REHABILITATION OF MODERATE TO SEVERE TBI: SENSORY-PERCEPTUAL AND BALANCE DISORDERS IN TBI: PERCEPTUAL DEFICITS 

  • Agnosias - Deficits in stimulus or object recognition
    • Forms:
      • Apperceptive agnosia - impairment caused by disturbed integration of otherwise normally perceived components of a stimulus
      • Associative agnosia - defective recognition of normally perceived and normally integrated percepts
    • Types seen in TBI:
      • Tactile agnosia - an inability to identify objects placed in the affected hand (astereognosis), due to lesions of the parietal post-rolandic cortex; common following TBI
      • Auditory agnosia - a rare inability to differentiate between various nonverbal sounds, probably due to bilateral temporal lobe lesions; rare and usually occurs in conjunction with other auditory processing disorders
      • Visual agnosia - a rare inability to recognize visual stimuli in otherwise normal visual perception:
        • Apperceptive visual agnosia may be correlated with dysfunction of the bilateral visual association cortices
        • Associative visual agnosia is a disconnection sydrome between the visual and language systems in which the patient can recognize the object but is unable to name it; may be due to occlusion of the left posterior cerebral artery and subsequent infarction of the left occipital lobe and posterior corpus callosum
      • Prosopagnosia - an inability to recognize familiar faces and/or objects, associated with nondominant parietal lobe involvement
        • Frequently involves problems with color agnosia and alexia
        • Enduring prosopagnosia is associated with bilateral lesions in the inferomesial visual association cortices or their adjacent white matter, due, in most cases, to embolization of the posterior cerebral artery circulation
      • Finger agnosia may involve all 5 digits, but usually occurs in the middle, index, and ring fingers, due, in most cases, to a lesion in the angular gyrus of the dominant parietal lobe

  • Neglect and Hemiinattention
    • Neglect - an inability to report, respond, or orient to novel or meaningful stimuli presented to the side opposite a brain lesion, due to faulty mediation of both sensory and motor intention
      • Unilateral neglect involves inattention to contralateral stimuli with a lesser degree of ipsilateral inattention, and has been correlated with lesions in the posterior parietal cortex, lateral prefrontal cortex, cingulate gyrus, striatum, and thalamus
      • Hemiinattention is the middle of the spectrum between extreme neglect to extinction, only with double simultaneous stimulation
    • Associated with neglect are:
      • Anosognosia - the explicit verbal denial of illness or deficit
      • Anosodiaphoria - verbal acknowledgement of the problem, but lack of associated concern
      • Alloesthesia - misplacement of the location of the stimulus to the normal side, when the side contralateral to a lesion is stimulated
    • Testing for neglect:
      • Assess at least 3 sensory modalities, such as touch, vision, and audition (unilateral hearing loss is almost aways due to peripheral dysfunction and not hemiinattention)
      • Present stimuli bilaterally, randomly, and simultaneously
    • Recovery/Treatment:
      • Neglect and hemiinattention tend to improve over time
      • Rehabilitative approaches may be of some value, such as "anchoring" and "scanning", vestibular stimulation, and bromocriptine

  • Visuoperceptual Disorders
    • Cortical blindness due to bilateral visual cortex damage;
    • Anton's syndrome, a type of visual agnosia that involves the denial of blindness, in which both the blindness and denial are transitory
    • Balint's syndrome, an inability to perceive the entire visual field which results in unpredictable perception and recognition of field components
      • Marked by visual disorientation, optic ataxia (deficient visual reaching), and ocular apraxia (visual scanning deficits)
      • Associated symptoms include an inability to shift gaze at will toward new stimuli and impaired target pointing under visual guidance
      • Usually due to bilateral parietooccipital damage secondary to hypoperfusion and infarctions of the posterior circulation
    • Alexia, a disorder charcterized by recognition of disordered visual patterns due to lesions that cause a disconnection between visual and language centers
    • Topographic disorientation, such as an inability to find one's way back, is likely due to deficits in visuospatial memory and differs from geographic disorientation, such as the inability to identify cities on a map
    • Achromatopsias are disorders of color perception
    • Stereopsis is the inability to discern depth based on binocular vision (as opposed to depth perception which is based on monocular vision)
    • Visual hallucinations in patients with epileptic foci

Based on information in Medical Rehabilitation of Traumatic Brain Injury, L.J. Horn and N.D. Zasler, eds. St. Louis, MO, Mosby, 1996, except for information where other papers are cited.