Department of Physiology and Pharmacology, University of Western Ontario, London, ON, Canada N6A 3K7.
Neuroimage. 2013 Jan 1;64:458-65. doi: 10.1016/j.neuroimage.2012.09.034. Epub 2012 Sep 20.
Much of what is known about the cortical organization for audition in humans draws from studies of auditory cortex in the cat. However, these data build largely on electrophysiological recordings that are both highly invasive and provide less evidence concerning macroscopic patterns of brain activation. Optical imaging, using intrinsic signals or dyes, allows visualization of surface-based activity but is also quite invasive. Functional magnetic resonance imaging (fMRI) overcomes these limitations by providing a large-scale perspective of distributed activity across the brain in a non-invasive manner. The present study used fMRI to characterize stimulus-evoked activity in auditory cortex of an anesthetized (ketamine/isoflurane) cat, focusing specifically on the blood-oxygen-level-dependent (BOLD) signal time course. Functional images were acquired for adult cats in a 7 T MRI scanner. To determine the BOLD signal time course, we presented 1s broadband noise bursts between widely spaced scan acquisitions at randomized delays (1-12 s in 1s increments) prior to each scan. Baseline trials in which no stimulus was presented were also acquired. Our results indicate that the BOLD response peaks at about 3.5s in primary auditory cortex (AI) and at about 4.5 s in non-primary areas (AII, PAF) of cat auditory cortex. The observed peak latency is within the range reported for humans and non-human primates (3-4 s). The time course of hemodynamic activity in cat auditory cortex also occurs on a comparatively shorter scale than in cat visual cortex. The results of this study will provide a foundation for future auditory fMRI studies in the cat to incorporate these hemodynamic response properties into appropriate analyses of cat auditory cortex.
关于人类听觉皮层的结构，我们的大部分认知都来源于对猫听觉皮层的研究。然而，这些数据主要基于电生理记录，这些记录不仅具有高度侵入性，而且提供的关于大脑激活宏观模式的证据也较少。使用内源性信号或染料的光学成像是一种非侵入性的方法，可以可视化基于表面的活动，但也具有很强的侵入性。功能磁共振成像（fMRI）通过提供一种非侵入性的方式，从大脑的大范围角度观察分布活动，克服了这些限制。本研究使用 fMRI 来描述麻醉（氯胺酮/异氟烷）猫听觉皮层的刺激诱发活动，特别关注血氧水平依赖（BOLD）信号的时间过程。功能图像是在 7T MRI 扫描仪中对成年猫进行采集的。为了确定 BOLD 信号的时间过程，我们在每次扫描前，在广泛间隔的扫描采集之间以随机延迟（1-12 秒，以 1 秒递增）呈现 1 秒宽带噪声爆发。还采集了没有呈现刺激的基线试验。我们的结果表明，BOLD 反应在猫初级听觉皮层（AI）中约 3.5 秒达到峰值，在非初级区域（AII、PAF）中约 4.5 秒达到峰值。观察到的峰值潜伏期在人类和非人类灵长类动物（3-4 秒）报告的范围内。猫听觉皮层的血液动力学活动的时间过程也比猫视觉皮层发生的时间短。这项研究的结果将为未来猫的听觉 fMRI 研究提供基础，以便将这些血液动力学反应特性纳入对猫听觉皮层的适当分析中。
