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PubMed1990

Associative agnosias and the functions of the left hemisphere.

Associative agnosias are traditionally regarded as perceptual, and ideational apraxia as motor, deficits, but they can be understood as amnesias for generic knowledge, caused by bilateral or unilateral left-hemispheric cortical lesions. Current theories of hemispheric specialization explain these syndromes' mandatory link with left-hemispheric damage, and are validated by this link. This link reflects the multiple nature of generic, categorical representational systems, not all reducible to natural language, and the left hemisphere's principal role as their substrate, regardless of their dependence on language. The distinction between processing novel information, and processing based on well-established, routinized representations, captures a fundamental difference between the functions of the right and left hemispheres. The complementary link of apperceptive agnosias with right-and associative agnosias with left-hemisphere lesions is an expression of this general principle in the posterior cortex. Future studies of the neuroanatomy of agnosias in animals may offer insights into the evolutionary continuities of hemispheric specialization.

Agnosia↗
PubMed1996

Tactile agnosia. Casuistic evidence and theoretical remarks on modality-specific meaning representations and sensorimotor integration.

Somaesthetic, motor and cognitive functions were studied in a man with impaired tactile object-recognition (TOR) in his left hand due to a right parietal convexity meningeoma which had been surgically removed. Primary motor and somatosensory functions were not impaired, and discriminative abilities for various tactile aspects and cognitive skills were preserved. Nevertheless, the patient could often not appreciate the object's nature or significance when it was placed in his left hand and was unable to name or to describe or demonstrate the use of these objects. Therefore, he can be regarded as an example of associative tactile agnosia. The view is taken and elaborated that defective modality-specific meaning representations account for associative tactile agnosia. These meaning representations are conceptualized as learned unimodal feature-entity relationships which are thought to be defective in tactile agnosia. In line with this hypothesis, tactile feature analysis and cross-modal matching of features were largely preserved in the investigated patient, while combining features to form entities was defective in the tactile domain. The alternative hypothesis of agnosia as deficit of cross-modal association of features was not supported. The presumed distributed functional network responsible for TOR is thought to involve perception of features, object recognition and related tactile motor behaviour interactively. A deficit leading primarily to impaired combining features to form entities can therefore be expected to result in additional minor impairment of related perceptual-motor processes. Unilaterality of the gnostic deficit can be explained by a lateralized organization of the functional network responsible for tactile recognition of objects.

Agnosia↗
PubMed2002

Hierarchical versus parallel processing in tactile object recognition: a behavioural-neuroanatomical study of aperceptive tactile agnosia.

The organization of the normal perceptual processing subserving tactile object recognition is poorly understood. While perceptual deficits associated with cases of tactile agnosia may pinpoint sites of critical interference with normal tactile information processing, the precise character of such deficits remains unclear. The aim of the present study was to explore the behavioural and neuroanatomical correlates of perceptual disturbances in two cases of unilateral aperceptive tactile agnosia. Perception of microgeometrical and macrogeometrical features was tested using an alternative forced choice paradigm. While both patients were impaired in the assessment of microgeometrical properties of objects (i.e. detecting subtle differences in grating profiles), one patient showed an additional deficit in the perception of macrogeometrical properties of objects (i.e. detecting differences in length of cuboids). The pattern of perceptual deficits for both patients suggested a severely compromised (if not totally lost) ability to recognize everyday objects. Perceptual performance improved when the patients had complementary tactile information (i.e. for intramodal comparison), despite a persistent inability to explicitly name the objects. That is, the patients were able to recognize objects, but only implicitly. Improved perceptual performance was also observed when complementary visual information was available (i.e. transmodal information transfer). In this case, the perceptual improvement was accompanied by a corresponding improvement in explicit object recognition. High resolution MRIs identified lesions in the postcentral gyrus in both patients, and additionally in the secondary somatosensory area (SII) and the posterior parietal cortex in the more severely affected patient. The results demonstrate that the underlying failure in tactile agnosia is mainly impaired perception of microgeometrical properties of objects due to a lesion of primary sensory cortex. The related neuroanatomical findings suggest a degradation of serial information processing within postcentral gyrus. In one case tactile agnosia was almost complete due to additionally impaired perception of macrogeometrical properties of objects, which correlated with the extension of lesion to the posterior parietal cortex. Importantly, the findings indicate traces of two distributed networks for tactile information processing and the associated parallel processing of complementary micro- and macrogeometrical information within postcentral gyrus and posterior parietal lobe.

