Cerebrum

DESCRIPTION

The cerebrum forms what most people think of as the "brain." It lies on top of the brainstem and is the largest area of the brain. It is divided into two halves — the right hemisphere, which controls the left side of the body, and the left hemisphere, which controls the right side of the body.

FUNCTION

The cerebrum's main functions include consciousness, thought, reason, memory, vision, hearing, touch, motor control, coordination, and emotions. The specific functional areas of the cerebrum are divided into four lobes: the frontal, parietal, temporal and occipital lobes.

RESULT OF INJURY

The effect of injury to the cerebrum depends on the specific part of the brain that is injured. In general, injury to the left half of the brain can cause problems on the right side of the body, and damage to the right side of the brain can cause problems on the left side of the body. The results of damage to specific areas of the brain are discussed in the sections for the individual lobes.

Parietal lobe

DESCRIPTION

The parietal lobes are positioned above the temporal lobes and between the frontal and occipital lobes. They contain the part of the brain primarily responsible for the sense of touch. They also play a very important role in integrating sensory information, particularly determining spatial sense and navigation.

FUNCTION

The parietal lobes contain the area of the brain primarily responsible for the sense of touch. This area is known as the somatosensory cortex. A large portion of the parietal lobe acts as an interchange for information for most of the other senses. These interconnections contribute a great deal to the ability to interpret people, places, and things around us. In essence, the parietal lobes "pull it all together."

RESULT OF INJURY

Damage to the parietal lobes can result in conditions known as agnosia and apraxia. Agnosia is the inability to recognise an object, using a specific sense, even though that sense is basically intact. For example, someone might not be able to recognise an orange by sight, although they could identify the orange by touch or smell.

Apraxia is the inability to perform a specific movement, although all of the muscles are intact and able to perform that task under different circumstances. For example, someone may be unable to touch their nose on command, but would be perfectly able to do so if their nose itched.

Damage to the parietal lobe can also cause word blindness, known as alexia, with writing impairments, called agraphia. Damage to the right parietal lobe can impair skills such as dressing and washing, and can also cause difficulty in making things, denial of deficits and loss of drawing ability. Damage can also cause a person to neglect the opposite side of their body, even to the point of not recognising their own limbs.

Frontal lobe

DESCRIPTION

The frontal lobes are located at the front of the cerebrum. They are the part of the brain that regulates and mediates the higher intellectual functions, known as executive functions. They play an important role in the control of social behaviours.

FUNCTION

The frontal lobes contribute to the regulation of emotions, cognition, error detection, volition, a sense of self, and more. The executive functions of the frontal lobes involve the ability to recognise future consequences resulting from current actions, to choose between good and bad actions, override and suppress unacceptable social responses, and determine similarities and differences between things or events. The frontal lobes also play an important part in retaining longer-term memories, which are often derived from input from the limbic system, or emotional brain. The frontal lobe modifies those emotions to generally fit socially acceptable norms. The frontal lobes also contain the primary motor cortex.

RESULT OF INJURY

Damage to the frontal lobes can lead to a wide variety of symptoms, including the loss of inhibitions and impaired mental flexibility. It may be difficult to prioritise tasks, and motivation may diminish. Talking may increase or decrease dramatically. Perceptions about taking risks and following rules can be impaired and socialisation can diminish or increase. Damage to some areas of the frontal lobe can affect sexual interest and habits.

Broca's area

DESCRIPTION

Named after 19th-century physician Paul Broca, Broca's area is a section of the brain located in the frontal lobe of the cortex. It is important in the production of written and spoken language.

FUNCTION

Broca's area is involved in both written and spoken language processing. It is critical in the complicated task of understandably combining words and grammar. Patients with this condition often do not have a problem with understanding language, but have difficulty finding the words or grammar necessary to communicate fluently.

RESULT OF INJURY

Injury to this area can cause a condition called Broca's aphasia, also referred to as expressive aphasia, motor aphasia, or non-fluent aphasia. People with this condition are not able to create complex sentences, and have difficulty finding the correct word. Patients struggle to form sentences. Their speech is often described as telegraphic, with short sentences containing only key words. Patients are usually aware that they cannot speak properly.

Example of speech affected by Broca's aphasia:
"Ah … Friday … ah, Mum and Steve and Mum … hospital. Two … ah, doctors … and ah … thirty minutes … and yes … ah … hospital. And, er, Wednesday … nine o'clock. And er Thursday, ten o'clock … doctors. Two doctors … and ah … teeth. Yeah, … fine."

Wernicke's area

DESCRIPTION

Wernicke's area is located in the left temporal lobe. It plays a role in the understanding of language, and is named after Carl Wernicke, a German neurologist and psychiatrist. In 1874, Wernicke discovered that damage to this area could cause a type of speech disorder that is now called Wernicke's aphasia.

