The process used to make a lab rodent perform a specific action is operant conditioning, a method that modifies behavior through consequences. This approach creates a situation where the rodent learns to associate a particular behavior with a specific outcome. The guiding principle is that actions followed by favorable results are more likely to be repeated.
The Principle of Reinforcement
Reinforcement is the core of this training and serves to strengthen a behavior. The most common form is positive reinforcement, where a desirable stimulus is presented immediately following the target action. For a lab rodent, this is often a food pellet delivered after it performs an action like pressing a lever, increasing the probability it will press the lever again.
Negative reinforcement also increases the likelihood of a behavior by removing an unpleasant stimulus. For instance, a rodent might be in a chamber with a mild electric current on the floor. Pressing a lever turns off the current, so the rodent learns to press the lever to escape the unpleasant sensation.
Shaping the Desired Behavior
A complex action is not learned all at once but is taught through a technique called shaping. This method involves breaking down the final desired behavior into a series of smaller, achievable steps. The trainer then reinforces each step sequentially until the full action is learned.
For example, to teach a rodent to press a lever, a researcher first provides a food pellet when the animal looks toward the lever. Once that behavior is consistent, reinforcement is only given when the rodent moves closer. This progression continues, with rewards for sniffing the lever, touching it, and finally, only when the rodent fully depresses the lever.
Through this step-by-step process, the animal learns to connect a sequence of simple actions to achieve the final, more complex task. Each reward refines the behavior, moving the rodent closer to the intended outcome without expecting it to perform the entire sequence correctly from the start.
Ensuring Repetition and Consistency
Once the rodent has learned the action, the goal is to ensure consistent repetition. This is managed by altering the pattern of reinforcement, known as schedules of reinforcement. Initially, a continuous reinforcement schedule is used, meaning the rodent receives a reward every time it performs the correct action, which helps establish the behavior quickly.
To build endurance and make the behavior resistant to extinction, researchers switch to an intermittent reinforcement schedule. On this schedule, the reward is delivered only sometimes after the correct action. For example, the rodent might receive a food pellet after pressing the lever five times or after a variable amount of time has passed.
This unpredictability compels the rodent to continue performing the action, as it does not know when the next reward will arrive. Intermittent schedules are effective in maintaining behavior over the long term. This shift from constant to occasional rewards solidifies the learned behavior, making it a durable response.