Cognitive function
alertness
The cognitive task battery was administered with E-Prime 2.0 (Psychology Software Tool, Inc). There were 4 separate cognitive tasks: CRT, Rapid Visual Information Processing (RVIP), a merged CRT-RVIP task, and Letter Memory. The CRT task was a measure of general alertness and psychomotor speed. For each trial, a fixation “x” appeared in the center of the screen, which was replaced by a target X either to the left or right of the fixation x. Participants were required to indicate whether the target appeared to the left or right of the fixation point by pressing the relevant key (z or m, respectively) as quickly as possible. The interstimulus interval that separated each trial ranged from 250 ms to 1500 ms in a random fashion (matched across versions). This task lasted for ∼3 min with a total of 60 targets presented. The DVs were accuracy score (maximum 60) and mean reaction time (ms) for correct responses.The RVIP was a measure of sustained attention and working memory. During this task, participants were presented with a continuous string of single numerical digits ranging from 1 to 9 in the center of the screen. The string of numbers was presented at a rate of 75 digits/min, with each trial fixed at 800 ms. Participants continuously monitored the digits for 2 specific target strings, which were “1, 3, and 5” and “6, 4, and 2”. When a target string was observed, the participant would press the space bar as quickly as possible. This task lasted ∼4 min, with a total of 270 single digits being presented, including 20 target strings. The DVs for the task were accuracy score (maximum 20) and mean reaction time (ms) for correct responses.The merged task was a novel concept designed to increase cognitive effort by combining the testing parameters of the CRT and RVIP tasks. Thus, this task is a measure of sustained attention, working memory, and psychomotor speed. The rationale for this task is that it combines 2 already standardized tasks; therefore, the level of demand can be evaluated by comparing the performance of the merged task with the performance of the individual tasks. By combining 2 simpler tests into a more difficult task, the effect of increasing task difficulty can be explored, as previous studies have shown that more difficult demanding tasks are more sensitive to the effects of glucose regulation [The Letter Memory task was a measure of executive function. During this task, participants were presented with a series of letters (consonants only) that appeared individually in the center of the screen. The number of letters presented was either 5 or 7 (8 of each), which randomly varied. When a sequence of letters had ended, participants were presented with a screen that displayed 4 options. Participants had to press the relevant button (1, 2, 3, or 4) to indicate which option contained the last 4 letters that had appeared. Once the participant had indicated their choice, the next sequence of letters would begin. The series of letters were presented at a rate of 30 letters/min, with each letter appearing for 2000 ms. At the end of each sequence, the participant had a maximum of 8000 ms to indicate their choice of the 4 options presented. If they made no choice during the 8000 ms, the next sequence would begin, and no selection was recorded. This task lasted for ∼5 min, with a total of 96 letters being presented across 16 separate sequences. The dependent variables for the task were accuracy score (maximum 16) and mean reaction time (ms) for correct responses.Alternate forms of all cognitive tests were counterbalanced across the test days and time points.