by internal, such as emotions, and external, such as event and movement-related stimuli, during sleep the brain follows a number of well-defined states, generating predictable continuous or intermittent rhythms.
The abnormality in the brain may originate from different brain zones (Figure 2.2). Hence, the assessment of the human brain through various screening and imaging modalities during different behavioural states promotes our understanding of the links between human behaviour and basic neurological and neurochemical processes or specific neuroanatomic pathways.
The number of diseases and disorders in the brain is probably more than that of any other organ in the body. Most brain abnormalities manifest themselves in well-defined patterns in multichannel EEG recordings. However, not all these abnormalities have been studied through EEG analysis. The most important and popular brain abnormalities and diseases are listed alphabetically:
Amnesia (amnestic syndrome): the loss of memories, such as facts, information, and experiences. Though it generally doesn't cause a loss of self-identity and those with amnesia are usually lucid and know who they are, they may have trouble learning new information and forming new memories. Amnesia can be caused by damage to areas of the brain that are vital for memory processing. Unlike a temporary episode of memory loss, amnesia can be permanent. There's no specific treatment for amnesia,
Amyotrophic lateral sclerosis (ALS): a motor neuron disease and a rare group of neurological diseases that mainly involve the nerve cells (neurons) responsible for controlling voluntary muscle movement such as for chewing, walking, breathing, and talking. The disease is progressive and therefore the symptoms become worse over time. Currently, there is no cure for ALS and no effective treatment to halt or reverse its progression. ALS belongs to a wider group of disorders known as motor neuron diseases caused by the gradual deterioration (degeneration) and death of motor neurons. Motor neurons are nerve cells that extend from the brain to the spinal cord and to muscles throughout the body. These motor neurons initiate and provide vital communication links between the brain and the voluntary muscles. Early symptoms of ALS usually include muscle weakness or stiffness. All muscles under voluntary control are gradually affected, and individuals lose their strength and the ability to speak, eat, move, and even breathe and mostly die from respiratory failure, usually within three to five years from when the symptoms first appear.
Ataxia: neurological symptoms (rather than disorders) related to the movement and control of posture and balance, resulting in poor coordination. Ataxia can be due to many different causes. Cerebellar ataxia means unsteadiness due to pathology in the cerebellum, which is a leaf-like structure in the back part of the brain.
Attention deficit hyperactivity disorder (ADHD): a brain disorder diagnosed by an ongoing pattern of severe inattention or hyperactivity impulsivity which affects the functioning or development of humans often from childhood and the impulsivity in action and behaviour continues into old age.
Autism or autism spectrum disorder (ASD): a neurodevelopmental disorder characterised by deficits in communication, social interaction, and the presence of restricted, repetitive behaviours. Social communication deficits include impairments in aspects of joint attention and social reciprocity, as well as difficulties in the use of verbal and nonverbal communicative behaviours for social interaction.
Bipolar disorder (used to be called manic depression): a mental abnormality that causes extreme mood swings including emotional highs (mania or hypomania) and lows (depression). When depressed, the subject may feel sad or hopeless and lose interest or pleasure in most activities. When the mood shifts to mania or hypomania (less extreme than mania) the patient may feel euphoric, full of energy, or unusually irritable. These mood swings can affect sleep, energy, activity, judgement, behaviour, and the ability to concentrate.
Cancer: there are mainly two types of brain cancers called primary and secondary brain cancers. The former appears as benign or metastatic tumours such as glioblastoma and the latter is due to spreading cancers originated in other parts of the body into the brain. Headache, feeling sick, and seizure are the typical symptoms of brain cancer. Some examples of brain tumours are explained in the related part of this section.
Central nervous system disease: a broad category of conditions in which the brain and the nerves in the spinal cord do not function normally, limiting health and the ability to function. This can be due to an inherited metabolic disorder, the result of damage from an infection, a degenerative condition, stroke, a brain tumour, or arise from unknown or multiple factors. Movement disorders such as Parkinson's disease, dystonia, and essential tremor are central nervous system conditions. What they have in common is the loss of sufficiently intact nervous system circuits that govern functions as varied as memory formation (in Alzheimer's) or voluntary motion (in movement disorders).
Cerebral palsy: a condition that affects muscle control and movement. It is usually caused by an injury or infection to the brain before, during, or after birth. It may also be due to lack or shortage of oxygen in the fetus brain, genetic problem, or other abnormal brain development. Children diagnosed with cerebral palsy often have difficulties in controlling muscles and movements as they grow and develop.
Cerebrovascular disease: the result of disease in the arteries and blood vessels in the brain which can cause blockage of food and oxygen supply to parts of the brain, leading to stroke.
Creutzfeldt–Jakob disease (CJD) (mad cow disease): a fatal neurodegenerative disease often with a lifetime of less than one year. Early symptoms include dementia, change of personality, and hallucinations [24]. The symptoms of CJD are caused by the progressive death of the brain's nerve cells, which is associated with the build-up of abnormal prion protein molecules forming amyloids [25].
Dementia (Alzheimer's, mild cognitive impairment): a worldwide problem which affects women more than men, and is the result of a number of brain diseases and abnormalities which lead to deterioration of memory, consciousness, and consequently physical disability and early death of the brain. It may also cause behavioural change, confusion and disorientation, delusion and hallucination, communication problems, problems in judging speed and distances, and even craving for particular foods. Alzheimer's is the most common dementia type but there are other dementias, including vascular dementia, dementia with Lewy bodies, and frontotemporal dementia. Research has shown that dementia causes loss of communication between brain cells and brain zones [17, 26].
Depression: a common mental disorder that causes people to experience depressed mood, loss of interest or pleasure, feelings of guilt or low self-worth, disturbed sleep or appetite, low energy, and poor concentration. It is different from feeling down or sad and affects people of every age. A person experiencing depression often has intense emotions of anxiety, hopelessness, negativity, and helplessness, and the feelings stay with them for a long time [24].
Encephalomyelitis: inflammation of the brain or spinal cord which can be the result of various diseases such as viral disease, mosquito bite, AIDS, or syndromes.
Encephalopathy: various brain disorders, and also reflects structural and anatomical defects in the brain.
Hydrocephalus: a condition in which there is an abnormal accumulation of cerebrospinal fluid in the brain [27]. This typically causes increased pressure inside the skull. Hydrocephalus can be due to birth defect or because of an injury in older age. In babies there may be a rapid increase in head size. Other symptoms may include vomiting, sleepiness, seizures, and downward pointing of the eyes. Older people may have headaches, double vision, poor balance, urinary incontinence, personality changes, or mental impairment.
Huntington's disease (after George Huntington 1872 – also known as Huntington's chorea): an inherited brain disorder which causes death of brain cells [28]. It starts with occasional