Adult↗
PubMedDate not supplied

Aphasia, apraxia, and agnosia in the diagnosis of dementia.

The association of aphasia, apraxia and agnosia with cortical but not subcortical dementias, is a widely held belief. The purpose of the present study was to determine the frequency of aphasia, apraxia, and agnosia in groups of cortical and subcortical dementia patients, and to assess the diagnostic utility of these symptoms. Subjects were 64 patients with subcortical dementias (Parkinson's disease and normal pressure hydrocephalus) and 192 patients with cortical dementia (probable Alzheimer's disease) matched for sex, age, and Mini-Mental State Examination score. Each patient was evaluated for the presence of aphasia, apraxia, and agnosia. Results indicated that only aphasia was reported significantly more often in cortical dementia patients than in subcortical dementia patients. The presence of either of these three symptoms has very low diagnostic sensitivity, specificity, and total predictive value. The severity of the patient's dementia was predicted whether the patient had aphasia or apraxia; type of dementia had no predictive value. These data led to the conclusion that cortical and subcortical dementias cannot be reliably dissociated on the basis of aphasia, apraxia, or agnosia.

Aged↗
PubMed2004

[Dysprosody associated with environmental auditory sound agnosia in right temporal lobe hypoperfusion--a case report].

A 60-year-old right-handed man showed dysprosody and agnosia for environmental sounds. His mother tongue was Japanese, and he could not speak foreign languages. He gradually developed difficulty in speaking from the age of 57 years, speaking non-native Japanese. In addition, he often complained of difficulty in hearing sounds, but audiometry showed no abnormalities. At the age of 60 years, the standard language test of aphasia showed no abnormalities in repetition, verbal comprehension, or reading, suggesting the absence of aphasia. However, in speaking, marked abnormality in rhythm, and occasional lack of postpositional particles and syllable-stumblings were observed. Writing was almost accurate, but a few grammatical errors were observed in speaking were observed. There were no cerebellar symptoms, pyramidal signs, pathologic reflexes, or abnormalities in phonation-related organs. Though the recognition of verbal sounds was maintained, impairment in the recognition of non-verbal sounds was observed. An environmental sound perception test showed correct answers only in 8 of 21 non-verbal sound sources (such as a car starting, glass breaking and so on), suggesting agnosia for environmental sounds. He insisted that the difficulty in perception was due to hearing impairment. However, re-examination with an increase in the sound volume showed similar results. He had no inconvenience in daily life and was not aware of agnosia for environmental sounds. He could recognize and differentiate sounds he heard once. His intelligence was normal, and neither apraxia nor frontal lobe symptoms were observed. MRI of the brain revealed slight atrophy of the right temporal lobe. Cerebral blood flow SPECT showed decreased blood flow from the superior temporal gyrus to the area around the arcuate fasciculi in the right temporal lobe. We considered that the lesion responsible for environmental auditory sound agnosia was present in the area around the secondary auditory area of the right temporal lobe and this patient differed from slowly progressive aphasia characterized by decreased blood flow in the left temporal lobe. Although the pathological process occurring in the area of hypoperfusion remained unclear, early stage of some degenerative disorders was more likely than cerebrovascular disease.

Agnosia↗
PubMed1984

[Visual and tactile agnosia].

A patient presented with visual and tactile agnosia due to a spontaneous left occipito-temporal hematoma. Major memory and spatial orientation disorders were also noted, but language, gestures, auditory and olfactory perception, and interior visual imagerie were unaffected. A review of the literature since 1970 found 6 cases of an association of this type among 17 patients with visual agnosia. There appears to be no relationship between the presence of tactile agnosia and the global or partial character of the visual agnosia, the severity of memory disturbances, the presence of visuoverbal disconnection or visual imagery disorders. In contrast, these cases differed in that the lesions were more extensive and extended beyond the internal occipital regions: they were widespread in 3 cases and in the left internal occipital and parietal region in 1 case. In the patient reported in this paper there was a wide lesion of the posterior white matter of the left hemisphere.

Agnosia↗
PubMed1997

The removal of binocular cues disrupts the calibration of grasping in patients with visual form agnosia.

The present study tested the idea that the visuomotor systems mediating prehension do not have independent access to pictorial cues processed by perceptual mechanisms. Individuals with visual form agnosia, whose perceptual systems are compromised but who have intact visuomotor control, were examined to determine whether they could use pictorial scene cues to calibrate manual prehension when binocular information was removed. The removal of binocular cues produced considerable disruptions in size-constancy of grip aperture, which, combined with earlier observations in normal subjects, suggests that binocular cues are of primary importance in calibration of grasping. In the absence of binocular vision, normal subjects can use pictorial information, information that is severely compromised in individuals with visual form agnosia, to compute the distance (and thus the size) of the goal object. Thus, individuals with visual form agnosia must rely on a retinal image that remains uncalibrated, leading to inaccurate calibrations of grip aperture. The fact that these individuals scaled their grasp much less accurately under the monocular viewing condition, despite showing normal binocular grasping, suggests that pictorial cues to depth, which are presumably processed by mechanisms mediating our perception of objects and events in the world, can be accessed by visuomotor mechanisms only indirectly. These results, together with others, suggest that the visuomotor system 'prefers' to use binocular information and uses pictorial cues only as a last resort.

Adult↗
PubMed1985

Visual agnosia contrasted with visual-verbal disconnection.

Serial neuropsychological findings are contrasted in two cases: one with a syndrome of visual agnosia, the other with a disorder resulting from visual-verbal disconnection. Both patients were impaired in confrontation naming of objects and pictures, but the patient with visual-verbal disconnection was able to perform tasks of color-object matching and pantomime recognition, whereas the patient with visual agnosia could not do so, demonstrating a failure to establish meaningful nonverbal visual-visual association. Additionally, the performance of the patient with visual agnosia reflected an evolution from the apperceptive to associative forms of the disorder, suggesting that the various impairments of visual identification form a continuum of related disorders.

Agnosia↗
PubMed2004

"I could see, and yet, mon, I could na' see": William Macewen, the agnosias, and brain surgery.

Two little noticed cases in which William Macewen used symptoms of visual agnosia to plan brain surgery on the angular gyrus are reviewed and evaluated. Following a head injury, Macewen's first patient had an immediate and severe visual object agnosia that lasted for about 2 weeks. After that he gradually became homicidal and depressed and it was for those symptoms that Macewen first saw him, some 11 months after the accident. From his examination, Macewen concluded that the agnosia clearly indicated a lesion in "the posterior portion of the operculum or in the angular gyrus." When he removed parts of the internal table that had penetrated those structures the homicidal impulses disappeared. Macewen's second patient was seen for a chronic middle ear infection and, although neither aphasic nor deaf, was 'word deaf.' Slightly later he became 'psychically blind' as well. Macewen suspected a cerebral abscess pressing on both the angular gyrus and the first temporal convolution. A large subdural abscess was found there and the symptoms disappeared after it was treated. The patients are discussed and Macewen's positive results analysed in the historical context of the dispute over the proposed role of the angular gyrus as the visual centre.

Agnosia↗
PubMed2005

Characteristics of auditory agnosia in a child with severe traumatic brain injury: a case report.

