Agnosia Health Dictionary

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Agnosia: From 3 Different Sources

An inability to recognize objects despite adequate sensory information about them reaching the brain via the eyes or ears or through touch. Agnosia is caused by damage to areas of the brain that are involved in interpretative and recall functions. The most common causes of this kind of damage are stroke or head injury.

Agnosia is usually associated with just one of the senses of vision, hearing, or touch and is described as visual, auditory, or tactile respectively. Some people, after a stroke that damages the right cerebral hemisphere, seem unaware of any disability in their affected left limbs. This is called anosognosia or sensory inattention. There is no specific treatment for agnosia, but some interpretative ability may return eventually.

Health Source: BMA Medical Dictionary
Author: The British Medical Association
The condition in which, in certain diseases of the brain, the patient loses the ability to recognise the character of objects through the senses

– touch, taste, sight, hearing.

Health Source: Medical Dictionary
Author: Health Dictionary
n. a disorder of the brain whereby the patient cannot interpret sensations correctly although the sense organs and nerves conducting sensation to the brain are functioning normally. It is due to a disorder of the *association areas in the parietal lobes. In auditory agnosia the patient can hear but cannot interpret sounds (including speech). A patient with tactile agnosia (astereognosis) retains normal sensation in his hands but cannot recognize three-dimensional objects by touch alone. In visual agnosia the patient can see but cannot interpret symbols, including letters (see alexia).
Health Source: Oxford | Concise Colour Medical Dictionary
Author: Jonathan Law, Elizabeth Martin

Astereognosis

An inability to recognize objects by touch when they are placed in the hand, even though there is no defect of sensation in the fingers or difficulty in holding the object.

Astereognosis is either left- or right-sided; tactile recognition is normal on the other side.

If both sides are affected, the condition is called tactile agnosia.

Astereognosis and tactile agnosia are caused by damage to parts of the cerebrum (main brain mass) involved in recognition by touch and may occur as a result of a stroke or head injury.... astereognosis

Nervous System

The body system that gathers and stores information and is in overall control of the body.

The brain and spinal cord form the central nervous system (CNS), which consists of billions of interconnected neurons (nerve cells). Input of information to the CNS comes from the sense organs. Motor instructions are sent out to skeletal muscles, the muscles controlling speech, internal organs and glands, and the sweat glands in the skin. This information is carried along nerves that fan out from the CNS to the entire body. Each nerve is a bundle consisting of the axons (filamentous projections) of many individual neurons.

In addition to the nervous system’s anatomical divisions, there are various functional divisions. Two of the most important are the autonomic nervous system, concerned with the automatic (unconscious) regulation of internal body functioning, and the somatic nervous system, which controls the muscles responsible for voluntary movement.

The overall function of the nervous system is to gather and analyse information about the external environment and the body’s internal state, and to initiate appropriate responses, such as avoiding physical danger.

The nervous system functions largely through automatic responses to stimuli (see reflex), although voluntary actions can also be initiated through the activity of higher, conscious areas of the brain.

Disorders of the nervous system may result from damage to or dysfunction of its component parts (see brain; spinal cord; neuropathy; nerve injury). They may also be due to impairment of sensory, analytical, or memory functions (see vision, disorders of; deafness; numbness; anosmia; agnosia; amnesia), or of motor functions (see aphasia; dysarthria; ataxia). ... nervous system

Vision, Disorders Of

The most common visual disorders are refractive errors, such as myopia, hypermetropia, and astigmatism, which can almost always be corrected by glasses or contact lenses. Other disorders include amblyopia; double vision; and disorders of the eye or optic nerve, of the nerve pathways connecting the optic nerves to the brain, and of the brain itself.

The eye may lose its transparency through corneal opacities, cataract, or vitreous haemorrhage. Defects near the centre of the retina cause loss of the corresponding parts of the visual field (see macular degeneration). Floaters, which are usually insignificant, may indicate a retinal tear or haemorrhage, or they may herald a retinal detachment. Optic neuritis can cause a blind spot in the centre of the visual field.

Damage to the brain (for example, from a stroke) may cause visual impairment such as hemianopia, agnosia, visual perseveration (in which a scene continues to be perceived after the direction of gaze has shifted), and visual hallucinations.... vision, disorders of

Alexia

n. an acquired inability to read. It is due to disease in the left (dominant) hemisphere of the brain in a right-handed person. In agnosic alexia (word blindness) the patient cannot read because he is unable to identify the letters and words, but he retains the ability to write and his speech is normal. This is a form of *agnosia. A patient with aphasic alexia (visual asymbolia) can neither read nor write and often has an accompanying disorder of speech. This is a form of *aphasia. See also dyslexia.... alexia

Perception

n. the process by which information about the world, as received by the senses, is analysed and made meaningful. Abnormalities of perception include *hallucinations, *illusions, and *agnosia.... perception

Stereognosis

n. the ability to recognize the three-dimensional shape of an object by touch alone. This is a function of the *association areas of the parietal lobe of the brain. See also agnosia.... stereognosis

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