Design and Use of an Apparatus for Presenting Graspable Objects in 3D Workspace

Podsumowanie

Presented here is a protocol to build an automatic apparatus that guides a monkey to perform the flexible reach-to-grasp task. The apparatus combines a 3D translational device and turning table to present multiple objects in an arbitrary position in 3D space.

Streszczenie

Reaching and grasping are highly-coupled movements, and their underlying neural dynamics have been widely studied in the last decade. To distinguish reaching and grasping encodings, it is essential to present different object identities independent of their positions. Presented here is the design of an automatic apparatus that is assembled with a turning table and three-dimensional (3D) translational device to achieve this goal. The turning table switches different objects corresponding to different grip types while the 3D translational device transports the turning table in 3D space. Both are driven independently by motors so that the target position and object are combined arbitrarily. Meanwhile, wrist trajectory and grip types are recorded via the motion capture system and touch sensors, respectively. Furthermore, representative results that demonstrate successfully trained monkey using this system are described. It is expected that this apparatus will facilitate researchers to study kinematics, neural principles, and brain-machine interfaces related to upper limb function.

Wprowadzenie

Various apparatuses have been developed to study the neural principles underlying reaching and grasping movement in non-human primate. In reaching tasks, touch screen^1,2, screen cursor controlled by a joystick^3,4,5,6,7, and virtual reality technology^8,9,10 have all been employed to present 2D and 3D targets, respectively. To introduce different grip types, differently shaped objects fixed in one position or rotating around an axis were widely used in the grasping tasks^11,12,13. An alternative is to use visual cues to inform subjects to grasp the same object with different grip types^14,15,16,17. More recently, reaching and grasping movements have been studied together (i.e., subjects reach multiple positions and grasp with different grip types in an experimental session)^{18,19,20,21,22,23,24,25,26,27,28,29}. Early experiments have presented objects manually, which inevitably lead to low time and spatial precision^20,21. To improve experimental precision and save manpower, automatic presentation devices controlled by programs have been widely used. To vary the target position and grip type, experimenters have exposed multiple objects simultaneously, but the relative (or absolute) position of targets and the grip types are bound together, which causes rigid firing patterns through long-term training^22,27,28. Objects are usually presented in a 2D plane, which limits the diversity of reaching movement and neural activity^19,25,26. Recently, virtual reality²⁴ and robot arm^23,29 have been introduced to present objects in 3D space.

Presented here are detailed protocols for building and using an automated apparatus³⁰ that can achieve any combination of multiple target positions and grip types in 3D space. We designed a turning table to switch objects and 3D translational device to transport the turning table in 3D space. Both the turning table and translational device are driven by independent motors. Meanwhile, the 3D trajectory of subject’s wrist and neural signals are recorded simultaneously throughout the experiment. The apparatus provides a valuable platform for the study of upper limb function in the rhesus monkey.

Protokół

All behavioral and surgical procedures conformed to the Guide for the Care and Use of Laboratory Animals (China Ministry of Health) and were approved by the Animal Care Committee at Zhejiang University, China.

1.Assembling the 3D translational device

1. Build a frame of size 920 mm x 690 mm x 530 mm with aluminum construction rails (cross section: 40 mm x 40 mm).
2. Secure four pedestals to the two ends of the Y-rails with screws (M4) (Figure 1B).
3. Fix two Y-rails onto the top surface of the frame in parallel by securing the four pedestals to the four corners of the top surface with screws (M6) (Figure 1B).
4. Connect two Y-rails with a connecting shaft and two diaphragm couplings. Tighten the lock screws of couplings to synchronize the shafts of two rails (Figure 1B).
5. Put six nuts (M4) into the back grooves of the Z-rail. Attach one side of the right triangle frame to the back of the Z-rail with screws.
6. Pull the triangle frame to the end that is distal to the shaft and tighten the screws. Attach the other right triangle frame to the other Z-rail in the same way (Figure 1C).
7. Secure the other right-angled sides of two triangle frames to the sliders of two Y-rails with screws (M6) (Figure 1C).
8. Connect two Z-rails with a connecting shaft and diaphragm couplings and tighten the lock screws of coupling (Figure 1C).
9. Attach the two T-shaped connecting boards to the back of the X-rail with nuts and screws (M4). Then pull the two T-shaped boards to the two ends of X-rail and tighten the screws (Figure 1D).
10. Secure the two T-shaped connecting boards onto the sliders of two Z-rails with screws (M6), respectively (Figure 1D).
11. Insert the stepping motor into the shaft hole of the gear reducer and screw their flanges together (Figure 1E).
12. Secure the connecting ring to the shaft end of the active X-rail with screws (M4).
13. Insert the shaft of X-rail into the coupling and fix the gear reducer to the connecting ring with screws (M4).  Tighten the lock screws of the coupling (Figure 1E).
14. Fix the other two stepping motors and gear reducers to the active Y-rail and Z-rail using the methods described in steps 1.11–1.12.
15. Insert the power and control cables of the three stepping motors to the power and control ports of their drivers, respectively and secure the cables with screws on the driver side.