We present a case that is unusual in many respects from other documented incidences of auditory agnosia, including the mechanism of injury, age of the individual, and location of neurological insult. The clinical presentation is one of disturbance in the perception of spoken language, music, pitch, emotional prosody, and temporal auditory processing in the absence of significant deficits in the comprehension of written language, expressive language production, or peripheral auditory function. Furthermore, the patient demonstrates relatively preserved function in other aspects of audition such as sound localization, voice recognition, and perception of animal noises and environmental sounds. This case study demonstrates that auditory agnosia is possible following traumatic brain injury in a child, and illustrates the necessity of assessment with a wide variety of auditory stimuli to fully characterize auditory agnosia in a single individual.

Agnosia↗
PubMed2004

Electrophysiological correlates of associative visual agnosia lesioned in the ventral pathway.

Visual agnosia has been well studied by anatomical, neuropsychological and neuroimaging studies. However, functional changes in the brain have been rarely assessed by electrophysiological methods. We carried out electrophysiological examinations on a 23-year-old man with associative visual agnosia, prosopagnosia and cerebral achromatopsia to evaluate the higher brain dysfunctions of visual recognition. Electrophysiological methods consisted of achromatic, chromatic and category-specific visual evoked potentials (CS-VEPs), and event-related potentials (ERPs) with color and motion discrimination tasks. Brain magnetic resonance imaging revealed large white matter lesions in the bilateral temporo-occipital lobes involving the lingual and fusiform gyri (V4) and inferior longitudinal fasciculi due to multiple sclerosis. Examinations including CS-VEPs demonstrated dysfunctions of face and object perception while sparing semantic word perception after primary visual cortex (V1) in the ventral pathway. ERPs showed abnormal color perception in the ventral pathway with normal motion perception in the dorsal pathway. These electrophysiological findings were consistent with lesions in the ventral pathway that were detected by clinical and neuroimaging findings. Therefore, CS-VEPs and ERPs with color and motion discrimination tasks are useful methods for assessing the functional changes of visual recognition such as visual agnosia.

Adult↗
PubMed2006

Covert colour processing in colour agnosia.

Patients with colour agnosia can perceive colours and are able to match coloured patches on hue, but are unable to identify or categorise colours. It is a rare condition and there is as yet no agreement on the clinical definition or a generally accepted explanation. In line with observations from object agnosia and prosopagnosia, we hypothesised that (some of) these patients might still be able to process colour information at an implicit level. In this study, we investigated this possibility of implicit access to colour semantics and colour names in a man (MAH) who suffers from developmental colour agnosia. We designed two experimental computer tasks: an associative colour priming task with a lexical decision response and a reversed Stroop task. The results of these experiments suggest that there is indeed automatic processing of colour, although MAH was unable to explicitly use colour information.

Adult↗
PubMed2002

Pure topographical disorientation--the anatomical basis of landmark agnosia.

We used MRI studies of four patients to investigate the lesions responsible for landmark agnosia. A detailed investigation of the relationship between the symptoms and the lesions suggests that the right posterior part of the parahippocampal gyrus is critical for the acquisition of novel information about buildings and landscapes, and that the same region plus the anterior half of the lingual gyrus and the adjacent fusiform gyrus play an important role in the identification of familiar buildings and landscapes. Furthermore, the lesion responsible for prosopagnosia, which frequently occurs with landmark agnosia, seems to involve the posterior half of the lingual and fusiform gyri. This suggests that the lesions responsible for landmark agnosia and prosopagnosia are close to each other, but distinct.

Aged↗
PubMed1992

Tactile agnosia and tactile aphasia: symptomatological and anatomical differences.

Two patients with tactile naming disorders are reported. Case 1 (right hand tactile agnosia due to bilateral cerebral infarction) differentiated tactile qualities of objects normally, but could neither name nor categorize the objects. Case 2 (bilateral tactile aphasia after operation of an epidural left parietal haematoma) had as severe a tactile naming disturbance as Case 1, but could categorize objects normally, demonstrating that tactile recognition was preserved. Case 1 may be the first case of tactile agnosia clearly differentiated from tactile aphasia. CT scans of Case 1 revealed lesions in the left angular gyrus, and in the right parietal, temporal, and occipital lobes. Case 2 had lesions in the left angular gyrus and of posterior callosal radiations. Our findings suggest that tactile agnosia appears when the somatosensory association cortex is disconnected by a subcortical lesion of the angular gyrus from the semantic memory store located in the inferior temporal lobe, while tactile aphasia represents a tactual-verbal disconnection.

