The basic principles of the artificial neural networks (ANNs) were first formulated
by McCulloch and Pitts in 1943, in terms of five assumptions, as follows:
(1) The activity of a neuron (ANN) is all-or-nothing.
(2) A certain xed number of synapses larger than 1 must be excited within a given
interval of neural addition for a neuron to be excited.
(3) The only signi cant delay within the neural system is the synaptic delay.
(4) The activity of any inhibitory synapse absolutely prevents the excitation of the
neuron at that time.
(5) The structure of the interconnection network does not change over time.

Guys, English isnt my first language, can somenone explain to me (2)? What is neural addition in this context? Any help would be appreciated