Kastner Sabine, O'Connor Daniel H, Fukui Miki M, Fehd Hilda M, Herwig Uwe, Pinsk Mark A
Department of Psychology, Center for the Study of Brain, Mind, and Behavior, Princeton University, Princeton, New Jersey 08544, USA.
J Neurophysiol. 2004 Jan;91(1):438-48. doi: 10.1152/jn.00553.2003. Epub 2003 Sep 17.
In the human brain, little is known about the functional anatomy and response properties of subcortical nuclei containing visual maps such as the lateral geniculate nucleus (LGN) and the pulvinar. Using functional magnetic resonance imaging (fMRI) at 3 tesla (T), collective responses of neural populations in the LGN were measured as a function of stimulus contrast and flicker reversal rate and compared with those obtained in visual cortex. Flickering checkerboard stimuli presented in alternation to the right and left hemifields reliably activated the LGN. The peak of the LGN activation was found to be on average within +/-2 mm of the anatomical location of the LGN, as identified on high-resolution structural images. In all visual areas except the middle temporal (MT), fMRI responses increased monotonically with stimulus contrast. In the LGN, the dynamic response range of the contrast function was larger and contrast gain was lower than in the cortex. Contrast sensitivity was lowest in the LGN and V1 and increased gradually in extrastriate cortex. In area MT, responses were saturated at 4% contrast. Response modulation by changes in flicker rate was similar in the LGN and V1 and occurred mainly in the frequency range between 0.5 and 7.5 Hz; in contrast, in extrastriate areas V4, V3A, and MT, responses were modulated mainly in the frequency range between 7.5 and 20 Hz. In the human pulvinar, no activations were obtained with the experimental designs used to probe response properties of the LGN. However, regions in the mediodorsal right and left pulvinar were found to be consistently activated by bilaterally presented flickering checkerboard stimuli, when subjects attended to the stimuli. Taken together, our results demonstrate that fMRI at 3 T can be used effectively to study thalamocortical circuits in the human brain.
在人类大脑中，对于包含视觉图谱的皮层下核团，如外侧膝状体核（LGN）和丘脑枕的功能解剖结构及反应特性，人们了解甚少。利用3特斯拉（T）的功能磁共振成像（fMRI），测量了LGN中神经群体的集体反应，作为刺激对比度和闪烁反转率的函数，并与在视觉皮层中获得的反应进行比较。交替呈现给左右半视野的闪烁棋盘格刺激可靠地激活了LGN。LGN激活的峰值平均位于高分辨率结构图像上确定的LGN解剖位置的±2毫米范围内。在除颞中回（MT）以外的所有视觉区域，fMRI反应随刺激对比度单调增加。在LGN中，对比度函数的动态反应范围更大，对比度增益低于皮层。LGN和V1中的对比度敏感性最低，在纹外皮层中逐渐增加。在MT区域，4%对比度时反应达到饱和。LGN和V1中闪烁频率变化引起的反应调制相似，主要发生在0.5至7.5赫兹的频率范围内；相比之下，在纹外区域V4、V3A和MT中，反应主要在7.5至20赫兹的频率范围内受到调制。在人类丘脑枕中，用于探测LGN反应特性的实验设计未获得激活。然而，当受试者关注刺激时，发现双侧呈现的闪烁棋盘格刺激能持续激活左右丘脑枕的内侧背侧区域。综上所述，我们的结果表明3T的fMRI可有效地用于研究人类大脑中的丘脑皮质回路。
