为了导航他们的环境,昆虫需要跟踪它们的方向。先前的工作表明,昆虫将其头部方向编码为围绕八列结构排列的神经元环的正弦活动模式。然而,尚不清楚这种头部方向的正弦编码是否只是进化的巧合,或者它是否提供了特定的功能优势。为了解决这个问题,我们建立了方向编码的基本数学要求,并表明它可以由许多电路执行,都有不同的活动模式。在这些活动模式中,我们证明了正弦是最有噪声弹性的,但仅当与编码神经元之间的正弦连接模式耦合时。我们将这种预测的最佳连接模式与蝗虫和果蝇头部方向回路的解剖数据进行比较,发现我们的理论与实验证据一致。此外,我们证明了我们预测的电路可以使用Hebbian可塑性出现,这意味着神经连接不需要在昆虫的遗传程序中明确编码,而是可以在发育过程中出现。最后,我们在我们的理论中说明了,跨多个昆虫物种的头部方向回路的八列组织的一致存在不是偶然的人为现象,而是可以用基本的进化原理来解释。
昆虫,包括果蝇和蝗虫,在整个环境中寻找食物,彼此互动或逃避危险。导航他们的周围环境,昆虫需要能够跟踪它们的方向。这种跟踪是通过视觉提示和整合有关飞行时运动的信息来实现的,这样他们就可以知道他们的头部面向哪个方向。负责中继有关头部方向(也称为标题)的信息的一组神经元在由八列细胞组成的环中连接在一起。先前的研究表明,整个神经元环的活动水平类似于正弦曲线形状:一条平滑的曲线,具有一个峰值,编码动物的航向。这个八柱环下游的神经元,传递速度信息,也显示激活的这种正弦模式。Aceituno,Dall'Osto和Pisokas想了解这种正弦模式是否是进化的巧合,或者它是否为昆虫提供了特殊的优势。为了回答这个问题,他们建立了八列环中神经元编码动物航向信息所需的数学标准。这表明,这些条件可以通过许多不同的激活模式来满足,不仅仅是正弦形状。然而,Aceituno,Dall'Osto和Pisokas表明,正弦形状对可能影响编码信息的神经元活动的变化最有弹性。进一步的实验表明,只有当电路中的神经元以某种模式连接在一起时,这种弹性才会发生。Aceituno,Dall'Osto和Pisokas然后将该电路与蝗虫和果蝇的实验数据进行了比较,发现两种昆虫都表现出预测的连接模式。他们还发现,动物不必天生具有这种神经元连接模式,但可以在他们的一生中发展它。这些发现为昆虫在飞行时如何传递有关头部方向的信息提供了新的见解。他们认为,负责编码头部方向的神经元回路的结构不是偶然形成的,而是由于其提供的进化优势而产生的。
To navigate their environment, insects need to keep track of their orientation. Previous work has shown that insects encode their head direction as a sinusoidal activity pattern around a ring of neurons arranged in an eight-column structure. However, it is unclear whether this sinusoidal
encoding of head direction is just an evolutionary coincidence or if it offers a particular functional advantage. To address this question, we establish the basic mathematical requirements for direction
encoding and show that it can be performed by many circuits, all with different activity patterns. Among these activity patterns, we prove that the sinusoidal one is the most noise-resilient, but only when coupled with a sinusoidal connectivity pattern between the
encoding neurons. We compare this predicted optimal connectivity pattern with anatomical data from the head direction circuits of the locust and the fruit fly, finding that our theory agrees with experimental evidence. Furthermore, we demonstrate that our predicted circuit can emerge using Hebbian plasticity, implying that the neural connectivity does not need to be explicitly encoded in the genetic program of the insect but rather can emerge during development. Finally, we illustrate that in our theory, the consistent presence of the eight-column organisation of head direction circuits across multiple insect species is not a chance artefact but instead can be explained by basic evolutionary principles.
Insects, including fruit flies and locusts, move throughout their environment to find food, interact with each other or escape danger. To navigate their surroundings, insects need to be able to keep track of their orientation. This tracking is achieved through visual cues and integrating information about their movements whilst flying so they know which direction their head is facing. The set of neurons responsible for relaying information about the direction of the head (also known as heading) are connected together in a ring made up of eight columns of cells. Previous studies showed that the level of activity across this ring of neurons resembles a sinusoid shape: a smooth curve with one peak which encodes the animal’s heading. Neurons downstream from this eight-column ring, which relay velocity information, also display this sinusoidal pattern of activation. Aceituno, Dall’Osto and Pisokas wanted to understand whether this sinusoidal pattern was an evolutionary coincidence, or whether it offers a particular advantage to insects. To answer this question, they established the mathematical criteria required for neurons in the eight-column ring to encode information about the heading of the animal. This revealed that these conditions can be satisfied by many different patterns of activation, not just the sinusoidal shape. However, Aceituno, Dall’Osto and Pisokas show that the sinusoidal shape is the most resilient to variations in neuronal activity which may impact the encoded information. Further experiments revealed that this resilience only occurred if neurons in the circuit were connected together in a certain pattern. Aceituno, Dall’Osto and Pisokas then compared this circuit with experimental data from locusts and fruit flies and found that both insects exhibit the predicted connection pattern. They also discovered that animals do not have to be born with this neuronal connection pattern, but can develop it during their lifetime. These findings provide fresh insights into how insects relay information about the direction of their head as they fly. They suggest that the structure of the neuronal circuit responsible for
encoding head direction was not formed by chance but instead arose due to the evolutionary benefits it provided.