Chemo brain is a mental cloudiness reported by about 30 percent of cancer patients who receive chemotherapy. Symptoms typically include impairments in attention, concentration, executive function, memory and visuospatial skills.

Since the 1990s researchers have tried to understand this phenomenon, particularly in breast cancer patients. But the exact cause of chemo brain remains unclear. Some studies indicate that chemotherapy may trigger a variety of related neurological symptoms. One study, which examined the effects of chemotherapy in 42 breast cancer patients who underwent a neuropsychological evaluation before and after treatment, found that almost three times more patients displayed signs of cognitive dysfunction after treatment as compared with before (21 versus 61 percent). A 2012 review of 17 studies considering 807 breast cancer patients found that cognitive changes after chemotherapy were pervasive. Other research indicates that the degree of mental fogginess that a patient experiences may be directly related to how much chemotherapy that person receives: higher doses lead to greater dysfunction.

There are several possible mechanisms to explain the cognitive changes associated with chemotherapy treatments. The drugs may have direct neurotoxic effects on the brain or may indirectly trigger immunological responses that may cause an inflammatory reaction in the brain.

Chemotherapy, however, is not the only possible culprit. Research also shows that cancer itself may cause changes to the brain. In addition, it is possible that the observed cognitive decline may simply be part of the natural aging process, especially considering that many cancer patients are older than 50 years.

Of interest, some studies have failed to document actual cognitive impairment in patients complaining of chemo brain. One such study, comparing the cognitive function in breast cancer patients with that of healthy individuals, did not find significant differences on neuropsychological tests but revealed that the cancer patients perceived that their cognitive functioning, quality of life and psychological well-being had all declined sharply. Experts estimate that in about 10 to 40 percent of cancer patients and survivors, chemo brain symptoms may arise from anxiety, depression or physical fatigue after treatment or diagnosis.

Regardless of the source, scientists are investigating interventions that can help reduce the symptoms of chemo brain. One study has tested the effectiveness of a cognitive-behavior therapy following chemotherapy in women newly diagnosed with breast cancer. After the intervention, these women showed significant improvements in verbal and executive function and reported subjective improvements in cognitive function and quality of life.

My colleagues and I have also tested the effects of the Senior WISE memory-training intervention, which includes relaxation and stress-reducing techniques, as well as confidence-building exercises and memory training. Overall, we have found that after the intervention, participants experienced memory gains and less anxiety. Thus, despite our murky understanding of where chemo brain comes from, there is hope and help for its sufferers.

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