The MULES captures extensive brain networks involving afferent/efferent visual, cognitive, and language pathways. MULES performance is impaired in concussion and multiple sclerosis. Many of the factors captured by MULES may also be abnormal in sleep-deprived residents.

MULES, which consists of 54 color photographs of various items (fruits, animals, and random objects) was administered to a cohort of NYU School of Medicine neurology residents on 24-hour in-hospital call (n=20) and a group of similar-aged controls not taking call (n=20). Differences in times and errors between baseline and follow-up MULES scores were compared between the two groups.

MULES time in post-call residents was significantly worse (slower) from baseline (average 1.5 seconds, range -6.3 to 11.5) compared to controls not taking call (average -11 seconds, range -0.4 to -28.4) (p<0.0001, Wilcoxon rank sum test). For all participants, the change in MULES time from baseline was significantly correlated to the change in subjective level of sleepiness (rs=0.63, p<0.0001) and to number of MULES errors (rs=0.32, p=0.048). For both groups, there was no significant correlation between MULES time and amount of sleep obtained (rs=0.08, p=0.62), time since last caffeine consumption (rs=0.35, p=0.07), or sleep quality questionnaire score (rs=0.22, p=0.17). For post-call residents, the duration of sleep obtained during call did not significantly correlate with change in MULES scores (rs=-0.1, p=0.69).