Friday, July 31, 2009

Hippocampus Essay

Through the studies of patients with hippocampus injury, it was revealed that the hippocampus helps with the formaton of declarative memories. For example, a patient whose initials are H. M. had severe epilepsy in which treatment consisted of the removal of the hippocampus. After the surgery was performed, it was clear that H. M. had a profound loss of memory for new events following the removal of the hippocampus. Although H. M was able to remember events prior the surgery, he was unable to form new memories and take in new facts into long term memory. One interesting note was that although his declarative memory was severely impaired, his procedural memory remained intact. This was discovered through a series of tasks administered to HM. One task was a mirror drawing task and required HM to draw a picture of an object from its mirror image. It was found that HM showed improvement in his drawing skills upon doing the task over a period of time, although HM denied any recollection of ever having done the task before. Moreover, HM was found to have a normal learning curve regarding the task, and retained his skills, regardless of his inability to remember the events. On another occasion, a psychologist had concealed a drawing pin in his hand and pricked HM as they shook hands. The following day, HM refused to shake the psychologist’s hand, although he denied he ever saw the psychologist before. Such observations are consistent with the associations that the hippocampus is necessary to form declarative, episodic memory. The hippocampus is thought to be associated with short term memory and in consolidating which episodic acts will be stored as long term memories.

Animal studies have shown that damage to the hippocampus hinders the learning process. For example, rats with removed hippocampi were unable to remember where they had or had not been, and hence were effectively hindered from learning a new maze. Such observations suggest that the hippocampus is needed in learning contextual or spatial information. In another study, it was found that monkeys with hippocampus damage were unable to navigate trhough once familiar areas. And in yet another study with monkeys, it was observed that destroying the hippocampus and amygdala, destroyed previous learning and prevented new learning from taking place.

From the observations with patients and animal studies alone, the important role of the hippocampus in memory and learning is quite obvious. However, the hippocampus is not the only area of the brain that accounts for the process of learning and memory storage as it seems that the hippocampus effects certain types of memory and learning more than others, such as declarive memory and spatial, contextual learning versus procedural tasks. The interplays of the hippocampus to other parts of the brain is an important area of study of memory and learning and much is still to researched and consolidated on the subject.

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Hodgkin's Disease Essay

Cancer is a disease that affects millions of people across the U.S. Hodgkin’s disease is one of its rare forms. Hodgkin’s disease is a lymphoma, characterized by an over abundance in the growth of Reed-Sternberg cells. This article will cover the ongoing research to find causes for Hodgkin’s disease in pediatric patients. Also to be discussed are the various stages of the disease and the correlation between its progression and treatment based upon a child’s developmental stage. Living with cancer during one’s youth can have lasting physical as well as psychological effects. In light of this, the frequency of late effects from both the illness itself and its treatment will be examined.

Hodgkin’s disease is responsible for 1% of pediatric cancer cases in the U.S. While cancer among children and adolescents is rare, the three most frequent major childhood cancers diagnosed over the course of a 21-year study conducted by the Surveillance, Epidemiology and End Results (SEER) Program were leukemias, CNS cancers and lymphomas with 4.4% being specified as Hodgkin’s disease. (1) Of all the childhood cancers examined in this study, which culminated in 1995, Hodgkin’s disease exhibited a modest, on a grand scale, but statistically significant decline thus allowing it to appear that all childhood lymphomas had decreased in occurrence. (1)

Incidence and Symptoms
There are no known causes for childhood Hodgkin’s. The general age distribution seems to have an early peak around the mid to late 20’s and a second around age 55 and older. Put simply, the potential for Hodgkin’s increases with age. In youths, onset of the disease is extremely rare in children under 5 years old. However it has a higher occurrence in males less than 10 years of age. About one third of cases in the United States have been associated with the presence of Epstein- Barr virus, commonly known as mononucleosis. Though it is not believed to be genetic, brothers and sisters of Hodgkin’s patients have a higher chance of developing the disease themselves. (1,4) During the course of the many years research devoted to Hodgkin’s by various oncology specialists a common challenge arises in terms of setting a concrete set of common risk factors of the disease. Many of the common factors within Hodgkin’s cases are found equally as often in persons without the disease. On the other hand, patients may develop the disease without any of the conditions believed to make one susceptible. Hodgkin’s is by no means communicable; it cannot be caught. The earliest symptoms of Hodgkin’s are much like that of a common cold or flu. The recurrence or persistence of these symptoms should alert the attending physician to test for the possible presence of Hodgkin’s.

There are various methods of locating cancers in the body such as x-rays, a CT scan, or an MRI. However, the diagnosis of Hodgkin’s generally requires a lymph node biopsy to find the excessive Reed-Sternberg cells definitive of Hodgkin’s disease. When a patient’s biopsy is conclusive to Hodgkin’s disease, the process of clinical staging begins. Determination of the stage to which the disease has progressed is critical in choosing the proper method of treatment. In pediatric cases this often presents a challenge due to the highly invasive nature of clinical staging tests. Currently the standard clinical staging methods that include further CT scans of the chest, abdomen and pelvis, x-rays, and laboratory studies, are rarely included in the staging of children. (2) There are usually more false-positives in children than adults thus making the studies more difficult to perform. In the event that the initial biopsy is not conclusive, the steps of diagnosis and identifying the stage of the disease can be simultaneous. Under these circumstances the progression of the illness is still unknown and a patient may be at risk for cardiac arrest if placed under anesthesia, therefore a physician should consider a CT guided core needle biopsy.

Hodgkin’s disease is currently classified into four stages.

“These stages can be sub-classified into A and B categories and subcategory E: A for those patients who are asymptomatic and B for those patients with any of following specific symptoms:
-Unexplained loss of more than 10% of body weight in the 6 months before diagnosis
-Unexplained fever with temperatures above 38 degrees C for more than 3 days drenching night sweats”

The sub-classification E is reserved for confusing problems in staging resultant of extralymphatic disease. The E classification is not meant for widespread cases of Hodgkin’s that would fall under Stage IV.

The staging of Hodgkin’s disease has a stair-step progression of severity. Put simply the stage increases as the cancer increases the number lymph node regions in the body it effects. As the stages move up in severity of the disease not only lymph nodes but extralymphatic adjacent organs, such as the thymus, spleen, tonsils and bone marrow, are effected as well.

When devising a treatment plan for pediatric Hodgkin’s patients a variety of factors must be considered. The age of the patient is among these, of course, but more specifically the developmental stage of the patient is considered. The methods used in treating adult cancers successfully, may have adverse affects upon a growing child. The most common methods include, radiation therapy, chemotherapy and bone marrow transplantation. The choice of which method is best truly depends upon the individual cases. In studies of late, the National Cancer Institute is attempting to limit the use of radiation in childhood cancers due the late effects it tends to have. *give an intro “Adolescents that have reached maximum growth but have localized childhood Hodgkin’s are treated as adults with standard radiation. For patients that have not yet reached their full growth chemotherapy along with involved-field radiation at lower dose is generally used.”(2)

Treatment of pediatric patients can most often result in a cure. However, in the event of relapse or in advanced stages of the disease the combination of chemotherapy along with another regimen has been known to produce prolonged remissions. Even so many survivors of childhood Hodgkin’s are met with late effects resulting from the treatment. Most often these occur in sexually mature male patients and in female patients from about age 10-16. In these incidences the ability to reproduce may be compromised. Male patients are encouraged to investigate storing sperm as treatment may leave them sterile; however this also presents a challenge as many have low sperm counts from the outset.

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