Chemotherapy is an aggressive attack on the cancer, and on the body. For some women treated with chemo for breast cancer, the effects of chemo seem to reach as far as the brain. These women report mental fogginess, the inability to concentrate, and general difficulties with cognitive tasks that didn't use to be problematic. This side effect is dubbed the "chemobrain."
Though scientists have known about this effect, it wasn't until recently that they found the proof that chemobrain is real and measurable. The study came from mice treated with a chemo regimen, and subsequently scored on a memory-related task. Not only did the chemo-treated mice perform worse, scientists found that these mice had 26 percent fewer surviving hippocampal neurons born during chemo treatment. This lasted months after the treatment was over, which, in human terms, translates to years of chemobrain.