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Body functions under brain control, thus any factor affecting the human brain, consequently influence the behavioural and physical states of the body. The new technology, the tremendous research, and the conceptual advances in the behavioural, biological, and medical sciences can certainly aid recognition of bidirectional and multilevel relationships between behaviour and health. Psychological, neurological, and anatomical diagnoses often involve different screening and testing procedures. For example, epileptic seizure has different symptoms including whole body movement, heart rate variation, and most importantly changes in the EEG dynamics and waveforms. On the other hand, an anatomical problem, often caused by a brain tumour, should be diagnosed through medical imaging followed by pathological tests.

Figure 2.2 Different brain sensory zones. (See color plate section for color representation of this figure)

Although the brain's action is unpredictable during wakefulness and is influenced 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 mood swings or mental abilities [28]. It is followed with lack of coordination and unsteady movement [29]. As the disease advances, uncoordinated, jerky body movements become more apparent [28]. The physical abilities gradually worsen until movement coordination becomes severe and the person is unable to walk [28, 29]. Mental abilities generally decline into dementia [30]. The specific symptoms vary somewhat between people [28]. The disease symptoms usually begin between 30 and 50 years of age but can start at any age [30, 31].

 Idiopathic intracranial hypertension: a neurological condition of unknown cause, with symptoms very similar to those of a brain tumour, defined by increased intracranial pressure around the brain without the presence of tumour or disease.

 Meningitis: an inflammation of the meninges (the protective membranes that cover the brain and spinal cord) caused by an infection. The inflammation can cause damage to the brain and spinal cord. Acute bacterial meningitis is rapidly developing inflammation of the tissue layers and of the fluid-filled space between the meninges (subarachnoid space) when it is caused by bacteria.

 Migraine: affects approximately 15% of the population. It is a primary headache disorder characterised by recurrent headaches mostly severe [32]. Typically, the headaches affect one side of the head, are pulsating in nature, and last for 2 to 72 hours [32]. The symptoms can be nausea, vomiting, and sensitivity to light, sound, or smell [33]. The pain is generally made worse by physical activity [34]. Up to one-third of people have an aura: typically a short period of visual disturbance which announces the onset of headache in advance [34]. Occasionally, an aura can occur with little or no headache after that [35]. Migraines are believed to be due to a mixture of environmental and genetic factors [36].

 Multiple sclerosis (MS): a disease affecting or damaging the myelin which is the covering layer of nerve cells in the brain or spinal cord [37]. This damage disrupts communication between cells in the nervous system resulting in many signs and symptoms, including physical, mental, and sometimes psychiatric problems [38–40]. Double-vision, blindness of one eye, muscle weakness, trouble with sensation, and trouble with coordination are the specific symptoms [37]. MS is a degenerative disease and gradually goes to complexity. Brain MS is more severe. Although the actual cause is not clear, the underlying mechanism is thought to be either destruction of the immune system or failure of the myelin-producing cells.

 Paralysis: the inability to move a part of the body temporarily or permanently. In almost all cases, paralysis is due to nerve damage, not to an injury to the affected region. Often an injury in the middle or lower regions of the spinal cord is likely to disrupt function below the injury, including the ability to move the feet or feel sensations, even though the actual structures are completely healthy. In this situation, the brain is unable to relay a signal to an area of the body due to injuries to the brain. However, in some cases the brain is able to sense touch and other sensations in the body, but is unable to effectively relay a response due to injuries in the spinal cord.

 Parkinson's: a degenerative brain disorder. The cause is generally unknown but believed to be genetic or due to environmental factors [41]. Physiologically, the dopamine generators of the brain fail in generating sufficient dopamine as the result of death of cells in the substantia nigra in the midbrain region [42]. Diagnosis of typical cases is mainly based on symptoms such as tremor, rigidity, slowness of movement, difficulty in walking, dementia, depression, and anxiety.

 Pick's disease: a rare form of dementia and similar to Alzheimer's, except that it often affects only certain brain zones. It has unknown causes and people with Pick's disease have abnormal substances (called Pick bodies and Pick cells) inside nerve cells in the damaged areas of the brain.

 Seizure and epileptic seizure;: a temporary loss of control often, but not always, accompanied by convulsions, unconsciousness, or both. Most common types are epileptic seizures, or seizures, are caused by sudden abnormal electrical discharges in the brain. An epileptic seizure, also known as an epileptic fit, seizure, or fit, manifests itself in the form of a brief episode of signs or symptoms due to abnormal excessive or synchronous neuronal activity in the brain [43]. The outward effect can vary from uncontrolled jerking movement (tonic–clonic seizure) to something as subtle as a momentary loss of awareness (absence seizure). Diseases of the brain characterised by an enduring predisposition to generate epileptic seizures are collectively called epilepsy [44]. On the other hand, for nonepileptic seizures the brain activity remains normal. Nonepileptic seizures have no identifiable physical cause, but they are believed to be physical reactions to psychological stress, change of emotions, in some cases due to tumour in the brain, or as symptoms of hypertension.

