Agnosia - This is a perceptual dysfunction that occurs on the background of the preservation of consciousness and sensitivity. In other words, agnosia is a disorder of different types of perception and appears due to a lesion of the cortex and nearby subcortical areas of the brain. This pathology is characterized by a connection with damage to the secondary (projection-association) areas of the cerebral cortex, which are responsible for the analysis and synthesis of the information obtained. This leads to a disorder in the recognition of stimuli, causing a violation of the recognition of objects and the wrong response to the stimuli obtained.
Damage to the cerebral cortex, responsible for the analysis and synthesis of information, generates agnosia. Therefore, the symptoms will depend on the location of the affected area of the brain. For example, due to the defeat of the left zone of the occipital region, subject agnosia is born, which consists in the loss of patient data about the object and its purpose. In other words, an individual suffering from this violation of perception sees the object, can describe it, but is unable to name it and tell about its purpose. When the temporal region is damaged, there is an acoustic-speech perception disorder: the patient perceives the speaker's speech, as if this is a normal set of sounds, he is unable to perceive the meaning of phrases and distinguish individual words. Statistics show that the disorder in question is quite rare.
The causes of agnosia are as follows: dysfunctions of the temporal and parietal areas of the brain, where data on the use of familiar objects are stored (often occurs suddenly after a stroke, heart attack or head injury, when the cortex and nearby subcortical brain formations are affected, and damage to the cortex can cause a tumor process ). In addition, the pathology in question may arise as a result of degeneration of brain areas that are responsible for the integration of perception, memory and identification processes.
Thus, the main causes of agnosia are damage to the parietal and occipital areas of the cerebral cortex, which occur, in addition to the above pathologies, for the following ailments:
- chronic circulatory disorders in the brain, further developing into dementia;
- inflammatory processes of the brain (for example, encephalitis);
- Alzheimer's disease, which is associated with the accumulation of amyloid in the brain (a specific protein that normally normally quickly disintegrates in the brain);
- Parkinson's disease, characterized by the occurrence of progressive muscle stiffness, tremors, and a number of neuropsychological disorders, including apraxia.
Different types of perceptual dysfunction can be distinguished depending on the location in the brain of the affected area. For example, when the parietal-occipital zone is damaged, there is a violation of topographic orientation, with a lesion of the right subdominant portion of the parietal lobe - anosognosia, which is the absence in patients of a critical assessment of their own illness or defect. For example, people suffering from this form of dysfunction, consider themselves completely healthy, even against the background of the immobility of one side of the body (state of paralysis).
Many people, far from medicine, are asking agnosia, what is it, what are the symptoms of this disease, how do they appear?
The following manifestations and symptoms of agnosia can be distinguished:
- violation of spatial orientation and the ability to "read" on the map, that is, to understand the location of cities, districts and other places on the map;
- disorder of the ability to recognize objects by touch (it is difficult for sick people to determine the texture, shape and shape of the object;
- denial of the fact that they have a physical defect or illness (for example, blindness, deafness), despite the indisputability of existing defects;
- indifference to the presence of a defect (a person may be disturbed a little by suddenly frolicking deafness, blindness or other defects;
- impaired sound recognition (the patient is not able to make out the nature of the sound, to understand where it comes from, for example, when he hears a call in his own house or the voice of a relative;
- dysfunction of perception of his own body (people are not able to correctly determine the number of their limbs or their length);
- a disorder of the ability to recognize the faces of acquaintances, along with this, patients are able to give them an approximate age or sex;
- impaired recognition of complex visual images, while patients retain the ability to recognize individual components of these images, for example, an individual, looking at an image, recognizes a jug on the table, but is unable to understand that there is a jug, glasses, plates, and food on the table, it shows that a feast was shown in the picture;
- ignoring part of the visible space (for example, a patient in the process of eating food eats food only from the right side of the plate).
Types of agnosia
The described disorder is characterized by three main varieties: tactile, visual and auditory perception disorders. In addition, it is possible to identify a number of less common forms of the ailment under consideration (for example, spatial agnosia).
Visual agnosia is characterized by the presence of a lesion in the occipital region of the brain. This form of the disease manifests itself in the inability of patients to recognize images and objects while maintaining visual acuity. The type of pathology considered may manifest itself in different ways. The following forms of visual agnosia are distinguished: subject, color, visual, simultaneous agnosia, protopagnosia, and Balint syndrome.
Auditory perceptual dysfunctions occur due to damage to the cortex of the temporal zone of the right hemisphere. This type of agnosia is represented by the inability of individuals to recognize speech and sounds against the background of the normal working capacity of the auditory analyzer. Auditory agnosias, in turn, are subdivided into simple auditory perception disorder, auditory and tonal auditory agnosia.
A simple violation of auditory perception is characterized by the inability of people to recognize simple, previously familiar sounds, such as the sound of rain, the rustle of the sea, knocking, doorbell, squeak, etc.
Oral-verbal agnosia is the impossibility of speech recognition. To a person suffering from the described form of agnosia, native speech seems to be a set of unfamiliar sounds.
The tonal derangement of the auditory perception is characterized by the inability to grasp the emotional coloring, tone, timbre of speech against the background of preserving the ability to perceive words adequately and to correctly distinguish grammatical structures.
Tactile agnosia is the inability to identify objects, things to the touch. The following varieties of the considered species of agnosia are distinguished: somatoagnosia, astereognosia, and impaired spatial perception. The inability of the patient to recognize parts of his own body and assess their location relative to each other is called somatoagnosis. A violation of tactile perception, in which the process of recognizing objects and things through touch is called astereognosia.
There are also violations of spatial perception, expressed in the form of incorrect identification of space parameters. Lesions of the middle sections of the occipital-parietal region are found in the inability to measure values closer or further, and to correctly place objects in three-dimensional space, especially in depth, damage to the left hemisphere entails spatial agnosia, manifested by impaired stereoscopic vision. In addition, there are such types of agnosia as unilateral violation of spatial perception and perceptual disorder, which consists in the inability to topographically navigate the terrain. Unilateral spatial agnosia is the inability to recognize one half of the space. Violation of topographic orientation is expressed in the inability to recognize familiar places against the background of preservation of the memory function.
One of the rarest varieties of agnosia is dysfunction of perception of movement and time. This ailment is manifested in the violation of the correct understanding of the movement of objects and an adequate assessment of the speed of time. The impossibility of perceiving objects in motion is called akinotepsia.