That's is based on old assumption of neuron function.

Firstly, Kurzweil underestimates the number connections by order of magnitude.

Secondly, dentritic computation changes things. Individual dentrites and the dendritic tree as a whole can do multiple individual computations. logical operations low-pass filtering, coincidence detection, ... One neuronal activation is potentially thousands of operations per neuron.

Single human neuron can be equivalent of thousands of ANN's.