Cognitive Disorders and Nervous System Functions

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Table of Contents

Split Brain
Amnesia
Natural Aging
Parkinsonism
Aphasias
Language disorders
Dyslexia
Traumatic brain injury
Visuospatial disorders
References

The brain is a supercomputer with a complicated network of neurons subserving many of the activities of our daily life. Many of us are unaware of the various interconnected processes that work in unison to let us lead a simple uncomplicated life. Only when someone is ill or not normal do we feel the messing up of a great system. Of the many functions that the Brain performs, I have selected the cognitive functions for my essay. I have highlighted the various ways that the Central Nervous system could be upset and the consequences that could derange the normal functions, creating havoc in one’s life.

Cognitive function is the intellectual process by which a person becomes aware of, perceives, or comprehends ideas. Recognition, conception, sensing, thinking, reasoning, remembering, and imagining all come under cognitive functions. Behaviour, being emotional or angry are other features of cognitive functions of the brain. They are related to specific centers. We find that each part of the brain has different functions to deliver. Cognitive impairment would occur if these centers were to be affected by injury or illness. My essay gives more details, supported by conclusions of studies conducted by various scientists.

All aspects of perception are involved in an injury to the cerebral cortices of both hemispheres of the brain. Cognitive impairment causes difficulty in dealing with a new, unfamiliar situation. Loss of memory and cognitive dysfunction affects people all over the world due to various causes.

The cerebral cortex is classified into motor and sensory. The sensory cortex is again sub-divided into primary, secondary, and association cortices. Primary is where the stimulus reaches first. The secondary is the area that is connected to the primary and helps in the processing. Association cortices have 2 stimuli inputs.

There are 3 identified associative cortices. They are the basis of thought and perception with practically no influence on behavior. They are the parietal-temporal-occipital cortex, prefrontal area, and limbic association area. The first receives somatosensory, auditory, and visual projections. These associative areas integrate the information from the sensory modalities for language. Injury affecting this area causes faulty language.

The prefrontal area if affected produces problems in several cognitive behaviors. The difficulty arises in control of motor planning.

The limbic area is the area of the brain that affects emotions, rage, fear, and sex. Integration of recent memory and biological rhythms are decided here. If this area is affected, an angry but frightened personality without emotional control would be the result. Recent memory would be lost

A cognitive disorder could occur as a part of aging or illnesses. However, all aged individuals do not have cognitive problems. Both hemispheres are involved in analyzing sensory data, performing memory functions, learning new information, forming thoughts, and making decisions. The left takes care of the sequential analysis. New information is systematically and logically interpreted. Symbolic information like language, mathematics, abstraction, and memory is also dealt with. Memory is stored in a language format. The right hemisphere deals with the interpretation of multiple sensory inputs. Visual-spatial skills are exhibited. One’s environment is understood. The interpretation of dancing and gymnastics is possible through the right hemisphere functions. Memory is stored as auditory, visual, and spatial functions.

Split Brain

The corpus callosum connects the 2 hemispheres and coordinates the functions of both. Any injury to this area causes ‘Split brain’ where the coordination between the 2 hemispheres is lost. A ‘split brain’ patient does not speak of emotions or feelings. The right hemisphere and the left behave independently. The patient appears to have 2 minds. It was revealed in studies by Robert Sperry, a psychobiologist, who conducted studies in patients in whom commissurotomy (severing the corpus callosum from each hemisphere ) was done as a treatment for intractable epilepsy.

He found that the two halves of the brain had specific functions and each side acted independently, whereas, in the normal brain, the two halves act in coordination. This is the theory of hemispheric independence (Zaire et al, 1990) After the operation, the right half showed predominance when it came to spatial tasks like the arrangement of blocks. When researchers showed drawings to each side to be copied, the left-handed drawings were better done.

In a patient who incidentally had a right hemisphere strong in language, it was found that he answered most questions differently when each hemisphere was questioned. Once he would say that his ambition was to be a motor racer, and then he would say he wanted to be a draughtsman. One patient was noticed pulling his pants down one side while the other hand was pulling them up. All these confirm the separate functions of the right and left hemispheres and their connectivity through the corpus callosum.

