Aphasia is a condition caused by brain damage that affects a person’s ability to use language and communicate effectively. In aphasia, damage to parts of the brain that are responsible for speaking, writing, reading and understanding speech may cause a person to have difficulty making sense of conversations, understanding instructions, or following what people are saying, for example.
The brain’s language centre
There is no single brain area that is responsible for language. The language centre is made up of specific areas of the brain that work in unison to allow fluency and comprehension of written and spoken language. These areas include:
- Broca’s area, involved in speech
- Wernicke's area, involved in understanding the spoken and written word
- The sensory cortex, which helps process the sounds we hear and images we see when listening and reading
- The auditory cortex helps specifically with the conversion of spoken language into meaningful information
- The motor complex controls the voluntary muscles of the mouth and tongue in creating speech
Aphasia results from damage to any of these areas, but the resulting language deficit is not necessarily specific to the brain area involved. Damage to Broca’s area, for example, will not necessarily lead to difficulty in stringing a sentence together, for example.
Damage to a certain area has unpredictable effects that vary considerably between individuals. Damage to more than one language area in the brain often causes more severe forms of aphasia such as global aphasia.
Some of the causes of aphasia include:
- Stroke – In stroke, the brain is deprived of oxygen and vital nutrients, which causes brain tissue to die off. If the language centres are affected, a stroke may lead to aphasia. This is the most common cause of aphasia and almost all victims of stroke suffer from some degree of aphasia.
- Severe head injury, such as injury resulting from a road traffic accident or serious fall
- A brain tumor
- Brain infections such as meningitis or encephalitis
- Progressive neurogenerative diseases such as Alzheimer’s disease, progressive supranuclear palsy and corticobasal degeneration. Parkinson’s disease does not usually cause aphasia.
Reviewed by Sally Robertson, BSc