Time of day and caffeine influence some neuropsychological tests in the elderly

We report that performance on neuropsychological tests used in the diagnosis of dementia can be influenced by external factors such as time of day (TOD) and caffeine. This study investigates TOD effects on cognitive performance in the elderly. The optimal TOD at which an individual is at his or her maximal arousal alters with age, and in the elderly, typically occurs in the morning. Neuropsychological test scores from healthy elderly participants were analyzed to determine whether TOD affected performance. Interactions between caffeine and TOD were also investigated. Across 2 data sets that were analyzed, significant TOD effects were noted for Pattern-Comparison Speed (PCS), Letter-Comparison Speed (LCS; Salthouse & Babcock, 1991), Trail Making Test Part A (Reitan, 1958), Mini-Mental State Examination (MMSE; Folstein, Folstein, & McHugh, 1975) and the Graded Naming Test (GNT; McKenna & Warrington, 1980), revealing a decline in test scores as TOD increases. Significant interactions between TOD, age, and the PCS, LCS, and Trail Making Part A were noted in Data Set 1. In Data Set 2, caffeine intake had been controlled for, and significant interactions between caffeine, TOD, and scores on the MMSE and GNT were found. The TOD and caffeine effects highlight the need to control for these external factors when scoring the assessments. This conclusion has implications for the clinical procedure of diagnosis and treatment of dementia and Alzheimer's.