<unk>  occurring by itself may be caused by damage to almost anywhere in the left hemisphere and in some cases can be seen in instances of right hemisphere damage.<unk>  can be genetic or caused by damage to various parts of the parietal lobe or the temporal lobe of the brain due to traumatic injury, stroke, or a brain tumor. While<unk>  is primarily caused by structural lesions, they may also originate in Alzheimer's disease <unk>  may be the earliest language deficit in posterior cortical atrophy variant of Alzheimer's) or other neurodegenerative diseases. Although the main causes are not specifically known, many researchers have found factors contributing to<unk> . People with damage to the left hemisphere of the brain are more likely to have<unk> . Broca's area, the speech production center in the brain, was linked to being the source for speech execution problems, with the use of functional magnetic resonance imaging (fMRI), now commonly used to study<unk>  patients. Other experts believe that damage to Wernicke's area, which is the speech comprehension area of the brain, is connected to<unk>  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<unk> , current studies have shown that damage in the left parietal lobe is the cause of<unk> . One study was conducted using a word repetition test as well as fMRI 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<unk>  in the subjects. Therefore, the original<unk>  model, which theorized that damage occurred on the surface of the brain in the grey matter was debunked, and it was found that the damage was in the white matter deeper in the brain, on the left hemisphere. More specifically, the damage was in a part of the nerve tract called the arcuate fasciculus, for which the mechanism of action is unknown, though it is known to connect the posterior (back) of the brain to the anterior (front) and vice versa. While<unk>  is associated with lesions throughout the left hemisphere, severe and isolated<unk>  has been considered a sign of deep temporal lobe or lateral temporo-occipital damage. Damage to these areas is seen in patients showing infarction limited to regions supplied by the dominant posterior cerebral artery (PCA) and is referred to as posterior cerebral artery syndrome.
Anomic aphasia
Global aphasia
Receptive aphasia
Expressive aphasia
Jargon aphasia
Visuospatial dysgnosia
Integrative agnosia
Progressive nonfluent aphasia