Aged↗
PubMed1993

Partial recovery from visual object agnosia: a 10 year follow-up study.

We describe a young woman, J.R., who sustained a very severe head injury in 1981 at the age of 17 years. She was assessed in 1982 and found to have visual agnosia. Since then J.R. has been assessed on several occasions over a period of ten years. Her agnosia for real objects has resolved and she has improved on the identification of other classes of stimuli. However, she still has some problems with the identification of line drawings, photographs and model animals. Her drawing from memory remains particularly poor and she has difficulty with visual imagery. We consider her residual deficits in the light of Farah's (1990) theoretical framework; this proposes that associative agnosia could be due to a disconnection syndrome, a loss of stored visual representations or to the loss of knowledge of how to perceive objects. J.R.'s residual impairments appear to be mainly due to a loss of access to visual representations in the absence of visual input.

Adult↗
PubMed1989

Auditory agnosia with relative sparing of speech perception.

We report a case of auditory agnosia in which the initial clinical picture began with generalized auditory agnosia for verbal and non verbal sounds, but rapidly changed to a selective auditory agnosia confined to the perception of non verbal sounds. CT scanning and MRI did not demonstrate cortical or subcortical damage, except for bilateral ventricular enlargement. The patient was submitted to audiological investigations including physical and psychoacoustic studies. Deficits were revealed during the decay and loudness discrimination test, but no temporal auditory acuity deficit was observed. The results of these studies are discussed in relation to the clinical picture. Also the dissociation between verbal perception and non verbal perception is discussed.

Adult↗
PubMed1996

Congenital visual agnosia and prosopagnosia in a child: a case report.

We present an eight years old child, L.G. with congenital agnosia and prosopagnosia. This is a special case of perceptual deficits in a child which are discrete and exist in the context of a very high verbal intelligence. L.G. was administered an extensive battery of tests of cognitive functioning. He has intact basic visual skills, although his visual analysis is sometimes slow. L.G. can read, write and do math at age level or above. Four normal eight years old boys were used as controls on a selection of the perceptual tests, administered to L.G., which did not have normative data. L.G.'s object recognition skills bear the hallmarks of adult apperceptive agnosia. His visual memory and imagery are normal. Tests of face processing skills reveal, unlike adult prosopagnosics, severe deficits in addition to the familiar face recognition problem. L.G.'s agnosia and prosopagnosia are compared to the relevant literature.

Agnosia↗
PubMed1991

Rediscovering tactile agnosia.

Eighty-four patients with damage to various levels of the nervous system, ranging from the peripheral nerves to the cerebral cortex, underwent somesthetic assessment in order to determine the degree to which basic and complex perceptual and motor disorders affect tactile object recognition (TOR) and to determine whether TOR can be impaired in the absence of more basic sensorimotor imperception. The results suggest that (1) basic and intermediate disorders of somesthetic function impair TOR but are commensurately more severe for any given degree of TOR impairment in patients with peripheral lesions than in patients with cortical lesions; (2) neither hemiparesis nor hemianopia alone precludes normal TOR; (3) hemineglect contributes substantially to TOR impairment; (4) impairment of TOR can occur in the absence of more basic somesthetic dysfunction and constitutes tactile agnosia; (5) tactile agnosia is a subtle, nondisabling disorder that should be distinguished from the nonagnosic, severe and disabling disorder, astereognosis; and (6) tactile agnosia results from unilateral damage to parietotemporal cortices, possibly including the second somatosensory cortex, in either hemisphere.

Adolescent↗