Increased frontal brain activation during walking while dual tasking: an fNIRS study in healthy young adults

Background: Accumulating evidence suggests that gait is influenced by higher order cognitive and cortical control mechanisms. Recently, several studies used functional near infrared spectroscopy (fNIRS) to examine brain activity during walking, demonstrating increased oxygenated hemoglobin (HbO(2)) levels in the frontal cortex during walking while subjects completed a verbal cognitive task. It is, however, still unclear whether this increase in activation was related to verbalization, if the response was specific to gait, or if it would also be observed during standing, a different motor control task. The aim of this study was to investigate whether an increase in frontal activation is specific to dual tasking during walking. Methods: Twenty-three healthy young adults (mean 30.9 +/- 3.7 yrs, 13 females) were assessed using an electronic walkway. Frontal brain activation was assessed using an fNIRS system consisting of two probes placed on the forehead of the subjects. Assessments included: walking in a self-selected speed; walking while counting forward; walking while serially subtracting 7s (Walking+S7); and standing while serially subtracting 7s (Standing+S7). Data was collected from 5 walks of 30 meters in each condition. Twenty seconds of quiet standing before each walk served as baseline frontal lobe activity. Repeated Measures Analysis of Variance (RM ANOVA) tested for differences between the conditions. Results: Significant differences were observed in HbO(2) levels between all conditions (p = 0.007). HbO(2) levels appeared to be graded; walking alone demonstrated the lowest levels of HbO(2) followed by walking+counting condition (p = 0.03) followed by Walking+S7 condition significantly increased compared to the two other walking conditions (p < 0.01). No significant differences in HbO2 levels were observed between usual walking and the standing condition (p = 0.38) or between standing with or without serial subtraction (p = 0.76). Conclusions: This study provides direct evidence that dual tasking during walking is associated with frontal brain activation in healthy young adults. The observed changes are apparently not a response to the verbalization of words and are related to the cognitive load during gait.