Constraints on the source of short-term motion adaptation in macaque area MT. I. The role of input and intrinsic mechanisms
Constraints on the source of short-term motion adaptation in macaque area MT. I. The role of input and intrinsic mechanisms
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DOI：
10.1152/jn.00852.2001
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发表时间：
2002-07-01
影响因子：
2.5
通讯作者：
Lisberger, SG
中科院分区：
文献类型：
--
作者：
Priebe, NJ;Churchland, MM;Lisberger, SG
脑皮层外运动敏感区MT的神经元对目标速度的一步反应具有短暂持续的放电模式。从高初始放电速率到低持续放电速率的转变发生在20-80毫秒的时间过程中，被认为是一种短期适应形式。本文提出适应性是由于输入特异性机制，如短期突触抑制，还是由于固有的细胞机制，如尖峰率适应。我们通过使用条件/测试范式来衡量适应的空间尺度，评估了投入特定机制的贡献。条件反射刺激和测试刺激被放置在MT接受野中，但在空间上是分开的，这样两种刺激会激活来自初级视觉皮层（V1）的不同输入群。在一个视觉位置的调节运动导致在第二个位置的随后的测试运动的瞬态射击的减少。适应野，即条件反射运动引起适应的视觉空间区域，总是大于MT感受野。使用相同的刺激配置在记录从V1 direction-selective神经元没能证明适应或transient-sustained响应模式,短期适应的签名太,我们得出结论,从瞬态转向持续发射太细胞并不能从一个输入具体机制应用于输入从V1,因为它运行在一个广泛的视野比被V1神经元的接受域覆盖。我们使用直接分析相同运动刺激多次重复的MT神经元尖峰序列来评估与尖峰相关的内在细胞机制对适应的贡献。在逐个试验的基础上，暂态间隔中的峰值数量与瞬态间隔之后的间隔之间没有相关性。这与预测相反，如果峰值直接导致适应，则应该存在相关性。此外，在实验中，当神经元在平均放电速率为零的间隔内发出峰值时，瞬态被抑制或熄灭，而不是延迟。我们得出结论，MT区域神经元从短暂放电到持续放电的转变是由既不是输入特异性的机制引起的，也不是由适应神经元的尖峰控制的。我们认为在脑后皮层观察到的短期适应来自脑后皮层内的回路。
Neurons in area MT, a motion-sensitive area of extrastriate cortex, respond to a step of target velocity with a transient-sustained firing pattern. The transition from a high initial firing rate to a lower sustained rate occurs over a time course of 20-80 ms and is considered a form of short-term adaptation. The present paper asks whether adaptation is due to input-specific mechanisms such as short-term synaptic depression or if it results from intrinsic cellular mechanisms such as spike-rate adaptation. We assessed the contribution of input-specific mechanisms by using a condition/test paradigm to measure the spatial scale of adaptation. Conditioning and test stimuli were placed within MT receptive fields but were spatially segregated so that the two stimuli would activate different populations of inputs from the primary visual cortex (V1). Conditioning motion at one visual location caused a reduction of the transient firing to subsequent test motion at a second location. The adaptation field, estimated as the region of visual space where conditioning motion caused adaptation, was always larger than the MT receptive field. Use of the same stimulus configuration while recording from direction-selective neurons in V1 failed to demonstrate either adaptation or the transient-sustained response pattern that is the signature of short-term adaptation in MT. We conclude that the shift from transient to sustained firing in MT cells does not result from an input-specific mechanism applied to inputs from V1 because it operates over a wider range of the visual field than is covered by receptive fields of V1 neurons. We used a direct analysis of MT neuron spike trains for many repetitions of the same motion stimulus to assess the contribution to adaptation of intrinsic cellular mechanisms related to spiking. On a trial-by-trial basis, there was no correlation between number of spikes in the transient interval and the interval immediately after the transient period. This is opposite the prediction that there should be a correlation if spikes cause adaptation directly. Further, the transient was suppressed or extinguished, not delayed, in trials in which the neuron emitted zero spikes during the interval that showed a transient in average firing rate. We conclude that the transition from transient to sustained firing in neurons in area MT is caused by mechanisms that are neither input-specific nor controlled by the spiking of the adapting neuron. We propose that the short-term adaptation observed in area MT emerges from the intracortical circuit within MT.