2. Assembling the turning table

1. Download the .DWG design files from the Supplemental Files of this paper. Prepare the objects, mental shaft, locating bar, rotator and case by 3D printing or mechanical processing.
2. Put the touch sensors into the groove of the object body and stick them onto the predefined touch areas with double sided tape (Figure 2B).
   NOTE: Each object consists of four subcomponents: a backboard, object body with groove inside, cover board, and touch sensors.
3. Pass the wires through the hole of the object backboard and secure the cover board onto the object body with screws (Figure 2B).
4. Pass wires of touch sensors through the holes on the sides of rotator and fix the objects onto the rotator with screws. (Figure 2C).
5. Solder the wire ends of touch sensors to the rotating wire ends of the electric slip ring and wrap the joints with electrical tape (Figure 2D).
6. Secure the case to the slider of the X-rail with screws. Place the bearing in the bottom hole of the box and secure the locating bar to the top surface of case with screws (Figure 2E).
7. Place the rotator into the case from side, coinciding the axes of rotator, bearing and box. Pass the wires of the electric slip ring through the top hole of the case (Figure 2F).
8. Insert the metal shaft into the bearing from the top hole of case and fit the shaft key to the keyway of the rotator (Figure 2G).
9. Set the electric slip ring around the metal shaft. Place the end of locating bar into the notch of electric slip ring to prevent the outer ring from rotating (Figure 2G).
10. Insert the shaft of stepping motor into the hole of metal shaft and secure the motor on the top of the box with screws. (Figure 2H).
11. Insert the power and control cables of the motor into the power and control ports of its driver and secure them with screws.
12. Stick a tricolor LED (RGB) onto the front side of the case with tape and fix the right side board onto the case.

3. Setup of the control system

1. Insert the direction and pulse control wires of the four motor drivers into the digital I/O ports (pins 81, 83, 85, 87) and digital counter ports (pins 89, 91, 93, 95) of the data acquisition (DAQ) board, respectively. Secure the wires with screws.
2. Insert the control wires of LED (green color used for the “go” cue, blue color used for the “error” cue, and red color representing idle) into the digital I/O ports (pin 65 and 66) of the DAQ card and secure them with screws.
3. Insert the output wires of touch sensors and switch button into the digital I/O ports (pin 67–77) of the DAQ board and secure the wires with screws.
4. Insert the start-stop and direction control wires of the peristaltic pump into the digital I/O pins 1 and 80, respectively. Insert the flow velocity control wire into the analog I/O port AO2. Secure the wires with screws.
5. Setup a motion capture system as described by the manufacturer to record the hand trajectory in 3D space.
   NOTE: A commercial motion capture system (see Table of Materials) was used, which consists of eight cameras, a power hub, an Ethernet switch and a supporting software (e.g., Cortex). Please refer to the manual to get more details about setup of the system.
6. Setup a neural signal acquisition system as described by the manufacturer to record electrophysiology signal from subject.
   NOTE: A commercial data acquisition system (Table of Materials) was used, which consists of a neural signal processor (NSP), front-end amplifier (FEA), amplifier power supply (ASP), head stages, and its supporting software (e.g., Central). Refer to the manual for more details about the setup of the system.

4. Preparation of the experimental session

1. Initialize the 3D translational device and the turning table. Specifically, pull the sliders of all linear slide rail to the starting point (lower left corner) and turn the first object (i.e., the vertically placed handle) of turning table to face the front side of the turning table.
2. Power on the experimental devices, including motion capture system, neural signal acquisition, DAQ board, peristaltic pump, and four motors.
3. Setup the paradigm software (Figure 3A).
   1. Double click Paradigm.exe to open the paradigm software (available on request).
   2. Define the number of the reaching positions and their 3D coordinates (x, y, and z, in millimeters) relative to initial positions (step 4.2).
   3. Write coordinates of all positions in the form of matrix in a .txt document. Make sure that each row includes the x-, y-, and z-coordinates of one position separated with a space. Save the txt document.
   4. Click Open File in the Pool panel of paradigm software and select the .txt document saved before to load the presentation positions into the paradigm software.
      NOTE: In this study, eight target positions were set according to animal’s reaching range, which are located at vertices of a cuboid workspace^9,10 (90 mm x 60 mm x 90 mm).
   5. Check the objects to be presented in the experiment in the Object Pool of paradigm software.
   6. Adjust experimental parameters in the Time Parameters panel of paradigm software. Set Baseline = 400 ms, Motor Run = 2,000 ms, Planning = 1,000 ms, max Reaction Time = 500 ms, max Reach Time = 1,000 ms, min Hold Time = 500 ms, Reward = 60 ms, and Error Cue = 1,000 ms.
4. Seat the rhesus monkey (with a micro-electrode array implanted in motor cortex) on the monkey chair by inserting its collar into the groove of chair and fixing its head.
5. Fix the monkey chair to the aluminum construction frame. Keep the head 250 mm away from the front side of the cuboid and keep the eyes 50 mm above the top side of the cuboid workspace (horizontal visual angle: 20°; vertical visual angle: 18°).
6. Construct a tracking template of motion capture system.
   1. Attach three reflective markers at the end of the arm (close to wrist) with double-sided tape. Make sure that the three markers form a scalene triangle.
   2. Click the Run button of the paradigm software to start the task.
   3. Click the Record button on the Motion Capture panel of Cortex software to record trajectories of three markers for 60 s when the monkey is doing the task. Click the Stop button to suspend the experiment.
   4. Build a tracking template of three markers on the Cortex software using the recorded trajectories and save the template.
      NOTE: Please refer to the manual of Cortex to get more details about how to build a model.
7. Connect the GND ports of FEA and micro-electrode array implanted in the monkey’s motor cortex with a wire and pinch cocks. Then insert the head stages into the connector of the micro-electrode array³¹.
8. Open the Central software of neural signal acquisition system and set recording parameters including storage path, line noise cancellation, spike filter, spike threshold, etc.
   NOTE: Please refer to the manual of neural signal acquisition system for more details of software setting.
9. Open the synchronization software (Figure 3B, available on request). Click the three Connect buttons in the Cerebus, Motion Capture, and Paradigm panels to connect the synchronization software with the neural signal acquisition system, motion capture system and paradigm software, respectively.
10. Click the Run button of the paradigm software to continue the experiment.
11. Click the Record button on the File Storage panel of Central software to start recording the neural signals.
12. Check the saved tracking template and click the Record button on the Motion Capture panel of Cortex software to start recording the trajectory of monkey’s wrist.

