Understanding parts of the brain

Learn about the parts of the brain and  how dementia damages them, as well as about the symptoms the damage causes.

Dementia and the brain
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Dementia is caused when the brain is damaged by diseases, such as Alzheimer’s disease or a series of strokes. Alzheimer’s disease is the most common cause of dementia, but not the only one.

A person with dementia will experience symptoms depending on the parts of the brain that are damaged, and the disease that is causing the dementia.

The cerebral cortex

The cerebral cortex is a thin layer of cells covering the outside surface of the brain. It is responsible for:

  • memory
  • reasoning
  • decision-making
  • language
  • social skills.

It controls actions such as moving around or talking, as well as processing sight, hearing, taste, smell, touch and pain.

The lobes of the brain

The cerebral cortex can be divided into four ‘lobes’ (regions). These are the:

  • temporal lobes
  • frontal lobes
  • parietal lobes
  • occipital lobes.
Illustration of the four lobes of the cerebral cortex. The brain is divided into four parts. The lobe to the front is the frontal lobe. Towards the top of the brain and behind the frontal lobe is the Parietal lobe. At the back of the brain is the occipital lobe, and in front of this and underneath the other two lobes sits the temporal lobe.

Illustration of the four lobes of the cerebral cortex

More details about the lobes of the brain

Temporal lobes

The temporal lobes are on either side of the brain, nearest to the ears. Their main roles involve memory processing, hearing and language.

Both temporal lobes store general knowledge. General knowledge (known as semantic memory) is different from the types of memory that relate to day-to-day experiences. The left temporal lobe helps to understand language, and usually stores facts and the meanings of words. The right temporal lobe deals with visual information, such as recognising familiar objects and faces.

Within each temporal lobe is a region called the hippocampus, which processes memories to allow them to be stored and found when needed. Damage to the hippocampus makes it difficult to learn new things. The hippocampus also sends important information to be stored in other parts of the cerebral cortex. It is important for memory of events and experiences (episodic memory).

The temporal lobes also help to understand what is being heard. Damage to the temporal lobes, particularly to an area called the auditory cortex, can make it more difficult for the hippocampus to form memories of what has just been heard.

Alzheimer’s disease often starts in and around the hippocampus, before it spreads to other parts of the brain. This is why one of the first symptoms many people notice is memory loss.

Frontal lobes

The frontal lobes are at the front of the brain, behind the forehead. This part of the brain eventually becomes damaged in most types of dementia. They are where information is stored and processed, which allows a person to make rational decisions and judgements.

Frontotemporal dementia (FTD) is most closely linked to damage in the frontal lobes. Early symptoms of FTD can be changes in personality or behaviour. People may also experience difficulty with planning, organising and making decisions.

In other types of dementia, such as Alzheimer’s disease, dementia with Lewy bodies and vascular dementia, the frontal lobes tend to be damaged later on.

Damage to the frontal lobes can make it hard to pay attention for very long, switch between tasks or do more than one thing at a time.

A person with damaged frontal lobes may become easily distracted or easily lose focus, particularly if they are given too much information all at once.

The frontal lobes also control interest and motivation. As a result, damage to these parts of the brain may cause a person to become:

  • apathetic (lacking interest in things, or motivation to do things)
  • lethargic (lacking energy)
  • much less interested in doing things they have enjoyed in the past.

The frontal lobes also control how a person acts in social situations. They may stop a person from saying inappropriate things. Damage to this part of the brain means people with dementia may say things that are hurtful or rude without meaning to. This can be difficult for people supporting them.

Within the frontal lobes is the motor cortex. This deals with planning and movement by controlling muscles. Damage to the motor cortex happens very late in most types of dementia. Some people experience problems with movement in the early stages of dementia. This is normally caused by damage deeper in the brain and not the motor cortex.

Parietal lobes

The parietal lobes are located in the upper part of the back of the brain. In most people, the right-hand side helps them to understand the position of their bodies and objects in space. For example, it helps them bring a fork to their mouth when eating. The left parietal lobe allows a person to tell left from right, as well as to read, write and process numbers.

Damage to the parietal lobes is common in Alzheimer’s disease. It can lead to problems with performing gestures and skilled movements (apraxia) when the person is trying to do things like tie shoelaces or put on clothes. It can also make doing tasks that involve reading or writing much more difficult.

