Anomic Aphasia - Causes

Causes

Anomia is caused by damage to various parts of the parietal lobe or the temporal lobe of the brain. This damage can be brain trauma, such as an accident, stroke, or tumor. This type of phenomenon can be quite complex, and usually involves a breakdown in one or more pathways between various regions in the brain.

Although the main causes are not specifically known, many researchers have found contributing factors to anomic aphasia. It is known that people with damage to the left hemisphere of the brain are more likely to have anomic aphasia. Broca’s area, the speech production center in the brain, was linked to being the source for speech execution problems, and with the use of functional magnetic resonance imaging (fMRI), Broca’s area was connected with speech repetition problems, which is commonly used to study anomic patients. Other experts believe that damage to Wernicke's area, which is the speech comprehension area of the brain, is connected to anomia because the patients cannot comprehend the words that they are hearing.

Although many experts have believed that damage to Broca’s area or Wernicke's area are the main causes of anomia, current studies have shown that damage in the left parietal lobe is the epicenter of anomic aphasia. One study was conducted using a word repetition test as well as magnetic resonance imaging (MRI) in order to see the highest level of activity as well as where the lesions are in the brain tissue. Fridrikkson, et al. saw that damage to neither Broca’s area nor Wernicke's area were the sole sources of anomia in the subjects. Therefore, the original model, which showed that damage occurred on the surface of the brain on the grey matter for anomia, was debunked and it was found that the damage was done in the white matter deeper in the brain on the left hemisphere. More specifically, the damage was done to a part of the nerve tract called the arcuate fasciculus, which the mechanism of action is unknown but it is shown to connect the posterior (back) of the brain to the anterior (front) and vice versa.

New data has shown that although the arcuate fasciculus’s main function does not include connecting Wernicke's area and Broca’s area, damage to the tract does create speech problems because the speech comprehension and speech production areas are connected by this tract. Some studies have found that in right-handed people the language center is 99% in the left hemisphere; therefore, anomic aphasia almost exclusively occurs with damage to the left hemisphere. However, in left-handed people the language center is about 60% in the left hemisphere; thus, anomic aphasia can occur with damage to the right hemisphere in left-handed people. Therefore, the specific cause of anomia is unknown; however, research is bringing the answer into focus.