Food for Thought: the Efficiency of Glucose Metabolism Predicts the Self-generation of Temporally Distant Cognition

The generation of thought independent of environmental input occupies almost half of mental life and is important for skills such as creativity and planning. To understand how this ubiquitous cognitive process relates to the brain's ‘energy budget’, a cross-sectional study is carried out to examine how the capacity for mental time travel relates to the efficiency with which adults metabolize glucose, the brain’s primary source of fuel. On day 1 the ability of a group of 36 younger and 36 older individuals to metabolize glucose was assessed using the gold standard two-hour glucose tolerance test. Twenty-four hours later, the same group of participants returned to the laboratory to perform a non-demanding choice reaction time task during which experience sampling was used to assess the frequency with which they generated thoughts that were unrelated to the here and now. Analysis indicated that younger individuals who were the most efficient at metabolizing glucose exhibited mental time travel that spanned longer time periods. Given the importance of self-generated thought in daily life these results suggest that the capacity to mentally simulate events not present in the immediate environment is highly dependent on efficient glucose metabolism