On all four neurocognitive measures repeated at euglycemia, hypoglycemia, and recovery, performance decreased significantly during hypoglycemia, regardless of group. This finding is not surprising, given the numerous studies demonstrating that hypoglycemia is associated with neurocognitive deficits in children and adults with T1DM in the literature (11
). One finding of the present study that was unique is that it demonstrated a return to baseline neurocognitive functioning immediately upon return of BG to euglycemia, regardless of driving history group. It is widely believed, with some empirical support in the literature, that recovery of neurocognitive functioning following hypoglycemia is a slow and gradual process, possibly taking up to 1.5 days (13
). The only other study to our knowledge that also demonstrates a return to baseline functioning upon return to euglycemia employed an admittedly simple cognitive task assessing selective attention (15
). The present study provides preliminary evidence that individuals with type 1 diabetes may rapidly recover higher-level executive functions, such as cognitive flexibility and working memory, immediately after returning to euglycemia following hypoglycemia, when the hypoglycemia conditions is brief.
With regard to between-group differences and implications for driving behavior, subjects with T1DM who were considered to be at high-risk of driving mishaps (+ History) consistently demonstrated poorer performance compared to the lower risk group (− History) on the Serial Subtractions and PASAT, regardless of their glycemic condition (i.e., at pre-admission and during euglycemia, nadir, and recovery from hypoglycemia). None of the other neurocognitive tests showed significant group differences pre-admission or during BG manipulation. What distinguishes the Serial Subtraction and PASAT tests from the remainder of the battery is that these tasks assess working memory, the ability to temporarily store and mentally manipulate information. In these neurocognitive tasks, participants were required to remember auditorily-presented information and quickly perform simple mental arithmetic problems based on temporarily stored bits of numeric information. While hypoglycemia has been associated with working memory impairment, (12
), to our knowledge, this study is the first to identify a potential neurocognitive indicator that may differentiate adults with T1DM with and without a history of driving mishaps.
It is unclear why individuals with T1DM who have a history of two or more driving mishaps over the last two years demonstrate poorer working memory, even during euglycemia. The groups did not differ on any demographic, diabetes or driving variables, except for a recent history of severe hypoglycemia and hypoglycemia driving mishaps. One possible explanation is that the +History group has a greater absolute deficit in working memory based on the fact that they demonstrated poorer performance on the above-mentioned measures before the hyper-insulinemic clamping procedure when compared to the −History group. If this is the case, it may be that this absolute deficit in working memory exceeds a threshold during hypoglycemia that is essential for safe driving. The findings do not suggest a general deficit that could be attributable to neuropathy, retinopathy or other complications of diabetes, given that the + and − History groups did not differ on other neurocognitive measures.
While the role of working memory in driving performance has not been studied extensively, one study examining left turn performance at intersections in a simulated driving task found that working memory is associated with the ability to successfully judge and choose gaps in oncoming traffic prior to making a left turn (16
). Interestingly, greater working memory performance was associated with longer decision time in this study, which the authors suggest may reflect the tendency of individuals with better working memory ability to allow more time to gather relevant information before deciding to proceed through an intersection. In contrast, the authors speculate that individuals with poorer working memory are less able to hold and process all relevant information, and therefore may make more hurried decisions to execute a left turn. This study highlights the process by which working memory may mediate driving performance, as well as a specific driving domain (left turn performance) on which to focus in future research examining working memory and driving performance in T1DM individuals with and without driving mishaps. Future studies should also attempt to replicate and extend the present study findings to identify specific neurocognitive indicators of driving performance aimed at identifying T1DM individuals at high risk for future driving mishaps.
While the present study provides only preliminary evidence that performance on working memory measures may be used to identify T1DM drivers at higher risk for future driving mishaps, the relevance of this area of study to clinical practice and public health is readily apparent. If specific neurocognitive predictors of driving risk in individuals with T1DM can be established, brief evidence-based neurocognitive evaluations can be used to identify those at risk of driving mishaps, possibly even early on in their driving careers, and provide targeted interventions aimed at reducing future driving risk. Given that increasingly more evidence is indicating that only a subgroup of individuals with T1DM is at higher risk for driving mishaps, the existing social stigma of driving with diabetes may be reduced, and existing driving restrictions for individuals with T1DM may be refined.