Neurol. 2015;129:573-87. Pratesi M, Santini S, Lombardo G, Corsi P, Salvadori G, Cocco F. [Prosopagnosia. Description and discussion of a clinical case]. Recenti Prog Med. 1992 May;83(5):282-5. Cicmil N, Meyer AP, Stein JF. Tactile Toe Agnosia and Percept of a "Missing Toe" in Healthy Humans. Perception. 2016 Mar;45(3):265-80. Burns MS. Clinical management of agnosia. Top Stroke Rehabil. 2004 Winter;11(1):1-9.] Heutink J, Indorf DL, Cordes C. The neuropsychological rehabilitation of visual agnosia and Balint's syndrome. Neuropsychol Rehabil. 2019 Dec;29(10):1489-1508. Trivelli C, Turnbull OH, Sala SD. Recovery of object recognition in a case of simultanagnosia. Appl Neuropsychol. 1996 Aug-Nov;3(3-4):166-73. 5