Cerebral asymmetry is the feature of the normal human brain. The left is the dominant hemisphere with language functions while the right is involved more with visuospatial functions

An acquired language deficit accompanying right-sided stroke (left hemisphere involvement) is the best indication that the left hemisphere is dominant for language. The right hemisphere stroke does not involve speech problems.

Hemispherectomy is a procedure where the hemisphere causing intractable epilepsy is removed or disabled. It is usually done in children where the chances of recovery of the brain are more. Studies have found that there is no long-term effect on memory, personality, humor, or any harmful effect on cognitive functions. The greater the intellectual capacity before surgery, the greater is the decline in function seen after surgery. Advanced language disorders may be saved but it depends on how old the child was and his language at the time of hemispherectomy.

Lateralisation is evident in the right and left-handedness of people. However, this is no indication of the dominance of any hemisphere. 95% of people have left-hemisphere language function, 18.8% have right hemisphere language function. 19.8 % have bilateral language functions. Linear reasoning, speech, and vocabulary are lateralized to the left hemisphere. Dyscalculia is caused by damage to the left temporoparietal region. This leads to difficulty in doing mathematics. Some language functions like intonation and accentuation are with the right hemisphere. Musical and visual stimuli, spatial manipulation, facial perception, and artistic ability are functions of the right too. Logical reasoning is with the left but intuitive reasoning is with the right.

Amnesia

Memory loss, a feature of cognitive impairment, is the delay or failure to recall recent or distant events. Amnesia is an extreme form of memory loss when caused by a more severe injury to the brain, probably in a road accident, bomb explosion, or shooting incident. Involvement due to injury or aging can produce loss of memory of varying levels. Loss can be a mild dysfunction (MCI ) or severe and named as dementia. Old people of 55-80 years of age could have cognitive impairment without having any illness. Memory loss is seen in degenerative disorders or dementias like Alzheimer’s, traumatic brain injuries, following ECT, or in Korsakoff’s psychosis.

Mental slowing is the difficulty experienced when trying to perform learned tasks in time or processing new matter. This could happen in aging. The intellectual decline is when we lose the ability to do what we used to previously and also lose the memory of a familiar place or date, usually due to an illness.

Korsakoff’s disease or syndrome is characterized by a strong memory defect, especially for recent events. It occurs in chronic alcoholics by a direct effect of alcohol or due to the severe nutritional deficiencies associated. B Complex deficiency is noticed in this illness. The syndrome follows delirium tremens. It is also associated with severe brain dysfunctions in paralysis, poisonings, dementia, and infections.

The patient covers up his recent memory defect by churning up tales. It would be difficult to weed the tales from the true story. Confabulation is a prominent feature in the severe or classic form. Other symptoms would be delirium, anxiety, depression, confusion, insomnia, and delusions. Memory loss will progress. Korsakoff’s psychosis is alcoholic neuropathy with severe mental disturbances. Korsakoff’s syndrome is a nonalcoholic form resulting from a head injury, tumors, and encephalitis.

Information from 82 autopsies was documented by Victor et al in 1971 to study the changes in the brain accompanying Korsakoff’s illness. In 1977, a genetic disturbance of transketolase was discovered by Blass and Gibson. Transketolase was a thiamine pyrophosphate binding factor from the fibroblasts of the affected person. It is considered that persons who are homozygous for this defect are at a higher risk of developing thiamine deficiency in case of nutritional inadequacy as can happen in chronic alcoholism. It may be assumed that Korsakoff’s psychosis is an autosomal recessive disorder that manifests in predisposed persons to alcoholism.

ECT-induced amnesia follows episodes of ECT in a psychiatric illness. The amnesia is transient and may last a year. It resolves to leave a little residual impact. Patients have been found to have implicit memory. They remember to do some things even in the absence of explicit memory. The implicit memory is probably due to an automated process and not dependent on the areas of the brain involved. Studies have hinted that two kinds of memory losses are possible, implicit and explicit. Familiarity and retrieval could tap some memory processes (Dorf et al, 1994)

Natural Aging

There is a progressive decline in the cognitive functions in natural aging too. The ability to store and retrieve short-term memory is affected. Abstract reasoning becomes difficult. New information cannot be easily learned. Diabetes, Alzheimer’s Disease, or Parkinsonism may occasionally contribute to the onset and progress. The cumulative effect of damage to the brain by free radicals or a fall in the energy output could be reasons. Key hormones also decrease after the age of 40. Diminished oxygen availability to brain cells is seen in atherosclerosis, heart disease, limited exercise, poor diet, stress, excessive drinking, and drug abuse. These can contribute further. Changes in lifestyle and nutritional deficiencies can play a role also in causing cognitive impairment in the aged.

