DeMarse Thomas B, Pan Liangbin, Alagapan Sankaraleengam, Brewer Gregory J, Wheeler Bruce C
J. Crayton Pruitt Family Department of Biomedical Engineering, University of FloridaGainesville, FL, USA; Department of Pediatric Neurology, University of FloridaGainesville, FL, USA.
J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida Gainesville, FL, USA.
Front Neural Circuits. 2016 Apr 22;10:32. doi: 10.3389/fncir.2016.00032. eCollection 2016.
Transient propagation of information across neuronal assembles is thought to underlie many cognitive processes. However, the nature of the neural code that is embedded within these transmissions remains uncertain. Much of our understanding of how information is transmitted among these assemblies has been derived from computational models. While these models have been instrumental in understanding these processes they often make simplifying assumptions about the biophysical properties of neurons that may influence the nature and properties expressed. To address this issue we created an in vitro analog of a feed-forward network composed of two small populations (also referred to as assemblies or layers) of living dissociated rat cortical neurons. The populations were separated by, and communicated through, a microelectromechanical systems (MEMS) device containing a strip of microscale tunnels. Delayed culturing of one population in the first layer followed by the second a few days later induced the unidirectional growth of axons through the microtunnels resulting in a primarily feed-forward communication between these two small neural populations. In this study we systematically manipulated the number of tunnels that connected each layer and hence, the number of axons providing communication between those populations. We then assess the effect of reducing the number of tunnels has upon the properties of between-layer communication capacity and fidelity of neural transmission among spike trains transmitted across and within layers. We show evidence based on Victor-Purpura's and van Rossum's spike train similarity metrics supporting the presence of both rate and temporal information embedded within these transmissions whose fidelity increased during communication both between and within layers when the number of tunnels are increased. We also provide evidence reinforcing the role of synchronized activity upon transmission fidelity during the spontaneous synchronized network burst events that propagated between layers and highlight the potential applications of these MEMs devices as a tool for further investigation of structure and functional dynamics among neural populations.
信息在神经元集合中的短暂传播被认为是许多认知过程的基础。然而,这些传播中所嵌入的神经编码的本质仍不确定。我们对信息在这些集合之间如何传播的许多理解都来自于计算模型。虽然这些模型在理解这些过程中发挥了重要作用,但它们往往对可能影响所表达的性质和特性的神经元生物物理特性做出简化假设。为了解决这个问题,我们创建了一个体外前馈网络类似物,它由两小群(也称为集合或层)解离的活大鼠皮层神经元组成。这两群神经元被一个包含微尺度隧道带的微机电系统(MEMS)装置隔开并通过其进行通信。先对第一层中的一群神经元进行延迟培养,几天后再培养另一群,这诱导轴突单向生长通过微隧道,从而在这两个小神经群体之间形成主要的前馈通信。在本研究中,我们系统地操纵连接每一层的隧道数量,进而操纵提供这些群体之间通信的轴突数量。然后我们评估减少隧道数量对跨层和层内传输的尖峰序列之间的层间通信能力和神经传输保真度特性的影响。我们基于维克多 - 普尔普拉(Victor-Purpura)和范罗斯姆(van Rossum)的尖峰序列相似性指标展示了证据,支持这些传输中同时存在速率和时间信息,当隧道数量增加时,这些信息在层间和层内通信期间的保真度会提高。我们还提供了证据,强化了自发同步网络爆发事件期间同步活动对传输保真度的作用,这些事件在层间传播,并突出了这些MEMS装置作为进一步研究神经群体之间结构和功能动力学工具的潜在应用。