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Middle-aged (12 month old) male rats show selective latent learning deficit
Neurobiology of Aging 32 (2011) 2320.e11–2320.e14 www.elsevier.com/locate/neuaging
Middle-aged (12 month old) male rats show selective latent learning deficit Eric M. Stouffer*, Jessica E. Yoder Department of Psychology, Bloomsburg University, Bloomsburg, PA, USA Received 6 March, 2010; received in revised form 14 April 2010; accepted 22 April 2010
Abstract While many cognitive aging studies have been conducted using old (20⫹ months old) rats, few have demonstrated cognitive deficits in middle-aged (12 months old) rats. The present study was conducted to determine if deficits in latent learning (the acquisition of neutral information that does not immediately influence behavior) arise during middle age in rats. Twelve young (3 months old) and 12 middle-aged male Sprague–Dawley rats completed the latent cue preference (LCP) task, a conditioned cue preference (CCP) task in the same apparatus, and a reinforced spatial learning task using the Barnes maze. Results showed that the middle-aged rats were impaired on the latent learning (LCP) task relative to the young rats, but were not impaired on the CCP task or the spatial learning task. This may be because latent learning requires a functional entorhinal cortex, and the entorhinal cortex is one brain region that shows early age-related functional degeneration. © 2011 Elsevier Inc. All rights reserved. Keywords: Latent learning; Aging; Middle age; Conditioning; Spatial learning; Entorhinal cortex
Studies examining age-related cognitive decline in rats have generally shown that many cognitive skills, such as spatial learning, become impaired at old-age (20⫹ months) (e.g. Barnes, 1979; Barnes et al., 1980; Mizumori et al., 1996; Rapp et al., 1987). However, few studies have demonstrated impaired cognitive abilities during middle-age (12 months) in the rat. This may be due to the fact that most cognitive abilities studied in rats are dependent on the hippocampus, a structure that does not begin to show agerelated functional deterioration until after middle-age (Rosenzweig and Barnes, 2003). However, the entorhinal cortex has been demonstrated to show earlier age-related functional deterioration (Duyckaerts et al., 2009). Therefore, cognitive tasks that are dependent on a functional entorhinal cortex may be impaired starting at middle-age. One such cognitive task is the latent cue preference (LCP) task. Stouffer (2009) and Stouffer and White (2007) used
* Corresponding author at: Department of Psychology, Bloomsburg University, 400 E 2nd Street, Bloomsburg, PA 17815, USA. Tel.: (570) 389-4473; fax: (570) 389-2019. E-mail address: [email protected] (E. Stouffer). 0197-4580/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.neurobiolaging.2010.04.021
the LCP task to demonstrate that latent learning is dependent on a functional entorhinal cortex and is relatively independent of the dorsal hippocampus. Therefore, performance on the LCP task may be impaired early in the aging process due to the potential early functional deterioration of the entorhinal cortex. However, performance on learning tasks that do not require a functional entorhinal cortex, such as the conditioned-cue preference (CCP) task and reinforced spatial learning, should be spared during middle-age.
