The brain is a super computer with a complicated network of neurones 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 some 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. Behavior, being emotional or angry is other cognitive functions. 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.
A podcast transcript in the Scientific American magazine comments that “the brain is more plastic than we thought” (Learn to be kind, Scientific American Inc.) Researchers at Wisconsin-Madison University have published in a study this week that our capacity for empathy can be developed through meditation. The insula, the area of brain responsible for feelings of compassion, was highly active in the Tibetan monks and trained meditators who formed the index group for the study (28/3/08). The right temporo-parietal junction, connected to understanding another’s emotional state, was also more active in these meditation experts. We have not fully revealed the enigma that is brain.
The Sensory cortex is sub-divided into primary, secondary and association cortices. There are 3 identified associative cortices, which have a 2 stimuli input. They are the basis of thought and perception with practically no influence on behavior. They are the parieto-temporal-occipital cortex, pre-frontal area and the 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 a faulty language. The prefrontal area if affected, produces problems in several cognitive behaviors. Difficulty arises in control of motor planning. The limbic area is the area of the brain that affects the 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 normal 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.
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 visuo-spatial 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. 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 are possible through the right hemisphere functions. Memory is stored as auditory, visual and spatial functions.
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. The patient appears to have 2 minds. It was revealed by Robert Sperry, a psychobiologist, who conducted studies in patients in whom commissurectomy (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)
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 lateralised to the left hemisphere.
Dyscalculia is caused by damage to the left temporo-parietal region. This leads to difficulty in doing mathematics. Malcolm Sherman, Professor in the Department of Mathematics and Statistics, University of Albany , New York (Author argues that everyone is born with a head for numbers, American Scientist Inc.) elaborates how Brian Butterworth, a British Cognitve Neuropsychologist discusses the brain area for mathematics in his book, “The Mathematical Brain” ( 1999, Free press). Butterworth, it seems, agrees with linguist Noam Chomsky about the area for knowledge in the brain but differs from him where mathematics is concerned. Butterworth believes that maths and knowledge are subserved by two different areas of the brain.
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.
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. Korsakoff’s psychosis is an autosomal recessive disorder which manifests in predisposed persons in alcoholism.
There is a progressive decline in the cognitive functions in natural aging too. The ability to store and retrieve from 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. 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 is a physiological malfunction due to deterioration in the substantia nigra of the brain. It is characterised 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). Cognitive defects associated with cortical pathology may be the marker of dementia in Parkinson’s disease ( Paganobarraga, J., Department of Human and Health Services). Paganobarraga et al have designed a new scale, Parkinson’s Disease cognitive rating scale, which covers the full spectrum of cognitive defects found in this illness. The researchers also mention that there is a need to improve the diagnostic criteria of Parkinsonism. Gill, D.J. et al also speak of the Montreal Cognitive Assessment
as a reliable cognitive rating scale but it has to be developed further (Pubmed)
Alzheimer’s Disease is a very serious illness affecting the pre-senile age group. It is attributed to biologic 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. The patients would never be aware of their memory problem. Feeling confused and repeating questions are features which 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 bed-ridden during the later stage. Their care-taker needs to be extremely patient as all her time would be spent for looking after the patient ( Ballenger, 2006).
Studies in Alzheimer’shave 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% neurones 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
Aphasia is an extreme form of cognitive impairment. A problem or injury to the dominant cortex causes a 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 specialises 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. Talk is incongruent and coherent but is spoken at 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.
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)
Dyslexia is a persisting disturbance in the coding of written language associated with a defect in the phonological system. The main defects would be the 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 which 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 biologic cause for dyslexia. The 20 dyslexics were then brain-scanned and 10 were put on an intensive training programme. They were taught to use their right parietal lobe for the training and reading. All learnt to read well and even formed a book reading club. The study concluded that the adult brain is capable of change.
Sudden trauma to the brain when the head suddenly and violently hits an object or something pierces through the skull into the brain tissue can cause cognitive dysfunction.
