Jeewajee A, Barry C, Douchamps V, Manson D, Lever C, Burgess N
Department of Cell and Developmental Biology, UCL, , London WC1E 6BT, UK.
Philos Trans R Soc Lond B Biol Sci. 2013 Dec 23;369(1635):20120532. doi: 10.1098/rstb.2012.0532. Print 2014 Feb 5.
Place and grid cells in the rodent hippocampal formation tend to fire spikes at successively earlier phases relative to the local field potential theta rhythm as the animal runs through the cell's firing field on a linear track. However, this 'phase precession' effect is less well characterized during foraging in two-dimensional open field environments. Here, we mapped runs through the firing fields onto a unit circle to pool data from multiple runs. We asked which of seven behavioural and physiological variables show the best circular-linear correlation with the theta phase of spikes from place cells in hippocampal area CA1 and from grid cells from superficial layers of medial entorhinal cortex. The best correlate was the distance to the firing field peak projected onto the animal's current running direction. This was significantly stronger than other correlates, such as instantaneous firing rate and time-in-field, but similar in strength to correlates with other measures of distance travelled through the firing field. Phase precession was stronger in place cells than grid cells overall, and robust phase precession was seen in traversals through firing field peripheries (although somewhat less than in traversals through the centre), consistent with phase coding of displacement along the current direction. This type of phase coding, of place field distance ahead of or behind the animal, may be useful for allowing calculation of goal directions during navigation.
当动物在直线轨道上穿过细胞的放电场时，啮齿动物海马结构中的位置细胞和网格细胞往往会相对于局部场电位θ节律在相继更早的相位发放尖峰。然而，在二维开放场环境中的觅食过程中，这种“相位进动”效应的特征尚不明确。在这里，我们将穿过放电场的运行映射到一个单位圆上，以汇总来自多次运行的数据。我们询问了七个行为和生理变量中的哪一个与海马体CA1区位置细胞以及内侧内嗅皮层表层网格细胞的尖峰θ相位表现出最佳的圆线相关性。最佳相关因素是投影到动物当前奔跑方向上到放电场峰值的距离。这比其他相关因素（如瞬时放电率和场内时间）明显更强，但与穿过放电场的其他行进距离测量的相关性强度相似。总体而言，位置细胞中的相位进动比网格细胞更强，并且在穿过放电场周边时观察到稳健的相位进动（尽管略低于穿过中心时），这与沿当前方向的位移相位编码一致。这种对动物前方或后方位置场距离的相位编码类型，可能有助于在导航过程中计算目标方向。