 Brain tumour: a growth of cells in the brain that multiplies in an abnormal, uncontrollable way. Brain tumours can be malignant, slow growing, or benign. The most common brain tumour is a glioma, which has different types including astrocytomas, glioblastomas, oligodendrogliomas, mixed gliomas, and ependymomas. Some grow slowly while others grow more quickly.

 Meningioma: a common brain tumour. It starts in the meninges, the tissue covering the brain and spinal cord, and is usually benign. A lymphoma is a cancer of the lymphatic system. It rarely starts in the brain. An acoustic neuroma is a benign tumour of the hearing nerve. Another benign brain tumour that starts in cells lining blood vessels is a haemangioblastomas.

 Tumours that start in the pituitary gland, which helps control hormones, are also benign. There are also tumours which start in the spinal cord and they are usually benign. Tumours of the pineal gland, such as germinomas and teratomas, are rare. They can be slow or fast growing. Medulloblastoma tumours are rare in adults but more common in children.

In the next chapters of this book we will see how single or multiple sensor systems can record and detect the clinically important features related to most of the above abnormalities.

Human development, often referred to as developmental psychology, explains the changes in human cognitive, emotional, and behavioural capabilities and functioning over the entire life.

On the other hand, the availability of monoclonal antibodies, routine production of genetically altered animals, and new understanding of the genetic code have contributed to the exploration of how genetics interacts with development and early experiences to influence both vulnerability to disease and resistance to age-related decline.

The combination of biology and society makes us what we are and what we do. The three main elements of biology contributing to human behaviour are: (i) self-preservation; (ii) the reason for self-preservation, reproduction; and (iii) a method to enhance self-preservation and reproduction [45].

As another important biological effect, biological rhythms are related to the changes in mood and consequently the human behaviour. These rhythms control much of the body's normal functions, including performance, sleep, and endocrine rhythms as well as behaviour. These functions are primarily regulated by the circadian clock, a cluster of nerves located in the hypothalamus in the brain. The circadian clock relies on environmental cues to regulate its function, primarily light cues from the day/night cycle. Any shift in these cues, such as by travel resulting in jet lag, can alter the sleep cycle and have a detrimental effect on normal circadian rhythms. In addition, season changes, which are accompanied by a decrease in the number of daylight hours, can negatively impact the function of the circadian clock, primarily the secretion of melatonin to induce sleep. If the alterations in biological rhythms are sufficiently strong, they may lead to mood disorders including mild depression and seasonal affective disorder [46].

There are two major categories of biological rhythms: endogenous and exogenous. Endogenous rhythms come from within the organism and are regulated by the organism itself, for example the body temperature cycle, brain rhythms, or heart rate. Exogenous rhythms are the result of external factors, such as a change in the seasons or transition from day to night. The environmental stimuli referred also to as zeitgebers, from the German for ‘time givers’, help to maintain these cycles. They include sunlight, noise, food, and even social interaction and help the biological clock maintain a 24-hour day.

There are many factors influencing biological rhythms. A cluster of approximately 10 000 nerve cells located on the suprachiasmatic nuclei (SCN) found on the hypothalamus in the brain. The circadian clock's primary function is to interpret external changes of light and darkness, as well as social contact, in order to establish diurnal rhythms. It is not uncommon for the circadian clock to be disrupted temporarily; events such as changes in work schedule from day to night, changing time zones, and to some extent old age can impact the consistency of circadian rhythms.

The circadian clock relies heavily on changes in light to determine day/night transitions. During the night, SCN emits melatonin hormone, which induces sleep. The process of wake to sleep itself has its own stages and each stage has its own duration [17].

Another major disruptive factor related to the circadian clock's interpretation of light is seasonal change. During the winter months, there are fewer daylight hours. As a result, the level of melatonin secretion increases along with the number of hours of darkness. The normal cycles may also be interrupted by changing one's daily habits, for example changing feeding time, following a gradual force-to-sleep or sleep depriving.

In addition to these major influences there are a variety of other environmental factors that may have an impact on biological rhythms. One of them is caffeine. A series of experiments on caffeine revealed differences in the effects of the drug depending on time of day. In the morning caffeine has been shown to hinder low impulsiveness, while the opposite is true in the evening [47]. This finding suggests that low impulsiveness and high impulsiveness differ in the phase of their diurnal rhythms, resulting in a difference in the effects of caffeine.

By establishing an understanding of various environmental factors that influence biological rhythms it is possible to draw connections between the significant time shifts and changes in nature and mood disorders.

Moreover, the influence of those factors may be quantified by developing a hybrid measurement system incorporating measures of brain activity, heart rate, and respiration as well as changes in the level of adrenalin in the blood over time.