Garson´s weight method or Connection Weight approch proposed by Olden et al., (2004)?
Garson, G. D. (1991). Interpreting neural-network connection weights. AI expert, 6(4), 46-51.
Olden, J. D., Joy, M. K., & Death, R. G. (2004). An accurate comparison of methods for quantifying variable importance in artificial neural networks using simulated data. Ecological Modelling, 178(3-4), 389-397.