Physiology & Behavior, Vol. 18, pp. 747--750. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A. BRIEF COMMUNICATION A Digital Readout Vibrational Activity Monitor for Newborn Animals MARTIN H. TEICHER AND WILLIAM T. GREEN Department of Psychology, The Johns Hopkins University, Baltimore, MD 21218 (Received 6 November 1976) TEICHER, M. H. AND W. T. GREEN. A digital readout vibrational activity monitor for newborn animals. PHYSIOL. BEHAV. 18(4) 747-750, 1977. - We describe a device to monitor activity in the preambulatory neonatal rat. It can be readily accommodated to larger animals as well. It consists of (1) an inexpensive mechanical-to-electrical transducer, (2) a pulse height analyzer, limiter, and one-shot multivibrator, and (3) a digital electronic counter with LED display. These components attach to a polygraph and record, in real time, the number of vibrations produced above an adjustable threshold. The device is extremely sensitive, highly adjustable and thoroughly reliable. Detailed description, calibration, and supporting data for the activity monitor are presented. Development Activity Digital electronics Pulsecounters ACTIVITY was introduced as a physiological measure by Stewart [10] at the turn of the century. Since then, activity has been used to test drive theory, study emotion- ality and arousal, screen drugs, explore biological rhythms, and detect the onset of olfaction and forebrain inhibition. Stewart's device measured activity by counting cylinder rotations, a product of locomotion. Syzmanski [ 11] and Richter [7] introduced as alternatives the tambour cage from which vibrational activity could also be inferred. Today, activity monitors respond essentially to corre- lates of locomotion (e.g., stabilimeters [ 1], square cross counters [5], photocell beam interrupters [9], open field force platforms [2]) or correlates of vibration using pressure sensitive mattresses [3] or spring loaded platforms connected to sensitive tranducers such as crystal phono- graph cartidges [8] or optical wedge phototransducers [4]. Since devices sensitive to vibration do not require subjects to appreciably alter their spatial location, they are particu- larly suitable for studying preambulatory neonates, suckling animals on the teat, or restrained subjects. These devices also provide a rapid measure, often revealing activity differences in a matter of seconds. Their major disadvantage lies in decoding the data. Usually [4,8] a polygraph records the vibrations as numerous tightly clustered peaks. Count- ing is laborious, time consuming, and inaccurate. Because of our interest in relating behavioral development with emerg- ing neurological and neurochemical systems, we developed the device described herein to remedy this drawback; attached directly to the polygraph, it displays in real time, the number of vibrations produced above an adjustable threshold. 747 INSTRUMENTATION The unit was developed to study activity in neonatal rats, particularly during the first few days of life when their open field displacement is minimal. The device is flexible, however, and slight changes in either the transducer or the sensitivity-threshold will accommodate it to older animals. The device consists of four main parts (1) a mechanical- to-electrical transducer; (2) a polygraph; (3) a pulse height analyzer, limiter, and one-shot multivibrator; and (4) a digital electronic counter. For the transducer we used an inexpensive 3 in. (7.6 cm) permanent magnetic speaker. A rubber ring was glued around the voice coil, and a styrofoam cup (10 cm dia. x 4 cm) was glued to the ring. A cardboard chamber (13 cm × 12 cm × 7 cm) was glued to another styrofoam cup and inserted into the primary cup. The chamber served as a platform for the animal. Speakers and platforms of other sizes can be used to accommodate any size or number of animals. The speaker leads were connected to a Narco System DMP-4B Physiograph equipped with a DC-AC Coupler (7170) and channel amplifier (7070). Most other polygraphs would be equally suitable. The polygraph output was obtained from the channel monitor jack (+ 30 V maximum for full pen displacement). The voltage at the jack registers zero when the pen is centered. The jack output was fed to the pulse height analyzer, limiter, and one-shot multivibrator (Fig. la). Diode 1 clips the negative-going transients, and transistor 1 serves as a monophasic limiter. Positive peaks greater than threshold (5-9 V, adjustable through R1) produce an