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Chapter 10

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Psychology 2220A/B
Scott Mac Dougall- Shackleton

Chapter 10: Brain Damage and Neuroplasticity CAUSES OF BRAIN DAMAGE • Six causes of brain damage: brain tumors, cerebrovascular disorders, closed-head injuries, infections of the brain, neurotoxins, and genetic factors • Brain Tumors • A tumor, or neoplasm is a mass of cells that grows independently of the rest of the body • In other words, it is cancer • About 20% of tumors found in the human brain are meningiomas - tumors that grow between meninges, the three membranes that cover the central nervous system • All meningiomas are encapsulated tumors - tumors that grow within their own membrane • They can influence the function of the brain only by the pressure they exert on surrounding tissue, and they are almost always benign tumors - tumors that are surgically removable with little risk of further growth in the body • Encapsulation is the exception rather than the rule when it comes to brain tumors • Aside from meningiomas, most brain tumors are infiltrating • Infiltrating tumors are those that grow diffusely through surrounding tissue • They are usually malignants tumors; that is, it is difficult to remove or destroy them completely, and any cancerous tissue that remains after surgery continues to grow • About 10% of brain tumors do not originate in the brain • They grow from infiltrating cells that are carried to the brain by the bloodstream from some other part of the body • These tumors are called metastatic tumors; metastasis refers to the transmission of disease from one organ to another • Cerebrovascular Disorders: Strokes • Strokes are sudden-onset cerebrovascular disorders that cause brain damage • The symptoms of a stroke depend on the area of the brain that is affected, but common consequences of stroke are amnesia, aphasia, paralysis, and coma • The area of dead or dying tissue produced by a stroke is called an infarct • Surrounding the infarct is a dysfunctional area called the penumbra • The tissue in the penumbra may recover or die, depending on a variety of factors, and the goal of treatment following stroke is to save it • There are two major types of strokes: those resulting from cerebral hemorrhage and those resulting from cerebral ischemia • Cerebral Hemorrhage •Cerebral hemorrhage occurs when a cerebral blood vessel ruptures and blood seeps into the surrounding neural tissue and damages it •Bursting aneurysms are a common cause of intracerebral hemorrhage •An aneurysm is a pathological ballonlike dilation that forms in the wall of an artery at a point where the elasticity of the artery wall is defective •Aneurysms can be congenital (present at birth) or can result from exposure to vascular poisons or infection • Cerebral Ischemia •Cerebral ischemia is a disruption of the blood supply to an area of the brain Chapter 10: Brain Damage and Neuroplasticity • The three main causes of cerebral ischemia are thrombosis embolism, and arteriosclerosis • Thrombosis, a plug called thrombus is formed and blocks blood flow at the site of its formation • May be composed of a blood clot, fat, oil, and air bubble, tumor cells, or any combination thereof • Embolism is similar, except that the plug, called an embolus is this case, is carried by the blood from a larger vessel, where it was formed, to a smaller one, where it becomes lodged • Arteriosclerosis, the walls of blood vessels thicken and the channels narrow, usually as the result of fat deposits; this narrowing can eventually lead to complete blockage of the blood vessels • Much of the brain damage associated with stroke is a consequence of excessive release of excitatory amino acid neurotransmitters, in particular glutamate, the brain’s most prevalent excitatory neurotransmitter • After a blood vessel becomes blocked, many of the blood-deprived neurons becomes blocked, many of the blood-deprived neurons become overactive and release excessive quantitates of glutamate • The glutamate in turn overactivates glutamate receptors in the membranes of postsynaptic neurons; the glutamate in turn overactivates glutamate receptors in the membranes of postsynaptic neurons; the glutamate receptors that are most involved in this reaction are the NMDA (N-methyl-D-asparate) receptors • As a result, large numbers of Na+ and Ca2+ ions enter the postsynaptic neurons • The excessive internal concentrations of Na+ and Ca2+ ions affect the postsynaptic neurons in two ways: • They trigger the release of excessive amounts of glutamate from the neurons, thus spreading the toxic cascade to yet other neurons • And they trigger a sequence of internal reactions that ultimately kill the postsynaptic neurons • Ischemia-induced brain damage has three important properties: • First, it takes a while to develop • Second, ischemia-induced brain damage does not occur equally in all parts of the brain • Third, the mechanisms of ischemia-induced damage vary somewhat from structure to structure within the brain, and in at least some areas, astrocytes have been implicated • Closed-Head Injuries • It is not necessary for the skull to be penetrated for the brain to be seriously damaged • Contusions are closed-head injuries that involve damage to the cerebral circulatory system • Such damage produces internal hemorrhaging, which results in a hematoma • A hematoma is a localized collection of clotted blood in an organ or tissue • Contusions from closed-head injuries occur when the brain slams against the inside of the skull Chapter 10: Brain Damage and Neuroplasticity • Blood from such injuries can accumulate in the subdural space and severely distort the surrounding neural tissue • Contusions frequently occur on the side of the brain opposite the side struck