Acquisition and Retention in Rats: Comparing Olfactory and Visual Cues as Facilitators of Learning

1. Acquisition and Retention in Rats: Comparing Olfactory and Visual Cues as Facilitators of Learning Cathryn Chandler and Katherine Wetzel Randolph-Macon Woman’s College Lynchburg, VA 24503 Introduction The sand maze is a less aversive spatial task that can be employed as an alternative to the water maze in some studies (Gotthard, 2006). While the water maze requires rats to swim in a pool of water to locate a hidden platform (Morris, 1981), the sand maze requires rats to dig in a pool of sand to retrieve buried cereal rewards (Hanson, 2003). In experiments using rats in the sand maze, visual cues are often used as facilitators for acquisition and retention of operant tasks. The vision of the rat has evolved to accommodate for the nocturnal nature of the species in the wild, as a means of avoiding predators. Thus, only the ability to distinguish natural colors (i.e. black, white and brown) is the extent of the visual complexity of the rat. (Park, 1940). The rats sense of smell is considerably stronger than their visual accuity, therefore it is hypothesized that the rats will better learn operant tasks in the sand maze when directed by olfactory cues as opposed to visual cues. Results In earlier trials both groups took longer to learn the task, yet in later trials the mean latency for the Olfactory Group decreased. For both groups, rats demonstrated a quadrant preference that can only be attributed to chance for the correct quadrant during testing. Latency Latency to retrieve the reward was measured for each rat during each of 7 trials [Olfactory Group: M1 = 21.41, SD1 = 6.3, M2 = 30.61, SD2 = 40.46, M3 = 31.09, SD3 = 11.6; M4 = 36.55, SD4 = 37.95; M5 = 103.56, SD5 = 67.58; M6 = 68.53, SD6 = 99.00; M7 = 25.31, SD7 = 13.41. Visual Group: M1 = 22.15, SD1 = 12.57; M2 = 15.53, SD2 = 8.99; M3 = 52.24, SD3 = 29.36; M4 = 31.42, SD4 = 21.43; M5 = 53.41, SD5 = 49.38; M6 = 60.09, SD6 = 31.03; M7 = 67.8, SD7 = 41.92). A paired samples t-test was run comparing Olfactory Trials 5 and 7, Visual Trials 5 and 7, and Olfactory Trial 7 to Visual Trial 7 , Quadrant Preference A one-sample t-test was conducted for each group to determine whether preference for the correct quadrant was exhibited. Neither the Visual Group, t(3) = .652, p = .561 (two-tailed) or theOlfactory Group, t(3) = -2.400, p = .096 (two-tailed) demonstrated statistical significance. 180˚ Method Subjects The subjects were 6-month-old, male Long-Evans rats (N=8) divided into two groups of 4 rats. Rats were reduced to and maintained at 85% of their free-feeding weights one week prior to experimentation. Water was available ad libitum. Apparatus The sand maze was a plastic pool (36 inches wide by 6 inches deep) filled with a sand/crushed Froot Loops (FL) cereal mixture that was 2 inches deep (approximately 11 ounces of FL was crushed and mixed with 100 pounds of play sand to make the mixture). Four white index cards, three on which a white circle was taped, one on which a black circle was taped, were used for the visual cues trials. Four white index cards were used for the olfactory cues trials, three of which were blank, one on which a 1” diameter circle of milk and honey scented lotion was applied. The maze was elevated 36 inches off the floor. Procedure Each rat was a member of either the Visual or Olfactory groups, and was placed in the sand maze and required to find Froot Loops cereal (FL). The FL were located in one of the four quadrants (NW, SW, SE, NE), coinciding with an intra-maze cue - either the card with the black circle (for the Visual Group) or the scented card (for the Olfactory Group). Rats were started from a consistent location, the South end of the maze, for each trial. After finding the reward on any given trial, the rat was allowed to consume approximately one to two FL prior to termination of the trial (the low number of FL was a preventative measure to avoid satiation.) Rats were handled prior to shaping. The location of the FL and the correct cue card was rotated for each Trial in a counterclockwise direction, beginning at NW (i.e. NW for the first rat in the trial, SW for the second, and so forth.) Seven trials were conducted; the FL were buried deeper with each succeeding trial. During Trials 1 and 2 the FL were completely exposed; during Trials 3 and 4 the FL were partially exposed (shallow buried.) During Trials 5, 6 and 7 the FL were completely buried. A final probe trial was conducted where no FL were buried, and each participant spent exactly 2 minutes in the maze. The time spent in each quadrant was recorded in order to determine quadrant preference. • Discussion • The mean latency of the rats increased as they were learning to locate the FL. Once the task was learned, • the mean latency steadily declined for the Olfactory Group, but did not for the Visual Group. • Rat #20 took an substantially long time (11:40:47) during Trial 4, creating outlying data which would have skewed our results. Therefore this latency record was not included the analysis. • Observations indicated that the rats could smell the FL even when completely buried. Subsequent research could be conducted on the depth at which FL must be in order that rats cannot detect the scent. • Lack of time was also a potential factor in success of acquisition and retention. Had many more trials been conducted, the results may have indicated more marked differences in the learning of the two groups. References Gotthard, G.H. (2006). Experimental Psychology: Learning Laboratory Lab Manual. Randolph-Macon Woman’s College. Hanson, G.R. (2003).  The sand maze: An appetitive alternative to the Morris water maze (Doctoral dissertation, Kent State University, 2003). Dissertation Abstracts International, 63, 4958.   Park, O. (1940). Nocturnalism: The development of a problem. Ecological Monographs, Vol. 10, 3, 485-536. Morris, R.G.M. (1981). Spatial localization does not require the presence of local cues. Learning and Motivation, 12, 239-260.