1. Methods 1.1. Animals Twenty-four male Sprague–Dawley rats (Harlan Laboratory, Indianapolis, IN) were used in the experiment. Twelve of the rats were 3 months old (“young”) and 12 of the rats were 12 months old (“middle-aged”) at the beginning of the experiment. All rats were housed individually in hanging cages in a temperature controlled room (22 °C) that was kept on a 12-hour light cycle (lights on 7:00 hr). The rats were given unlimited access to food (LabDiet Prolab
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E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
Animal Diet), but access to water varied according to the procedure they were given (see below). 1.2. Apparatus Two apparatus were used in the study. The first was an LCP box that has been previously described in detail by Stouffer (2009). In brief, four LCP boxes were created using modified Coulbourn Instruments TruScan Rat Arenas (E63-20) with photobeam sensor rings. Each arena was divided into three compartments using opaque Plexiglas partitions, and each compartment had one unique visual cue present on the walls. The Plexiglas partitions had door openings that were blocked during training, but were unblocked during the preference test trial. The left and right compartments served as the waterpaired and unpaired compartments, counterbalanced. A 50 mL water bottle was mounted on the outside of each box with a spout protruding into either the left or right compartment through a small hole in the front wall. In addition to the LCP boxes, a Barnes maze (Med Associates, ENV-562-R) was also used. The maze consisted of a white round platform (122 cm diameter) that contained 18 holes (9.5 cm in diameter) evenly spaced around the perimeter, which was surrounded by several distal cues in the experimental room. A black Plexiglas escape box (Med Associates, ENV-562-R-GB) was able to be placed under any of the 18 hole locations. Mounted above the maze were two 500 watt halogen lights, a video camera, and a pulley system. The pulley system allowed an opaque plastic bucket to be raised and lowered onto the platform from an adjacent laboratory room.
the LCP task, each rat was alternated between the waterpaired or unpaired compartment of the LCP box for 30 min each day for 6 days. The amount of water consumed while in the water-paired compartment was recorded to ensure water-deprivation. Supplemental access to water was given for 30 min on days when rats were placed in the unpaired compartment. One day after the last training trial, the rats were given a 20 min preference test trial with the water bottles removed, and the amount of time the rats spent in each compartment was recorded. Following the CCP task, all rats (young and middleaged) were given another 7 day rest period before the Barnes maze training began. Each rat was given two training trials per day for 4 days, and then one training trial on Day 5. During each training trial, each rat was first placed under the bucket on the maze platform. The experimenter then turned on the halogen lights above the maze, left the room, lifted the bucket using the pulley system, and observed the rat on a monitor with the video feed. The amount of time required to find the hidden escape box and the number of nose-pokes into incorrect hole locations were recorded. If the rat did not locate the escape box within a 2 min period, the experimenter entered the room and led the rat to the escape box. The intertrial interval for each rat ranged from 10 to 30 min across training. 2. Results Figure 1 illustrates the compartment preferences shown by the young and middle-aged rats in the LCP task prefer-
1.3. Procedure All rats were first trained on the LCP task, also described in detail by Stouffer (2009). In brief, all rats were given three training trials over 6 days, in which each rat was placed in either the water-paired or unpaired compartment for 30 minutes, and then was placed in the opposite compartment the following day. Rats were water-replete during these trials, but all rats sampled from the water at least once. One day after the last training trial, the rats were given 20 hours of waterdeprivation, followed by a 20 min preference test trial in which the water bottles were absent. Each rat was placed in the center compartment and was allowed to move between the right and left compartments. The amounts of time spent in each compartment were recorded by the TruScan v2.01 program. Following the preference test trial, each rat was given 30 min access to water and the amount of water consumed was recorded to ensure water-deprivation. Following the LCP task, all rats were given a 7 day rest period. Only middle-aged rats were then trained on the CCP task. This was done to ensure that they could discriminate between the compartments of the LCP box. After the rest period, each middle-aged rat was given 30 min daily access to water for 5 days, and then was given three CCP training trials while under this state of water-deprivation. As with
Fig. 1. An illustration of the compartment preference times during the preference test trials in the latent cue preference (LCP; on the left) and conditioned cue preference (CCP; on the right) tasks. Young rats (3 months old) showed a significant preference for the water-paired compartment in the LCP task preference test trial, indicating that they had formed a latent association between the compartment cue and the water. However, middleaged rats (12 months old) did not show this preference, indicating that they did not show latent learning for the compartment cue associated with the water. In contrast, during the CCP preference test trial, middle-aged rats did show a significant preference for the water-paired compartment due to conditioning. This demonstrates that middle-aged rats had the ability to associate the compartment cue with the water and could discriminate among the compartments of the LCP box. *p ⬍ .05.
