From Big Medical Encyclopedia

AGNOSIA (agnosia, grech, the negative a-and gnosis prefix — knowledge, knowledge) — disturbance of complex cognitive processes at defeat of Gnostic departments of bark of big cerebral hemispheres.

The phenomena of AGNOSIA were described by Munch (N. of Munk, 1881) observing that destruction at animal certain departments of occipital area of a brain does not lead to a vision disorder, but makes impossible recognition of objects. First clinical descriptions And. are made Jackson (N. Jackson, 1876), Sharko (J. M of Charcot, 1882, 1887). Lissauer (N. of Lissauer, 1890) described various forms optical (visual) And., arising at destruction of front departments of occipital area of a brain.

The significant contribution to the doctrine about And. it was brought by Pettsl (O. Potzl, 1926) and it sotr., suggesting a row about physiological mechanisms of this phenomenon, Poppelreyter (W. Poppelreuter, 1917 — 1918), and then G. Holmes, Zangvill (O. Zangwill), Teyber (N. L. Teuber), the disorders of visual attention which were pulling together the phenomena optical Ampere-second. In modern neurology, coming from ideas of mechanisms of analyzers and the modern doctrine about entities of cognitive activity (gnozis), the doctrine about And. and its mechanisms received sufficient scientific justifications.

AGNOSIA most often arises at vascular damages, injuries, tumors of a brain.

AGNOSIA radically differs from the elementary forms of disorder of perception coming at damages of an eye, a visual way or primary (projective) zones of touch departments of a cerebral cortex. At defeat of the last there occurs loss or narrowing of sharpness of a pla of volume of elementary feelings of this or that modality (visual — at defeat of an occipital share, acoustical — at defeat temporal, skin and kinaesthetic — at defeat of bark of a postcentral crinkle of a brain). Unlike it, at And. elementary forms of sensitivity remain safe, but irregular shapes of analitiko-synthetic activity within this analyzer and therefore the possibility of transformation in a cerebral cortex of elementary feelings in difficult (most often the reflecting whole objects) forms of perception is at a loss or becomes impossible are broken.

And. has always modal and specific character. So, at defeat of secondary zones of an occipital share at the patient perception of irregular shapes of distinguishing of objects, drawings, letters is broken, but he well distinguishes sounds of the speech, musical sounds or recreates an image of the whole subject by means of palpation.

On the contrary, at defeat of secondary zones of a temporal share (dominant — left at right-handed persons — a hemisphere) an opportunity to accurately distinguish and learn sounds of the speech disappears, but ability to perceive elementary sounds remains.

The similar phenomena can arise also in the tactile sphere at defeat of secondary departments of bark of a postcentral crinkle of a brain, and also in the field of sense of smell and taste at defeat of medio-basal departments of bark of a temporal share. For this reason distinguish optical (visual), acoustic (acoustical), tactile and kinaesthetic And., which is known also under the name of an astereognosis, olfactory and flavoring And.

Optical, or visual, agnosia. The greatest clinical value have various forms optical And. (so-called psychic blindness). In the expressed cases of the patient cannot learn objects and their realistic image (subject agnosia of Lys of a sauer), perceiving only their separate signs and guessing a general meaning of a subject or its image. E.g., perceiving the image of points, the patient speaks: «a ring, and still a ring, and a crossbeam — probably, the bicycle».

Similar phenomena visual And. arise at massive (most often bilateral) defeats of secondary departments of an occipital share. In primary (projective) zones of bark of an occipital share (the field 17 of Brodmann) the prevailing place is taken by the nervous cells located in IV — an inner granular (afferent) layer of bark, reacting to high-specific characters of visual irritations: angularity or rotundity of lines, the movement from a midfield of sight to the periphery etc. It allows primary zones of occipital bark to catch fractional, very specific characters of visual influences.

