Van Camp N, Verhoye M, Van der Linden A
Bio-Imaging Laboratory, University of Antwerp, Groenenborgerlaan 171, 2020 Antwerp, Belgium.
NMR Biomed. 2006 Feb;19(1):10-7. doi: 10.1002/nbm.986.
Functional MRI (fMRI) during electrical somatosensory stimulation of the rat forepaw is a widely used model to investigate the functional organization of the somatosensory cortex or to study the underlying mechanisms of the blood oxygen level-dependent (BOLD) response. In reality, somatosensory stimuli have complex timing relationships and are of long duration. However, by default electrical sensory stimulation seems to be performed at an extremely short pulse width (0.3 ms). As the pulse duration may alter the neuronal response, our aim was to investigate the influence of a much longer stimulus pulse width (10 ms) using BOLD fMRI during electrical forepaw stimulation. The optimal neuronal response was investigated by varying the stimulus frequency at a fixed pulse duration (10 ms) and amplitude (1 mA). In a parallel experiment we measured the neuronal response directly by recording the somatosensory evoked potentials (SEPs). Quantification of the BOLD data revealed a shift in the optimal response frequencies to 8-10 Hz compared with 1 Hz at 0.3 ms. The amplitude of the recorded SEPs decreased with increasing stimulation frequency and did not display any correlation with the BOLD data. Nevertheless, the summated SEPs, which are a measure of the integrated neuronal activity as a function of time, displayed a similar response profile, with a similar maximum as observed by relative BOLD changes. This shift in optimal excitation frequencies might be related to the fact that an increased pulse width of an electrical stimulus alters the nature of the stimulation, generating also sensorimotor instead of merely somatosensory input. This may influence or alter the activated pathways, resulting in a shift in the optimal response profile.
在对大鼠前爪进行电躯体感觉刺激期间进行的功能磁共振成像（fMRI），是一种广泛用于研究躯体感觉皮层功能组织或探究血氧水平依赖（BOLD）反应潜在机制的模型。实际上，躯体感觉刺激具有复杂的时间关系且持续时间较长。然而，默认情况下电感觉刺激似乎是在极短的脉冲宽度（0.3毫秒）下进行的。由于脉冲持续时间可能会改变神经元反应，我们的目的是在电前爪刺激期间使用BOLD fMRI研究更长刺激脉冲宽度（10毫秒）的影响。通过在固定脉冲持续时间（10毫秒）和幅度（1毫安）下改变刺激频率来研究最佳神经元反应。在一项平行实验中，我们通过记录躯体感觉诱发电位（SEP）直接测量神经元反应。对BOLD数据的量化显示，与0.3毫秒时的1赫兹相比，最佳反应频率转移到了8 - 10赫兹。记录的SEP幅度随刺激频率增加而降低，并且与BOLD数据没有任何相关性。然而，作为时间函数的综合神经元活动度量的总和SEP显示出类似的反应曲线，其最大值与相对BOLD变化所观察到的相似。最佳兴奋频率的这种转移可能与以下事实有关：电刺激脉冲宽度增加会改变刺激的性质，还会产生感觉运动而非仅仅是躯体感觉输入。这可能会影响或改变激活的通路，导致最佳反应曲线发生转移。
