Fig 1.
(A) The thumbtack electrode, containing a 3 mm long shaft with an array of insulated fine wires and a silicone disk (www.plexon.com). (B) Design concept of the multimodal polymer-based MEMS electrode array.
Fig 2.
The processes yield a PI (bottom insulator)–TiOx/Pt (conductive)–SU-8 (top insulator) layer structure.
Fig 3.
The microfabricated components.
The surface MEA, shown in (A) and (C) is provided with a hole in the middle of the array, into which the depth MEA (shown in (B) and (D) can be inserted. Above the depth electrodes, two handles protrude from the sides of the shank.
Fig 4.
The assembly of the sensor components.
(A) The surface MEA is clamped with glass slides. (B)-(C) The depth MEA is inserted and it is constrained by the lower glass slides. (D) The components are glued together with epoxy resin. (E) The glass slides are removed.
Fig 5.
Photographs of the assembled device.
(A) Macroscopic view. (B) A microscopic image of the sensor region, containing the microelectrodes.
Fig 6.
The average magnitude and phase values of electrode impedances at different frequencies, measured in physiological saline.
The depth electrodes were subjected to electrochemical deposition of Pt, which reduced the impedance magnitudes from 559.5±148.4 kΩ to 27.6±8 kΩ at 1 kHz. The impedance of the surface sites were 18.6±0.5 kΩ on the average at 1 kHz, no modification was performed on them.
Fig 7.
(A) Simultaneously recorded waveforms from the ECoG (channels no. 1–8, green curves) and the depth component (channels no. 9–24, red curves). The 1–1.5 Hz oscillation is the result of ketamine-xylazine anesthesia. During upstates, positive LFP can be detected on the brain surface and the upper cortical layers and negative LFP in deeper cortical layers. The intensity of unit activity (black curves) closely correlates with the upstate periods in the cortex, but not in the hippocampus. The brain atlas image has been reprinted from The rat brain in stereotaxic coordinates 2009, (ISBN 9780123742438), Paxinos et al ed, figure 61 under a CC BY license, with permission from Elsevier Ltd., original copyright 2009. (B) Changes of current sources and sinks in time, yielded from the signals recorded by the depth electrode array.
Fig 8.
(A) Variation of the average amplitude spectral density of the signals provided by surface electrodes in the 0–4 Hz band (characteristics of the sleeping state) (B) Variation of SU yield, average SU amplitude and average SU SNAR during 15 weeks, obtained from the chronically implanted rats. standard error to. Error bars indicate standard errors within a MEA. Piled single units waveforms, obtained from the last measurement of each rat are shown in the middle. Perpendicular scale bars are 20 μV. Examples of average single unit waveforms, corresponding to the different clusters are shown on the right.