Representative spontaneous neuronal activity exhibited by (A) immature and (B) mature cortical cultures recorded via MEA under control conditions. (i) Array-wide neuronal activity. (ii) An extended period of spontaneous neuronal activity (160 s) recorded from a single channel. (iii) An expanded single channel trace obtained from the period indicated by a star in ii. (iv) Expanded burst events from the left and (v) right star in iii. Superimposed black sections within grey bars represent bursts identified within the raw traces shown by the adapted SIMMUX algorithm. Note that neural activity was generally more evident across the array channels in the immature culture.