Neurological Conditions

Neurological Conditions

ALZHEIMER’S DISEASE

Alzheimer’s Disease is the most common form of dementia, and involves progressive deterioration in memory, cognitive function and language abilities. Increasing aggression, irritability and mood swings appear, and can be incredibly distressing for those caring for them.

The deterioration is caused by accumulation of plagues and tangles of abnormal protein in the brain, which starts in the hippocampus (an area specialised for memory) and spreads out across the rest of the brain.

A variant known as Posterior Cortical Atrophy causes degeneration at the back of the brain, in the visual cortex, resulting in progressive disruption of visual processing. Sufferers, however, tend to have well preserved memory and language.

Alzheimer’s Society

BALINT’S SYNDROME

This is a rare and little understood group of neuropsychological impairments: difficulty fixating the eyes (ocular apraxia), inability to more the hand to a specific object when guided by vision (optic ataxia), and the inability to perceive the visual field as an integrated whole (simultanagnosia).

This last problem is the most curious of all the impairments suffered by people with Balint’s syndrome: the world is perceived as a series of single objects rather than seeing a whole scene. When they focus their attention on one object, all the others disappear. If a new object appears, or an existing object starts moving, it grabs the person’s attention, and the first object disappears as they change focus.

Balint’s Syndrome is very rare as it only occurs with symmetrical infarction (through a stroke or a dramatic drop in blood pressure) in both hemispheres of the brain. The damage must occur in the occipito-parietal junction in both the left and right hemispheres simultaneously. The most frequent cause of Balint’s syndrome is a sudden and severe drop in blood pressure due, for example, to shock.

Balint’s Syndrome Wiki

CHARLES BONNET SYNDROME (CBS)

CBS involves recurrent and complex visual hallucinations unrelated to neurological damage or disease. It is a strange consequence of severe progressive visual loss, in particular of macular degeneration. People with CBS hallucinate complicated figures such as animals, faces or cartoons.

The defining feature of CBS is the fact that sufferers are fully aware that the image is not real, and in all other areas, are neurologically and psychiatrically healthy.The hallucinations are the result of under-stimulation of the visual cortex: the brain creates images to fill the blind area in which it was accustomed to perceiving the visual scene.

Charles Bonnet Syndrome Wiki

EPILEPSY

Epileptic seizures result from abnormal, excessive or hypersynchronous activity in the brain. Their nature varies according to the origin of the activity and its subsequent spread.

Some seizures (‘Generalized tonic-clonic’) have no origin and are thought to be due to diffuse neuronal activity across the brain. Others (‘Partial seizures’) can be clearly localised, but do not spread. These focal seizures have localisable effects: activity in the motor cortex will affect a limb, or spread progressively from area to area of the body (Jacksonian March).

Seizures that have an origin, and then spread are termed ‘Secondarily generalised,’ and often start with a focal sign and end in a full seizure with loss of consciousness. For example, when the origin is in the visual cortex, the person will often have visual hallucinations of zigzag lines or expanding shapes. Following this, a generalised often ‘tonic-clonic’ seizure will occur. During this, the muscles initially stiffen (tonic phase), and then convulse (clonic phase).

While other types of loss of consciousness can look alarmingly like a seizure, true epileptic fits have a number of defining features. There is often a warning sign before the seizure, such as a strange feeling or a sense of deja vu. The recovery phase is also prolonged: the person will feel drowsy and won’t be able to remember the period of about 5 to 10 minutes after the seizure had ended.

Epilepsy Action

FRONTO-TEMPORAL DEMENTIA

Fronto-temporal dementia (FTD), also known as Pick’s Disease, is a degenerative condition similar to Alzheimer’s disease.

For an as yet unknown reason, cells in the brain make an abnormal form of a protein, which accumulates, damaging the neurons. Many different abnormal genes have been found that can cause Pick’s disease. Many cases of FTD are passed down through families.

Although the disease is rare, and commonly occurs in those over 40, it has been known to occur in people as young as 20.

Tissues in the temporal and frontal lobes of the brain start to shrink over time. These areas are responsible for higher cognitive functions (such as logical thought and reasoning) and language. As such the progressive symptoms reflect these functions. The main changes include behaviour changes, speech difficulty, and impaired thinking.

