Gregory Arnone & Martin Kent

Sponsor:

Dr. Ryan Clement, Ph.D.

The Pennsylvania State University

Department of Bioengineering

University Park, PA 16802

Spring 2006

Executive Summary

Researchers at Penn State involved in recording neural information via the implantation of electrodes in the brain of rats are having difficulties with the connection mechanism of the electrodes to an interface. One aspect of the experimental setup that is difficult for researchers is connecting electrode arrays embedded in the animal skull to an interface for data collection. The connecting wires are Omnetics nano-pin^TM connectors which are on the order of 0.025 inches per lead, which causes problems when trying to connect to a live animal. During the connection process, the leads are often bent and damaged due to misalignment. Furthermore, the connection is not snug and the wires repeatedly come apart during experiments, wasting valuable time.

The following design will eliminate that problem by incorporating an additional connection point between the headstage and the preamplifier. This connection is housed in a back-pack, which reduces the stress placed on the implanted region of the skull. Because the initial connection of the headstage is done while the rat is under an anesthetic, any additional disconnection and reconnection will be at the back-pack, which is much easier to access. In addition, since the main point of connection will be safely contained within the back-pack, any possibility of disconnection will be eliminated. A prototype of a manual commutator is presented, which prevents twisting and chewing of the leads. After assembly is completed, the design will be tested at the neural research laboratory. All materials and labor are projected to cost a total of $776.80 and the completed connection device will be delivered no later than May 1st, 2006.

Design Criteria

• Allow for an easy connection of a 16 channel Tucker Davis headstage, model number RA16CH SN:3197, which houses 16 recording channels (in addition to 4 leads for the reference, ground and power supply), while the animal is awake and moving.

• The other end must be compatible with a DB-25 connector.

• Prevent disconnection midexperiments.

• Keep clear of the animal’s body so that it does not tangle or promote chewing.

• Prevent twisting of the leads.

• Adapt onto the current model headstage without adding more than 20 grams

  additional weight and 3 mm additional radius to the electrode arrays on the skull.

Alternative Designs

Retractable Cable Mechanism & Locking-Clip Headstage

The locking clip, such as the one found on the Plexon® CON/8o50f-10P-L input connector and Plexon® CON/8o50m-10P-L mating connector, will allow the headstage to lock onto the mating connector and secure the link for the duration of the experiment. The retractable cable mechanism will prevent the cable from dropping low enough for the subject to become tangled in it or chew on the cable. The retractable cable placed too much stress on the subject's skull, which would constrict its movement during experiments.

Motorized Commutator

 A motorized commutator consists of sensors which continuously measure the rotational angle  

 applied to the headstage, and spin the motor to compensate, eliminating the turn-induced 

 torque at the subject's end of the cable. Ultimately, the decision was made to not purchase this

 device because the prices ranged from $1000 to over $3000, which would have exceeded the

 budget.

Wireless Recording System

This wireless recording system would include an analog headstage transmitter and receiver system. It consists of a headstage transmitter with an internal battery—capable of lasting 5 hours—as well as a DSP based signal processing system with a configurable gain from 20 to 800. Unfortunately, this system was not compatible with equipment in the laboratory because a gain of 10,000 was required for this experiment. In addition, the cost would have exceeded the budget.

Funnel-Like Adapter

This funnel-like adapter would be attached to the headstage andl allow for the connectors to be brought into close proximity relatively easily. The connection would be guided by the geometry of the funnel and also include the locking clip mechanism mentioned above. Unfortunately, mounting it to the skull would have been too difficult and it would be too bulky, raising concerns that it would have exceeded the weight limit of 20 grams.

Final Design

The design consists of three main components:

The Back-Pack

The back-pack provides a space for the two connector pieces that is 1.5 inches wide, 2.5 inches long, and 0.5 inch tall. Because the initial connection of the headstage is done while the rat is under an anesthetic, any additional disconnection and reconnection will be at the back-pack, which is much easier to access. In addition, since the main point of connection will be safely contained within the back-pack, any possibility of disconnection will be eliminated. The back-pack is attached to the rat by having two straps—each with a circumference of 10 inches—wrap around its waist and connect to the back-pack through the use of Velcro. The back-pack is made of a canvas material because it is flexible enough to accommodate the shape of wires easily, as well as providing the it with a soft exterior that makes wearing the back-pack a more comfortable experience for the rat.

The Connection Parts

The connection, extending from the neural recording machine to the subject's skull, was split into two wires that connect inside of the back-pack. These two wires each had a connector piece attached to them—one was equipped with a CLINCHER 10 POS - RoHS connection piece from Mouser Electronics, while the other was equipped with a 10POS PIN ASSEM Sn - RoHS connection piece, which was also from Mouser Electronics. Each of the two parts had two 10 position connector pieces stacked on top of each other, allowing for the full 20 channel connection needed. These parts were chosen for their slim design and ease of connection. When both parts are connected, they fit perfectly inside of the back-pack, with no parts exposed.

The Commutator

The base of the device consists a rotating wheel. This lower wheel, which is arranged in a horizontal position, leads up to two vertically-arranged wheels, connected through a series of plastic rods, which were chosen for their light weight and inexpensive price. The system is arranged by having the cable go from the neural recording machine and down through the two upper wheels and finally down through the lower wheel and into the back-pack. The lower wheel rotates as the subject moves around its confined space. As the lower wheel rotates, any tangling that results above is eliminated by the two upper wheels rotating horizontally as well and thus straightening out the cable. In addition, the two upper wheels, equipped with a mechanism that allows them to vertically spin, can be rotated either forwards or backwards, allowing either more or less cable to reach the subject's cage. Ultimately, this manual commutator should prevent any and all twisting and chewing of the leads that may occur during the course of the experiment.

Overall Setup

Deliverables & Summary

The system meets all of the design criteria and comes in well under budget. Each soldered point on the connection pieces was tested with a multimeter, using the continuity feature. All connections were successful and shown to be continuous from the headstage to the DB-25 piece.

The deliverables of the final chronic neural interface connection system consists of:

• A rat back-pack, which fits comfortably around the subject and accommodates the connector pieces, as well as not exceeding 1.5 inches in width. In addition, the back-pack eliminates the stress on the skull.

• A 20-channel connection between the DB-25 and the headstage, which provides a quick and easy connection and disconnection midexperiment.

• Manual commutator prototype, which prevents twisting and chewing of the leads.

The overall design is attractive because of its expandability and adaptability to future experimental setups. For example, this design can be modified later on to accommodate a second headstage lead for recording experiments, which involve two separate implanted electrodes on either sides of the brain. Different-sized straps can also be applied in order to accommodate the varying sizes of the subjects.

Final Budget