Agnosia
refers to the inability to recognize people or objects even
when basic sensory modalities, such as vision, are intact. As
an example, patients with visual agnosia may not recognize an
object upon visual presentation even though they can describe
its shape and other visual characteristics or the person cannot
recognize their wife's face and in some cases even their own.
It is therefore apparent that sensory perception of the object
/ face is disconnected from memories associated with the object
/ face. The patient can perceive the object but has no meaningful
associations to it. In agnosia, while perception itself, feeling
an objects shape, normal, recognition of objects is not.
There are
basically three different forms of agnosia; visual agnosia where
the person has difficultly recognizing objects, faces and words.
The second is Auditory Agnosia which involves the inability
to recognize sounds and thirdly, Somatosensory Agnosia where
the person has difficulty perceiving objects through tactile
stimulation.
The characteristic
and sub-types of the three forms of Agnosia are as follows:
Visual Agnosia
Visual agnosia is a neurological disorder distinguished by the
inability to recognize familiar objects. There are a number
of sub-types of visual agnosia. The most common are:
Prosopagnosia
- Inability to identify faces even though the person is known
to the sufferer. More on Prosopagnosia
Click Here
Agnostic Alexia - Reading Material
Color Agnosia - Inability to discriminate
between colors and therefore cannot name the colour.
Object Agnosia - Inability to name objects.
Simultanagnosia - Inability to recognize
a whole image although individual details are recognized.
Visual agnosia is associated with lesions of the left occipital
and temporal lobes. Many patients have a severe visual field
defect on the right side because of the injury to the left occipital
lobe. It is common for patients to have visual agnosia but intact
recognition in the tactile and auditory modalities.
In prosopagnosia
bilateral lesions of the gray and white matter of the occipitotemporal
gyrus cause prosopagnosia. In particular, the inferior longitudinal
fasciculus, a pathway that interconnects the occipital and temporal
lobes, has been suggested as the lesioned area in prosopagnosia.
Auditory Agnosia
There are three sub-types of visual agnosia:
Auditory/verbal
information Agnosia - Inability to hear words.
Auditory
Agnosia - Inability to hear environmental sounds
such as a car starting or a dog barking.
Receptive
Amusia - Inability to hear music.
Cortical
deafness is also a term applied to patients who essentially
do not respond to any auditory information even when hearing
is intact.
Somatosensory Agnosia (Astereognosis - Tactile Agnosia)
Patients with this disorder have difficulty perceiving objects
through tactile stimulation although basic tactile sensation
is intact. There is a distinction between the inability to recognize
basic features of an object, such as size, weight, and texture,
and the inability to name or recognize the object. Patients
who cannot recognize an object by touch may still be able to
draw the object and recognize the object pictured in the drawing.
Sometimes they can describe the physical features of the object
but cannot recognize it.
Pure astereognosis is thought to be caused by lesions of the
somatosensory cortex (post central gyrus) in the area subsumed
by the hand.
Differential
Diagnosis:
Some disorders have similar symptoms. The clinician, therefore,
in his diagnostic attempt, has to differentiate against the
following disorders which need to be ruled out to establish
a precise diagnosis.
Not a
General Memory Disorder.
Capgras Syndrome
Mental Retardation
Dementia
Head Traima
Acoustic (Loud Noise) in the case of Auditory Agnosia.
Cause:
Damage to
the brain, arising from a head injury or a stroke for example,
sometimes results in highly specific impairments of the person's
cognitive processes.
Brain
Damage
Stroke
Dementia
Neurological Disorders
Treatment:
Treatment is generally
symptomatic and supportive. The primary cause of the disorder
should be determined in order to treat other problems that may
contribute to or result in agnosia.
Counseling
and Psychotherapy [ See
Therapy Section ]:
