Brain Science Institute and
Brain/MINDS, Tokyo, 100-0004, Japan.
J Neurosci. 2019 Jan 16;39(3):485-502. doi: 10.1523/JNEUROSCI.1584-18.2018. Epub 2018 Nov 26.
It is well known that the posterior parietal cortex (PPC) and frontal motor cortices in primates preferentially control voluntary movements of contralateral limbs. The PPC of rats has been defined based on patterns of thalamic and cortical connectivity. The anatomical characteristics of this area suggest that it may be homologous to the PPC of primates. However, its functional roles in voluntary forelimb movements have not been well understood, particularly in the lateralization of motor limb representation; that is, the limb-specific activity representations for right and left forelimb movements. We examined functional spike activity of the PPC and two motor cortices, the primary motor cortex (M1) and the secondary motor cortex (M2), when head-fixed male rats performed right or left unilateral movements. Unlike primates, PPC neurons in rodents were found to preferentially represent ipsilateral forelimb movements, in contrast to the contralateral preference of M1 and M2 neurons. Consistent with these observations, optogenetic activation of PPC and motor cortices, respectively, evoked ipsilaterally and contralaterally biased forelimb movements. Finally, we examined the effects of optogenetic manipulation on task performance. PPC or M1 inhibition by optogenetic GABA release shifted the behavioral limb preference contralaterally or ipsilaterally, respectively. In addition, weak optogenetic PPC activation, which was insufficient to evoke motor responses by itself, shifted the preference ipsilaterally; although similar M1 activation showed no effects on task performance. These paradoxical observations suggest that the PPC plays evolutionarily different roles in forelimb control between primates and rodents. In rodents, the primary and secondary motor cortices (M1 and M2, respectively) are involved in voluntary movements with contralateral preference. However, it remains unclear whether and how the posterior parietal cortex (PPC) participates in controlling multiple limb movements. We recorded functional activity from these areas using a behavioral task to monitor movements of the right and left forelimbs separately. PPC neurons preferentially represented ipsilateral forelimb movements and optogenetic PPC activation evoked ipsilaterally biased forelimb movements. Optogenetic PPC inhibition via GABA release shifted the behavioral limb preference contralaterally during task performance, whereas weak optogenetic PPC activation, which was insufficient to evoke motor responses by itself, shifted the preference ipsilaterally. Our findings suggest rodent PPC contributes to ipsilaterally biased motor response and/or planning.
众所周知，灵长类动物的后顶叶皮层（PPC）和额运动皮层优先控制对侧肢体的随意运动。大鼠的 PPC 是基于丘脑和皮质连接模式来定义的。该区域的解剖学特征表明，它可能与灵长类动物的 PPC 同源。然而，其在随意前肢运动中的功能作用尚未得到很好的理解，特别是在运动肢体代表的偏侧化方面，即右前肢和左前肢运动的特定肢体活动代表。我们在雄性大鼠进行右或左单侧运动时，检查了 PPC 和两个运动皮层（初级运动皮层（M1）和次级运动皮层（M2）的功能尖峰活动。与灵长类动物不同，我们发现啮齿动物的 PPC 神经元优先代表同侧前肢运动，而 M1 和 M2 神经元则偏向对侧。与这些观察结果一致，光遗传学激活 PPC 和运动皮层分别诱发了同侧和对侧偏向的前肢运动。最后，我们检查了光遗传学操作对任务表现的影响。光遗传学 GABA 释放抑制 PPC 或 M1，分别使行为肢体偏侧化向对侧或同侧转移。此外，微弱的光遗传学 PPC 激活本身不足以引起运动反应，但会使偏侧化；尽管类似的 M1 激活对任务表现没有影响。这些矛盾的观察结果表明，PPC 在灵长类动物和啮齿动物的前肢控制中发挥着不同的进化作用。在啮齿动物中，初级和次级运动皮层（分别为 M1 和 M2）参与了具有对侧偏侧化的随意运动。然而，目前尚不清楚 PPC 是否以及如何参与控制多肢体运动。我们使用行为任务记录这些区域的功能活动，以分别监测右前肢和左前肢的运动。PPC 神经元优先代表同侧前肢运动，光遗传学激活 PPC 诱发同侧偏向的前肢运动。在任务执行过程中，通过 GABA 释放进行光遗传学 PPC 抑制会使行为肢体偏侧化向对侧转移，而弱的光遗传学 PPC 激活本身不足以引起运动反应，会使偏侧化向同侧转移。我们的发现表明，啮齿动物的 PPC 有助于同侧偏向的运动反应和/或计划。
