Task complexity relates to activation of cortical motor areas during uni- and bimanual performance: A functional NIRS study

Hand motor tasks are frequently used to assess impaired motor function in neurology and neurorehabilitation. Assessments can be varied by means of hand laterality, i.e. unimanual or bimanual performance, as well as by means of task complexity, i.e. different degrees ranging from simple to complex sequence tasks. The resulting functional activation in human primary motor cortex (M1) has been studied intensively by traditional neuroimaging methods. Previous studies using functional near-infrared spectroscopy (fNIRS) investigated simple hand motor tasks. However, it is unknown whether fNIRS can also detect changes in response to increasing task complexity. Our hypothesis was to show that fNIRS could detect activation changes in relation to task complexity in uni- and bimanual tasks. Sixteen healthy right-handed subjects performed five finger-tapping tasks: unimanual left and right, simple and complex tasks as well as bimanual complex tasks. We found significant differences in oxy-hemoglobin (O(2)Hb) and deoxy-hemoglobin (HHb) concentration in the right hemisphere over M1. Largest O(2)Hb concentration changes were found during complex (0.351 +/- 0.051 mu mol/l) and simple (0.275 +/- 0.054 mu mol/l) right hand tasks followed by bimanual (0.249 +/- 0.047 mu mol/l), complex (0.154 +/- 0.034 mu mol/l) and simple (0.110 +/- 0.034 mu mol/l) left hand tasks. Largest HHb concentration changes were found during bimanual (-0.138 +/- 0.006 mu mol/l) tasks, followed by simple right hand (-0.12 +/- 0.016 mu mol/l), complex left (-0.0875 +/- 0.007 mu mol/l), complex right (-0.0863 +/- 0.005 mu mol/l) and simple left (-0.0674 +/- 0.005 mu mol/l) hand tasks. We report for the first time that fNIRS detects oxygenation changes in relation to task complexity during finger-tapping. The study aims to contribute to the establishment of fNIRS as a neuroimaging method to assess hand motor function in clinical settings where traditional neuroimaging methods cannot be applied. (C) 2009 Elsevier Inc. All rights reserved.