An inexpensive automated system for the measurement of rotational behavior in small animals

DAVID K. McFARLANE 0 1 BUDA J. MARTONYI 0 1 TERRY E. ROBINSON 0 1 0 We are indebted to Chris Leiby for his earlier rotometer software on the Rockwell AIM 65. This work was supported by Grant DA04294 to T.E.R. and USPHS NS 22157 to Jill B. Becker, and portions of it were presented at the Annual Meeting of the Society for Neuroscience (McFarlane , Becker, Martonyi, & Robinson, 1990). Requests for reprints should be addressed to T. Robinson, University of Michigan, 3064 Neuroscience Bldg. , 1103 E. Huron St., Ann Arbor, MI48109-1687 . Inquiries regarding the system should be sent to D. McFarlane, Smart Tech Systems Engineering , 1293 Orlando Dr., Haslett, MI 48840 1 University of Michigan , Ann Arbor, Michigan A reliable, low-cost automated system for the quantification of rotational behavior from up to 10 subjects simultaneously is described. The system resolves quarter and full turns to the left and right, and can relay data to another computer for statistical analysis. The system is easily constructed from simple and inexpensive components, including the computer, that total less than $1,000 and can be used with a variety of different test chambers. Automated systems for measuring animal rotations, often called rotometers, have been in use since 1970 (Ungerstedt & Arbuthnott, 1970), and a number of commercial and lab-built systems have been described (Barber, Blackburn, & Greenwood, 1973; Bonatz, Steiner, & Huston, 1987; Greenstein & Glick, 1975; Jerussi, 1982; Schmidt & Dubach, 1988; Schwarz, Stein, & Bernard, 1978; Yehuda & Wurtman, 1975; Walsh & Silbergeld, 1979). However, commercial systems are very expensive and some lab-built systems require relatively expensive acquisition hardware and dedicated PCs. We developed an automated data collection system based on the inexpensive Commodore 64, which comes with an array of acquisition hardware built-in, and its capability was easily extended by the use of an inexpensive commercial 1/0 board. Sensor units were also developed, and these resolve every 90 movement and fit over a variety of test chambers. The flexible software allows the acquisition of data simultaneously from up to 10 different rotometers, and then data can be transmitted to a more sophisticated computer for statistical analysis. The cost of the hardware for the entire 100unit system, including the Commodore 64, is less than $1,000, and it is easily constructed from readily available components. Alternatively, the sensor units could be added to a system built by using any PC and appropriate lIO hardware, and the software could be adapted from the following description. - Figure 1 shows a block diagram of the hardware for a lO-unit automated rotometer system. Briefly, the sys tem consists of a Commodore 64 computer and periph erals (video monitor, disk drive, printer, and RS-232 adapter), an SSloo Plus Simplified Digital lIO Board, sen sor units, a routing and distribution box (not shown), ex ternal5-VDC power supply, and connecting cables. The Commodore 64 computer provides a slightly modified 6502 processor running at 1 MHz, 64K of RAM, I/O ports and timers on two 6526 complex interface adapters (CIA), and a 6581 sound interface device (SID). The au tomated rotometer software uses the time-of-day (TOO) timer on CIA 2 to time acquisition epochs and uses the SID to supply white noise through an audio loudspeaker (usually part of the monitor). Rotation of the subject is detected and encoded by a sen sor unit suspended over the testing chamber. The sensor unit consists of a custom-built 2-bit quadrature, 4-position optical encoder powered by an external 5-VDC power supply: A 3-em long axle and bushing derived from com mon model aircraft supplies is mounted partially inside a simple plastic enclosure so that the axle extends out side; the subject can be attached to this end by means of a flexible wire cable (model aircraft cable) with claw clips on each end that fasten either to the subject's harness or to a clasp soldered onto the end of the axle. The internal end of the axle is soldered to a 2-cm disk that is half black and half white. A circuit board directly above the disk holds two reflective-object detectors (ROD) separated by 90. Each ROD contains its own LED light source and photodetector, which allows it to detect whether it is above a light or a dark sector of the disk, and together the pair provides an encoded signal to the computer indicating the direction the subject faces as it turns, as is illustrated in Figure 2. Higher rotational resolution could be achieved with the same hardware simply by dividing the disk into more sectors and properly placing the two photocells, al2 inpullines I unit 40 in lines though this would reduce the maximum rotational rates and total number of epochs acquired, and the software must be changed to process the desired resolution. Two trim-pots are used to adjust the sensitivity of the photo detectors to produce a solid transition from logic' 'high" to "low" when the disk under them turns from black to white. This circuit is connected to the computer over ca bles up to 20 ft (7 m) in length, with no signal condition ing other than that provided by the I/O board. All input is memory-mapped to 8-bit ports, and groups of four or fewer sensor units are connected to one port so that the D1 signal of each unit connects to the first available even numbered bit of the port and its D2 signal connects to the next bit (Figures 2 and 3). The single user port of the C-64 could serve four such sensor units (provided the software input address is changed to the uset port), but to extend this the SSl00 Plus Simplified Digital I/O Board was used. (The board Figure 2. Principle of sensor unit encoding. Dl and D2 are the two photodetectors placed above tbe light/dark disk in the sensor unit. The columns on the right show tbe encoded signal from the detector pair as the disk rotates through the four quarter turns in the illustration on the left. Sensor Units is available from Schnedler Systems, 25 Eastwood Rd., P.O. Box 5964, Asheville, NC 28813, telephone 704-274 4646.) This board provides 40 lines of digital input and 40 lines of digitally switched output, each arranged as five 8-bit ports; the rotometer software uses 20 of the input lines (2.5 ports) to support 10 sensor units. More units could be supported by this board, but this limit was chosen both in consideration of operator interventions that oc cur between acquisition periods and to allow 100 epochs of data to fit within a secure area of RAM (discussed below). The software consists of an acquisition routine and a user-interface "shell." The acquisition routine is writ ten in machine language, but the rest of the program is written in Commodore BASIC 2.0. In the interest ofbrev ity, and because others may wish to institute their own user-interface shell around the acquisition routine, the BASIC shell program is only briefly described here. Com plete source code is avail (...truncated)