Fig. 7: Synaptic latency and transmission velocity between two somatic regions in the compartmentalized two-group 3D neural network model.

a–c Transiently spiking signals of neurons recorded from 63 electrodes of the 3D MEA by optical stimulation in the first somatic (a; electrodes 1–21), neurite (b; electrodes 22–42), and the second somatic (c; electrodes 43–63) regions at DIV 14. The blue triangle indicates the onset time of the optical stimulation. d 3D color-mapped synaptic latency at each electrode, relative to the optical stimulation on shank 1. Black-colored circle indicates no signals recorded from the electrodes. The light blue indicates transmitted light from the shank 1. e Synaptic latency at each electrode (white circle) in the first somatic (shanks 1-6), neurite (shanks 7–12), and the second somatic (shanks 13–18) regions. The red line indicates mean synaptic latency of the signal recorded from each electrode on each shank. Data are presented as mean values +/− s.d. with individual data points (white circle; n = 3 signal recorded electrodes for shank 4, 5, 9, 10, 11, 12, 14, 15, 16, 18 and n = 4 signal recorded electrodes for shank 1, 2, 3, 6, 7, 8, 13, 17). f–g 3D visualization of the shank map from the stimulation site to electrode 21 on shank 6 in the first somatic region (f) and electrode 57 on shank 16 in the second somatic region (g) (red dotted line in left panel). Transiently spiking signals of neurons recorded from electrodes 1 and 21 (f), and from electrode 1 and 57 (g) (right panel) to display synaptic latency within the first somatic region from the stimulation site. The blue triangle indicates the onset time of the optical stimulation. The light blue indicates transmitted light from the shank 1. h Color-mapped mean synaptic latency at each shank. i Scatter plot of distance to all electrodes from the stimulation site depending on synaptic latency. The dotted line and shaded area indicate the best fit of linear regression and the 95% confidence level, respectively. The slope of the linear regression is the synaptic transmission velocity. j Scatter plot of distance from the stimulation site to the electrodes along the longitudinal (orange; orange arrow in inset image) and transverse (green; green arrow in inset image) directions depending on synaptic latency. k Bar graph showing the synaptic transmission velocity along the transverse and longitudinal directions. Data are presented as mean values +/− s.d. with individual data points (white circle; n = 7 signal recorded electrodes for the transverse direction and n = 19 signal recorded electrodes for the longitudinal direction).**P = 0.0010. Statistical significance was tested with a two-tailed unpaired t-test. Source Data is available as a Source Data file for Fig. 7e, h-k.