FUNCTION

Wernicke's area plays an important role in the processing and comprehension of language. Proper function of Wernicke's area is required for patients to form coherent sentences and to understand the speech of others.

RESULT OF INJURY

Damage to Wernicke's area can cause a condition called Wernicke's aphasia or receptive aphasia. This condition affects a person's ability to understand language when listening, the ability to read, and the ability to speak with meaning. Speech often sounds like babble, fluent and grammatical, though totally nonsensical. Wernicke's aphasics have severe difficulties with comprehension but are often unaware of it. They may become annoyed or frustrated when others can't seem to understand them.

Example of speech affected by Wernicke's aphasia:
"I can't tell you what that is, but I know what it is, but I don't know where it is. But I don't know what's under. I know it's you couldn't say it's … I couldn't say what it is. I couldn't say what that is. This shu … that should be right in here. That's very bad in there. Anyway, this one here, and that, and that's it. This is the getting in here and that's the getting around here, and that, and that's it. This is getting in here and that's the getting around here, this one and one with this one. And this one, and that's it, isn't it? I don't know what else you'd want."

Temporal lobe

DESCRIPTION

The temporal lobes are the part of the cerebrum that are involved in speech, memory, and hearing. They are located on both sides of the brain, below the parietal lobes and in front of the occipital lobes.

FUNCTION

The temporal lobe is involved in hearing and understanding what is heard, and is home to the primary auditory cortex. It is also responsible for the formation and retrieval of long-term memories. The temporal lobe also plays a role in vision, sexual behaviour, and personality.

RESULT OF INJURY

Individuals with temporal lobe damage have difficulty placing words or pictures into categories. Language skills can also be impaired by temporal lobe damage. The impairment or loss of long-term memory can result from injury to the temporal lobes. Specifically, damage to the right side of the temporal lobes can result in the inability to recall non-verbal material, such as music and drawings. It can also cause a loss of inhibition when talking. Left temporal lobe damage can impair the ability to recognise words and can result in impaired memory for verbal material.

Occipital lobe

DESCRIPTION

The occipital lobes are located in the back of the brain and are the smallest of the four lobes. They are the visual center, and are the primary portion of the brain responsible for receiving input from the eyes.

FUNCTION

The occipital lobes receive and process all input from the eyes. Area A is the primary visual cortex and the recipient of visual input from the eyes. Area A performs the initial processing of the information, for example combining input from the two eyes, and beginning to analyse depth. This information is then passed on to Areas B and C. Areas B and C are the associative visual cortex, where motion, color, and other parameters are interpreted to provide meaning.

RESULT OF INJURY

Damage to the right occipital lobe can result in loss of the left visual field of both eyes, and damage to the left occipital lobe results in loss of the right visual field of both eyes. Damage to both the left and right occipital lobes can result in blindness, even though the eyes themselves may be functioning normally. This condition is called cortical blindness. If the front part of the occipital lobe is damaged, people have difficulty recognising familiar objects and faces and accurately interpreting what they see.

Olfactory system

DESCRIPTION

The olfactory system includes the olfactory epithelium, located inside the nose, the olfactory bulb, which is located just above the olfactory epithelium, and the olfactory cortex, which is on the surface of the temporal lobe. The olfactory system is responsible for the sensing, processing, and identifying of smells.

FUNCTION

The olfactory system is responsible for the sense of smell. In addition, it combines with taste information in the brain to create the sensation of flavour. Many people with a lost sense of smell retain the ability to detect salty, sweet and bitter tastes, but complain that food tastes bland. The sense of smell is strongly associated with memory. As a result, smells are often powerful triggers for specific memories, both good and bad. Because the sense of smell is also closely associated with the limbic system, or emotional brain, smell is known to provoke strong emotional responses.

RESULT OF INJURY

Damage to the olfactory system can cause an impairment or loss of the sense of smell and the sense of taste. Much of what we attribute to our sense of taste actually depends on the aromas of what we eat and drink.

Cerebellum

DESCRIPTION

The word cerebellum means "little brain." The cerebellum is located at the base of the brain and is involved with the coordination of movement. It makes up approximately 10 percent of the brain's volume and contains at least half of the brain's neurons. It is divided into two hemispheres that are covered by a thin layer of grey matter known as the cortex.

FUNCTION

The cerebellum receives input from other areas of the brain and spinal cord, along with information about the position and movement of the body's limbs and joints. It uses all of this information to control equilibrium, and to provide precise coordination of movements.

RESULT OF INJURY

A patient may experience problems with one or more of the following:

• Gait, where the manner of standing or walking is not normal.
• Ataxia, which is unsteadiness or lack of coordination of the limbs, posture, and gait.
• Hypotonia, which is decreased muscle tone.
• Tremor, where parts of the body can tremble uncontrollably, especially with any purposeful movement such as trying to pick up or point at an object.
• Abnormal eye movement, such as impaired tracking, fixation, and an involuntary, constant, twitching of the eye called nystagmus.