Parkinsonism

This illness is a physiological malfunction due to deterioration in the substantia nigra of the brain. It is characterized by intellectual decline and mental slowing, cognitive impairment, memory loss, anxiety, or depression. These dementia patients have hallucinations, delusions, or uninhibited behavior. Dementia may not be obvious to the patient. However, it would be apparent to the people around him (Memory/Cognitive Function loss, MedMemory).

Alzheimer’s Disease is a very serious illness affecting the pre-senile age group. It is attributed to biological and genetic causes The symptoms of aging and the degeneration of the brain cells would be seen prematurely, starting in the language areas and extending beyond. The foremost problem is the loss of memory. They would never be aware of their memory problem. Feeling confused and repeating questions are features that reveal the condition to family and friends.

Forgetting their identity, they usually get lost while out on a walk. They would forget some phases of their life. Recent memory is the one most affected. The meanings of certain words would be lost forever. The stage where simple daily activities like dressing and brushing the teeth are lost. Soon they lose control of the sphincters. The condition worsens with age. Unable to make logical sentences, they would fumble for some answer. They become bedridden during the later stage. Their caretaker needs to be extremely patient as all her time would be spent looking after the patient ( Ballenger, 2006).

Studies have shown that there is a 60-90% reduction in an enzyme involved in producing acetylcholine, a neurotransmitter essential for memory function. The acetylcholine level would be lower too. In autopsy, the hippocampus, the portion related to short-term memory, was found to have 75% neurons dysfunctional. 2 lesions are seen: neurofibrillary tangles and senile plaques. Researchers have identified a protein, amyloid, which kills the brain cells and transform them into the 2 lesions.

Aphasias

Aphasia is an extreme form of cognitive impairment. A problem or injury to the dominant cortex causes dysfunction in speech and writing. Injury affecting the Broca’s area or Wernicke’s area or both cause aphasia. These areas are located in the left hemisphere of the brain in 80% of people. Broca’s area is situated below the motor cortex representing the face. It specializes in the expression of speech. A lesion here allows the patient to understand language and conversation but he cannot speak coherently. He can also pronounce well but there is no flow in the language. The words come out abruptly at intervals.

If Wernicke’s is the area affected, the patient does not comprehend correctly what is being said to him. He can understand simple instructions and respond when called by name.

However, he cannot understand a conversation. The talk is incongruent and coherent but is spoken in odd instances. He speaks a few words which are not connected to the occasion. When asked a question, he responds with another phrase as answer very much out of context. Wernicke’s area is situated above the left temporal auditory cortex.

Transcortical aphasia is caused by damage to the language areas of the left hemisphere outside the primary language areas of the brain. The patient is able to repeat words, phrases, and sentences, unlike the other aphasic patients. Other language functions may be impaired according to the part damaged.

Language disorders

The person may have trouble understanding others in a receptive language disorder. In an expressive language disorder, the person is unable to share his feelings, thoughts, and ideas. Both are language disorders. Children and adults may be affected. Developmental expressive language disorder has no known cause and is noticed during childhood when the child begins to talk. Acquired expressive language disorder occurs due to traumatic head injury, seizures, or a stroke and involving the respective areas of speech, Broca’s or Wernicke’s. Depending on the extent of damage, the expressive language disorder could remain or recover along with the causative illness ( Expressive language disorder, American Speech-Language-Hearing Association )

Speech disorders are difficulty in pronunciation, stuttering, or articulation problems.

