measuring local field potentials (LFP) at week 1, 3, and 4 post culturing. As shown in Fig. 1c, PHFNs started to show LFP activity at 3 weeks and reached the peak levels at 4 weeks post culturing. Neuronal cultures at 1 week were called immature neurons with minimal LFP recordings and 4 weeks cultures were named mature (functional) neurons with maximum LFP recordings.