Department of Physiology, Monash University, Clayton, 3800 Victoria, Australia.
J Neurosci. 2013 Mar 6;33(10):4359-68. doi: 10.1523/JNEUROSCI.3165-12.2013.
The response of a sensory neuron to an unchanging stimulus typically adapts, showing decreases in response gain that are accompanied by changes in the shape of tuning curves. It remains unclear whether these changes arise purely due to spike rate adaptation within single neurons or whether they are dependent on network interactions between neurons. Further, it is unclear how the timescales of neural and perceptual adaptation are related. To examine this issue, we compared speed tuning of middle temporal (MT) and medial superior temporal neurons in macaque visual cortex after adaptation to two different reference speeds. For 75% of speed-tuned units, adaptation caused significant changes in tuning that could be explained equally well as lateral shifts, vertical gain changes, or both. These tuning changes occurred rapidly, as both neuronal firing rate and Fano factor showed no evidence of changing beyond the first 500 ms after motion onset, and the magnitude of tuning curve changes showed no difference between trials with adaptation durations shorter or longer than 1 s. Importantly, the magnitude of tuning shifts was correlated with the transient-sustained index, which measures a well characterized form of rapid response adaptation in MT, and is likely associated with changes at the level of neuronal networks. Tuning curves changed in a manner that increased neuronal sensitivity around the adapting speed, consistent with improvements in human and macaque psychophysical performance that we observed over the first several hundred ms of adaptation.
对不变刺激的感觉神经元的反应通常会适应，表现出反应增益的降低，同时调谐曲线的形状发生变化。目前尚不清楚这些变化是纯粹由于单个神经元中的尖峰率适应引起的，还是依赖于神经元之间的网络相互作用。此外，尚不清楚神经和感知适应的时间尺度如何相关。为了研究这个问题，我们比较了猕猴视觉皮层中中间颞（MT）和内侧上颞神经元在适应两种不同参考速度后的速度调谐。对于 75%的速度调谐单元，适应会导致调谐发生显著变化，这些变化可以同样很好地解释为横向移位、垂直增益变化或两者兼而有之。这些调谐变化发生得很快，因为神经元放电率和 Fano 因子在运动开始后的前 500 毫秒内没有变化的迹象，并且调谐曲线变化的幅度在适应持续时间短于或长于 1 秒的试验之间没有差异。重要的是，调谐转移的幅度与瞬态-持续指数相关，该指数衡量 MT 中一种特征明显的快速反应适应形式，并且可能与神经元网络层面的变化有关。调谐曲线的变化方式增加了适应速度周围的神经元敏感性，这与我们在适应的前几百毫秒内观察到的人类和猕猴心理物理性能的改善一致。
