Non-invasive measurement of neural inhibition in the human visual cortex

大脑必须不断筛选复杂的世界，从背景噪音中分离出相关信息。大脑通过抑制无关信号来实现这一壮举——有时是有意识地利用注意力，但通常是无意识地通过神经回路中的低级过程。随着我们对大脑如何对我们的经历做出反应有了更好的了解，我们越来越需要了解抑制是如何调节大脑的反应的。这是一个重大挑战。虽然现在可以使用功能磁共振成像（fMRI）等非侵入性方法来测量大脑活动，但我们不知道如何以类似的方式测量抑制。我们最近发现了一个潜在的抑制指数。使用一个我们知道抑制发生的模型，我们发现当抑制发生时，大脑的fMRI反应略有延迟。因此，我们认为这种拖延可以作为一种抑制措施，并设法对此进行详细研究。具体来说，我们需要知道是什么原因导致了这种明显的延迟——这是由于成像方法的分辨率导致我们无法看到的两个空间分离信号的关联，还是由于特定时间大脑的神经化学组成？这种延迟是否也发生在其他抑制模型中？是否同样的原因导致了这种延迟？不管其原因是什么，这种延迟是否携带了相关信息，可以帮助我们理解潜在的神经回路？为了回答这些问题，这个研究项目将改进高分辨率的功能磁共振成像方法，并结合自然和人工刺激大脑来调节抑制，将能够回答这些问题。研究结果将对我们测量和解释大脑信号的方法以及理解在自然处理过程中抑制是如何参与和调节的具有革命性意义。

The brain must constantly sift through a complex world to separate relevant information from background noise. The brain achieves this feat by suppressing irrelevant signals--sometimes consciously through use of attention, but often unconsciously through low-level processes in neural circuits. As we gain a better understanding of how the brain responds to aspects of our experience, we increasingly need to understand how suppression modulates the response of the brain. This is a major challenge. While it is now possible to measure activity in the brain using non-invasive methods such as functional magnetic resonance imaging (fMRI), we do not know how to measure suppression similarly. We have recently discovered a potential index of suppression. Using a model where we know suppression occurs, we have found that the fMRI response of the brain is slightly delayed when suppression is engaged. We therefore think that this delay could serve as a measure of suppression, and seek to study it in detail. Specifically, we need to know what causes the apparent delay--is it a correlate of two spatially separate signals that we cannot see because of the resolution of our imaging method, or is it due to the neurochemical makeup of the brain at a given time? Does the delay occur in other suppression models, and do the same causes contribute to it? Regardless of its causes, does the delay carry relevant information that can help us understand the underlying neural circuits? To answer these questions, this program of research will refine high-resolution fMRI methods and, combined with natural and artificial stimulation of the brain to modulate suppression, will be able to answer these questions. The results will be transformative in both our approach to measuring and interpreting brain signals and in understanding how suppression is engaged and modulated during natural processing.