E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
ence test trial. A 2 ⫻ 2 (Age ⫻ Compartment) mixed ANOVA revealed a significant Age ⫻ Compartment interaction, F1,22 ⫽ 5.369, p ⫽ .030. Planned comparisons on the interaction showed that the young rats spent significantly more time in the water-paired compartment than the unpaired compartment, F1,22 ⫽ 10.34, p ⬍ .01. However, the middle-aged rats showed no significant compartment preference, F1,22 ⫽ 1.04, p ⫽ .319. A 2 ⫻ 3 (Age ⫻ Training Trial) mixed ANOVA on training trial water consumption indicated there was no difference in water consumption during the training trials between young and middle-aged rats, F1,22 ⫽ 1.692, p ⫽ .207. In addition, an independentmeasures t-test on post-test trial water consumption data showed there was no difference between young and middleaged rats in terms of their level of water deprivation during the preference test trial, t(22) ⫽ 1.258, p ⫽ .222. Figure 1 also illustrates the compartment preferences shown by the middle-aged rats in the CCP task. A repeatedmeasures t-test revealed that the middle-aged rats spent significantly more time in the water-paired compartment than the unpaired compartment during the preference test trial, t(11) ⫽ 2.356, p ⫽ .038. Figure 2 illustrates the escape latencies shown by the young and middle-aged rats in the Barnes maze task. A 2 ⫻ 9 (Age ⫻ Trial) mixed ANOVA revealed a significant main effect for Trial, F8,176 ⫽ 8.387, p ⬍ .001. However, there was no main effect for Age, F1,22 ⫽ 1.835, p ⫽ .189, nor was there a significant interaction, F8,176 ⫽ 0.513, p ⫽ .845. The results of a 2 ⫻ 9 (Age ⫻ Trial) mixed ANOVA on the number of incorrect nose-pokes also revealed no significant difference between young and middle-aged rats, F1,22 ⫽ 1.835, p ⫽ .189. 3. Discussion The results showed that middle-aged rats were impaired on the latent learning task relative to young rats, but showed no impairment on the conditioning task using
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the same apparatus. In addition, middle-aged rats were not impaired on the reinforced spatial learning task relative to young rats. These findings confirm that the cognitive impairment shown by middle-aged rats was specific to latent learning. The fact that middle-aged rats showed a learning deficit specific to latent learning may be because this latent learning task is dependent on a functional entorhinal cortex (Stouffer, 2009), and the entorhinal cortex begins to show age-related functional deterioration during middle age (Duyckaerts et al., 2009). In addition, it cannot be ruled out that structures that have direct connections with the entorhinal cortex, such as the perirhinal cortex and postrhinal cortex, may also contribute to this learning impairment. The latent learning deficit shown in middle-aged rats may also be paralleled in human research. In human research, latent learning is often termed incidental learning. Crook et al. (1993) conducted an experiment in which participants had to recall information that they intentionally tried to learn, as well as information that was incidentally presented during the learning trials. Crook et al. (1993) showed that deficits in recalling the incidentally presented information began to appear in the middle-aged (40 – 49 years old) participants. This middle-aged impairment in incidental learning tasks has also been demonstrated by Willoughby (1929). The present findings are of practical importance because they demonstrate that latent learning tasks, such as the LCP task, could provide a behavioral signal of cognitive aging at a much earlier age than other cognitive tasks. Therefore, the LCP task could be used to evaluate potential treatments of early cognitive impairment, such as physical exercise, antioxidant-enriched diets, and environmental enrichment. Disclosure statement Neither author has any actual or potential conflicts of interest to report. The use of animal subjects in this study was approved by the Bloomsburg University Institutional Animal Care and Use Committee. Acknowledgements Financial support of the present study was provided through a seed-grant provided by the Dean’s Office of the College of Liberal Arts of Bloomsburg University of Pennsylvania.
