Figure 2.

Penetrating microelectrode array for recording. A, Left, Unfolded hippocampus positioned on the microelectrode array. Activity from a spontaneous source (solid dot in the tissue) can travel in four possible directions: a, septal (S) to temporal (T); b, T to S; c, CA3 to CA1; d, CA3 to DG. Right, A transverse cross-section of the unfolded hippocampus with microelectrodes inserted into the tissue. B, A sample of the unfolded hippocampus placed on the array is imaged using OCT. Left, A tissue placed on the array. Right, Transverse slices of the tissue in different positions along the longitudinal directions. The white spots indicated by the arrows are the tips of the microelectrodes. The dark lines in the tissue show the pyramidal cell layers. The microelectrodes, with a height ∼200 μm, usually sit in the basal dendrites below the cell layer.