Also strictly somato-topical organization of visual irritations, the caught primary (projective) centers of a cerebral cortex, an occipital share therefore their partial defeat is led to space and limited losses of certain sites of the visual field (see is characteristic. Hemianopsia , Scotoma ). Unlike it, among beads of secondary zones of bark of an occipital share (fields 18, 19 of Brodmann) the prevailing place is taken by the nervous cells with short axons which are located in II — outside granular and III — pyramidal layers of a cerebral cortex and the allocations of separate components of visual irritations and their association serving as the device in the whole structures. These cells have no that high specificity, a cut cells of primary zones of bark are characterized. Therefore the irritation leads them to a wide spread occurance of excitement on nearby sites of bark of an occipital share, not elementary visual hallucinations (the shining points, spots, lines), and the whole complex visual objects result. On the contrary, destruction of these zones of bark of an occipital share causes not space and limited losses in the certain field, and results in inability to synthesize visual objects in the whole structures and to impossibility of visual recognition of images of objects and irregular geometrical shapes.

alt = the Test characterizing disturbance of visions at agnosia. Signatures under the drawings and words offered for an identification are made by patients: 1 — at an extra brain tumor of occipital area; 2 — at an encephalomalacia in the depth of the left parietooccipital area.

In less expressed cases signs visual And. are shown only in the complicated conditions, in particular at perception crossed out or «noisy» by foreign influences of images (fig).

The special place among visual And. occupies a characteristic syndrome so-called simultaneous And., shown in inability synthetic to perceive groups of the images forming whole.

At defeat of secondary departments of an occipital share dominant (left at right-handed persons) hemispheres a syndrome visual And. acts especially clearly at picture perception of letters or figures or in the change of a subtlety of perception of objects leading to disturbance of their naming (see. Aphasia ).

At defeat of the secondary centers of occipital or occipitoparietal area of a subdominant (right) cerebral hemisphere a syndrome And. can take peculiar forms of not recognition of persons (prozopagnoziya) or ignorings of the left side of the visual field (unilateral space And.).

Since classics of neurology (Lissauer, etc.) it is accepted to distinguish two main forms visual And. — apperceptive and associative. At the first — the patient perceiving only separate signs of a subject or its image cannot apprehend and recognize him in general; at the second — the patient clearly perceives objects in general and the whole images, but does not learn and on can call them. This form also approaches the phenomena mentioned above visual And.

Space agnosia represents absolutely special group A., at a cut vision of separate objects or their images remains safe, but ability to estimate the space relation is broken. The patient cannot distinguish the right and left side, makes mistakes in the analysis of an arrangement of arrows on hours, during the reading and the image of the map. Space And. arises at defeat of tertiary (parietooccipital) departments of a cerebral cortex.

Acoustic, or acoustical, agnosia («sincere deafness») it is characterized the fact that the patient who clearly is distinguishing sounds and not showing signs of loss of perception of any sites tone scale is not able to distinguish sounds of the speech (phoneme).

The patient cannot catch distinctions between relatives (so-called oppositional) the phonemes differing in any one sign, e.g. dullness and sonority (p — and t — d) and therefore cannot catch sense of the heard words (see. Aphasia, touch ) and it is correct to reproduce and write them. He loses also a possibility of recognition of objects of the sounds made by them, e.g. does not recognize hours by their tick, water on its murmur, etc.

Acoustical And. arises at defeat of the secondary centers of a temporal share of a dominant (left) cerebral hemisphere.

Tactile agnosia it is expressed that the patient, at to-rogo kept rather thin tactile sensitivity, she is not able to learn to the touch objects. These phenomena received the name of an astereognosis. Some researchers emphasizing a role of disturbances of synthesis of the perceived signs characteristic of these cases separate taktilno designate this form And. term «amorfosintez» [Denny-Brown]. In these cases, as well as at disturbance of a space gnozis, phenomenon And. lead to disturbance of a Gnostic basis of motive processes, and the patient has disturbances of irregular shapes of a praksis which can be designated the term «apractognosis».

Are closely connected with the described disturbances of the phenomenon of the autotopagnosia consisting in difficulty to define an arrangement of separate points of a pla of body parts, to learn parts of the body, and the phenomenon of a metamorphopsia, at a cut of the patient begins to perceive parts of the body or foreign objects unusual, changed in a form or size.

At a macropsia objects seem to the patient excessively big, at a micropsia — excessively small. Sometimes there is a phenomenon of a so-called polymelia — feeling of false extremities which can seem motionless or moving.

