Beyond the straight path: high-density laminar recordings in the ventral hippocampus with curved microprobes

Brain function is governed by neural circuits distributed across an intricate, three-dimensional landscape of anatomically complex structures. Current methods for monitoring neural activity are limited to investigating structures that lie along a single, linear trajectory. While this approach is effective for columnar regions, such as dorsal cortical areas or the relatively planar dorsal hippocampus, it fails in deep or curved structures, like the ventral hippocampus, where a linear probe can only achieve with difficulty the combination of physical access and perpendicular orientation required for recordings across all layers. To overcome this limitation, we developed a multisite microelectrode array with a pre-formed curved geometry, engineered to align perpendicularly with neuronal layers in deep anatomical targets regardless of their orientation. This interface integrates a polymer-based array, featuring 16 PEDOT:BF4-coated microelectrodes for robust signal acquisition, with a dissolvable silk stiffener for precise surgical insertion. The resulting device exhibited excellent electrical properties (avg. impedance 18 kΩ) and enabled accurate placement across the distinct neuronal layers of the ventral hippocampus CA1 region. These capabilities allowed for successful recordings of both local field potentials and single-unit activity from this region, providing a powerful new tool to investigate the network dynamics of previously inaccessible neural circuits.