Fig. 2. An illustration of the amount of time the rats took to find the hidden escape box during the Barnes maze training trials. There was no difference between young rats (3 months old) and middle-aged rats (12 months old) in terms of their ability to find the escape box. This demonstrates that middle-aged rats showed no impairment in reinforced spatial learning.
References Barnes, C.A., 1979. Memory deficits associated with senescence: a neurophysiological and behavioral study in the rat. J Comp Physiol Psychol 93, 74 –104. Barnes, C.A., Nadel, L., Honig, W.K., 1980. Spatial memory deficit in senescent rats. Can J Psychol 34, 29 –39.
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E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
Crook, T.H. 3rd, Larrabee, G.J., Youngjohn, J.R., 1993. Age and incidental recall for a simulated everyday memory task. J Gerontol 48, 45– 47. Duyckaerts, C., Delatour, B., Potier, M.C., 2009. Classification and basic pathology of Alzheimer disease. Acta Neuropathol 118, 5–36. Mizumori, S.J., Lavoie, A.M., Kalyani, A., 1996. Redistribution of spatial representation in the hippocampus of aged rats performing a spatial memory task. Behav Neurosci 110, 1006 –16. Rapp, P.R., Rosenberg, R.A., Gallagher, M., 1987. An evaluation of spatial information processing in aged rats. Behav Neurosci 101, 3–12.
Rosenzweig, E.S., Barnes, C.A., 2003. Impact of aging on hippocampal function: plasticity, network dynamics, and cognition. Prog Neurobiol 69, 143–79. Stouffer, E.M., 2009. The entorhinal cortex, but not the dorsal hippocampus, is necessary for single-cue latent learning. Hippocampus Oct 5 [Epub ahead of print]. Stouffer, E.M., White, N.M., 2007. Roles of learning and motivation in preference behavior: mediation by entorhinal cortex, dorsal and ventral hippocampus. Hippocampus 17, 147– 60. Willoughby, R.R., 1929. Incidental learning. J Ed Psychol 20, 671– 82.
Middle-aged (12 month old) male rats show selective latent learning deficit Eric M. Stouffer*, Jessica E. Yoder Department of Psychology, Bloomsburg University, Bloomsburg, PA, USA Received 6 March, 2010; received in revised form 14 April 2010; accepted 22 April 2010
Abstract While many cognitive aging studies have been conducted using old (20⫹ months old) rats, few have demonstrated cognitive deficits in middle-aged (12 months old) rats. The present study was conducted to determine if deficits in latent learning (the acquisition of neutral information that does not immediately influence behavior) arise during middle age in rats. Twelve young (3 months old) and 12 middle-aged male Sprague–Dawley rats completed the latent cue preference (LCP) task, a conditioned cue preference (CCP) task in the same apparatus, and a reinforced spatial learning task using the Barnes maze. Results showed that the middle-aged rats were impaired on the latent learning (LCP) task relative to the young rats, but were not impaired on the CCP task or the spatial learning task. This may be because latent learning requires a functional entorhinal cortex, and the entorhinal cortex is one brain region that shows early age-related functional degeneration. © 2011 Elsevier Inc. All rights reserved. Keywords: Latent learning; Aging; Middle age; Conditioning; Spatial learning; Entorhinal cortex
Studies examining age-related cognitive decline in rats have generally shown that many cognitive skills, such as spatial learning, become impaired at old-age (20⫹ months) (e.g. Barnes, 1979; Barnes et al., 1980; Mizumori et al., 1996; Rapp et al., 1987). However, few studies have demonstrated impaired cognitive abilities during middle-age (12 months) in the rat. This may be due to the fact that most cognitive abilities studied in rats are dependent on the hippocampus, a structure that does not begin to show agerelated functional deterioration until after middle-age (Rosenzweig and Barnes, 2003). However, the entorhinal cortex has been demonstrated to show earlier age-related functional deterioration (Duyckaerts et al., 2009). Therefore, cognitive tasks that are dependent on a functional entorhinal cortex may be impaired starting at middle-age. One such cognitive task is the latent cue preference (LCP) task. Stouffer (2009) and Stouffer and White (2007) used
* Corresponding author at: Department of Psychology, Bloomsburg University, 400 E 2nd Street, Bloomsburg, PA 17815, USA. Tel.: (570) 389-4473; fax: (570) 389-2019. E-mail address: [email protected] (E. Stouffer). 0197-4580/$ – see front matter © 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.neurobiolaging.2010.04.021
the LCP task to demonstrate that latent learning is dependent on a functional entorhinal cortex and is relatively independent of the dorsal hippocampus. Therefore, performance on the LCP task may be impaired early in the aging process due to the potential early functional deterioration of the entorhinal cortex. However, performance on learning tasks that do not require a functional entorhinal cortex, such as the conditioned-cue preference (CCP) task and reinforced spatial learning, should be spared during middle-age.
