People typically associate mazes with long, winding labyrinths that offer no hope of navigating, let alone escape. That sounds scary and confusing for most people, but there is a simpler maze that does offer ease of navigation. Of course we’re talking about the Y maze. While it isn’t the most creative name for a Y-shaped maze, it’s one of the most successful and widely used mazes in neuroscience research, especially where spatial memory is concerned.
Spatial memory refers to the ability to memorize and recall locations and spaces, which comes in handy when navigating spaces. With its simple three-armed design, the Y maze has been effective in spatial memory studies, especially since no rules need to be learned. This also makes it ideal for studying various facets of spatial memory, especially impairments to it.
Today we’re going to explore some studies that looked at the effects of stress, sex differences, and morphine on spatial memory tasks in the Y-maze.
Stress, as we all know, is quite unpleasant, and in the right doses, can even kill you. It’s even been found that chronic stress negatively impacts spatial memory and produces depressive-like symptoms, which leads to a decrease in activity.
Wright and Conrad (2005) at Arizona State University decided to put this to the test. To do this, they placed some rats they’d been stressing out (poor creatures) into two different versions of the Y-maze: one standard, and one with special built-in cues.
For the standard maze task, the rats had to rely on cues that were placed outside of the maze, such as the surrounding environment, to help navigate it. The second maze was built to be somewhat easier to navigate thanks to these built-in cues.
In the task, the rats explored the three arms of the maze (Start, Novel, Other) for 15 minutes, but were unable to explore the Novel arm during training since it was blocked off by Plexiglas; they were able to explore the full maze unobstructed for 5 minutes during the actual task. The rats continued to display novelty-seeking behaviors but also exhibited problems in spatial memory, thus supporting the hypothesis of stress impairing spatial memory.
Recent studies have found that there are differences in the ways that male and female brains process information and perform tasks. Carrying on the institution’s traditions of curiosity and investigation, some other researchers at Arizona State asked themselves if sex differences played a role.
Conrad, Grote, Hobbs, and Ferayorni (2003) hypothesized that female rat brains might have better immunity to stress-related memory impairments that male rat brains. To test this, they began by placing the rats in tight mesh containers to stress them out. Following that, the rats were set loose in the Y-maze across several 15 minute trials. Overall, both male and female rats in the stressed group performed similarly, but the female rats recovered more quickly from stress than their male counterparts, and even entered the novel arm more consistently than males.
It’s not clear as to how and why female rats were able to recover and perform as quickly as they did, but one explanation relates to how the male and female brains are wired differently, and thus gender differences might just play a role in memory.
Since we were kids we’ve been told that drugs are bad, and that they zap our brains and bring us all kinds of harm. But how true is this?
Over in China, Ma et al (2007) investigated the effects of morphine on spatial memory performance in the Y-maze across three experiments, and if there was any difference between ingesting morphine and withdrawal symptoms.
For the first experiment, the mice in the experimental group (we’ll call them EXM) were given a small dose of morphine during the training phase, while the control group were given saline (and through the other experiments). During the training phase they were given 10 mg/kg of morphine, while in the actual test they were given 2.5 or 5 kg/mg.
In the second experiment, EXM received the same amount of morphine shortly before it began, and they were tested on their memory of the maze. Before the third experiment, the experimenters injected the EXM group with morphine for four days. After that, they stopped giving them morphine for before placing them back in the maze 1, 3, and 5 days of withdrawal.
In experiment 1, the EXM group given 2.5, 5 mg/kg spent more time in the novel arm one hour after exposure, but with each hour the amount of time spent in each arm decreased. Experiment 2 had similar results, but a few hours after treatment differences in arm visits began to show. In experiment 3, performance was found to be the poorest among mice who experienced withdrawal from morphine injections.
Thanks to its simple design the Y-maze remains a staple of rodent and memory studies. Its versatility is another one of its strengths and has given us more insight into memory than thought possible. In the hands of creative researchers, the Y-maze will continue to lead to greater discoveries and results.
Conrad CD, Grote KA, Hobbs RJ, & Ferayorni A (2003). Sex differences in spatial and non-spatial Y-maze performance after chronic stress. Neurobiology of learning and memory, 79 (1), 32-40 PMID: 12482677
Ma MX, Chen YM, He J, Zeng T, & Wang JH (2007). Effects of morphine and its withdrawal on Y-maze spatial recognition memory in mice. Neuroscience, 147 (4), 1059-65 PMID: 17601672
Wright RL, & Conrad CD (2005). Chronic stress leaves novelty-seeking behavior intact while impairing spatial recognition memory in the Y-maze. Stress (Amsterdam, Netherlands), 8 (2), 151-4 PMID: 16019606