Brain insulin resistance and cognitive function: influence of exercise.

Exercise has systemic health benefits in people, in part, through improving whole body insulin sensitivity. The brain is an insulin-sensitive organ that is often underdiscussed relative to skeletal muscle, liver, and adipose tissue. Although brain insulin action may have only subtle impacts on peripheral regulation of systemic glucose homeostasis, it is important for weight regulation as well as mental health. In fact, brain insulin signaling is also involved in processes that support healthy cognition. Furthermore, brain insulin resistance has been associated with age-related declines in memory and executive function as well as Alzheimer's disease pathology. Herein, we provide an overview of brain insulin sensitivity in relation to cognitive function from animal and human studies, with particular emphasis placed on the impact exercise may have on brain insulin sensitivity. Mechanisms discussed include mitochondrial function, brain growth factors, and neurogenesis, which collectively help combat obesity-related metabolic disease and Alzheimer's dementia.

A randomized trial of aerobic exercise for major depression: examining neural indicators of reward and cognitive control as predictors and treatment targets.

BACKGROUND: Aerobic exercise has demonstrated antidepressant efficacy among adults with major depression. There is a poor understanding of the neural mechanisms associated with these effects. Deficits in reward processing and cognitive control may be two candidate targets and predictors of treatment outcome to exercise in depression. METHODS: Sixty-six young adults aged 20.23 years (s.d. = 2.39) with major depression were randomized to 8 weeks of moderate-intensity aerobic exercise (n = 35) or light stretching (n = 31). Depressive symptoms were assessed across the intervention to track symptom reduction. Reward processing [reward positivity (RewP)] and cognitive control [error-related negativity (ERN)] were assessed before and after the intervention using event-related brain potentials. RESULTS: Compared to stretching, aerobic exercise resulted in greater symptom reduction (gs = 0.66). Aerobic exercise had no impact on the RewP (gav = 0.08) or ERN (gav = 0.21). In the aerobic exercise group, individuals with a larger pre-treatment RewP [odds ratio (OR) = 1.45] and increased baseline depressive symptom severity (OR = 1.18) were more likely to respond to an aerobic exercise program. Pre-treatment ERN did not predict response (OR = 0.74). CONCLUSIONS: Aerobic exercise is effective in alleviating depressive symptoms in adults with major depression, particularly for those with increased depressive symptom severity and a larger RewP at baseline. Although aerobic exercise did not modify the RewP or ERN, there is preliminary support for the utility of the RewP in predicting who is most likely to respond to exercise as a treatment for depression.

Does aerobic fitness moderate age-related cognitive slowing? Evidence from the P3 and lateralized readiness potentials.

Reaction time (RT) slowing occurs among older adults, although it remains unclear whether general or specific aspects of information-processing are implicated in this phenomenon. Aerobic fitness moderates age-related RT slowing, although it is unknown whether fitness benefits earlier versus later stages of information-processing. To test these hypotheses, 40 younger and 43 older adults classified by level of aerobic fitness were tested using a visual oddball paradigm to assess behavioral measures of RT and accuracy along with the P3 wave and lateralized readiness potential (LRP) to index stimulus categorization and response selection and execution processes, respectively. Older adults had slower RT, decreased P3 amplitude, and increased P3 latency and LRP amplitude, suggestive of generalized age-related cognitive slowing decline. While aerobic fitness was significantly correlated with median RT and P3 latency across the entire sample, these correlations did not persist when adjusting for age. Subsequent moderation analysis also failed to support an influence of aerobic fitness on any of the cognitive outcomes. These findings indicate that, at least in simple discrimination tasks, aging is associated with slower processing that occurs proximal to stimulus categorization and extends to motor response and execution processing. These age-related deficits, however, are not moderated by aerobic fitness.