Magosso Elisa, Cuppini Cristiano, Serino Andrea, Di Pellegrino Giuseppe, Ursino Mauro
Department of Electronics, Computer Science and Systems, University of Bologna, Italy.
Neural Netw. 2008 Aug;21(6):817-29. doi: 10.1016/j.neunet.2008.06.003. Epub 2008 Jun 22.
Neurons in the superior colliculus (SC) integrate stimuli of different modalities. In this work, a mathematical model of the integrative response of SC neurons is presented, to gain a deeper insight into the possible mechanisms involved, and on individual differences in integrative abilities. The model includes two unimodal areas (auditory and visual), which communicate via feedforward and feedback synapses with a third multisensory area. Each neuron is represented via a sigmoidal relationship and a first-order dynamic. Neurons in the same area interact via lateral synapses. Simulations show that the model, with a basal parameter set, can mimic various responses described in the literature: (i) multimodal enhancement in response to two cross-modal stimuli within the receptive field, according to the inverse-effectiveness principle; (ii) within-modality suppression and cross-modality suppression by a stimulus (of the same or other modality) placed outside the receptive field. Sensitivity analysis on model parameters demonstrate that different classes of neurons observed in the literature (such as, neurons which exhibit within modality suppression without cross-modality suppression, or neurons with asymmetrical cross-modality suppression) can be reproduced by simply modifying synaptic strengths in the multimodal area. Finally, exempla of the possible role of feedback mechanisms in ambiguous conditions (such as reinforcement of a poor perception by a second cross-modal stimulus, or ventriloquism) are shown and critically discussed. The model may be of value to assess the different mechanisms responsible for multisensory integration in the SC, and, in future, to study neural plasticity in multisensory systems during development or rehabilitation.
上丘（SC）中的神经元整合不同模态的刺激。在这项工作中，提出了一种SC神经元整合反应的数学模型，以更深入地了解其中可能涉及的机制以及整合能力的个体差异。该模型包括两个单模态区域（听觉和视觉），它们通过前馈和反馈突触与第三个多感觉区域进行通信。每个神经元通过S形关系和一阶动力学来表示。同一区域内的神经元通过侧向突触相互作用。模拟表明，该模型在基础参数设置下可以模拟文献中描述的各种反应：（i）根据逆有效性原则，对感受野内的两个跨模态刺激做出多模态增强反应；（ii）感受野外放置的刺激（相同或其他模态）引起的模态内抑制和跨模态抑制。对模型参数的敏感性分析表明，通过简单修改多模态区域中的突触强度，可以重现文献中观察到的不同类型的神经元（例如，表现出模态内抑制但无跨模态抑制的神经元，或具有不对称跨模态抑制的神经元）。最后，展示并批判性地讨论了反馈机制在模糊条件下可能发挥的作用的示例（例如，第二个跨模态刺激增强较差的感知，或腹语术）。该模型可能有助于评估负责SC中多感觉整合的不同机制，并且在未来可用于研究发育或康复过程中多感觉系统的神经可塑性。
