Program in Rehabilitation Science, University of Minnesota, Minneapolis, MN, USA.
Cortex. 2010 Mar;46(3):310-21. doi: 10.1016/j.cortex.2009.02.024. Epub 2009 Apr 7.
Controversy exists regarding within-limb somatotopy, i.e., organization of representations of within-limb segments (e.g., elbow, fingers), in the primary motor cortex (M1). While some believe that within-limb representations overlap, others postulate somatotopic distinction. The purpose of our study was to aid the resolution of this controversy by exploring a) overlap between finger and elbow representations using high-resolution functional magnetic resonance imaging (fMRI), b) somatotopic differences between the two representations with and without the overlap, c) different location markers--center of mass (COM) and peak of activation (POA) and d) intensity differences between the two representations with and without the overlap.
Twenty-four subjects underwent fMRI during finger and elbow tracking for definition of activation-based finger and elbow representations and their overlapping parts. Differential analysis was used to generate parts of finger and elbow representations that did not overlap. Location measures, COM and POA and fMRI signal intensity for all parts of finger and elbow representations were recorded.
Finger and elbow representations overlap but still possess distinct somatotopic centers, i.e., finger is lateral to overlap, which is lateral to the elbow. When overlap is excluded, locations of finger and elbow representations become more distinct. COM shows distinction along x, y and z-axes, but POA only shows distinction along the x-axis. Overlap has the highest intensity, while non-overlapping finger and elbow representations have the lowest intensity during finger and elbow tracking, respectively.
Somatotopic gradients exist in M1 despite the overlap. This finding supports 'functional somatotopy', i.e., within-limb representations overlap for multi-joint coordination, yet possess discrete centers for individuated control. Such a flexible somatotopy might allow representational reorganization. COM could be marker for 'location' and POA within in a high-intensity zone could emphasize 'reorganization' following learning/disease. Also, fMRI intensity could be a marker of change of overlap or somatotopic distinction.
肢体内部的躯体定位，即肢体内部各部位（如肘部、手指）在初级运动皮层（M1）中的代表区域，存在争议。一些人认为肢体内部的代表区域是重叠的，而另一些人则假设存在躯体定位差异。我们的研究目的是通过探索以下几个方面来帮助解决这一争议：a）使用高分辨率功能磁共振成像（fMRI）探索手指和肘部代表区域之间的重叠，b）在存在和不存在重叠的情况下，研究这两个代表区域之间的躯体定位差异，c）不同的位置标记——质心（COM）和激活峰值（POA），以及 d）在存在和不存在重叠的情况下，这两个代表区域之间的信号强度差异。
24 名受试者在手部和肘部跟踪期间接受 fMRI 检查，以定义基于激活的手部和肘部代表区域及其重叠部分。使用差异分析生成不重叠的手指和肘部代表区域部分。记录所有手指和肘部代表区域的位置测量值（COM 和 POA）和 fMRI 信号强度。
手指和肘部代表区域重叠，但仍具有明显的躯体定位中心，即手指位于重叠区域的外侧，而重叠区域位于肘部的外侧。当排除重叠时，手指和肘部代表区域的位置变得更加明显。COM 在 x、y 和 z 轴上具有明显的区别，但 POA 仅在 x 轴上具有明显的区别。在手指和肘部跟踪期间，重叠区域的信号强度最高，而不重叠的手指和肘部代表区域的信号强度最低。
尽管存在重叠，但 M1 中仍存在躯体定位梯度。这一发现支持“功能躯体定位”，即多关节协调导致肢体内部代表区域重叠，但为个体控制提供离散的中心。这种灵活的躯体定位可能允许代表区域的重组。COM 可以作为“位置”的标记，而 POA 位于高强度区域内，可以强调学习/疾病后“重组”。此外，fMRI 强度可以作为重叠或躯体定位差异变化的标志物。
