The largest part of the brain, called the cerebrum, is divided into several areas called lobes. A portion of the parietal lobe, lying just above the temporal lobe, is called the supramarginal gyrus. Located near other brain regions involved in language and hearing, this plays a role in processing heard and spoken language, as well as written words. Alternate classifications of the brain based on cell structures consider this area to be a part of Brodmann area 40, and it is sometimes referred to by this name.
Studies have been conducted to determine the role of the supramarginal gyrus while reading. In one study, participants underwent two tests that required them to focus on either the phonological, sound-based similarities between two words, or the semantic, meaning-based similarities between them. The supramarginal gyrus was found to be activated in both activities. Researchers believe that even when a reading task does not require focusing on the sounds of words, this brain region automatically assists in processing them for phonological content.
A nearby brain region, the angular gyrus, works closely with the supramarginal gyrus to process linguistic information. Processing the meaning and semantics of words seems to be the domain of the angular gyrus, whereas the supramarginal gyrus acts to determine their sound. These two gyrii are connected to parts of the brain involved in emotional processing, such as the amygdala, and this connection may mediate the emotional response to language.
Damage to the supramarginal gyrus can create deficits in language, known as aphasias. Wernicke's aphasia is one disorder that can arise from damaging this area, and it is characterized by nonsensical, abundant speech. Alternately, lesions can lead to a condition called transcortical sensory aphasia, which cases problems with comprehending words, while still being able to generate language properly and clearly.
The supramarginal gyrus is known as an association center in the brain, since it receives input from many sensory systems. Some research indicates that this region may have important roles outside of language comprehension. One study found that magnetically stimulating this gyrus led to subjects believing that they perceived a visual stimulus for longer than they actually did. These results suggest that this area may play a role in the perception of time.
Another study magnetically stimulated this gyrus and other brain regions while subjects performed a movement task that required planning. Stimulation resulted in significantly longer times for planning what hand movements to use to accomplish the task. Researchers believe there may be a connection between this region and object manipulation involving specific outcomes.