Serial position curves in rats: Automatic versus effortful information processing.

20 male Long-Evans rats were trained to remember lists of 5 arms on an 8-arm radial maze. A forced-choice memory recognition test procedure was used that required the S to choose between an arm previously visited during the study phase of a trial and an arm not visited. To receive additional food reinforcement, 10 Ss were required to return to the previously visited arm (win-stay) and 10 Ss were required to choose the novel, unvisited arm (win-shift). In this way, a direct comparison was made between the serial position curves (SPCs) generated by win-stay trained and win-shift trained Ss. Only win-stay trained Ss produced the classical U-shaped SPC, which included significant primacy and recency effects. Win-shift Ss showed only recency effects. Findings are discussed in terms of differential processing requirements for the 2 procedures. It is suggested that the win-stay rule necessitates relatively more effortful, elaborative processing than does the win-shift rule, which is used automatically. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory for food hidden by rats (Rattus norvegicus) on the radial maze: Studies of memory for where, what, and when.

Rats (Rattus norvegicus) were allowed to hide food items on an 8-arm radial maze by carrying the items from the center to boxes at the end of each arm. Retrieval tests given after rats had hidden 4 items showed that they selectively returned to the maze arms where food had been hidden (Experiments 1 and 2). When rats were allowed to hide pieces of cheese (preferred food) and pretzels (less preferred food) on different arms, they both hid and retrieved cheese before pretzels (Experiments 2-5). In Experiment 6, rats chose between arms where cheese and pretzels were hidden, with cheese degraded at one delay interval but not the other. Together, these experiments indicate memory for what and where but not when. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory in pigeons on a four-arm radial maze.

Examined spatial memory in 6, 8-arm maze experienced pigeons, using a 4-arm radial maze. The maze arms were spaced at 90° intervals, extending radially from a central choice area. Ss were forced into 3 arms, then permitted 2 choices to enter the remaining arm. Five Ss chose accurately (90% correct) with delays of 5 min or less, their choices depended on extramaze cues, and the food in the target arm provided no essential cues. After an incorrect 1st choice, Ss' 2nd choices were more accurate than chance. Data suggest that, while spatial memory has many similar characteristics in rats and pigeons, pigeon spatial memory appears less durable. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short- and long-term components of working memory in the rat.

In Experiment 1 of this report, we examined the neuropharmacological nature of short-term working memory of rats trained to retrieve food from all arms of a 12-arm radial maze. Delay intervals of varying length were placed between Choices 6 and 7. Lanthanum (LaCl?) and glutamate (GLU) injected bilaterally into the hippocampus effectively impaired retention over short delay intervals, which suggests a possible role for calcium and/or potassium and for glutamate in working memory. However, another equally likely explanation for the amnesic effects of LaCl? and GLU is that these drugs impaired reference memory. To test more directly the hypothesis that LaCl?, GLU, or ANI might differentially affect working and reference memory, we tested the effects of these drugs on performance of rats trained to retrieve food from only 8 arms of the 12-arm maze in Experiment 2. The remaining 4 arms were never baited, in order to test reference memory function. We predicted that rats would make errors only in baited arms (i.e., errors of working memory). Instead, results of Experiment 2 showed that LaCl?, GLU, or ANI injection produced errors in unbaited arms even before a 120-min delay. If rats were injected with LaCl? or GLU, baited-arm errors were observed only after the delay period. No impairment of performance on baited arms were observed after injection of ANI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective memory impairments produced by transient lidocaine-induced lesions of the nucleus accumbens in rats.

