Micro electrode arrays (MEAs) are employed to study extracellular electrical activity in neuronal tissues (Morin at al., 2005). Nevertheless, commercially available MEAs provide a limited number of recording sites and do not allow a precise identification of spatial-temporal oscillations. To overcome this limitation, high density MEAs were recently developed and validated on dissociated preparations (Berdondini et al., 2009). The platform enables extracellular electrophysiological recordings from 4096 electrodes arranged in a squared area of 2.7 mm x 2.7 mm with inter-electrode distance of 21 mm (Imfeld et al., 2008), at a sampling rate of 7,7 kHz/electrode.

Here, we demonstrate the performances of this high-resolution platform for the acquisition of electrophysiological activity from acute brain slices. The unique recording performances and the large recording area of the chip permit the observation of fast propagating activities involving multiple areas. In particular, epileptic-like discharges were induced on horizontal hippocampal slices by applying 4-aminopyridine (200 mM) or bicuculline (30 mM). Spontaneous activity was recorded over the CMOS-MEA up to one hour under constant perfusion and at controlled temperature conditions. Furthermore, we show that the high density MEA platform can be mounted on a microscope stage and can be coupled with conventional extracellular electrodes or intracellular patch clamp electrodes for local stimulation or recording.

In particular, fast propagating activities involving multiple slice areas, induced by convulsing agents on mouse cortico-hippocampal slices were studied by precisely following the spread of activity during long-lasting epileptic-like discharges.