Correlation between force and motor cortical activation measured by near-infrared spectroscopy (NIRS)

NemoImage 13, Number 6.2001, Part 2 of 2 Parts 10 E bL@

SENSORMOTOR

Correlation between force and motor cortical activation measured by near-infrared spectroscopy(NIRS) Nobue K. Iwata*, Katsuyuki

Sakai*t, Yoshikazu Ugawa*, Ichiro Kanazawa*

*Department of Neurology, University of Tokyo, Japan t Wellcome Department of Cognitive Neurology, Institute of Neurology, London, UK Near-infrared spectroscopy (NJRS) is a new non-invasive method to image human brain activities. The method has successfully used to study various human brain functions such as motor, visual, or language processes.However, the relationship between NJRS signals and task loads has not been well described so far. In the present study, we modulated grip-force levels, and examined correlation of NJRS signals in the primary hand motor cortex with the force levels. Subjects

and Methods

Seven normal right-handed volunteers participated in the study. They were tested on 5 conditions with different force levels, ranging from 10 to 50% of maximal handgrip power. Each condition was repeated for 5 blocks. In each block subjects made phasic force-grip of right hand for 15 seconds at a rate of 1 Hz paced by a metronome. Brain activation was continuously measured by NJRS using a 24-channel optical topography system (ETG-100; Hitachi Medical Corporation, Tokyo, Japan) with sampling intervals of 500 ms (l)(2) (3). The detecting optical fiber array covered the 9 x 9 cm square area of the left fronto-parietal region, with the presumed hand motor area at the center. The NJRS system was equipped with incident light fibers for two wavelengths, which allowed us to calculate changes in oxyhemoglobin (oxy-Hb) and deoxy-hemoglobin (deoxy-Hb). We calculated total hemoglobin (total- Hb) changes, defined as the sum of oxy-Hb and deoxy-Hb changes in each of the force-grip conditions. Results

and Discussion

The concentration changes of total-Hb at the primary hand motor area increased with the force levels. This relationship between to&U-lb increase in the primary hand motor area and the force levels was logarithmic. Such relationship between cerebral activity in tire motor areas and the force levels was also reported in positron emission topography (PET) and functional magnetic resonance imaging (fMRf) studies (4)(5), and cross validation among different imaging techniques was demonstrated in human motor cortex. Our results suggest that NIRS can be used for quantitative measurement of brain activation. References

(1) (2) (3) (4)

Maki, A., Yamashita, Y., Ito, Y., Watanabe, E., Mayanagi, Y., and Koizumi, H., Med. Physics 22: 1997-2005 (1995). Watanabe, E., Yamashita, Y., Maki, A., Ito, Y., and Koizumi, H., Neurosci. Lett. 205: 41-44 (1996). Yamashita, Y., Maki, A., and Koizumi, H., J. Biomedical Optics 4: 414-417 (1999). Dettmers, C., Fink, G. R., Lemon, R. N., Stephan, K. M., Passingham, R. E., Silbersweig, D., Holmes, A., Ridding, M. C., Brooks, D. J. and Frackowiak, R. S., J. Neurophysiology 74: 802-15 (1995). (5) Dettmers, C., Connelly, A., Stephan, K. M., Turner, R., Friston, K. J., Frackowiak, R. S. and Gadain, D., G., Neuroimage 4: 201-9 (1996).

S1196