Operant Testing    
 

Operant testing has been in existence since the 1940’s and is most closely associated with the experimental endeavors of B.F. Skinner. The training and testing principles used in rodent operant testing are directly applicable to most living creatures, including most importantly, humans. At the very essence of operant behavior, a positive reinforcer will tend to increase the likelihood that the event preceding it will occur again. Within the operant testing apparatus, as rodent behavior is shaped during training, a lever press is immediately followed by a positive reinforcer (usually a small amount of food or water). Once lever pressing is established, behaviors associated with lever pressing can be dramatically altered to fit the needs of the experimenter.
 

The BN Lab employs several operant paradigms that capitalize on the rodent’s ability to lever press. Although operant chambers have been around since the early 1940s, recent developments allow for automated computer controlled data collection. Not only is data collection more precise but we can also measure behavior across multiple dimensions.
 
   

Ultrasonic Vocalizations (USV)
The noises made by rodents are outside the audible range of the human ear and thus they cannot be quantified like other, more overt behaviors. The ultrasonic vocalization detector (Med Associates Inc.) employed in the lab detects vocalizations in bands ranging from 20 KHz to 100 KHz. The emmited frequencies can then be analzed using either sonogram or spectrogram (right) graphing utilities.

 
 


Delayed Nonmatch-to-Sample
(DNMTS)

Clearly, memory is an extremely important brain function. As such, memory may be the most widely studied brain function. The delayed non-match to sample task (DNMTS) is an operant task that assesses short -term working memory in the rodent.

The operant DNMTS task has three behavioral components; the sample phase, the retention phase, and the choice phase.

During the sample phase the rat is presented with a “to be remembered stimulus”. That stimulus is presented as the illumination of one of two lights, each of which has a corresponding lever located just underneath. The rat signals to the experimenter that it has indeed seen the sample stimulus by pressing the corresponding lever.

The retention phase is a period of time (ranging from 1 to 15 seconds) during which the rat retains the sample phase information. During this time rats are typically required to orient away from the area of the operant chamber that conveyed the sample information. Having the rat go to the rear of the operant chamber and execute a series of lever presses during the retention phase greatly reduces the chances of “cheating”.

During the choice phase the rodent will once again orient towards the front of the operant chamber. If the rat remembers the location of the sample stimulus (e.g. the left light illuminated, with a corresponding left lever press), a non matching lever response will be successfully executed (e.g. non matching to the sample by pressing the right lever). A correct non match to sample results in a small food or water reward.

Signal Detection

Arguably, memory is not a single entity but instead is comprised of many individual types of cognitive processing. One component of memory is attention. As it relates to our laboratory a rodent must correctly attend to a stimulus to encode it properly and thus remember it. It is this type of logic that has led to the formation of this novel operant task. The Signal Detection task is a measure of sustained attention in the rodent. This task developed by Dr John Robinson is based on the sample phase of the DNMTS task (see Echevarria et al., 2005 for more details).

To perform this task correctly animals must attend to the front of the operant chamber. A trial begins with an auditory warning and the illumination of one of two lights, each of which has a corresponding lever located just underneath. Upon viewing the visual cue the rodent presses the corresponding lever. If the rodent’s response is correct the result is a small food or water reward.

Although the task may seem simple it should be noted that the visual cue not only appears randomly on the left or right but also will randomly occur for one of three different durations (1000, 300, or 100 milliseconds).

As a validated measure of sustained attention, performance on this task has been shown to be adversely effected by behavioral and drug manipulation that are known to adversely effect attention in the human (see Presburger and Robinson 1999, and Echevarria et al., 2005 for more details).

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