With the novel probes it is possible to record stable biologically relevant data over a time span exceeding the usual time needed for epileptic focus localisation in human patients. This is the first time that single units are recorded along cylindrical polyimide probes chronically implanted 22 mm deep into the brain of a monkey, which suggests the potential usefulness of this probe for human applications.

Neural recording devices normally require one output connection for each electrode. This constrains the number of electrodes that can be accommodated by the thin shafts of implantable probes. Sharing a single output connection between multiple electrodes relaxes this constraint and permits designs of ultra-high density neural probes.Here we report the design and in vivo validation of such a device, a complementary metal-oxidesemiconductor (CMOS) scanning probe with 1344 electrodes and 12 reference electrodes along an 8.1 mm x 100 μm x 50 μm shaft; the outcome of the European research project NeuroSeeker. This technology presented new challenges for data management and visualization, and we also report new methods addressing these challenges developed within NeuroSeeker.Scanning CMOS technology allows the fabrication of much smaller, denser electrode arrays. To help design electrode configurations for future probes, several recordings from many different brain regions were made with an ultra-dense passive probe fabricated using CMOS process. All datasets are available online.

Stereo-electroencephalography depth electrodes, regularly implanted into drug-resistant patients with focal epilepsy to localize the epileptic focus, have a low channel count (6-12 macro- or microelectrodes), limited spatial resolution (0.5-1 cm) and large contact area of the recording sites (~mm2). Thus, they are not suited for high-density local field potential and multiunit recordings. In this paper, we evaluated the long-term electrophysiological recording performance and histocompatibility of a neural interface consisting of 32 microelectrodes providing a physical shape similar to clinical devices. The cylindrically-shaped depth probes made of polyimide (PI) were chronically implanted for 13 weeks into the brain of rats, while cortical or thalamic activity (local field potentials, single-unit and multi-unit activity) was recorded regularly to monitor the temporal change of several features of the electrophysiological performance. To examine the tissue reaction around the probe, neuron-selective and astroglia-selective immunostaining methods were applied. Stable single-unit and multi-unit activity were recorded for several weeks with the implanted depth probes and a weak or moderate tissue reaction was found around the probe track. Our data on biocompatibility presented here and in vivo experiments in non-human primates provide a strong indication that this type of neural probe can be applied in stereo-electroencephalography recordings of up to 2 weeks in humans targeting the localization of epileptic foci providing an increased spatial resolution and the ability to monitor local field potentials and neuronal spiking activity.

This paper reports on the design, fabrication, and characterization of neural probes for stereoelectroencephalography (SEEG). The probe specifically targets focal epilepsy as key application. However, probes of this type can also be used for the diagnosis and treatment of other neural dysfunctions such as Parkinson's disease or tremor, typically requiring deep brain probes. The probe fabrication, of which most processes are parallel batch processes, relies on a novel fabrication concept for rolling and gluing thin film polyimide sheets with integrated electrodes into permanent cylindrical shapes with diameters down to 800 μm. The SEEG probes, comprise several macro-electrodes designed to record local field potentials, and micro-electrodes positioned in-between, dedicated to monitoring single unit activity, with a total channel count of 32, despite the small diameter. While platinum micro-electrodes with a diameter of 35 μm have impedances of about 255 kΩ at 1 kHz, impedance values down to about 1.5 kΩ have been measured for the macro-electrodes. The devices have shown good compatibility with magnetic resonance imaging in a 9.4 T magnet, enabling the precise post-operative probe localization within the brain.

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