Fig 1.
Electrode microdrive positioning setup.
This setup allows movements in 3 translational and 3 rotational axes during online position tracking with IR-cameras. (A) The arch that is holding the microdrive is mounted on two vertical and parallel aluminum beams which allows to change its height. The arch can be rotated along the horizontal line connecting the vertical beams. A set of three linear micromanipulators is mounted on the arch and can be moved along the arch to rotate around the center point of the arch, where the target is placed. The linear micromanipulators can be used to adjust the 3 translational axes and to finally drive the tip of the guide tube down into the tissue. Lastly, the microdrive is connected to the linear micromanipulators on a table that is rotatable 360 degrees. (B) Layout of the CortEXplore System interacting with the TREC Microdrive. The CortEXplore Navigation PC is connected to IR-cameras that are tracking the monkey’s head as well as the microdrive’s position relative to each other. A recording trajectory is defined based on an experimental planning file that utilizes CT and MR imaging. The rotational and translational offsets of the realtime electrode trajectory are then displayed by the CortEXplore system, and the micromanipulators set accordingly to minimize the positioning error. Once the positioning error is minimized on all axes (excluding the penetration axis of the electrode), the TREC Matrix computer advances the electrode out of the guide tube along that axis to the desired target depth (adapted Figure, originally provided by CortEXplore GmbH). (C) Photograph of the setup with a monkey head plastic. Physical objects (red) and their representations in digital 3D space (yellow) are encircled. After co-registration, the stiff connection between the reference geometry A and the monkeys head B, allows positioning of the TREC Mini Matrix C relative to the monkey’s anatomy.
Fig 2.
Realtime electrode positioning is guided by CORTEXPLORER SCI.
The rotational offset of each axis is displayed on top of each axis section with the planned trajectory (blue) and realtime trajectory (red). The red dot along the realtime trajectory equals the guide tube tip of the MiniMatrix. The upper blue dot along the planned trajectory is the planned guide tube tip position, and the lower dot shows the electrode target position. The figure shows the realtime trajectory and positioning errors before the fine adjustment. Rotational offsets, displayed at the top of each window, are minimized first by adjusting the respective micromanipulators (rotational errors in this figure: coronal: 6.74°, sagittal: 7.44°, axial: 74.65°). Afterwards, the translational offset of the realtime trajectory to the target location is minimized using the translational micromanipulators. Once the distance depicted in ‘Tool axis to target’ (here 8.35 mm) in the lower right corner is minimized (close to 0 mm), the microdrive is advanced into the tissue along the tool axis which is matching the guide tube.
Fig 3.
TREC MiniMatrix guide tube layout and coordinate system for distance measurements.
The coordinate system used to report data in this study is based on the penetration axis of the TREC Mini Matrix microdrive’s guide tubes. The coordinate system is centered around the tip of the central guide tube. The penetration axis of the guide tubes is set as the SI-axis of the coordinate system. The anterior direction A of the AP-axis is defined as the direction facing the cameras, identifiable by the 4 spherical IR-reflective markers. The right-side R of the RL-axis is results from the definition of the other two axes. The guide tubes were ordered in a cross shape, centered around guide tube 3.
Fig 4.
T1- and T2-weighted MRI images of the monkey.
Planned (dots) and evaluated (squares) locations of the guide tube penetration entry point and iron deposits are added in blue and red, respectively. Due to the higher resolution and signal quality, T2-imaging was used for precise localization of iron deposits and guide tube penetration marks. A & C are T2-weighted images; B & D are T1-weighted images. A & B are images taken before the experiment; C & D were taken after the iron deposition.
Fig 5.
Translational error of the planned to physical location of iron deposits and penetration marks in the denatured egg-white container (A) and monkey (B) in mm. R is the offset to the right, A to the anterior and RA the 2-dimensional distance in the RA-plane. S is the offset in the superior direction and RAS depicts the 3-dimensional distance.
Fig 6.
Example recording trajectories and the respective receptive field maps of the recorded neurons.
(A). The recording location of neuron 19 in the bend of the wall of the superior temporal sulcus. This slice is more inferior than slice B. A = anterior, P = posterior, M = medial, L = left. (B). The recording locations of neurons 5, 11 and 12 as well as the location of electrode 19 passing through this slice. Area MT is rendered in orange based on warping of the D99 monkey atlas onto this monkey’s brain. (C). A 3D rendering of the 4 electrode trajectories (colored cylinders) and Area MT and V4. Viewing direction is from anterior to posterior. (D). Receptive field maps of neurons 5, 11, 12 and 19.