Constable R T, Carpentier A, Pugh K, Westerveld M, Oszunar Y, Spencer D D
Department of Diagnostic Radiology, Yale University, New Haven, Connecticut, 06510, USA.
Neuroimage. 2000 Jul;12(1):55-62. doi: 10.1006/nimg.2000.0583.
Functional neuroimaging of the hippocampal formation has presented a challenge to neuroscientists because of the small size of the hippocampus proper and its location at the basal level of the brain. Choosing the appropriate control condition for subtraction-based studies has also proved difficult. Event-related experimental designs are a powerful tool in behavioral and electrophysiological studies. Recently, such experimental designs have been applied to functional MR imaging studies but these studies used large intertrial intervals in order to separate the slow blood flow response from temporally adjacent events, severely limiting the number of events that can be presented in a single run. This leads to poor statistical power and restrictions on the design of the experimental paradigm. We present data obtained using a rapidly presented, randomized event-related paradigm, combined with a novel fMRI imaging method designed to improve imaging in basal brain regions. The results demonstrate bilateral activation in the hippocampal formation in identification of novel complex scenes distinct from a learned basis set of complex scenes. Differential activation is obtained in the counter task of identifying a learned target complex scene against a background of novel scenes. The results are also compared with the more conventional block design complex scene paradigms previously reported by others. The block design provides strong posterior activation, likely related more to visual scene processing, whereas the event-related design provides more anterior hippocampal activation with the encoding of novel scenes.
海马结构的功能神经成像一直是神经科学家面临的一项挑战，这是因为海马本身体积小且位于脑基底部。事实也证明，为基于减法的研究选择合适的对照条件很困难。事件相关实验设计是行为和电生理研究中的有力工具。最近，此类实验设计已应用于功能磁共振成像研究，但这些研究使用了较长的试次间隔，以便将缓慢的血流反应与时间上相邻的事件区分开，这严重限制了单次扫描中可呈现的事件数量。这导致统计效能低下以及对实验范式设计的限制。我们展示了使用快速呈现的随机事件相关范式获得的数据，并结合了一种旨在改善脑基底部区域成像的新型功能磁共振成像方法。结果表明，在识别与一组学习到的复杂场景不同的新复杂场景时，海马结构出现双侧激活。在从新场景背景中识别学习到的目标复杂场景的反向任务中获得了差异激活。研究结果还与其他人先前报道的更传统的组块设计复杂场景范式进行了比较。组块设计提供强烈的后部激活，可能更多地与视觉场景处理有关，而事件相关设计在对新场景进行编码时提供更多的海马前部激活。