Reversible lidocaine-induced lesions of the nucleus accumbens (NAC) impaired performance on the spatial win-stay, but not on the cued win-stay, radial arm maze task. Pretraining lesions on the former task did not affect foraging for 4 pellets during either the training or test phases. In contrast, lesions given prior to the test phase significantly disrupted retrieval of 4 pellets on the 8-arm maze. Comparable deficits also were observed in rats trained to forage for 4 pellets on an 8-arm maze without prior win-shift experience. State-dependent drug effects were ruled out by replicating the disruptive effects of lidocaine infusions into the NAC on spatial win-shift performance in rats receiving this treatment prior to both training and test phases. These results suggest that the NAC may interact with the hippocampus to guide foraging behavior requiring memory of previous spatial locations on a maze. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food searching strategies of rats: Variables affecting the relative strength of stay and shift strategies.

Examined the extent to which the food searching strategies of rats are influenced by training, information about food in an initially visited site, and type of memory required for correct choices. Exp I used a discrete-trial, delayed conditional-discrimination procedure on a T-maze with 32 male Sprague-Dawley rats. Ss entered 1 arm of the maze and were given a choice between that arm (stay strategy) or the other arm (shift strategy). During the initial visit, S either consumed all the food (depletion condition) or only some of it (nondepletion condition). Ss given the shift-depletion task learned most rapidly; those given the stay-depletion task learned most slowly. Depletion increased the rate at which the shift discrimination was learned but decreased the rate at which the stay discrimination was learned. Exp II used a similar procedure with the Maier 3-table maze and 16 male albino rats; the same pattern of results was found. Exp III, conducted with 15 male Sprague-Dawley rats, required each S to learn both a win-stay and a lose-shift contingency and to use associative memory. Early in training, Ss used only a shift strategy but eventually learned the discrimination. Results indicate that the shift-stay balance is influenced by the rat's species-specific predisposition, reinforcement contingencies, amount of food in the initially visited place, and the extent to which recognition memory by itself is sufficient to solve the discrimination. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of selective immunotoxic lesions of medial septal cholinergic cells on spatial working and reference memory.

The effect of injection into the medial septum of a toxin selective for cholinergic neurons, 192 IgG-saporin, was examined in rats trained to perform 2 versions of the radial 8-arm maze task. Rats were first trained to perform a task with varying delays (0, 1, 2 min) imposed between the 4th correct arm choice and access to all 8 arms. Lesioned rats made significantly more errors in the first 4 choices compared with controls and significantly more errors after delays; however, this effect was not delay dependent. Rats were then trained on a different version of this 8-arm maze task in which they learned to avoid 2 arms that were never baited. There was no treatment effect on acquisition of this task. These data are consistent with the hypothesis that the cholinergic projection to the hippocampus facilitates the acquisition of information into the system responsible for short-term memory for locations visited (spatial working memory) but is not involved in retention of this information. It also appears to play no role in either the acquisition or retention of place-nonreward associations (spatial reference memory). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Further evidence for hierarchical chunking in rat spatial memory.

In Experiment 1, rats were given a test to determine the order of preference among 3 types of food. Two groups of rats then were trained on a 12-arm radial maze in Experiment 2, with the 3 foods placed in fixed-arm locations for 1 group and in locations that varied randomly across sessions for the other group. The results replicated those of Dallal and Meck (1990) by showing faster learning and more clustering of arm choices by food type in the fixed locations group than in the random-locations group. Two further experiments were performed to test the chunking hypothesis. Observations of working memory in Experiment 3 and the reorganization of reference memory in Experiment 4 both supported the chunking hypothesis by showing superior spatial memory and arm chunking by food type when chunk integrity was maintained than when it was compromised. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Foraging on the radial maze: The role of travel time, food accessibility, and the predictability of food location.

Reports on an experiment in which rats foraged in a 4-arm radial maze containing 4 feeders in each arm, with different percentages of baited feeders in each arm (0%, 25%, 50%, or 75%). The effects of three variables were examined: (1) Arm entrances were open or blocked to increase travel time between arms; (2) Feeders were uncovered or covered to decrease accessibility to food; (3) Food locations were randomly changed between sessions or remained fixed. Rats learned to discriminate between the 0% arm and arms containing food when food locations were fixed but not when food locations were random. Rats also learned the locations of baited feeders within arms with fixed food locations, but selectively visited baited feeders only if the feeders were covered. Comparisons of obtained data with computer simulations indicated that rats foraged near optimality. Patterns of foraging were best accounted for by a molecular maximizing model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory in pigeons on the radial maze.

