add longtin1993 reference to bib

references.bib

@@ -4022,6 +4022,16 @@ We collected weakly electric gymnotoid fish in the vicinity of Manaus, Amazonas,
   Volume                   = {21}
 }
 
+@article{Longtin1993,
+  title={Stochastic resonance in neuron models},
+  author={Longtin, Andr{\'e}},
+  journal={Journal of statistical physics},
+  volume={70},
+  pages={309--327},
+  year={1993},
+  publisher={Springer}
+}
+
 @Article{Longtin1996,
   title={Encoding with bursting, subthreshold oscillations, and noise in mammalian cold receptors},
   author={Longtin, Andre and Hinzer, Karin},