Discriminating between working memory and reference memory in rodent behavioral studies involves designing tasks that specifically test these two types of memory:
- Working memory refers to the ability to hold and manipulate information over short periods of time, typically within the context of a single task or trial.
- Reference memory refers to the long-term retention of information about the rules or regularities of a task that remain constant across trials.
Key Methods to Discriminate Working Memory and Reference Memory
Radial Arm Maze (RAM)
Working Memory Component:
- In a typical RAM setup with 8 arms, food is placed at the end of each arm.
- During a single trial, the rodent must remember which arms it has already visited to avoid revisiting them within the same session.
Reference Memory Component:
In some versions of the RAM, only specific arms are consistently baited across multiple trials (days). The rodent must learn and remember which arms are always baited, using this information across trials.
Assessment:
- Working Memory Errors: Entries into arms that have already been visited within the same trial.
- Reference Memory Errors: Entries into arms that are never baited.
Learn more about Radial Arm Maze by Ugo Basile
Morris Water Maze (MWM)
Working Memory Component:
In a modified version, the platform location changes every day. The rodent must remember the platform location during multiple trials on a single day.
Reference Memory Component:
In the standard version, the platform location remains constant over days. The rodent learns and remembers the fixed location across trials and days.
Assessment:
- Working Memory: Performance improvement within the same session or day.
- Reference Memory: Improved performance over successive days with the platform in the same location.
Learn more about Morris Water Maze by Ugo Basile
T-Maze and Y-Maze
Working Memory Component:
Spontaneous Alternation Task: Rodents are allowed to explore two arms of a T- or Y-maze. In the absence of rewards, rodents naturally tend to alternate between arms, showing their working memory of the most recently visited arm.
Reference Memory Component:
Delayed Non-Match to Sample Task: The rodent is trained to remember which arm was visited in a sample phase and then, after a delay, must choose the opposite arm in a choice phase to receive a reward. The rules of the task remain constant.
Assessment:
- Working Memory: Success in alternation tasks or short delays between sample and choice phases.
- Reference Memory: Learning and performance improvement in tasks with fixed rules or locations over multiple sessions.
Learn more about T-Maze and Y-Maze by Ugo Basile.
Object Recognition Tasks
Working Memory Component:
Object Location Memory (OLM): In a single session, the rodent is exposed to objects in specific locations. After a short delay, one object is moved to a new location. The rodent's ability to detect this change relies on working memory.
Reference Memory Component:
Object Recognition Memory (ORM): The rodent is exposed to objects, and then after a longer delay (hours or days), one object is replaced with a novel object. The rodent's ability to recognize the familiar versus novel object relies on reference memory.
Assessment:
- Working Memory: Time spent exploring the moved object within a single session.
- Reference Memory: Time spent exploring the novel object after longer delays.
Contextual Fear Conditioning
Working Memory Component:
Rodents learn to associate a specific context with an aversive stimulus (e.g., foot shock) within a single session.
Reference Memory Component:
The memory of the context and its association with the aversive stimulus is tested after a longer delay (e.g., 24 hours or more).
Assessment:
- Working Memory: Freezing behavior immediately or shortly after training within the same session.
- Reference Memory: Freezing behavior observed when re-exposed to the context after longer delays.
Learn more about Fear Conditioning System by Ugo Basile.
Summary
By using specific tasks and manipulations, researchers can effectively separate working memory from reference memory. Working memory tasks typically require rodents to remember information within a single session or trial, whereas reference memory tasks involve learning rules or information that must be retained over multiple sessions or days. Accurate discrimination between these types of memory is crucial for understanding the different aspects of cognitive function and the underlying neural mechanisms.