Jung Patrick, Baumgärtner Ulf, Bauermann Thomas, Magerl Walter, Gawehn Jochen, Stoeter Peter, Treede Rolf-Detlef
Institute of Physiology and Pathophysiology, Johannes Gutenberg-University, Saarstr. 21, 55099 Mainz, Germany.
Neuroimage. 2003 Jul;19(3):913-23. doi: 10.1016/s1053-8119(03)00164-2.
Brain asymmetry is a phenomenon well known for handedness and language specialization and has also been studied in motor cortex. Less is known about hemispheric asymmetries in the somatosensory cortex. In the present study, we systematically investigated the representation of somatosensory function analyzing early subcortical and cortical somatosensory-evoked potentials (SEP) after electrical stimulation of the right and left median nerve. In 16 subjects, we compared thresholds, the peripheral neurogram at Erb point, and, using MRI-based EEG source analysis, the P14 brainstem component as well as N20 and P22, the earliest cortical responses from the primary sensorimotor cortex. Handedness was documented using the Edinburgh Inventory and a dichotic listening test was performed as a measure for language dominance. Whereas thresholds, Erb potential, and P14 were symmetrical, amplitudes of the cortical N20 showed significant hemispheric asymmetry. In the left hemisphere, the N20 amplitude was higher, its generator was located further medial, and it had a stronger dipole moment. There was no difference in dipole orientation. As a possible morphological correlate, the size of the left postcentral gyrus exceeded that of the right. The cortical P22 component showed a lower amplitude and a trend toward weaker dipole strength in the left hemisphere. Across subjects, there were no significant correlations between laterality indices of N20, the size of the postcentral gyrus, handedness, or ear advantage. These data show that asymmetry of median nerve SEP occurs at the cortical level, only. However, both functional and morphological cortical asymmetry of somatosensory representation appears to vary independently of motor and language functions.
脑不对称是一种因利手和语言特化而广为人知的现象，并且也已在运动皮层中得到研究。关于躯体感觉皮层的半球不对称，人们了解得较少。在本研究中，我们通过分析电刺激右侧和左侧正中神经后早期的皮层下和皮层躯体感觉诱发电位（SEP），系统地研究了躯体感觉功能的表征。在16名受试者中，我们比较了阈值、在埃尔布点的外周神经电图，并且使用基于磁共振成像的脑电图源分析，比较了P14脑干成分以及N20和P22，后者是来自初级感觉运动皮层的最早皮层反应。使用爱丁堡量表记录利手情况，并进行双耳分听测试作为语言优势的一项测量。虽然阈值、埃尔布电位和P14是对称的，但皮层N20的振幅显示出显著的半球不对称。在左半球，N20振幅更高，其发生器位于更内侧，并且具有更强的偶极矩。偶极方向没有差异。作为一种可能的形态学关联，左侧中央后回的大小超过右侧。皮层P22成分在左半球显示出较低的振幅和偶极强度较弱的趋势。在所有受试者中，N20的偏侧性指数、中央后回的大小、利手情况或耳优势之间均无显著相关性。这些数据表明，正中神经SEP的不对称仅发生在皮层水平。然而，躯体感觉表征的功能性和形态学皮层不对称似乎独立于运动和语言功能而变化。
