Brain areas decoded
17 August 2021
Many brain areas may be affected by dementia - this blog post takes a look at the most common of these.
The human brain is split into two sides, called hemispheres. Each hemisphere controls the opposite side of the body and contains four regions called lobes, which house certain brain areas. This means we have two copies of each brain area – one on the right, and one on the left.
The frontal lobes are right at the front of the brain and are the largest of the four lobes. The frontal lobes are responsible for complex functions like:
- social behaviour
- working memory
- organisation and planning
The frontal lobes are the area first damaged in the behavioural variant of frontotemporal dementia (bvFTD). People with bvFTD experience changes in their behaviour and personality including apathy, inappropriate social conduct, and impulsive behaviour. Read more about frontotemporal dementia in this blog post.
Also affected by FTD are the temporal lobes, located in the lower side part of the brain near the ears. Their main roles are memory (both conscious and long-term memory), emotion, and processing sounds. These functions make the temporal lobes vital for language as well as remembering and recognising things.
Damage to the temporal lobes causes the language variant of FTD – known as primary progressive aphasia (PPA). People with PPA have problems with their language and speech. Read more about PPA in this blog post.
Another brain area located within the temporal lobes is the hippocampus, a small, curved structure crucial for memory. Its role is to form new memories, convert them into long-term memories, and retrieve old memories.
This is the first brain area affected by Alzheimer’s disease, which is why memory loss – particularly forming new memories – is one of the first symptoms people with Alzheimer’s experience.
Just in front of the hippocampus lies the amygdala, the part of the brain that is responsible for processing emotions. The amygdala is damaged early on in Alzheimer’s disease, meaning people with the condition may experience neuropsychiatric symptoms like anxiety, agitation, and hallucinations.
At the back of the brain sits the occipital lobe, the visual processing centre that receives signals from the eyes. It interprets features of vision like colour and movement and is vital for reading and understanding language.
Posterior cortical atrophy (PCA) is a type of early-onset dementia characterised by damage to the occipital lobe. People with PCA have problems with their vision without any damage to their eyes. Learn more about PCA in this blog post by Dementia Science.
The final lobe in the brain is the parietal lobe, located in the middle of the brain between the other three lobes. It is crucial for sensory perception and integration, meaning it receives information from our sensory organs and processes it.
The parietal lobe is also important for understanding written language, solving mathematical problems, and comprehending spatial information like judging distances. The parietal lobe is also damaged in PCA.
The substantia nigra is a small structure involved in reward and movement that is located in the lower middle part of the brain. Lewy bodies – clumps of a protein called alpha-synuclein – often form in the substantia nigra which contributes to the onset of Parkinson’s disease and Parkinson’s dementia.
Because the substantia nigra is critical for movement, people with these conditions experience problems with their movement, such as tremors, shuffling, shaking, and trouble initiating movement. Read more about how Parkinson’s disease overlaps with dementia in this blog post.
Lewy bodies can also form in the cerebral cortex, the outer layer of the brain. It is comprised of grey matter, which is mainly only the cell bodies of neurons (see diagram below), rather than their axons. By contrast, white matter is mainly made of long lines of insulated axons – the cells that insulate the axons are white in colour, giving rise to the colour difference between the two types of brain matter.
The four lobes – frontal, temporal, occipital and parietal – make up the cerebral cortex. So, when Lewy bodies settle here in Lewy body dementias, they can disrupt a wide range of functions. Read more about Lewy body dementias in this blog post.
There are many more parts of the brain, all of which can be affected by dementia, especially in the later stages of the disease. There are many resources that explore other parts of the brain, including this video on YouTube.