1. Methods 1.1. Animals Twenty-four male Sprague–Dawley rats (Harlan Laboratory, Indianapolis, IN) were used in the experiment. Twelve of the rats were 3 months old (“young”) and 12 of the rats were 12 months old (“middle-aged”) at the beginning of the experiment. All rats were housed individually in hanging cages in a temperature controlled room (22 °C) that was kept on a 12-hour light cycle (lights on 7:00 hr). The rats were given unlimited access to food (LabDiet Prolab
2320.e12
E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
Animal Diet), but access to water varied according to the procedure they were given (see below). 1.2. Apparatus Two apparatus were used in the study. The first was an LCP box that has been previously described in detail by Stouffer (2009). In brief, four LCP boxes were created using modified Coulbourn Instruments TruScan Rat Arenas (E63-20) with photobeam sensor rings. Each arena was divided into three compartments using opaque Plexiglas partitions, and each compartment had one unique visual cue present on the walls. The Plexiglas partitions had door openings that were blocked during training, but were unblocked during the preference test trial. The left and right compartments served as the waterpaired and unpaired compartments, counterbalanced. A 50 mL water bottle was mounted on the outside of each box with a spout protruding into either the left or right compartment through a small hole in the front wall. In addition to the LCP boxes, a Barnes maze (Med Associates, ENV-562-R) was also used. The maze consisted of a white round platform (122 cm diameter) that contained 18 holes (9.5 cm in diameter) evenly spaced around the perimeter, which was surrounded by several distal cues in the experimental room. A black Plexiglas escape box (Med Associates, ENV-562-R-GB) was able to be placed under any of the 18 hole locations. Mounted above the maze were two 500 watt halogen lights, a video camera, and a pulley system. The pulley system allowed an opaque plastic bucket to be raised and lowered onto the platform from an adjacent laboratory room.
