Maddaluno Ottavia, Guidali Giacomo, Zazio Agnese, Miniussi Carlo, Bolognini Nadia
Department of Psychology & NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy.
Department of Psychology & NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy; Ph.D. program in Neuroscience, School of Medicine and Surgery, University of Milano-Bicocca, Monza, Italy.
Cortex. 2020 May;126:173-181. doi: 10.1016/j.cortex.2020.01.008. Epub 2020 Jan 30.
Paired associative stimulation (PAS) protocols can be used to induce Hebbian plasticity in the human brain. A modified, cross-modal version, of the PAS (cross-modal PAS, cm-PAS) has been recently developed. The cm-PAS consists in the repetitive pairings of a transcranial magnetic stimulation (TMS) pulse over the primary somatosensory cortex (S1) and a visual stimulus depicting a hand being touched; a 20 ms of inter-stimulus interval (ISI) is required to affect S1 plasticity, in turn modulating tactile acuity and somatosensory evoked potentials. The present study explores the role of anticipatory simulation in the cm-PAS efficacy, which could be responsible for such a short ISI. To this aim, we compared the effect of the original, fixed-frequency, cm-PAS to that of a jittered version, in which the time interval between trials was not steady but jittered, hence avoiding the anticipation of the upcoming visual-touch stimulus. Moreover, in the jittered PAS, the ISI between the paired stimulations was varied: it could match the early, somatosensory-driven, activation of S1 (20 ms), or the mirror recruitment of S1 by touch observation (150 ms). Results showed that tactile acuity is enhanced by the fixed-frequency cm-PAS, with an ISI of 20 ms between paired stimulation (visual-touch stimulus and TMS pulse over S1), and also by the jittered cm-PAS but only if the ISI is of 150 ms. These findings suggest that the cm-PAS with a jittered frequency, by preventing an anticipatory pre-activation of S1, delays the timing of the interaction between the visual-touch stimulus and the cortical pulse. On a broader perspective, our study highlights the possible involvement of sensory anticipation, likely through mirror-like simulation mechanisms, in tactile mirroring, as well as its influence of the optimal interval between the afferent and the magnetic pulse during PAS protocols.
配对联想刺激（PAS）方案可用于在人脑中诱导赫布可塑性。最近开发了一种改良的、跨模态版本的PAS（跨模态PAS，cm-PAS）。cm-PAS包括在初级体感皮层（S1）上重复配对经颅磁刺激（TMS）脉冲和描绘手部被触摸的视觉刺激；需要20毫秒的刺激间隔（ISI）来影响S1可塑性，进而调节触觉敏锐度和体感诱发电位。本研究探讨了预期模拟在cm-PAS疗效中的作用，这可能是如此短的ISI的原因。为此，我们将原始的、固定频率的cm-PAS与抖动版本的效果进行了比较，在抖动版本中，试验之间的时间间隔不稳定而是抖动的，从而避免了对即将到来的视觉-触觉刺激的预期。此外，在抖动的PAS中，配对刺激之间的ISI是变化的：它可以与S1的早期体感驱动激活（20毫秒）相匹配，或者与通过触摸观察对S1的镜像募集（150毫秒）相匹配。结果表明，固定频率的cm-PAS（配对刺激之间的ISI为20毫秒，即视觉-触觉刺激和S1上的TMS脉冲）可提高触觉敏锐度，抖动的cm-PAS也可提高触觉敏锐度，但前提是ISI为150毫秒。这些发现表明，频率抖动的cm-PAS通过防止S1的预期预激活，延迟了视觉-触觉刺激与皮层脉冲之间相互作用的时间。从更广泛的角度来看，我们的研究强调了感觉预期可能通过类似镜像的模拟机制参与触觉镜像，以及其在PAS方案中对传入脉冲和磁脉冲之间最佳间隔的影响。
