title: Measuring prefrontal cortical activity during dual task walking in patients with Parkinson's disease: feasibility of using a new portable fNIRS device.
abstract: BACKGROUND
  Many patients with Parkinson's disease (PD) have difficulties in performing a second task during walking (i.e., dual task walking). Functional near-infrared spectroscopy (fNIRS) is a promising approach to study the presumed contribution of dysfunction within the prefrontal cortex (PFC) to such difficulties. In this pilot study, we examined the feasibility of using a new portable and wireless fNIRS device to measure PFC activity during different dual task walking protocols in PD. Specifically, we tested whether PD patients were able to perform the protocol and whether we were able to measure the typical fNIRS signal of neuronal activity.
  
  
  METHODS
  We included 14 PD patients (age 71.2 ± 5.4 years, Hoehn and Yahr stage II/III). The protocol consisted of five repetitions of three conditions: walking while (i) counting forwards, (ii) serially subtracting, and (iii) reciting digit spans. Ability to complete this protocol, perceived exertion, burden of the fNIRS devices, and concentrations of oxygenated (O2Hb) and deoxygenated (HHb) hemoglobin from the left and right PFC were measured.
  
  
  RESULTS
  Two participants were unable to complete the protocol due to fatigue and mobility safety concerns. The remaining 12 participants experienced no burden from the two fNIRS devices and completed the protocol with ease. Bilateral PFC O2Hb concentrations increased during walking while serially subtracting (left PFC 0.46 μmol/L, 95 % confidence interval (CI) 0.12-0.81, right PFC 0.49 μmol/L, 95 % CI 0.14-0.84) and reciting digit spans (left PFC 0.36 μmol/L, 95 % CI 0.03-0.70, right PFC 0.44 μmol/L, 95 % CI 0.09-0.78) when compared to rest. HHb concentrations did not differ between the walking tasks and rest.
  
  
  CONCLUSIONS
  These findings suggest that a new wireless fNIRS device is a feasible measure of PFC activity in PD during dual task walking. Future studies should reduce the level of noise and inter-individual variability to enable measuring differences in PFC activity between different dual walking conditions and across health states.
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands ; Departments of Neurology, Geriatric Medicine, and Radboud Alzheimer Center, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Freek
authors.initials: F
authors.lastname: Nieuwhof
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands ; Departments of Neurology, Geriatric Medicine, and Radboud Alzheimer Center, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Miriam F
authors.initials: MF
authors.lastname: Reelick
authors.affiliation: Department of Neurology, Center for the study of Movement, Cognition, and Mobility, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel.
authors.forename: Inbal
authors.initials: I
authors.lastname: Maidan
authors.affiliation: Department of Neurology, Center for the study of Movement, Cognition, and Mobility, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel ; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Anat
authors.initials: A
authors.lastname: Mirelman
authors.affiliation: Department of Neurology, Center for the study of Movement, Cognition, and Mobility, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel ; Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Hausdorff
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands ; Departments of Neurology, Geriatric Medicine, and Radboud Alzheimer Center, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Marcel G M
authors.initials: MG
authors.lastname: Olde Rikkert
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands ; Departments of Neurology, Geriatric Medicine, and Radboud Alzheimer Center, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Bastiaan R
authors.initials: BR
authors.lastname: Bloem
authors.affiliation: EuroMov, University of Montpellier, Montpellier, France.
authors.forename: Makii
authors.initials: M
authors.lastname: Muthalib
authors.affiliation: Donders Institute for Brain, Cognition and Behaviour, Nijmegen, The Netherlands ; Departments of Neurology, Geriatric Medicine, and Radboud Alzheimer Center, Radboud University Medical Center, Nijmegen, The Netherlands.
authors.forename: Jurgen A H R
authors.initials: JA
authors.lastname: Claassen
keywords: Gait; Hemodynamics; Near-infrared; Parkinson’s disease; Prefrontal cortex; Spectroscopy