The Journal of Neurophysiology Vol. 83 No. 3 March 2000, pp. 1701-1709
Copyright ©2000 by the American Physiological Society

Fast Reaction to Different Sensory Modalities Activates Common Fields in the Motor Areas, but the Anterior Cingulate Cortex is Involved in the Speed of Reaction

 ¹Department of Neuroscience, Division of Human Brain Research, The Karolinska Institute, 171 77 Stockholm, Sweden;  ²Institute of Equilibrium Research, Gifu University School of Medicine, Gifu 500;  ³Department of Nuclear Medicine and Radiology, Institute of Development, Aging and Cancer, Tohoku University, Sendai 980, Japan;  ⁴Department of Neuroanatomy and C. and O. Vogt Institute for Brain Research, University of Düsseldorf, D-40001 Düsseldorf; and  ⁵Institute of Medicine, Research Center Jülich, D-52425 Jülich, Germany

Naito, Eiichi, Shigeo Kinomura, Stefan Geyer, Ryuta Kawashima, Per E. Roland, and Karl Zilles. Fast Reaction to Different Sensory Modalities Activates Common Fields in the Motor Areas, but the Anterior Cingulate Cortex is Involved in the Speed of Reaction. J. Neurophysiol. 83: 1701-1709, 2000. We examined which motor areas would participate in the coding of a simple opposition of the thumb triggered by auditory, somatosensory and visual signals. We tested which motor areas might be active in response to all three modalities, which motor structures would be activated specifically in response to each modality, and which neural populations would be involved in the speed of the reaction. The subjects were required to press a button with their right thumb as soon as they detected a change in the sensory signal. The regional cerebral blood flow (rCBF) was measured quantitatively with ¹⁵O-butanol and positron emission tomography (PET) in nine normal male subjects. Cytoarchitectural areas were delimited in 10 post mortem brains by objective and quantitative methods. The images of the post mortem brains subsequently were transformed into standard anatomic format. One PET scanning for each of the sensory modalities was done. The control condition was rest with the subjects having their eyes closed. The rCBF images were anatomically standardized, and clusters of significant changes in rCBF were identified. These were localized to motor areas delimited on a preliminary basis, such as supplementary motor area (SMA), dorsal premotor zone (PMD), rostral cingulate motor area (CMAr), and within areas delimited by using microstructural i.e., cytoarchitectonic criteria, such as areas 4a, 4p, 3a, 3b, and 1. Fields of activation observed as a main effect for all three modalities were located bilaterally in the SMA, CMAr, contralateral PMD, primary motor (M1), and primary somatosensory cortex (SI). The activation in M1 engaged areas 4a and 4p and expanded into area 6. The activation in SI engaged areas 3b, 1, and extended into somatosensory association areas and the supramarginal gyrus posteriorly. We identified significant activations that were specific for each modality in the respective sensory association cortices, though no modality specific regions were found in the motor areas. Fields in the anterior cingulate cortex, rostral to the CMAr, consistently showed significant negative correlation with mean reaction time (RT) in all three tasks. These results show that simple reaction time tasks activate many subdivisions of the motor cortices. The information from different sensory modalities converge onto the common structures: the contralateral areas 4a, 4p, 3b, 1, the PMD, and bilaterally on the SMA and the CMAr. The anterior cingulate cortex might be a key structure which determine the speed of reaction in simple RT tasks.