Agnosia

There are to major forms of agnosia, and different subtypes as well from visual, somesthetic, or auditory input.

//Associated brain region:// parietal occipital cortex, bilateral damage to the inferior-occipital cortex
 * Apperceptive visual agnosia:** disturbance in perceptual and visual-motor integration, such that patients have difficulty copying or matching various objects, failing to draw the complete object. May trace but will not be able to recognize where they started. They seem unable to synthesize visual details into an integral whole, recognizing only isolated details. If unnecessary lines are drawn across the picture, the abilty to recognize the object deterioriates even futher.

**Associative visual agnosia:** deficit in naming, such that auditory equivalents cannot be matched to a visual perception (may also have alexia) //Associated brain region:// left inferior and middle temporal (area 37) occipital abnormalities; parietal occipital cortex

//Associated brain region:// bilateral superior occipital lobe lesions; superior occipital-parietal region (area 7)
 * Simultanagnosia**: inability to see more than one thing, or all aspects of an item, at a time


 * Auditory Agnosia: **

reading or viewing words: left medial extrastriate visual cortex looking at pictures: right inferior occipital lobe

Laterality
right vs left inferior/medial vs superior temporal lobe, patients may display category specific agnosias.

Example: 27-year old man with massive right inferior-posterior temporal lobe injury & surgical removal was able to recognize pictures of tools (he had been a carpenter) but could not recognize or correctly name pictures of animals and he could not correctly remember facial stimuli that he had been shown five minutes earlier and could not differentiate them from faces he had not seen.

Example 2: 47-year old woman with a calcium cyst growing from the skull into the right superior temporal lobe, was able to name pictures of animals, tools and household objects. However, she was almost completely unable to recognize and correctly name animal and humans sounds (e.g. a baby crying, a crowd cheering, a lion roaring) which had been briefly presented, but was better able to recognize non-living sounds such as a creaking door, or a hammer hammering--though these abilities were also compromised.

These findings, which require independent confirmation, raises the possibility that the temporal lobes are not only able to distinguish between living and non-living things including tools and faces, but that the right temporal lobe is specialized for perceiving living creatures (and the sounds they make) whereas the left is specialized for perceiving and naming non-living things, such as tools and household objects.

Visual Agnosias
Visual agnosia is a condition where the patient loses the capacity to visually recognize objects, although visual sensory functioning is largely normal. -Often with inferior medial occipital lobe lesions. -In general, objects are detected but they lose the ability to evoke meaning and cannot be correctly identified or named -Many patients are unable to sort pictures or objects into categories or match pictures with the actual object such that there appears to be a deficit in the ability to not only recognize but to classify visual percepts. -In severe cases they are unable to point to objects that are named.

Nevertheless, this is not a naming disorder, because regardless of modality, anomics continue to have word finding and naming difficulties. In contrast, those with agnosia show enhanced recognition if an object is presented via a second intact modality (e.g. if they palpate it by hand). Thus agnosia can often be limited to a single input channel, i.e. visual vs. tactual. Moreover, If an object is used in context, recognition can be greatly enhanced.

-May complain that objects change while they are looking at them, and /or that they disapear; a condition which suggests optic ataxia. <span style="font-family: 'Times New Roman',serif; font-size: 11pt;">-Usually, however, the deficit is conceptual rather than perceptual.

<span style="font-family: 'Times New Roman',serif; font-size: 11pt; line-height: 1.5;">Agnosic individuals also often (but not always) have difficulty with reading and may suffer from prosopagnosia and/or impaired color naming. Interestingly, in some cases visual memory be intact.

<span style="font-family: 'Times New Roman',serif; font-size: 11pt;">Like alexia, agnosia can occur following lesions to the medial and deep mesial portion of the left occipial lobe <span style="font-family: 'Times New Roman',serif; font-size: 11pt;">The left inferior temporal lobe and posterior hippocampus may also be damaged in some cases.

<span style="font-family: 'Times New Roman',serif; font-size: 11pt;">In some cases, it is likely that agnosia is due not only to tissue destruction but to tissue disconnection. That is, if the visual form recognition neurons in the temporal lobe are no longer able to receive input from the visual association areas, then this particular region becomes "cortically blind" and form recognition is prevented. However, like some other disconnection syndromes, if a different input channel is employed, i.e. if the object is verbally described or tactually explored, recognition is enhanced.

**Finger Agnosia**
Finger agnosia is not a form of finger blindness, as the name suggests. It is difficulty naming and differentiating among the fingers of either hand as well as the hands of others. This includes pointing to fingers named by the examiner, or moving or indicating a particular finger on one hand when the same finger is stimulated on the opposite hand.

Ex:If you touch their finger while their eyes are closed, and ask them to touch the same finger they may have difficulty. Many patients have difficulty on these tests regardless of there being administered in a verbal (naming) or non-verbal (touching) format. In general, it is the middle three fingers which are hardest to recognize and the angosia is demonstrable in both hands.

Although finger agnosia is only rarely shown with those who have **right inferior parietal lobe lesions** many patients also demonstrate some visual-constructive disabiliity. Hence, in testing for this disorder both verbal vs. non-veral forms are of assistance in determining the side of lesion. Often patients who have difficulty identifying fingers by name or simply differentiating between them non-verbally also suffer from receptive language abnormalities. Nevertheless, this disorder is not merely a manifestation of aphasia because finger agnosia may appear in the absence of language abnormalities.

LEFT vs, RIGHT: note if patients have more problems recognizing fingers on the right vs. left hand, or in transferring from the right to left hand (or vice versa); that is, by stimulating a finger (or fingers) on the right hand (while it is out of sight) and then having the patient indicate the same fingers on the left hand. One must rule out deficient attentional functioning in making this diagnoses. Of course, one should not diagnose brain damage based merely on poor performance of this one index but should look at the overall pattern of deficiency.

Alexia for numbers and digits is found in over 80% of individuals with left temporal-occipital lesions, and in less than 10% of those with right hemisphere lesions. As the name implies, the patient is unable to recognize numbers. Usually these individuals also suffer from generalized or literal alexia; i.e. an inability to recognize letters.
 * ALEXIA/AGNOSIA/AGRAPHIA FOR NUMBERS**

In some cases acalculia may be associated with an alexia and/or an agraphia for numbers, as well as aphasic abnormalities (referred to as aphasic acalculia. Individuals with this disorder are unable to recognize or properly produce numbers in written form.

Ex: May be unable to write out or point to the number "4" vs the number "7" or the letter "B".

Lesion is usually in the **left inferior parietal lobule** and localized within the angular gyrus. Not all patients are aphasic however. See also Acalculia