Is "If you don't use it you lose it" applicable to the brain and CTE?

In order to get a better idea of who is more susceptible for the clinical implications of CTE, researchers have begun to identify risk factors and factors that can delay progression of cognitive symptoms. One of the most recent papers has begun a preliminary discussion on Cognitive Reserve and its impact on delay of cognitive and behavioral symptoms. The theory is that a person with a higher cognitive reserve will be able to use pre-existing cognitive processes to deal with the neuropathological insult. This research was spurred on by other papers that showed that higher education can decrease cognitive dysfunction and improves recovery in traumatic brain injury (TBI) (Kesler et al 2003, Schneider et al 2014). The researchers used these studies to start their own study on cognitive reserves effect on CTE.

In this study, the researchers used brains with confirmed stage III or IV neuropathological criteria for CTE. They then reached out to the next of kin of these individuals and conducted structured and unstructured interviews as well as online surveys in order to get a better idea of the person's educational attainment, occupation and onset of symptoms (both behavioral/mood and cognitive). The educational attainment and occupation were used as proxies for cognitive reserve. The occupation for each individual was rated as low or high attainment based on the DOT guidelines. 

The results of this preliminary study showed that while educational attainment did not predict the onset of symptoms, occupational attainment had a very significant impact on both behavioral and cognitive onset of symptoms. In fact after controlling for duration of football play, cognitive symptoms appeared 10 years earlier in the individuals with low cognitive impairment (Alosco et al 2016). Below is a table of the study results:

Alosco ML, Mez, J, Kowall, NK et al: Cognitive Reserve as a Modifier of Clinical Expression in Chronic Traumatic Encephalopathy: A Preliminary Examination. J Neuropsychiatry Clin Neurosci 2017, 29:6-12.

The results of this data was very similar to the data found in Alzheimer's disease, another similar tauopathy (Stern et al 1994). Even though this data shows a difference between cognitive reserve and onset of symptoms, it appears that there is a generalized improvement in cognition with increased cognitive reserve, and it is not solely protective in CTE (Wilson et al 2013). Furthermore, we need more information as to the relationship between cognitive reserve and symptom onset, by using larger study groups and by performing longitudinal studies with living athletes at risk of CTE. Using a longitudinal study will help to move away from retroactive interviews with next of kin, which has the potential to be less reliable than more rigorous longitudinal observation. Nevertheless, this data provides some clues that professions that engage the mind can be beneficial in delaying the symptoms that can occur in CTE. Therefore it is recommended that retired athletes continue to challenge their brains and remain engaged in higher attainment occupations. 

Kesler SR, Adams HF, Blasey CM, et al: Premorbid intellectual functioning, education, and brain size in traumatic brain injury: an investigation of the cognitive reserve hypothesis. Appl Neuropsychol 2003; 10:153–162

Schneider EB, Sur S, Raymont V, et al: Functional recovery after moderate/severe traumatic brain injury: a role for cognitive reserve? Neurology 2014; 82:1636–1642

Alosco ML, Mez, J, Kowall, NK et al: Cognitive Reserve as a Modifier of Clinical Expression in Chronic Traumatic Encephalopathy: A Preliminary Examination. J Neuropsychiatry Clin Neurosci 2017, 29:6-12.

Stern Y, Gurland B, Tatemichi TK, et al: Influence of education and occupation on the incidence of Alzheimer’s disease. JAMA 1994; 271:1004–1010

Wilson RS, Nag S, Boyle PA, et al: Neural reserve, neuronal density in the locus ceruleus, and cognitive decline. Neurology 2013; 80: 1202–1208