Mild TBI can cause confusion, dizziness, blurred vision, fatigue and behavioral changes.
Moderate or severe TBI have all these symptoms and a headache with vomiting. (What is Traumatic Brain Injury, National Institutes of Health). The physical, behavioral and mental changes will depend on the area of damage of the brain. Most injuries cause a focal area of damage. Closed head injuries are more diffuse in damage. The damage is diffuse as the impact of the injury causes the brain to move back and forth within the skull. The frontal and temporal lobes, the major speech and language areas receive the most damage as they are situated in a more spacious area of the skull (Traumatic Brain Injury: Cognitive and Communication Disorders, National Institute of Deafness and other comunication disorders ).
Apart from the physical damage, a large extent of cognitive damage is evident in such injuries. The amount of cognitive and comunication problems depend on factors like individual’s personality, preinjury abilities and the severity of brain damage (Traumatic Brain Injury: Cognitive and Communication Disorders, National Institute of Deafness and other comunication disorders ). Conscious persons lose the thinking skills, awareness of the surroundings, memory, attention to tasks, reasoning and problem-solving qualities. Their self awareness, self monitoring and evaluation faculties are absent. They have difficulty to concentrate 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.
Rehabilitation is an important aspect of therapy in cognitive dysfunction following traumatic brain injury. Therapy should start early. Long term rehabilitation needs to be intensive when the patient can respond to speech-language pathologists, physical therapists, occupational therapists and neuropsychologists.
Lesions of the occipital lobe and association areas of the parietal and temporal lobes result in visuo-spatial 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 visulaised 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 characterised 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).
Proposagnosia is a neurological disorder characterised by an inability to recognise 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 prosagnosia can be initiated in cases of strokes or brain injuries where there is progress for the better. These patients can be retrained to recognise objects and faces.
References
Agnosia, 2/10/07 26/3/08 http://www.ninds.nih.gov/disorders/agnosia/agnosia.htm
National Institute of Neurological Disorders and Strokes
Ballanger, F.Jesse; “ Self Senility and Alzheimer’s Disease in Modern America”, 2006, Published by JHU Press
Gill,D.J. et al, “ The montreal cognitive assessment as a screening tool for
cognitive impairment in Parkinson’s disease”, 31/3/08 3/4/08
http://www.ncbi.nlm.nih.gov/pubmed , Pubmed, Department of Health and Human
Sciences
Hoien, Torlev; Lundberg, Ingvar; “Dyslexia: From Theory to Intervention”,
2000, Published by Springer, Memory/Cognitive Function loss, 26/3/08 www.geocities.com/Athens/Acropolis/4870/MEDMemoryCognitive.htm MEDMemory
“Learn to be kind”, 60 second Psyche podcast transcript, 28/3/08, 3/4/08
http://www.sciam.com/podcast/episode.cfm?id=F2D1DCCE-E9D8-AE36-FE3C1E6CAA3B0C6C Scientific American, Scientific American Inc.
Paganobarraga, J. et al, 31/3/08 3/4/08 “Parkinson’s disease-cognitive rating scale: A new cognitive scale specific for Parkinson’s disease” http://www.ncbi.nlm.nih.gov/pubmed Pubmed Department of Health and Human Services
Sherman, Malcolm J., “Author argues that everyone is born with a head for numbers”, American Scientist 1999, 3/4/08 http://www.mathematicalbrain.com/revs06.html Macmillan
Traumatic Brain Injury: Cognitive and Communication Disorders, 4/1/08, 3/4/08
http://www.nidcd.nih.gov/health/voice/tbrain.asp National Institute of Deafness and
other comunication disorders
What is Traumatic Brain Injury, 11/12/08 , 3/4/08, http://www.ninds.nih.gov/disorders/tbi/tbi.htm National Institutes of Health
Zeffiro, Thomas; Feb 16 2001, 24/3/08 http://www.dyslexia- teacher.com/t105.html WebMD Medical News
