Radiation Induced Cognitive Decline
Radiation-induced cognitive decline describes the possible correlation between radiation therapy and mild cognitive impairment. Radiation therapy is used mainly in the treatment of cancer. Radiation therapy can be used to cure care or shrink tumors that are interfering with quality of life. Sometimes radiation therapy is used alone; other times it is used in conjunction with chemotherapy and surgery. For people with brain tumors, radiation can be an effective treatment because chemotherapy is often less effective due to the blood–brain barrier. Unfortunately for some patients, as time passes, people who received radiation therapy may begin experiencing deficits in their learning, memory, and spatial information processing abilities. The learning, memory, and spatial information processing abilities are dependent on proper hippocampus functionality. Therefore, any hippocampus dysfunction will result in deficits in learning, memory, and spatial information processing ability.
The hippocampus is one of two structures of the central nervous system where neurogenesis continues after birth. The other structure that undergoes neurogenesis is the olfactory bulb. Therefore, it has been proposed that neurogenesis plays some role in the proper functionality of the hippocampus and the olfactory bulb. To test this proposal, a group of rats with normal hippocampal neurogenesis (control) were subjected to a placement recognition exercise that required proper hippocampus function to complete. Afterwards a second group of rats (experimental) were subjected to the same exercise but in that trial their neurogenesis in the hippocampus was arrested. It was found that the experimental group was not able to distinguish between its familiar and unexplored territory. The experimental group spent more time exploring the familiar territory, while the control group spent more time exploring the new territory. The results indicate that neurogenesis in the hippocampus is important for memory and proper hippocampal functionality. Therefore if radiation therapy inhibits neurogenesis in the hippocampus it would lead to the cognitive decline observed in patients who have received this radiation therapy.
In animal studies discussed by Monje and Palmer in "Radiation Injury and Neurogenesis", it has been proven that radiation does indeed decrease or arrest neurogenesis altogether in the hippocampus. This decrease in neurogenesis is due to apoptosis of the neurons which usually occurs after irradiation. However it has not been proven whether the apoptosis is a direct result of the radiation itself or if there are other factors that cause neuronal apoptosis, namely changes in the hippocampus micro-environment or damage to the precursor pool. Determining the exact cause of the cell apoptosis is important because then it maybe possible to inhibit the apoptosis and reverse the effects of the arrested neurogenesis.
Read more about Radiation Induced Cognitive Decline: Radiation Therapy, Acute Ablation of Precursor Cells, Precursor Cell Integrity, Alterations in Hippocampus Microenvironment, Doses, See Also
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