Brain-Behavior Relationships

Overview of Topics

Functions
Behavioral Deficits
References

Angular Gyrus

A. Functions

1. Tertiary in function: lies at the boundary between the occipital, temporal, and postcentral regions of the hemisphere, where the cortical areas for visual, auditory, vestibular, cutaneous, and proprioceptive sensations overlap (1).
2. Supramodal in function: plays a special role in inter-analyzer syntheses (1). The angular gyrus, as part of the inferior parietal lobule, is the association area of association areas and allows cross modal transfer and associations between either vision or touch and hearing (2). As the angular gyrus is important in the processing of associating a heard name to a seen or felt object, it is probably also important for associations in the reverse direction. A "name" passes through Wernicke's area, then via the angular gyrus arouses associations in the other parts of the brain (2). Thus, the angular gyrus acts as a way station between the primary sensory modalities and the speech area.(2).
3. The development of language is probably heavily dependent on this area. Object naming, one of the simplest aspects of language, depends on associations between other modalities and audition (2).
4. Association cortex that combines visual and auditory information necessary for reading and writing (3). Designed for storing the memory of the "rules of translation" from written to spoken language (2).

1. Alexia without agraphia: results when the inferior parietal lobule is disconnected from all visual input (3). Pure word blindness results due to a disconnexion from the "memory centre" (4).
   • Reading aloud and comprehension of written words is lost (2).
   • Ability to name and recognize objects is preserved (2). Objects have rich, multiple associations in other areas, e.g. one can recognize an apple by vision, touch, taste, smell, even by texture. The arousal of such associations permits the finding of an alternative pathway across an uninvolved more anterior portion of the corpus callosum.
   • Persistent difficulty in color naming but can match colors by hue without error (2).
   • Loss of ability to read music (4).
   • Spelling and spelling comprehension way he quite normal
   • Writing should be normal or nearly so; however, subtle defects can usually present (e.g. letters are too large or too widely spaced, there may be an absence or misuse of punctuation, capitals may be disregarded, letters dropped or reduplicated) (5).
   • This syndrome is referred to as agnostic alexia by Brown (5). He states that a right hemanopia is an almost constant.

2. Alexia with agraphia: results from damage to the angular gyrus itself and renders the patient unable to read and write (3). May be referred to as aqraphic alexia or angular gyrus alexia (5).
   • A loss of visual word memory returns the patient to the state of being illiterate; lack of reading, writing, and spelling, and an incomprehension of spelled words are all components of this more primitive state (2).
   • Reading has a global character, without facilitation by literal analysis or letter tracing. Paralexia is present in reading aloud, especially for letters (6).
   • Letters are misnamed and patients cannot Indicate or sort letters accurately to command, unless first given a visual model of the letter tested, nor can they select the correct letter name from a spoken group. Patients are unable to match spoken letter sounds to written letters (5).
   • There is an inability to spell all but the simplest words, either to command or to a presented object (5).
   • Printing is variable, but always impaired. The agraphia reflects the spelling deficiency, as well as, in severe cases, the loss of conceptualization of words as whole units (5).

Although specific assessment devices have not been mentioned, it would appear that qualitative analysis of reading, writing, and spelling abilities is warranted in assessing the above syndromes.

TOP

References

1. Luria, A.R. The Working Brain: An Introduction to Neuropsychology, Basic Books,Inc., New York:1973.
2. Geschwind, N. Disconnexion syndromes in animals and man. Brain, 88: 237-294, 585-644, 1965.
3. Strub, R.L. & Black, F.W. The Mental Status Examination in Neurology, F. A. Davis Co.: Philadelphia, 1977.
4. Brown, J.W., Aphasia, Apraxia, and Agnosia, Charles C. Thomas: Springfield, Ill, 1972.