Aphasia is caused by damage to the parts of the brain that are responsible for:
- speaking
- understanding others
- reading and writing
Collectively, these parts of the brain are known as the brain’s language centre.
The language centre
The language centre is not a single area of the brain. It is a network of specific sections of the brain that work together in a similar way to a computer network.
The language centre is made up of the following areas:
- Broca’s area, which is responsible for the production of speech
- Wernicke's area, which is responsible for understanding spoken and written language
- the sensory cortex, which is responsible for processing the various signals that the body receives, such as sounds (for language) and images (for reading)
- the auditory cortex, which is responsible for converting the actual physical sounds of spoken language into meaningful information
- the motor cortex, which is responsible for controlling the various parts of the body that are used to generate speech, such as the muscles, tongue and voice box
In the past it was thought that damage to a specific part of the brain would always result in a specific type of aphasia, for example, damage to the Broca’s area would always result in Broca’s aphasia. However, the way the language centre works is now thought to be less straightforward than this.
Damage to specific areas of the language centre does not always lead to the expected symptoms. Also, the after effects of brain damage can vary considerably from person to person, making them unpredictable.
Damage to many sections of the brain will usually result in more severe types of aphasia, such as global aphasia.
Brain damage
Ways that the brain can become damaged include the following.
- stroke: during a stroke the brain is deprived of blood and oxygen, which leads to the death of brain tissue
- severe head injury: for example, the sort of injury that occurs as a result of a road traffic accident or following a serious fall from height
- brain tumour: where an abnormal growth of cells develops inside the brain
- health conditions that cause progressive damage to the brain, such as Alzheimer’s disease, other forms of dementia or rarer conditions, such as progressive supranuclear palsy or corticobasal degeneration (two related conditions that are associated with both physical and mental disabilities as a result of brain damage)
- infections that affect the brain, such as meningitis (an infection of the outer layer of the brain) and encephalitis (an infection of the brain itself), although this is a much rarer cause of aphasia