the LCP task, each rat was alternated between the waterpaired or unpaired compartment of the LCP box for 30 min each day for 6 days. The amount of water consumed while in the water-paired compartment was recorded to ensure water-deprivation. Supplemental access to water was given for 30 min on days when rats were placed in the unpaired compartment. One day after the last training trial, the rats were given a 20 min preference test trial with the water bottles removed, and the amount of time the rats spent in each compartment was recorded. Following the CCP task, all rats (young and middleaged) were given another 7 day rest period before the Barnes maze training began. Each rat was given two training trials per day for 4 days, and then one training trial on Day 5. During each training trial, each rat was first placed under the bucket on the maze platform. The experimenter then turned on the halogen lights above the maze, left the room, lifted the bucket using the pulley system, and observed the rat on a monitor with the video feed. The amount of time required to find the hidden escape box and the number of nose-pokes into incorrect hole locations were recorded. If the rat did not locate the escape box within a 2 min period, the experimenter entered the room and led the rat to the escape box. The intertrial interval for each rat ranged from 10 to 30 min across training. 2. Results Figure 1 illustrates the compartment preferences shown by the young and middle-aged rats in the LCP task prefer-
1.3. Procedure All rats were first trained on the LCP task, also described in detail by Stouffer (2009). In brief, all rats were given three training trials over 6 days, in which each rat was placed in either the water-paired or unpaired compartment for 30 minutes, and then was placed in the opposite compartment the following day. Rats were water-replete during these trials, but all rats sampled from the water at least once. One day after the last training trial, the rats were given 20 hours of waterdeprivation, followed by a 20 min preference test trial in which the water bottles were absent. Each rat was placed in the center compartment and was allowed to move between the right and left compartments. The amounts of time spent in each compartment were recorded by the TruScan v2.01 program. Following the preference test trial, each rat was given 30 min access to water and the amount of water consumed was recorded to ensure water-deprivation. Following the LCP task, all rats were given a 7 day rest period. Only middle-aged rats were then trained on the CCP task. This was done to ensure that they could discriminate between the compartments of the LCP box. After the rest period, each middle-aged rat was given 30 min daily access to water for 5 days, and then was given three CCP training trials while under this state of water-deprivation. As with
Fig. 1. An illustration of the compartment preference times during the preference test trials in the latent cue preference (LCP; on the left) and conditioned cue preference (CCP; on the right) tasks. Young rats (3 months old) showed a significant preference for the water-paired compartment in the LCP task preference test trial, indicating that they had formed a latent association between the compartment cue and the water. However, middleaged rats (12 months old) did not show this preference, indicating that they did not show latent learning for the compartment cue associated with the water. In contrast, during the CCP preference test trial, middle-aged rats did show a significant preference for the water-paired compartment due to conditioning. This demonstrates that middle-aged rats had the ability to associate the compartment cue with the water and could discriminate among the compartments of the LCP box. *p ⬍ .05.
E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
ence test trial. A 2 ⫻ 2 (Age ⫻ Compartment) mixed ANOVA revealed a significant Age ⫻ Compartment interaction, F1,22 ⫽ 5.369, p ⫽ .030. Planned comparisons on the interaction showed that the young rats spent significantly more time in the water-paired compartment than the unpaired compartment, F1,22 ⫽ 10.34, p ⬍ .01. However, the middle-aged rats showed no significant compartment preference, F1,22 ⫽ 1.04, p ⫽ .319. A 2 ⫻ 3 (Age ⫻ Training Trial) mixed ANOVA on training trial water consumption indicated there was no difference in water consumption during the training trials between young and middle-aged rats, F1,22 ⫽ 1.692, p ⫽ .207. In addition, an independentmeasures t-test on post-test trial water consumption data showed there was no difference between young and middleaged rats in terms of their level of water deprivation during the preference test trial, t(22) ⫽ 1.258, p ⫽ .222. Figure 1 also illustrates the compartment preferences shown by the middle-aged rats in the CCP task. A repeatedmeasures t-test revealed that the middle-aged rats spent significantly more time in the water-paired compartment than the unpaired compartment during the preference test trial, t(11) ⫽ 2.356, p ⫽ .038. Figure 2 illustrates the escape latencies shown by the young and middle-aged rats in the Barnes maze task. A 2 ⫻ 9 (Age ⫻ Trial) mixed ANOVA revealed a significant main effect for Trial, F8,176 ⫽ 8.387, p ⬍ .001. However, there was no main effect for Age, F1,22 ⫽ 1.835, p ⫽ .189, nor was there a significant interaction, F8,176 ⫽ 0.513, p ⫽ .845. The results of a 2 ⫻ 9 (Age ⫻ Trial) mixed ANOVA on the number of incorrect nose-pokes also revealed no significant difference between young and middle-aged rats, F1,22 ⫽ 1.835, p ⫽ .189. 