Maurer Andrew P, Vanrhoads Shea R, Sutherland Gary R, Lipa Peter, McNaughton Bruce L
Neural Systems, Memory, and Aging, University of Arizona, Tucson, 85724, USA.
Hippocampus. 2005;15(7):841-52. doi: 10.1002/hipo.20114.
Spatial scaling of place specific activity in the hippocampus varies systematically from the septal pole (high resolution) to the temporal pole (low resolution). Place fields get progressively larger, and the probability of observing a field in a given environment gets progressively smaller. It was previously found that decoupling movement in space from ambulation, by having the animal actively ride on a mobile platform, results in marked enlargement of the spatial scale factor in the dorsal hippocampus and a reduction in the increase in theta rhythm power with running speed, suggesting that a self-motion signal determines the spatial scale at which the hippocampal population vector updates. These results led to the hypothesis that the gain of the self-motion signal may vary systematically along the septo-temporal axis of the hippocampus. To test this hypothesis, EEG theta rhythm and ensembles of CA1 pyramidal cells and interneurons were recorded from the extreme dorsal and middle portions of the hippocampus. Pyramidal cell population vectors representing successive locations became decorrelated over substantially shorter distances in the dorsal than in the middle hippocampus. Dorsal pyramidal cells had smaller place fields, higher mean and peak firing rates, and higher intrinsic oscillation frequencies during track running than that of middle pyramidal cells. Both dorsal pyramidal cells and interneurons had more elevated mean rates during running, compared with rest, than that of the corresponding cell classes in the middle hippocampus, and both cell classes increased their rates more as a function of speed in the dorsal hippocampus.The amplitude, but not the frequency of fissure recorded theta rhythm, increased more as a function of running speed in the dorsal than in the middle hippocampus. We conclude that variation in the neuronal response to movement speed is the likely basis for the systematic variation in spatial scaling along the septo-temporal axis of the hippocampus.
海马体中特定位置活动的空间尺度从隔极（高分辨率）到颞极（低分辨率）呈现出系统性变化。位置野逐渐变大，在给定环境中观察到一个位置野的概率逐渐变小。先前研究发现，通过让动物主动骑在移动平台上，使空间中的运动与行走解耦，会导致背侧海马体的空间尺度因子显著增大，且随着奔跑速度增加，θ节律功率的增幅减小，这表明自我运动信号决定了海马体群体向量更新的空间尺度。这些结果引出了一个假说，即自我运动信号的增益可能沿海马体的隔颞轴系统性变化。为了验证这一假说，从海马体的极背侧和中部记录了脑电图θ节律以及CA1锥体细胞和中间神经元的集合。代表连续位置的锥体细胞群体向量在背侧海马体中比在中部海马体中在实质上更短的距离内就变得去相关。在轨迹运行期间，背侧锥体细胞的位置野更小，平均放电率和峰值放电率更高，固有振荡频率也比中部锥体细胞更高。与中部海马体中的相应细胞类型相比，背侧锥体细胞和中间神经元在奔跑时的平均放电率都比休息时更高，并且这两种细胞类型在背侧海马体中随着速度增加其放电率增加得更多。在背侧海马体中，记录到的海马裂θ节律的振幅随奔跑速度增加的幅度比在中部海马体中更大，但频率没有差异。我们得出结论，神经元对运动速度反应的变化可能是海马体隔颞轴上空间尺度系统性变化的基础。
