Biological Bases of Backpropagation

对神经元中信息回流的可能机制进行了实验和理论研究。这种信息的逆行流动是涉及反向传播的神经网络学习和可塑性的关键方面。将使用的实验准备是大鼠大脑的海马片。将寻找膜电势以外的信息流逆行途径的证据。一种刺激是机械压迫传出轴突或轴突丘状突起。树突和轴突水平的突触反应的变化将被监测为反向传播的证据。感兴趣的时间尺度将是毫秒，而不是轴突胞质在两个方向上流动的较慢过程。如果功能可塑性被证明，将对突触进行电子显微镜检查，以寻找与功能变化相关的细胞骨架或囊泡变化。理论模型将由肌动蛋白-肌球蛋白凝胶的细胞骨架成分、微管结构和代表细胞质的粘弹性矩阵组成。肌动蛋白-肌球蛋白凝胶中会产生一种主动张力。将研究复合结构中可能的波传播模式。这项研究的意义在于将生物模型与神经网络的理论模型相关联。

Experimental and theoretical investigations of possible mechanisms of backflow of information in neurons are proposed. Such retrograde flow of information is a crucial aspect of learning and plasticity of neural networks involving backpropagation. The experimental preparations to be used are hippocampal slices of the rat brain. Evidence of retrograde pathways of informational flow other than membrane electrical potentials will be sought. One stimulus will be mechanical compression of efferent axons or axon hillocks. Changes in synaptic response at the dendritic and axonal levels will be monitored as evidence of backpropagation. The time scale of interest will be milliseconds as opposed to slower processes of axonal cytoplasmic flow in either direction. If functional plasticity is demonstrated, electron- microscopic examination of synapses will be made to seek cytoskeletal or vesicle alterations that correlate with the functional changes. Theoretical models will consist of cytoskeletal components of actin-myosin gel, microtubular structure and a viscoelastic matrix representing cytoplasm. An active tension will be assumed in the actin-myosin gel. Possible modes of wave propagation in the composite structure will be investigated. The significance of the proposed research will be very important of correlation of biological counterparts to theoretical models of neural networks.