FIGURE 2.

hCSF induces a general increase in neuronal activity and specific activation and inactivation of subpopulations of neurons. (A) The general activity measured by the number of active electrodes and spike rate, with an average of each hippocampus slice represented by a circle and each cortex slice as a triangle, increased when hCSF was washed in and then decreased again when hCSF was washed out. The average number of electrodes and spike rate in one cortical slice did not increase but decreased instead, this can also be seen in the corresponding heat map in Figure 1D (cortex slice 3). (B) Overview presenting identified electrodes recording activity only in hCSF (dark green), electrodes recording increased spike rate in hCSF (green), recording a decreased spike rate in hCSF (light red), electrodes only active in aCSF (red), and electrodes recording stable activity (for which spike rate increased or decreased by less than 50%). The majority of the electrodes only recorded spikes in hCSF or measured an increased spike rate in hCSF (522 and 186 electrodes, respectively, of a total of 1250 electrodes). Interestingly, 105 electrodes only recorded activity in aCSF and 141 electrodes recorded a decreased spike rate in hCSF compared to aCSF. Examples of electrode recording revealing (C) increased activity and (D) decreased activity when hCSF was washed in. Changed excitability was also detected in extracellular recordings using the CMOS-MEA. (E) Overview of identified single-unit activity (n = 73 cells in three slices) with extracellular voltage recorded by a selected sensor showing the increased excitability of one cell in hCSF compared to aCSF. Selected extracellular waveforms of cells active in (F) both conditions and (G) in hCSF or in aCSF only. (H) The waveform width was not different between the spikes recorded from neurons only active in aCSF, only active in hCSF, or active in both (stable); significance is indicated by *p < 0.05; **p < 0.01.