For the last week and a half, I have traveled by plane, by car, by ferry, by kayak, by boat, and by foot, visiting many beautiful locations within the Pacific Northwest in the United States. Whether it is due to my middle-aged brain or the fact that there have just been so many places, I frequently found myself trying to remember where I was when I thought about specific experiences, such as the harbor seal swimming in the water or the North American River Otter family rolling around with one another (images below).

Recollecting these events was especially challenging over a 72-hour period during which I moderated multiple sessions each day at a national psychological convention. So much information, along with trying to remember which building and room the next session was taking place, was its own Olympic sport (in honor of the Olympics, which just ended)! We jumped between three different buildings and multiple rooms within and across each day, so perhaps it wasn’t too surprising that I ended up in the wrong room on several occasions.

Needless to say, I found myself feeling a bit like a rat in an 8-arm radial maze (pictured below) trying to remember where I had been and where I was headed so that I could find the very tasty food reward. Unfortunately for me, there was no mint chocolate chip ice cream (my primary motivator) at the end of any session.

This experience of trying to find the correct building and room without the previous rooms and sessions interfering with the current experience is called proactive interference. This cognitive concept is often used to explain the construct of forgetting, but it does not explain all aspects of forgetting.

A recent paper, published in the Psychonomic Society’s journal Learning & Behavior, by Chiaki Tanaka and Tohru Taniuchi (pictured below) of Kanazawa University in Japan assessed the length of time rats could remember four locations of where food had been stored previously so that they could ignore those (and not be influenced by proactive interference) and visit the remaining four new locations in which food was present (the correct response during testing).

The current study attempted to minimize the possible proactive interference by instituting different types of intertrial interval lengths, which hypothetically created a more distinct memory experience based on the delay tested. The retention intervals (the length of time the rats were given to explore the maze initially and then be tested on their memory) were systematically increased from 1 hour to 24, 48, and ultimately 72 hours, with corresponding intertrial intervals expanding from 24 to 48, 120, and 144 hours (6 days). This testing protocol was thought to have been the primary factor in the success of the study as it allowed the retention interval to be clearly discriminated from trial timing. That is, the researchers (and others) speculated that previous studies may have created ambiguous trials when their retention interval was too similar in length to trial interval, such as a 24-hour retention interval for a test followed by a 24-hour period between trials.

The researchers conducted their study with a radial arm maze, a commonly used tool for studying working memory in rats and other animals. As shown in the adapted image above, a radial arm maze has a central platform and eight arms extending outward. In this setup, rats can find food rewards (45 mg food pellets for this study) at the end of each arm. In a standard task, where no additional food is provided during trials, the best strategy is for the rats to enter each arm only once to avoid returning to arms they have already explored.

The rats experienced 7 phases in which they had an opportunity to learn about the maze and tested under different retention intervals. Where the first three phases had opportunities to learn about the maze and be tested with unlimited access to all eight arms, the remaining four phases had limited access to four arms only. The researchers explained that this change was made to control for the possibility of the rats using a strategy different from the strategy the researchers were hoping to elicit from the rats. That is, the researchers wanted the rats to draw upon long-term memories that had been formed during the learning phase (i.e., I went to arms 2, 3, 6, & 8 24 hours ago, so I’ll go to arms 1, 4, 5, & 7 now) and not use a strategy based solely on short-term working memory, which could be done in the unlimited access procedure (i.e., I just visited 2, 3, 6, & 8 and there wasn’t any food).

As described by the researchers,

“the learning phase [in phases 3-7] required rats to make sequential forced choices among four specific arms, where food pellets were placed in each food dish. The rat entered the arm, consumed the food reward, and then returned to the central platform. Upon its return, we opened the door to the next arm while simultaneously closing the door to the arm the rat had just exited. The learning phase concluded when the rat had entered all four [baited] arms and returned to the central platform. After the learning phase, the experimenter removed the rats to their home cage for the retention interval. [During] the testing phase, a free-choice task was conducted with all eight arms opened simultaneously. The four arms that the rat had not entered during the learning phase were each baited with food pellets as rewards.”

The figure below shows the average percent correct for each phase during testing, indicating each retention interval. Whether the rats had unlimited access to all arms (Phase 1-3) or access to the first four arms they visited during testing (Phase 4-7), according to the authors, “performance significantly surpassed chance levels across all conditions, demonstrating that rats are capable of retaining spatial memory for up to 72 hours.” This finding extended previous work conducted by another research group (Crystal & Babb, 2008) which found that rats retained memories from a similar setting for 25 hours.

The researchers also highlighted several reasons why this study led to new insights into the field of animal cognition. First, the study provided evidence of a long retention period from 25 hours to 72 hours. Of greater interest to me was that the rats in this study were older than middle-aged. Usually, 24-month-old rats are regarded as aged and 17-month-old as middle-aged. In this study, the rats were more than 20 months old at the end of the 72-hour retention condition, suggesting that despite potential age-related declines, memory for the task was retained at a high level.

One reason for the high levels of performance may have been related to the extensive training in the radial maze task the rats experienced from a young age through adulthood. The researchers argued that this exposure could have been interpreted as “intellectual activities” in aging rats, and thus, their performances on the task may have been enhanced due to cognitive reserve – or the idea that certain human individuals maintain good cognitive performance despite age-related declines in brain function due to prior education and occupations that
involve intellectual activities.

Unfortunately, as the authors shared, that

“it is still uncertain whether the 72-hour memory retention observed in 20-month-old rats is a direct outcome of their prior spatial memory task experiences”

or perhaps the really “big” reward they received for going down the correct arm. Nevertheless,

“it is essential to investigate further the impact of such previous, continuous cognitive task engagement on the spatial memory capabilities of aged rats, particularly in the context of cognitive reserve.”

In the meantime, I will look forward to future work on cognitive reserve as I experience my own mid-life aging process. While I may have trouble remembering the sources of some of my memories due to proactive interference and not enough consolidation time between my experiences on my recent experiences with nature and psychological science, I will hopefully be able to continue to practice intellectual activities (e.g., writing content for Psychonomic Society for the next 20 years?) and retain the image and sensory experiences of viewing Mt Rainier in all her glory in front of a fragrant field of wildflowers and pines one summer night in August (image below).

Psychonomic Society featured paper

Tanaka, C., & Taniuchi, T. (2024). Rats show up to 72 h of significant retention for spatial memory in the radial maze. Learning & Behavior, 1-9. https://doi.org/10.3758/s13420-024-00633-4