Journal of Neuroscience Methods 201 (2011) 142–148 Contents lists available at ScienceDirect Journal of Neuroscience Methods j o ur nal homep age: www.elsevier.com/locate/jneumeth TMS: A navigator for NIRS of the primary motor cortex? K.L.M. Koenraadt a,∗ , M.A.M. Munneke b , J. Duysens a,c , N.L.W. Keijsers a a Sint Maartenskliniek Nijmegen, Department of Research, Development, and Education, PO Box 9011, 6500 GM Nijmegen, The Netherlands b Radboud University Nijmegen Medical Centre, Donders Institute for Brain, Cognition and Behaviour, Department of Neurology/Clinical Neurophysiology, PO Box 9101, 6500 HB, Nijmegen, The Netherlands c Katholieke Universiteit Leuven, Faculty of Kinesiology and Rehabilitation Sciences, Department of Biomedical Kinesiology, Tervuursevest 101, BE-3001 Leuven, Belgium a r t i c l e i n f o Article history: Received 14 March 2011 Received in revised form 13 July 2011 Accepted 25 July 2011 Keywords: NIRS TMS Optode positioning Motor cortex Hemodynamic response a b s t r a c t Near-infrared spectroscopy (NIRS) is a non-invasive optical imaging technique, which is increasingly used to measure hemodynamic responses in the motor cortex. The location at which the NIRS optodes are placed on the skull is a major factor in measuring the hemodynamic responses optimally. In this study, the validity of using transcranial magnetic stimulation (TMS) in combination with a 3D motion analysis system to relocate the TMS derived position was tested. In addition, the main goal was to quantify the advantage of using TMS to locate the optimal position in relation to the most commonly used EEG C3 position. Markers were placed on the TMS coil and on the head of the subject. In eleven subjects, a TMS measurement was performed to determine the individual motor-evoked potential center-of-gravity (MEP-CoG). This procedure was repeated in nine subjects to test the validity. Subsequently, hemodynamic responses were measured at the MEP-CoG position and at the C3 position during a thumb abduction and adduction task. On average, the MEP-CoG location was located 19.2 mm away from the C3 position. The reproducibility study on the MEP-CoG relocation procedure revealed no systematic relocations. No differences in early and delayed hemodynamic responses were found between the C3 and MEP-CoG position. These results indicate that using TMS for NIRS optodes positioning on the motor cortex does not result in higher hemodynamic response amplitudes. This could be explained if NIRS and TMS assess slightly different functions. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Near-infrared spectroscopy (NIRS) is a non-invasive optical imaging method, relatively new in neuroscience studies compared to fMRI, PET, and EEG. Using light in the near-infrared range, it measures local hemodynamic changes in oxy-hemoglobin (OHb) and deoxy-hemoglobin (HHb) (Cope and Delpy, 1988) and thereby indirectly the local neural activity (Villringer and Dirnagl, 1995). The advantage of NIRS being portable, non-invasive, and less expensive compared to fMRI and PET makes NIRS an interesting neuro-imaging technique in, for example, the field of brain com- puter interfacing (BCI). In addition, NIRS does not require stringent motion restrictions and the subject preparation time can be much smaller compared to EEG. During the last decades, several studies have performed near- infrared spectroscopy measurements on the prefrontal cortex ∗ Corresponding author. Tel.: +31 243659329; fax: +31 243659154. E-mail addresses: k.koenraadt@maartenskliniek.nl (K.L.M. Koenraadt), MAM.munneke@neuro.umcn.nl (M.A.M. Munneke), j.duysens@maartenskliniek.nl, Jacques.Duysens@faber.kuleuven.be (J. Duysens), n.keijsers@maartenskliniek.nl (N.L.W. Keijsers). (Hoshi and Tamura, 1997; Herrmann et al., 2005; Hatakenaka et al., 2007), the visual cortex (Colier et al., 1999b; Wolf et al., 2002; Herrmann et al., 2008), and the motor cortex (Obrig et al., 1996; Jasdzewski et al., 2003; Holper et al., 2009). Most stud- ies revealed the typical hemodynamic response, an increase in OHb and a decrease in HHb, while performing cognitive, visual, or motor tasks. However, the results are not always consistent and some studies revealed opposite changes in OHb and HHb in one or more subjects. For example, a study by Hoshi et al. (1994) revealed decreases in both the HHb and OHb responses in nine of 33 subjects over frontal regions during a mental arithmetic task. Quaresima et al. (2005) found the typical activation response in four of eight subjects, whereas various unexpected patterns of activation were found in the other four subjects (lack of HHb decrease or even an HHb increase). A study by Bauernfeind et al. (2008) revealed oppo- site hemodynamic changes for the prefrontal cortex during mental arithmetic tasks in 11 of 12 subjects, and the other subject revealed decreases in both HHb and OHb. Similarly, a study by Sato et al. (2005) revealed that the motor cortex also shows substantial inter- subject variability of the hemodynamic responses. The typical OHb increase was seen in 90% of the cases; however, the decrease in HHb was noted in only 76% of the cases. Although most studies found the typical hemodynamic response of an increase in OHb and a 0165-0270/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jneumeth.2011.07.024