by a blow • The reason for such so-called contrecoup injuries is that the blow causes the brain to strike the inside of the skull on the other side of the head • When there is a disturbance of consciousness following a blow to the head and there is no evidence of a contusion or other structural damage, the diagnosis is concussion • Evidence that the cognitive, motor, and neurological effects of concussion can last many years • The punch-drunk syndrome is the dementia and cerebral scarring observed in boxers and other individuals who experience repeated concussions • Infections of the Brain • An invasion of the brain by microorganisms is a brain infection, and the resulting inflammation is encephalitis • There are two common types of brain infections: • Bacterial Infections • When bacteria infect the brain, they often lead to the formation of cerebral abscesses - pockets of pus in the brain • Bacteria are also the major cause of meningitis • Syphilis bacteria are passed from infected to noninfected individuals through contact with genital sores • The syndrome of insanity and dementia that results from a syphilitic infection is called general paresis • Viral Infections • There are two types of viral infections of the nervous system: • Those that have a particular affinity for neural tissue • Those that attack neural tissue but have no greater affinity or it than for other tissues • Rabies is an example of a virus’ affinity for the nervous system • Rabies does not usually attack the brain for at least a month after it has been contracted, thus allowing time for a preventative vaccination • The mumps and herpes viruses are common viruses that can attack the nervous system but have no special affinity for it • Neurotoxins • Toxic psychosis - chronic insanity produced by a neurotoxin • Sometimes the very drugs used to treat neurological disorders prove to have toxic effects • Many of the patients developed a motor disorder termed tardive dyskinesia (TD) • It’s primary symptoms are involuntary smacking and sucking movements of the lips, thrusting and rolling of the tongue, lateral jaw movements, and puffing of the cheeks • Some neurotoxins are endogenous (produced by the patients own body) • Genetic Factors Chapter 10: Brain Damage and Neuroplasticity • Sometimes accidents of cell division occur, and the fertilized egg ends up with an abnormal chromosome or with an abnormal number of normal chromosomes • Most neuropsychological diseases of genetic origin are caused by abnormal recessive genes that are passed from parent to offspring • Genetic accident is another major cause of neuropsychological disorders of genetic origin • Down syndrome is such a disorder • The genetic accident associated with Down Syndrome occurs in the mother during ovulation, when an extra chromosome 21 is created in the egg • The consequences tend to be characteristic disfigurement, intellectual impairment, and troublesome medical complications • The probability of giving birth to a child with Down syndrome increases markedly with advancing maternal age • Programmed Cell Death • Apoptosis plays a critical role in early development by eliminating extra neurons • It also plays a role in brain damage • All of the six causes of brain damage have produced neural damage, in part, by activating apoptotic programs of self-destruction • It was once assumed that the death of neurons following brain damage was totally necrotic - neurosis is passive cell death resulting from injury • Now seems that is cells are not damaged too severely, they will attempt to marshal enough resources to “commit suicide” • However, cell death is not an either-or situation • Necrotic cell death is quick (a few hours); apoptotic cell death is slow (1-2 days) NEUROPSYCHOLOGICAL DISEASES • Epilepsy • The primary symptom of epilepsy in the epileptic seizure, but not all persons who suffer seizures are considered to have epilepsy • The diagnosis of epilepsy is applied to only those patients whose seizures are repeatedly generated by their own chronic brain dysfunction • Seizures that take the form of convulsions often involve tremors, rigidity, and loss of both balance and consciousness • But many seizures do not take this form; instead, they involve subtle changes of thought, mood, or behaviour that are not easily distinguishable from normal ongoing activity • All of the causes of brain damage can cause epilepsy, and over 70 different faulty genes have been linked to it • Many cases of epilepsy appear to be associated with faults at inhibitory synapses that cause many neurons in a particular area to fire in synchronous bursts, a pattern of firing that is rare in the normal brain • The diagnosis of epilepsy rests heavily on evidence from EEG • Epileptic seizures are associated with bursts of high-amplitude EEG spikes, which are often apparent in the scalp EEG during an attack and form the fact that individual spikes often punctuate the scalp EEGs of epileptics between attacks • Some epileptic experience peculiar psychological changes just before a convulsion Chapter 10: Brain Damage and Neuroplasticity • These changes, called epileptic auras, may take many different forms • Epileptic auras are important for two reasons • First, the nature of the auras provides clues concerning the location of the epileptic focus • Second, epileptic auras can warn the patient of an impending convulsion • Usual to assign the epilepsy to one of two general categories - partial epilepsy or generalized epilepsy - and then to one of their respective subcategories • Partial Seizures • A partial seizure is a seizure that does not involve the entire brain • The synchronous activity tends to spread to other areas of the brain - but, in the case of partial seizures, not to the entire brain • Because partial seizures do not involve the entire