Du Xiaoming, Choa Fow-Sen, Summerfelt Ann, Tagamets Malle A, Rowland Laura M, Kochunov Peter, Shepard Paul, Hong L Elliot
Department of Psychiatry, Maryland Psychiatric Research Center, University of Maryland School of Medicine, P.O. Box 21247, Baltimore, MD, 21228, USA.
Exp Brain Res. 2015 Feb;233(2):671-7. doi: 10.1007/s00221-014-4146-z. Epub 2014 Nov 16.
Integration of diverse synaptic inputs is a basic neuronal operation that relies on many neurocomputational principles, one of which is neural summation. However, we lack empirical understanding of neuronal summation in the human brains in vivo. Here, we explored the effect of neural summation on the motor cortex using two subthreshold pulses of transcranial magnetic stimulation (TMS), each with intensities ranging from 60 to 95% of the resting motor threshold (RMT) and interstimulus interval (ISI) varying from 1 to 25 ms. We found that two subthreshold TMS pulses can produce suprathreshold motor response when ISIs were less than 10 ms, most prominent at 1, 1.5 and 3 ms. This facilitatory, above-threshold response was evident when the intensity of the subthreshold pulses was above 80% of RMT but was absent as the intensity was 70% or below. Modeling of the summation data across intensity suggested that they followed an exponential function with excellent model fitting. Understanding the constraints for inducing summation of subthreshold stimulations to generate above-threshold response may have implications in modeling neural operations and potential clinical applications.
整合多样的突触输入是一种基本的神经元活动，它依赖于许多神经计算原理，其中之一是神经总和。然而，我们缺乏对人类大脑中神经元总和的体内实证理解。在此，我们使用两个阈下经颅磁刺激（TMS）脉冲来探究神经总和对运动皮层的影响，每个脉冲的强度范围为静息运动阈值（RMT）的60%至95%，刺激间隔（ISI）从1至25毫秒不等。我们发现，当ISI小于10毫秒时，两个阈下TMS脉冲可产生阈上运动反应，在1、1.5和3毫秒时最为显著。当阈下脉冲强度高于RMT的80%时，这种促进性的阈上反应很明显，但当强度为70%或更低时则不存在。对不同强度下总和数据的建模表明，它们遵循指数函数，模型拟合效果极佳。理解诱导阈下刺激总和以产生阈上反应的限制条件可能对神经活动建模和潜在的临床应用具有启示意义。
