It is often desirable to monitor the activity of laboratory animals, such as mice and rats, for scientific purposes. For example, a pharmaceutical company may wish to determine any changes in animal behavior resulting from the administration of a drug to that animal. This has conveniently been done with scientific equipment for continuously monitoring an animal's movement within a confined arena.
One useful device or system for detecting the animal's activity uses an array of two orthogonal sets of parallel light beams extending above the arena. One set of beam is radiated from a series of light sources mounted along one side of the arena. They travel parallel to the arena floor. Each beam of each set is radiated from a light source toward a series of associated light detectors on the opposite side of the arena. The second set of beams is created by similarly cooperating light sources along one of the remaining walls of the arena and light detectors along the opposite wall.
The light detectors are periodically scanned by data processing equipment to determine which light beam have been interrupted by the animal. From this an X and a Y coordinate in a set of rectangular coordinates can be determined and defines the instantaneous positions of the animal. The instantaneous position are recorded and totalized in accordance with known data collecting algorithms for experiments of this type. The circuitry, systems and data processing algorithms by which these X-Y positions are determined from the broken light beams and by which the X-Y positions are converted to the desired activity data is extensively discussed elsewhere in the techincal literature.
In the past, equipment having an arena of one size was manufactured for testing rats while equipment having a smaller arena was manufactured for testing mice. This meant that a laboratory wishing to test both rats and mice was required to purchase at least two different units, one of each size. Furthermore, if the laboratory was currently doing tests upon only one size of animal, then the equipment purchased for the other size animal sat idle.
It has been previously recognized that it would be desirable to construct an animal activity monitor system which, with only slight modification and slight additional cost, can be adapted for use with either mice or rats.
One prior art attempt to do this is illustrated in FIG. 3. FIG. 3 shows an arena with a first set of light sources 10 aimed toward a first set of light detectors 12 along with a second set of light sources 14 aimed toward a second set of light detectors 16. In ordinary use for monitoring the activity of each rat, each light beam, such as light beam 18, is directed entirely across the arena to a detector upon the opposite side in the conventional manner.
However, in an attempt to permit use of the same equipment for mice, a diagonal, doubly reflective partition 20 was inserted across the center of the arena. The idea was that a light beam from a light source, such as light beam 22, would then be reflected by the central partition 20 to a detector along the side adjacent to the light sources. In this manner each of the two halves of the arena has its own detection system comprising a series of sources and a series of detectors. It was then a simple manner to modify the data processing software to coordinate each light source with its associated light detector to derive data indicating which light beams the animal was blocking.
There are two major problems, however, with this system. First, in practical systems it is very difficult and impractical to form the central partition 20 in appropriate, precise alignment so that all of the light beams from each of the sources along the side 14, for example, would be aimed upon their associated detectors, such as the detectors 12. Furthermore, the data which is obtained in essentially one dimensional in that the only information which can be obtained is that an animal is somewhere in the light beam. Because there are no longer two sets of transverse light beams, no determination can be made exactly where along the reflected light beam the animal is positioned. Therefore, the data derived was reduced to a single parameter of study and X and Y position coordinates became impossible to obtain in this system.
There is therefore a need for a manner in which a test arena can be inexpensively modified so that it may be converted from the testing of larger animals to the testing of smaller animals and which nonetheless can provide instantaneous X and Y position coordinates.
It is also known in prior art systems to connect a multiplicity of test arenas, each with its own orthogonal sets of parallel light beams, to a single data processing computer. In the normal use of such prior art equipment, the animals are first all prepared. When all the animals have been placed in the appropriate arena, operation of the data processing equipment is begun.
This system, however, introduces an error in the test data or causes valuable test data to be lost or both. The reason is that it takes time to prepare each of several animals, for example by injecting them with a drug, and to then place them in the arena. There may, therefore, be a significantly longer time delay from the time the first animal is prepared until the time the last animal is prepared. Since the collection of data for all animals is begun immediately after the last animal is prepared, the time delay from preparation to data collection is different for each animal. This difference may in fact be 2 to 3 minutes. Such a time lag can be very significant particulary in experiments that may last only a short time, such as 2 to 3 minutes. For example, the testing scientist may wish to determine the animal's exploratory activity during its habituation period, the time during which the animal is becoming acquainted with the new environment of the arena. A 2 or 3 minute delay from preparation of some animals to initiation of data collection for that animal will give invalid or erroneous data for the first animals with such a prior art system.
There is therefore a need for an animal activity monitoring system which can preserve the desirable arrangement in which several arenas are connected to a single data processing system, but which can permit all tested animals to be given a uniform time delay after preparation. In this manner all animals would be tested under the same conditions so that the data representing their activity is more accurate and reliable.
Most testing laboratories need to study as many animals as they possibly can in the shortest time possible so that they may obtain a sufficiently large amount of data to be statistically significant. Thus, the faster and more reliably accurate the animal test can be processed, the better and more economical is the system.