brain, they are not usually accompanied by a total loss of consciousness or equilibrium • There are two major categories of partial seizures • Simple Partial Seizures - symptoms are primarily sensory or motor or both • Complex Partial Seizures - restricted to the temporal lobes, patient engages in compulsive, repetitive, simple behaviours commonly referred to as automatisms and in more complex behaviours that appear almost normal • Although patients appear to be conscious throughout their complex partial seizures, they usually have little or no subsequent recollection of them • Generalized Seizures • Involve the entire brain • Some begin as focal discharges that gradually spread through the entire brain • In other cases, the discharges seem to begin almost simultaneously • Grand mall seizures primary symptoms are loss of consciousness, loss of equilibrium, and a violent tonic-clonic convulsion - a convulsion involving both tonus and clonus • The hypoxia that accompanies a grand mall seizure can itself cause brain damage • Petit mal seizure are not associated with convulsions; their primary behavioral symptom is the petit mall absence - a disruption of consciousness that is associated with a cessation of ongoing behaviour, a vacant look, and sometimes fluttering eyelids • EEG is different form that of other seizures; it is bilaterally symmetrical 3-per- second spike-and-wave discharge • Common in children, and they frequently cease at puberty • Although there is no cure for epilepsy, the frequency and severity of seizures can often be reduced by antiepileptic medication • These drugs often have adverse side effects • Brain surgery is sometimes performed, but only in grave situations • Parkinson’s Disease • A movement disorder of middle and old age • It is about 2.5 times more prevalent in males than in females • The initial symptoms of Parkinson’s disease are mild but they inevitably increase in severity with advancing years Chapter 10: Brain Damage and Neuroplasticity • Although Parkinson’s patients often display cognitive deficits, dementia is not typically associated with the disorder • Parkinson’s disease seems to have no single cause; faulty genes, brain infections, strokes, tumors, traumatic brain injury, and neurotoxins have all been implicated in specific cases • Associated with widespread degeneration, but it is particularly severe in the substantia nigra - the midbrain nucleus whose neurons project via the nigrostriatal pathway to the striatum of the basal ganglia • Dopamine is normally the major neurotransmitter released by most neurons of the substantia nigra, there is little dopamine in the substantia nigra and striatum of long-term Parkinson’s patients • Autopsy often reveals clumps of proteins in the surviving dopaminergic neurons of the substantia nigra - the clumps are called Lewy bodies • Symptoms of Parkinson’s disease can be alleviated by injections of L-dopa - the chemical from which the body synthesizes dopamine • L-dopa typically becomes less and less effective with continued use, until its side effects outweigh its benefits • No drug that will block the progressive development of Parkinson’s disease or permanently reduce the severity of its symptoms • All of the mutations have been found to disrupt the function of mitochondria, the energy-creating structures in each cell • One of the most controversial treatments for Parkinson’s disease is deep brain stimulation, a treatment in which low intensity electrical stimulation is continually applied to an area of the brain through a stereotaxically implanted electrode • The treatment of Parkinsons disease by this method usually involves chronic bilateral electrical stimulation of a nucleus that lies just beneath the thalamus and is connected to the basal ganglia: the subthalamic nucleus • High-frequency electrical stimulation is employed, which blocks the function of the target structure, much as a lesion would • Once the current is turned on, symptoms are alleviated within minutes • Although the effectiveness of deep brain stimulation slowly declines, improvement relative to the patients pretreatment status is often still apparent 2 years after stimulation begins • Deep brain stimulation can cause side effects such as cognitive, speech, and gait problems • Huntington’s Disease • Progressive motor disorder of middle and old age • It is rare • It has strong genetic basis, and it is associated with severe dementia • The first sign of Huntington’s disease is often increased fidgetness • As the disorder develops, rapid, complex, jerky movements of entire limbs begin to predominate • Eventually, motor and intellectual deterioration become so severe that sufferers are incapable of feeding themselves, controling their bowels, or recognizing their own children Chapter 10: Brain Damage and Neuroplasticity • There is no cure; death typically occurs about 15 years after the appearance of the first symptoms • Huntington’s disease is passed from generation to generation by a single dominant gene, called huntingtin • The protein it codes for is known as the huntingtin protein • A test that can tell relatives of Hungtington’s patients whether they are carrying the gene • Multiple Sclerosis • Typically attacks young people just as they are beginning their adult life • First there are microscopic areas of degeneration on myelin sheaths but eventually damage to the myelin is so severe that the associated axons become dysfunctional and degenerate • MS is an autoimmune disorder - a disorder which the body’s immune system attacks part of the body, as if it were a foreign substance • Diagnosing MS is difficult because the nature and severity of the disorder depend on a variety of factors including the number, size, and position of the sclerotic
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