Dyslexia

Dyslexia is a persisting disturbance in the coding of written language associated with a defect in the phonological system. The main defects would be word decoding and spelling mistakes. Intelligence is not related. A gifted individual could be affected just as much as anyone with a low Intelligence Quotient. This problem can be overcome or corrected with plenty of effort and intensive training in individuals who are more intelligent and receptive to suggestions. Those who cannot respond become handicapped (Hoien and Lundberg, 2000)

However, reading is a complex action that may be responding to several parts of the brain according to some scientists. No one is actually sure about this according to Zeffiro Thomas, Co-Director of Georgetown Center for Study and Learning (WebMD Medical News). Frank Wood thinks that the defect is in the auditory-visual connection. Guinevere Eden, also Co-Director of Georgetown Center, monitored 20 dyslexics and 17 normal children. The left parietal lobe showed functioning for all the normal children and less for the dyslexics. This left parietal lobe could be the area affected. She concluded that there is a biological cause for dyslexia.

The 20 dyslexics were then brain-scanned and 10 were put on an intensive training program. They were taught to use their right parietal lobe for training and reading. All learned to read well and even formed a book reading club. The study concluded that the adult brain is capable of change.

Traumatic brain injury

Cognitive dysfunction is common following traumatic brain injury. They lose thinking skills, awareness of the surroundings, memory, attention to tasks, reasoning, and problem-solving qualities. They are unable to set goals, plan or initiate. Their self-awareness, self-monitoring, and evaluation faculties are absent. They have difficulty concentrating when there is a disturbance in the surroundings like a loud noise. They cannot do many things at the same time. Only smaller bits of new information can be understood. Messages may have to be repeated to be really grasped. You may have to speak slower for the patient to get it.

Recent memory is a problem. It may be difficult to learn new things. However old memory may not be lost. Traumatic Amnesia usually occurs as a transient phenomenon following a head injury. The level of memory loss will depend on the extent of damage to the cortices. The amnesia could be antegrade or retrograde. In the latter, the memory prior to the trauma is lost. The loss occurs for events after the trauma in antegrade.

They may seem disorganized and may need help from family and friends. Problem-solving becomes difficult and may react impulsively (What cognitive problems occur after TBI, American Speech-Language-Hearing Association ).

Visuospatial disorders

Lesions of the occipital lobe and association areas of the parietal and temporal lobes result in visuospatial disorders. The visual sensory defects are the visual field defects, sensory neglect, or agnosia. The most pronounced effect is when the right lobes are affected. 2 dimensional and 3-dimensional objects are not visualized in the correct perspective. Stereopsis

is also not possible. There is difficulty in judging distance and angular orientation. Spatial construction tasks are also not possible.

Agnosia is a rare disorder characterized by an inability to identify objects or persons by their geometric features. It can result from damage to the occipital or parietal lobes of the brain by dementia, strokes, developmental disorders, or other neurological conditions. These patients may retain their other cognitive abilities. The quality of life may be compromised. ( Agnosia, National Institute of Neurological Disorders and Stroke).

Prosopagnosia is a neurological disorder characterized by an inability to recognize faces.

It is also called face agnosia or face blindness. It is thought to be due to some damage to the right fusiform gyrus. This fold in the brain is believed to coordinate the neural systems that control facial perception and memory. The condition occurs in neurodegenerative disorders, strokes, traumatic brain injuries and is sometimes congenital. Children with autism and Asperger’s syndrome have this problem to varying extents.

Treatment for agnosia and prosopagnosia can be initiated in cases of strokes or brain injuries where there is progress for the better. These patients can be retrained to recognize objects and faces.

References

Agnosia, 2/10/07 26/3/08. National Institute of Neurological Disorders and Strokes. Web.
Ballanger, F.Jesse; “ Self Senility and Alzheimer’s Disease in Modern America”, 2006 Published by JHU Press/
Dorf et al, “Priming and recognition in ECT induced amnesia” Vol 2, Issue2, Pgs 244-248, 26/3/08 Psychonomic Bulletin and review, 1994.
Hoien, Torlev; Lundberg, Ingvar; “Dyslexia: From Theory to Intervention”, 2000, Published by Springer.
Memory/Cognitive Function loss, 26/3/08. MEDMemory. Web.
What cognitive problems occur after TBI, 25/3/08. American Speech-Language-Hearing Association. Web.
Zeffiro, Thomas; Feb 16 2001, 24/3/08. WebMD Medical News. Web.

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