Blood Anne J, Pouratian Nader, Toga Arthur W
Laboratory of Neuro Imaging, Department of Neurology, Division of Brain Mapping, University of California, Los Angeles, California 90095, USA.
J Neurophysiol. 2002 Jul;88(1):422-37. doi: 10.1152/jn.2002.88.1.422.
Characterization of neurovascular relationships is critical to accurate interpretation of functional neuroimaging data. We have previously observed spatial uncoupling of optical intrinsic signal imaging (OIS) and evoked potential (EP) responses in rodent barrel cortex following simultaneous whisker and forelimb stimulation, leading to changes in OIS response magnitude. To further test the hypothesis that this uncoupling may have resulted from "passive" overspill of perfusion-related responses between functional regions, we conducted the present study using temporally staggered rather than simultaneous whisker and forelimb stimulation. This paradigm minimized overlap of neural responses in barrel cortex and forelimb primary somatosensory cortex (SI), while maintaining overlap of vascular response time courses between regions. When contrasted with responses to 1.5-s lone-whisker stimulation, staggered whisker and forelimb stimulation resulted in broadening of barrel cortex OIS response time course in the temporal direction of forelimb stimulation. OIS response peaks were also temporally shifted toward the forelimb stimulation period; time-to-peak was shorter (relative to whisker stimulus onset) when forelimb stimulation preceded whisker stimulation and longer when forelimb stimulation followed whisker stimulation. In contrast with OIS and EP magnitude decreases previously observed during simultaneous whisker/forelimb stimulation, barrel cortex OIS response magnitude increased during staggered stimulation and no detectable changes in underlying EP activity were observed. Spatial extent of barrel cortex OIS responses also increased during staggered stimulation. These findings provide further evidence for spatial uncoupling of OIS and EP responses, and emphasize the importance of temporal stimulus properties on the effects of this uncoupling. It is hypothesized that spatial uncoupling is a result of passive overspill of perfusion-related responses into regions distinct from those which are functionally active. It will be important to consider potential influences of this uncoupling when designing and interpreting functional imaging studies that use hemodynamic responses to infer underlying neural activity.
神经血管关系的表征对于准确解释功能性神经成像数据至关重要。我们之前观察到，在同时刺激胡须和前肢后，啮齿动物桶状皮层中光学内在信号成像（OIS）和诱发电位（EP）反应存在空间解耦，导致OIS反应幅度发生变化。为了进一步检验这种解耦可能是由于功能区域之间灌注相关反应的“被动”溢出所致的假设，我们进行了本研究，采用时间上错开而非同时进行的胡须和前肢刺激。这种范式最小化了桶状皮层和前肢初级体感皮层（SI）中神经反应的重叠，同时保持了区域间血管反应时间进程的重叠。与对1.5秒单胡须刺激的反应相比，错开的胡须和前肢刺激导致桶状皮层OIS反应时间进程在朝向肢体刺激的时间方向上变宽。OIS反应峰值在时间上也向肢体刺激期偏移；当肢体刺激先于胡须刺激时，达到峰值的时间较短（相对于胡须刺激开始），而当肢体刺激跟随胡须刺激时，达到峰值的时间较长。与之前在同时进行胡须/前肢刺激时观察到的OIS和EP幅度降低相反，在错开刺激期间桶状皮层OIS反应幅度增加，并且未观察到潜在EP活动的可检测变化。在错开刺激期间，桶状皮层OIS反应的空间范围也增加了。这些发现为OIS和EP反应的空间解耦提供了进一步的证据，并强调了时间刺激特性对这种解耦效应的重要性。据推测，空间解耦是灌注相关反应被动溢出到与功能活跃区域不同的区域的结果。在设计和解释使用血流动力学反应来推断潜在神经活动的功能成像研究时，考虑这种解耦的潜在影响将很重要。
