A logical calculus of the ideas immanent in nervous activity Warren S. McCulloch and Walter Pitts Bulletin of Mathematical Biophysics, Volume 5, 1943 pdf

70th Anniversary of Publication: Warren McCulloch & Walter Pitts - A Logical Calculus of the Ideas Immanent in Nervous Activity Jiří Pospíchal & Vladimír Kvasnička Emergent Trends in Robotics and Intelligent Systems pdf

For easier understanding the notations in the first paper, read in pair

A Statistical Consequence of the Logical Calculus of Nervous Nets by H. D. Landahl, W. S. McCulloch and Walter Pitts in Bulletin of Mathematical Biology, 1943, Volume 5, Number 4, Pages 135-137. pdf