The physiological measurements we obtained are in line with published data showing lower blood glucose levels and body temperature in the afternoon during Ramadan [3,7,8,10]
. The main findings from our neuropsychological test panel suggest that the influence of Ramadan fasting on cognitive function is not homogeneous. During Ramadan, performance in the domains of psychomotor function/processing speed and visual attention/vigilance was better at 0900h. By late afternoon, there was a significant decrease in psychomotor function/processing speed, verbal learning and memory performance. This may be attributed to the combination of food, fluid and sleep restriction.
As glucose is an essential substrate for the central nervous system, with an increase in its metabolism documented in specific brain areas during cognitive activity [30,31]
, the performance impairment we observed at 1600h may be due to lowered blood glucose levels. The brain cannot manufacture its own glucose and is dependent on a continual peripheral supply, which will be limited in the late afternoon in fasted subjects.
The effect was not uniform across all the domains tested. This may be due to the different susceptibility of the various cognition domains. Doniger's study, performed during a 12-16 hour Jewish religious fast 
, showed that both time-dependent (attention and information processing) and spatial relation perception (non-verbal recognition memory, problem solving, verbal naming, visual-spatial skills) tasks were more likely to be adversely affected during fasting 
Electroencephalogram (EEG) studies provide further support for the domain specific effect. These show that although performance decrements and slower reaction times were present in fasted participants carrying out frontal-parietal dominant tasks requiring decision determination and response implementation, there was no significant effect on simple attention tasks involving stimulus encoding, memory retrieval and decision making 
Alpha frequency activity in the occipital cortex, which is the primary area associated with visual sensory stimuli processing and integration, was also not significantly altered during fasting 
. This is consistent with our findings of a lack of any significant performance decline in the non-speed dependent, predominantly occipital cortex centred one-card learning and one-back memory tasks, which supports the previously demonstrated robustness of these domains [15–17,22]
The improved performance in the visual attention/ vigilance and psychomotor function/processing speed tasks at 0900h in our participants may be the result of post feeding neural activity enhancement as well as reduced sleep inertia due to earlier awakening for prayers. In Pivik's study, frontal lobe activity was enhanced in fed participants performing frontal dominant processes related to stimulus encoding, memory retrieval, decision making and motor response execution 
In line with Dinges's study 
, sleep deprivation may be associated with the late afternoon decline in working memory and sustained attention observed in our participants. In sleep restricted subjects, Blood Oxygenation Level Dependent functional MRI (BOLD-fMRI) studies show a decrease in both global and task-specific brain activation during cognitive activity 
. EEG data also demonstrate reductions in intraparietal sulci and superior parietal lobe activation during short-term memory related tasks [34–36]
. BOLD-fMRI studies suggest that compensatory mechanisms exist to aid attention focus and suppress extraneous mental processes in sleep restricted individuals [37,38]
. This may ameliorate some of the adverse effects of sleep deprivation and explain the resilience of tasks involved in vigilance and simple reaction.
The reduction in mean body mass and increase in urine specific gravity indicates that the participants in our study were mildly dehydrated (1.3%) at 1600h. Dehydration has a dose-dependent effect on cognitive function. Speed and accuracy dependent tasks are adversely affected within 3 hours of fluid deprivation 
, and mathematical ability, short-term working memory, perceptive discrimination and eye-hand coordination are affected by levels of dehydration between 1%-4% [40,41]
. The effects may be mediated via altered cerebral neurotransmission due to hyperosmolality and electrolyte shifts and/or changes in blood brain barrier permeability. Current theories include alterations in the activity of nitric oxide synthase, which is a key enzyme facilitating learning and memory, and changes in central dopaminergic and noradrenergic pathways [42,43]
. The reticular activating system subserving attention and wakefulness; the autonomic structures regulating psychomotor functions; and the cortical and mid-brain structures responsible for thought, memory and perception appear most vulnerable, thus contributing to the late afternoon performance decline.
Our study was limited to a small group of athletes from a single martial art discipline. Furthermore, the participants’ lifestyle and training in between test sessions were not controlled. Other potential confounders include the duration of the previous night's sleep and daytime naps, as well as the time of awakening, which were not regulated in this study.