3. Discussion The results showed that middle-aged rats were impaired on the latent learning task relative to young rats, but showed no impairment on the conditioning task using
2320.e13
the same apparatus. In addition, middle-aged rats were not impaired on the reinforced spatial learning task relative to young rats. These findings confirm that the cognitive impairment shown by middle-aged rats was specific to latent learning. The fact that middle-aged rats showed a learning deficit specific to latent learning may be because this latent learning task is dependent on a functional entorhinal cortex (Stouffer, 2009), and the entorhinal cortex begins to show age-related functional deterioration during middle age (Duyckaerts et al., 2009). In addition, it cannot be ruled out that structures that have direct connections with the entorhinal cortex, such as the perirhinal cortex and postrhinal cortex, may also contribute to this learning impairment. The latent learning deficit shown in middle-aged rats may also be paralleled in human research. In human research, latent learning is often termed incidental learning. Crook et al. (1993) conducted an experiment in which participants had to recall information that they intentionally tried to learn, as well as information that was incidentally presented during the learning trials. Crook et al. (1993) showed that deficits in recalling the incidentally presented information began to appear in the middle-aged (40 – 49 years old) participants. This middle-aged impairment in incidental learning tasks has also been demonstrated by Willoughby (1929). The present findings are of practical importance because they demonstrate that latent learning tasks, such as the LCP task, could provide a behavioral signal of cognitive aging at a much earlier age than other cognitive tasks. Therefore, the LCP task could be used to evaluate potential treatments of early cognitive impairment, such as physical exercise, antioxidant-enriched diets, and environmental enrichment. Disclosure statement Neither author has any actual or potential conflicts of interest to report. The use of animal subjects in this study was approved by the Bloomsburg University Institutional Animal Care and Use Committee. Acknowledgements Financial support of the present study was provided through a seed-grant provided by the Dean’s Office of the College of Liberal Arts of Bloomsburg University of Pennsylvania.
Fig. 2. An illustration of the amount of time the rats took to find the hidden escape box during the Barnes maze training trials. There was no difference between young rats (3 months old) and middle-aged rats (12 months old) in terms of their ability to find the escape box. This demonstrates that middle-aged rats showed no impairment in reinforced spatial learning.
References Barnes, C.A., 1979. Memory deficits associated with senescence: a neurophysiological and behavioral study in the rat. J Comp Physiol Psychol 93, 74 –104. Barnes, C.A., Nadel, L., Honig, W.K., 1980. Spatial memory deficit in senescent rats. Can J Psychol 34, 29 –39.
2320.e14
E.M. Stouffer and J.E. Yoder / Neurobiology of Aging 32 (2011) 2320.e11–2320.e14
Crook, T.H. 3rd, Larrabee, G.J., Youngjohn, J.R., 1993. Age and incidental recall for a simulated everyday memory task. J Gerontol 48, 45– 47. Duyckaerts, C., Delatour, B., Potier, M.C., 2009. Classification and basic pathology of Alzheimer disease. Acta Neuropathol 118, 5–36. Mizumori, S.J., Lavoie, A.M., Kalyani, A., 1996. Redistribution of spatial representation in the hippocampus of aged rats performing a spatial memory task. Behav Neurosci 110, 1006 –16. Rapp, P.R., Rosenberg, R.A., Gallagher, M., 1987. An evaluation of spatial information processing in aged rats. Behav Neurosci 101, 3–12.
Rosenzweig, E.S., Barnes, C.A., 2003. Impact of aging on hippocampal function: plasticity, network dynamics, and cognition. Prog Neurobiol 69, 143–79. Stouffer, E.M., 2009. The entorhinal cortex, but not the dorsal hippocampus, is necessary for single-cue latent learning. Hippocampus Oct 5 [Epub ahead of print]. Stouffer, E.M., White, N.M., 2007. Roles of learning and motivation in preference behavior: mediation by entorhinal cortex, dorsal and ventral hippocampus. Hippocampus 17, 147– 60. Willoughby, R.R., 1929. Incidental learning. J Ed Psychol 20, 671– 82.