A recent study was published in the online issue of Neurology, the medical journal of the American Academy of Neurology, and looked at identical twins who share the same genes and similar childhood experiences. The study demonstrated that having a concussion early in life is tied to having lower scores on tests of thinking and memory skills years later as well as having a more rapid decline in those areas. The participants of the study were 8,662 men who served in World War II. They took a test of thinking skills at an average age of 67 and then again up to three more times over 12 years. A total of 25% of the participants had experienced a concussion in their life. The researchers found that each twin who had had a concussion was more likely to have a lower level of cognition (measured on a test score) and cognitive decline, than his twin without concussion, although the effects were modest.
In particular, a twin who had experienced concussion was more likely to have a lower test score at age 70, than his twin without concussion, especially if either the concussion had led to a loss of consciousness because of a head injury, or if they were 25 or older when the injury happened. It is worth highlighting that the study did not account for the effects of other factors that can be linked to cognition such as high blood pressure, alcohol use, smoking status, education, hearing loss or physical activity. Another limitation of the study was also that the participants self-reported whether they had suffered a traumatic brain injury so it is possible that some had forgotten whether they had experienced traumatic injury. https://n.neurology.org/content/early/2023/09/06/WNL.0000000000207819