网格细胞的放电率适应产生宏观六方向调制
Firing rate adaptation in grid cells produces macroscopic hexadirectional modulation
宏观神经活动随运动方向的六方向调制（HexMod）被广泛用于在人类神经影像中测量网格细胞活动，但其神经元起源尚不清楚。已有两种机制被提出：其偏好方向与网格轴对齐的联合型网格×方向细胞，以及在沿网格轴运动时网格野被快速连续经过而导致放电减少的放电率适应。通过分析觅食大鼠中近4,000个网格细胞，我们发现联合型细胞的方向调谐较宽且与网格轴不对齐，而放电在网格野被经过后不久即减少，这与放电率适应一致。对真实网格细胞群体的模拟在人类实验的典型轨迹下再现了HexMod，并展示了它如何依赖于网格尺度、适应时间常数、运动速度以及对位置变化的控制。我们表明放电率适应为HexMod提供了一个合理的机制，并为将人类神经影像与神经元活动相联系提供了一个框架。
用近4000个网格细胞的记录和仿真说明，宏观六方向调制更可能来自放电率适应而非联合网格方向细胞。
Hexadirectional modulation (HexMod) of macroscopic neural activity by movement direction is widely used to measure grid cell activity in human neuroimaging, but its neuronal origin is unclear. Two mechanisms have been proposed: conjunctive gridxdirection cells whose preferred directions align with the grid axes, and firing rate adaptation, which reduces firing when grid fields are visited in quick succession during movement along grid axes. Analysing almost 4,000 grid cells from foraging rats, we found that conjunctive cells' directional tuning was broad and unaligned with grid axes, whereas firing was reduced shortly after grid field visits, consistent with firing rate adaptation. Simulations of realistic grid cell populations demonstrate HexMod with the typical trajectories of human experiments, and show how it depends on grid scale, adaptation time constant, movement speed, and controlling for variation with location. We show firing rate adaptation provides a plausible mechanism for HexMod and a framework for relating human neuroimaging to neuronal activity.
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来源：bioRxiv · Neuroscience · biorxiv.org