Wyniki

The size of complete workspace of the apparatus is 600 mm, 300 mm, and 500 mm in x-, y-, and z-axes, respectively. The maximum load of the 3D translational device is 25 kg, while the turning table (including the stepping motor) is weighted 15 kg and can be transported at a speed of up to 500 mm/s. The kinematic precision of the 3D translational device is less than 0.1 mm and the noise of the apparatus is less than 60 dB.

To demonstrate the utility of the system, the mon...

Dyskusje

The behavioral apparatus is described here enables a trial-wise combination of different reaching and grasping movements (i.e., the monkey can grasp differently shaped objects in any arbitrary 3D locations in each trial). This is accomplished through the combination of a custom turning table that switches different objects and a linear translational device that transports the turning table to multiple positions in 3D space. In addition, the neural signals from the monkey, trajectory of wrist, and hand shapes were able to...

Materiały

Name	Company	Catalog Number	Comments
Active X-rail	CCM Automation technology Inc., China	W50-25	Effective travel, 600 mm; Load, 25 kg
Active Y-rail	CCM Automation technology Inc., China	W60-35	Effective travel, 300 mm, Load 35 kg
Active Z-rail	CCM Automation technology Inc., China	W50-25	Effective travel, 500 mm; Load 25 kg
Bearing	Taobao.com	6004-2RSH	Acrylic
Case	Custom mechanical processing	TT-C	Acrylic
Connecting ring	CCM Automation technology Inc., China	57/60-W50
Connecting shaft	CCM Automation technology Inc., China	D12-700	Diam., 12 mm;Length, 700 mm
Diaphragm coupling	CCM Automation technology Inc., China	CCM 12-12	Inner diam., 12-12mm
Diaphragm coupling	CCM Automation technology Inc., China	CCM 12-14	Inner diam., 14-12mm
Electric slip ring	Semring Inc., China	SNH020a-12	Acrylic
Locating bar	Custom mechanical processing	TT-L	Acrylic
Motion capture system	Motion Analysis Corp. US	Eagle-2.36
Neural signal acquisition system	Blackrock Microsystems Corp. US	Cerebus
NI DAQ device	National Instruments, US	USB-6341
Object	Custom mechanical processing	TT-O	Acrylic
Passive Y-rail	CCM Automation technology Inc., China	W60-35	Effective travel, 300 mm; Load 35 kg
Passive Z-rail	CCM Automation technology Inc., China	W50-25	Effective travel, 500 mm; Load 25 kg
Pedestal	CCM Automation technology Inc., China	80-W60
Peristaltic pump	Longer Inc., China	BT100-1L
Planetary gearhead	CCM Automation technology Inc., China	PLF60-5	Flange, 60×60 mm; Reduction ratio, 1:5
Right triangle frame	CCM Automation technology Inc., China	290-300
Rotator	Custom mechanical processing	TT-R	Acrylic
Servo motor	Yifeng Inc., China	60ST-M01930	Flange, 60×60 mm; Torque, 1.91 N·m; for Y- and Z-rail
Servo motor	Yifeng Inc., China	60ST-M01330	Flange, 60×60 mm; Torque, 1.27 N·m; for X-rail
Shaft	Custom mechanical processing	TT-S	Acrylic
Stepping motor	Taobao.com	86HBS120	Flange, 86×86 mm; Torque, 1.27 N·m; Driving turning table
Touch sensor	Taobao.com	CM-12X-5V
Tricolor LED	Taobao.com	CK017, RGB
T-shaped connecting board	CCM Automation technology Inc., China	110-120