Tactile And., concerning recognition of the irritations arriving from external environment it is observed at defeat of secondary departments of a parietal lobe, preferential dominant (left) hemisphere. In cases And., belonging to recognition of own body, defeat of the right hemisphere mostly is found. Very harakterets that fact that at some defeats of a subdominant (right) cerebral hemisphere of the phenomenon And. can be followed by a peculiar disturbance of perception of own defects. This phenomenon which received the name «anosognosias» (or Anton's syndrome — Babinsky), can carry either widespread, or more limited character p in the expressed cases leads to the fact that the patient does not notice at himself disturbances of sensitivity and movements (most often in the left side of a body).

It is described also painful And., extending evenly to all body; pricks at the same time are perceived as a touch, on the patient does not feel pain.

Olfactory and flavoring agnosia. At these forms identification of smells and flavoring feelings is broken. These forms of agnosia Dezherin called «purely theoretical» as they are almost indistinguishable from an anosmia and an ageusia and have no diagnostic value.

The vital issue which is of great importance for clinic is involution of symptoms And. or recovery cognitive functions, broken as a result of the corresponding local damages of a brain. This effect can be reached or in the course of the spontaneous compensation coming at rather insignificant defeats and at recovery haemo - and likvorodinamik, or as a result of special training, at Krom the broken cognitive processes are recovered at the expense of the kept analyzers or the complex speech (logical) analysis of the arriving information.

Methods of a research. Visual And. investigate, showing to the patient the corresponding subject or the image with the offer to recognize him.

As «sensibilized» test on And. presentation to the patient of not completely represented planimetric or silhouette figures (fig.) stylized shaded pl is used.

At a research tactile And. to the patient suggest to feel any objects. At a research slukho-speech And. to the patient relatives on sounding suggest to repeat speech sounds — phonemes (e.g. — p, t — d, z — c), or to avoid difficulty of their pronunciation, to point to the corresponding letters, or, at last, to develop the corresponding conditional motor reaction (e.g., in response to a sound to raise the right hand, in response to a sound «п» — left). At a research olfactory and flavoring And. show to the patient a number of various smells and flavoring irritations which he shall distinguish. It is natural that the received defects can be estimated as the phenomenon And. only when sharpness of elementary visual, tactile, acoustical and other processes remains kept.

A vital issue is differentiation original And. from those impulsive estimates which arise in similar experiences at patients with damage of frontal lobes of a brain. A basic sign in this case is the fact that the patient with damage of frontal lobes of a brain does not do active attempts to establish value of the offered object and its assessment has impulsive character while the patient with original And. comes to false assessment of the image, despite numerous active attempts to define its value.

Topiko-diagnostichesky value. Agnostic disturbances arise especially often at defeat of parietal and parietooccipital area of a brain: visual And. - at disturbance of back departments of parietooccipital area (fields 18 and 19 of an occipital share, the field 39 of a parietal lobe), an astereognosis — at defeat of the supramarginal field, sometimes and postcentral fields, acoustic And. — at defeat of secondary zones of a temporal share of a dominant (left) hemisphere.

And., concerning recognition of own body, arise usually at defeat of bark of a parietal lobe of a brain and its bonds with a visual hillock. Mostly at the same time defeat of the right hemisphere, especially in the presence of an anosognosia and a polymelia is found. Olfactory and flavoring And. develops at defeat of medio-basal sites of bark of a temporal share of a brain.

Forecast depends on the nature of a disease and efficiency of the carried-out therapy.

Bibliography: Kok E. P. Visual agnosias, L., 1967, bibliogr.; JI at r and I am A. R. the Highest cortical functions of the person and their disturbance at local damages of a brain, M., 1969, bibliogr.; Frederiki J. A. M. of The agnosias, Handb. clin. n «-urol., cd. by P. J. Vinken a. G. W. Bruyn, v. 4, p. 13, Amsterdam — N. Y., 1969, bibliogr.; Lange J. Agnosim und Apraxien, Ilandb. Neurol., hrsg. v. O. Bumke u. O. Focrster, Bd 6, S. 807. B-, 1936, Bibliogr.

A. P. Lursh.