Occipital lobes

The occipital lobes are located at the back of the brain and mostly deal with visual information. This region processes visual information and makes sense of it, including recognising colours and shapes. The resulting information can then be passed on to other areas of the brain.

Damage to the occipital lobes eventually occurs in most types of dementia, although not generally during the early stages. However, in posterior cortical atrophy (PCA), visual problems can be among the first symptoms.

When the occipital lobes become damaged, a person may experience difficulty working out what they see in front of them. Severe difficulties with visual perception can also contribute to visual hallucinations.

As well as making visual information more difficult to understand, damage to the visual cortex can contribute to deteriorating eyesight.

The hemispheres of the brain

The brain is divided into two hemispheres (halves), the left and right side. Each lobe has a left and right side. Each lobe does different things, but they work closely together.

Illustration of the two hemispheres of the brain. A birds eye view of the top of the brain. The brain is divided down the centre into a left half and a right half

Illustration of the two hemispheres of the brain

The sub-cortex

The sub-cortex is any part of the brain below the cerebral cortex. This region allows fast communication between the different parts of the brain.

It also contains some areas that are important for movement, thinking and emotion such as:

  • the basal ganglia
  • the limbic system
  • the cerebellum
  • the brainstem.
The sub-cortex of the brain made up of the basal ganglia, limbic system, cerebellum and brain stem

Illustration of the cerebral cortex and sub-cortex

More details about areas of the brain

Basal ganglia

The basal ganglia are a group of small structures located deep within the sub-cortex. They are mostly involved in the control of movement.

Damage to this part of the brain is common in types of dementia that are also movement disorders, such as Parkinson’s disease dementia, dementia with Lewy bodies and Huntingdon’s disease dementia.

In dementia with Lewy bodies and Parkinson’s disease movement can become very difficult, resulting in very slow movements or a person not being able to move at all sometimes. It can also cause involuntary movements, such as a tremor in the hands.

Limbic system

The limbic system is a collection of regions in the brain that are involved in processing emotions. It includes the amygdala, hippocampus, hypothalamus and thalamus.

Damage to the limbic system is common in most forms of dementia. It may change the way a person feels or would normally react to things. A person may feel more excited, anxious, sad or apathetic than before they developed dementia.

It can also lead them to have delusions (strongly believing things that aren’t true) – for example believing that a stranger is in the house, or that someone is stealing things from them.

The hypothalamus controls levels of:

  • hunger
  • thirst
  • body temperature
  • many of the hormones that control the body’s metabolism.

Damage to the hypothalamus may lead to changes in a person’s appetite and eating behaviour, particularly in frontotemporal dementia. These changes can include craving sweet foods, overeating, or becoming obsessed with particular foods. In some cases people may try to eat inedible objects.

Just above the hypothalamus is the thalamus, which works as an important ‘information hub’. It sends useful information to the cerebral cortex. It is heavily involved in consciousness, perception, attention, memory and movement. The thalamus is affected to some extent in most types of dementia.

Cerebellum

The cerebellum co-ordinates movements, balance and posture, and helps the eyes to work together. New evidence has shown significant tissue loss in the cerebellum in people with Alzheimer’s disease and frontotemporal dementia. However, few people with these conditions seem to experience symptoms from this damage.

Brainstem

The brainstem is at the bottom of the brain where it meets the spinal cord. It deals with survival functions, such as controlling:

  • heart beat
  • breathing rate
  • blood pressure
  • sleep cycle
  • swallowing
  • states of consciousness (being awake, asleep and dreaming, or unconscious).

Several types of dementia affect the brainstem. However, people with dementia with Lewy bodies are particularly affected during the early stages. They may experience severe sleep problems for several years before being diagnosed (for example acting out their dreams while asleep), as well as fluctuating levels of consciousness, slowness of movement and visual hallucinations. They can also have problems regulating their blood pressure – causing dizziness and fainting, which can lead to falls.

A region of the brainstem is responsible for making an important chemical called dopamine. Dopamine is essential for many different functions in the brain, including movement and feelings of pleasure and reward.

People with Parkinson’s disease, Parkinson’s disease dementia and dementia with Lewy bodies often have low levels of dopamine, which can make movement difficult. It can also affect their mood, causing depression or apathy.

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