The main differentiating feature from Alzheimer’s is the early onset of personality disturbance. People with FTD tend to behave the wrong way in different social settings, exhibiting compulsive, repetitive or uninhibited behaviours in public. They can have abrupt changes in mood, and begin to lack emotional warmth and empathy. Some patients will have more prominent difficulty with decision-making, or language (trouble finding or understanding words or writing). Patients suffering from these symptoms are usually unaware of the changes to their behaviour.

Alzheimer’s Society Page on FTD

HEMI-SPATIAL NEGLECT

A neuropsychological condition in which, after damage to the parietal cortex of one hemisphere of the brain, typically the right, there is a loss of awareness of all stimuli to the left of the person. The person is unable to process and perceive stimuli to the left despite intact visual perceptual function.

The reason left neglect occurs rather than right neglect has its basis in the distribution of attention functions across the two hemispheres. Either cortex controls function for the opposite visual field. While the right parietal cortex is responsible for the control of attention to the left and right visual fields, the left parietal cortex, is only responsible for the right visual field. Thus damage to the left parietal cortex goes un-noticed as the right parietal cortex still has control over the left visual field.

Two broad categories of neglect can be highlighted: egocentric and allocentric.

People with egocentric neglect will ignore stimuli to the left of their midline. For some this includes the left side of their own body: they may forget to shave half their face, or to put their left arm in its sleeve. When looking at a room full of objects, they will simply ignore the left hand side of the room.

Those with allocentric neglect, in contrast, perceive all the stimuli in a room but ignore the left half of each one. Incredibly, in these patients, if presented with a slanted or inverted object, they will mentally correct the orientation and then neglect the left side of the adjusted image. A patient looking at mirror image of a map of the world will neglect the Western hemisphere despite its position on the right of the map in the inverted image.

Hemi-Spatial Neglect Wiki

MIGRAINE

A chronic neurological condition characterised by severe headaches which can be localised to one side, and are associated with nausea, vomiting and photophobia (increased sensitivity to light).

Migraines can sometimes start with an aura which often take the form of vivid visual hallucinations. The causes is as yet unconfirmed, but some studies find evidence of ‘cortical spreading depression’ in which neural activity is activated and then depressed over an area of the cortex. This is thought to be the reason for the occurrence of visual auras. Other studies find that the constriction and subsequent dilatation of blood vessels in the brain are responsible for the aura and the subsequent migraine.

The visual aura have very characteristic shapes, possibly reflecting the breakdown of the visual image through the visual processing stream: vertical, horizontal and diagonal lines are reported, and jagged expanding and contracting shapes.

Migraine Action

PROSOPAGNOSIA

A disorder of face perception where the ability to recognise faces is impaired, despite intact recognition of other objects. The term comes from the Greek “prosopon,” meaning “face” and “agnosia,” meaning “not knowing.”

While it is often the result of brain damage, a hereditary form of the disease has been found. The problem is thought to be due to damage in an area called fusiform gyrus, also known as the occipitotemporal gyrus. This area contains the fusiform face area (FFA) which is specialised for the processing of faces.

There are two types, apperceptive and associative.

Those suffering from apperceptive prosopagnosia cannot make sense of faces. They are unable to work out attributes such as age, gender, race, and cannot make same-different judgements.

Those with associative prosopagnosia, in contrast, have intact perception of faces, but are impaired at linking their semantic knowledge to the face. They are able to make same-different judgements, but are unable to identify the name of the person. In both types, the person is able to recognise a face using non-face clues, such as clothes, hair or voice.

National Institute of Neurological Disorders and Stroke

AUTISM & ASPERGERS

Autism and Asperger syndrome are part of a range of developmental disorders referred to as Autistic Spectrum Disorders (ASD). Usually diagnosed in childhood, ASD causes a wide range of symptoms including impaired communication skills, difficulties with social interaction and restrictive or repetitive patterns of behaviour, interests and activities.

Asperger syndrome is considered the milder of the two conditions; linguistic and cognitive development is largely unaffected. Individuals with AS often demonstrate enhanced visual and auditory perception which can lead to sensitivity to sound or light causing discomfort. Comparatively, Autism is often characterised by learning difficulties.

There have been many theories as to the causes of ASD including: prenatal viral infections, problems in the development of cortical areas and, controversially in the late 90s, linked to childhood vaccinations. The current dominant theory considers ASD to be caused by genetic factors, however it is not yet clear what gene, or genes, are responsible.

ASD is often linked to savantism; a condition where a person with a mental health condition or disability demonstrates exceptional ability in a specific area, including extremely rapid mathematical calculations or producing highly accurate and detailed artworks.

The National Autistic Society

 

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