Measuring Prefrontal Hemodynamic Responses Using Functional Near-Infrared Spectroscopy During Mobility for a Child With Motor Impairment

PURPOSE: The purpose of this research was to investigate prefrontal workload using functional near-infrared spectroscopy (fNIRS) in a young child with motor impairment as part of a study examining robot-assisted mobility. The robot is controlled by the weight shift, as occurs when a child reaches toward an object. The study addressed two questions: (1) Will there be a difference in cognitive workload during passive movement compared to active? (2) Will cognitive workload during active movement decrease with greater robot driving experience and ability? The purpose of this study was to explore the use of fNIRS as a potential measure of brain activation during motor learning.

BACKGROUND: Functional near-infrared spectroscopy (fNIRS) provides a safe, noninvasive, and affordable method for measuring hemodynamic responses associated with brain activity. Although fNIRS has been available for several years, its use has not been documented in the occupational therapy literature. This study explores the feasibility of using fNIRS data to supplement behavioral observations related to motor learning with robotic-assisted locomotion.

DESIGN: A case study research design was selected for this study. The participant was a boy age 2.5 yr with cerebral palsy, recruited by convenience sampling. The criterion for inclusion was an absence of functional independent mobility (i.e., no ability to crawl on hands and knees or walk).

METHOD: The fNIRS was attached 2 cm above the child’s right eyebrow and secured using a soft headband. The child participated in 12 20-min robotic mobility sessions. Driving ability was measured by the child’s ability to retrieve an object offered at three specified distances to the front, the left, and the right of the child using a three-tiered prompting system. At the conclusion of each session, fNIRS data were recorded during active movement, when the child independently drove the robot toward a motivating item, and passive movement, when the experimenter carried the child to the item. ELAN 4.9.3 annotation software (Max Planck Institute for Psycholinguistics, Nijmegen, The Netherlands) was used to annotate behavior from videotapes of active and passive movement during fNIRS data recording. Data from the fNIRS system were analyzed and compared synchronously to observational data and to driving experience.

RESULTS: Results indicate that there was a decrease in oxygenation from early sessions to later sessions during active movement. The child’s performance in driving ability was very inconsistent, so that decrease in oxygenation could not be associated with increased driving ability. Findings were inconclusive regarding differences in active and passive movement.

DISCUSSION: The decrease in oxygenation observed from early to later sessions supports the hypothesis that cognitive workload would decrease as driving experience increased. However, some of our initial data were uninterpretable due to confounding variables, such as light exposure during transitions, leading us to believe that our results were not solely based on changes in our independent variable. We made a number of changes to our protocol over the first several sessions in order to adjust robot functions to the child’s abilities and to facilitate clearer fNIR readings, which negatively impacted our ability to make comparisons between variables.

IMPACT STATEMENT: This pilot study provides preliminary support for the use of fNIRS technology in future occupational therapy research as a measurement tool of cognitive workload.