A series of 7 experiments with 10 pigeons showed, contrary to recent suggestions that pigeons show little or no spatial memory on the radial maze, highly accurate performance by Ss on an 8-arm radial maze. In Exp I, Ss were trained on successive phases that raised the number of alleys to be remembered from 1 to 4. In Exp II, Ss were allowed to search the maze for food with all 8 arms open. Measures of spatial memory showed that Ss performed at a level equivalent to that found with rats in previous research by A. B. Bond et al (see record 1982-25052-001). In Exp III, testing with massed trials revealed proactive interference. Ss were able to form reference memory for subsets of baited and unbaited alleys in Exp VI. In Exp VII, Ss learned about quantities of food associated with 4 different alleys and ordered their alley choices from the largest to the smallest reward. Contrary to the previous findings with rats, Ss in Exp IV showed forgetting over retention intervals of 0–360 sec between forced and free choices. It is concluded that spatial memory in pigeons generally shows the same properties as that in rats. (49 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The von Restorff effect in rats (Rattus norvegicus).

Two experiments examined the functional equivalence of memory in the rat (Rattus norvegicus) with memory in humans for serially presented items. Memory was assayed with an 8-arm radial maze, in which rats were allowed access to 5 arms of the maze and were then removed. Following a retention interval of 16 min, the rats were replaced in the maze and allowed to retrieve pellets from the 3 unvisited arms. The errors in reentering previously visited arms were noted. Both primacy and recency effects were found as with humans. Presenting a stimulus change after entry to 1 of the maze arms improved recall for that arm relative to when no change occurred. This effect was found using both handling and tone cues, and irrespective of whether the change consisted of presentation or nonpresentation of the cue. These results suggest that rats are subject to a von Restorff-like effect similar to that in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Item and order information in spatial memory.

14 male Holtzman albino rats were taught to perform order and item discriminations in an 8-arm radial maze. In Exp I, 2 groups of Ss learned different order discriminations with reward contingent on repeating or avoiding the most recently visited of 2 locations. Each trial began with a random order of 8 forced choices and ended with a choice between the 1st and 7th arms. Rate of learning depended on the compatibility of reward contingencies and preexperimental response biases. In Exp II, each trial began with a list of 7 forced choices and ended in a choice between either the 1st or 6th arm and the arm not presented; accuracy of performing these item discriminations depended on both serial position and the response tendencies acquired in Exp I. In Exp III, a 1-hr postlist delay impaired the order discrimination more than the item discrimination, and the effects of intertrial interval depended on previously acquired response biases. Results are discussed in terms of a 2-stage model that segregates a single memory process from decision/response processes. Item and order discriminations do not appear to be based on separate sources of information and do not appear to require fundamentally different memory processes. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory deficits in a virtual radial arm maze in amnesic participants with hippocampal damage.

Extensive research with laboratory animals indicates that the hippocampus is crucial for the formation and use of spatial memory. Hippocampal lesions in rodents impair spatial memory on radial arm maze tasks. It is unknown whether amnesic patients with hippocampal damage would exhibit similar impairments on a virtual version of a radial arm maze. To evaluate the importance of the hippocampus in spatial learning and memory, we tested amnesic participants with hippocampal damage in a virtual radial arm maze environment. The virtual radial arm maze required participants to learn and remember 4 rewarded arms of 8 total arms. Spatial learning and memory were assessed using the participants' ability to use salient distal cues in the virtual room to remember the 4 rewarded arms. Amnesic participants' latencies were longer and distance traveled was greater to the rewarded arms compared with nonamnesic participants. Amnesic participants made more errors than nonamnesic participants by either entering nonrewarded arms or by revisiting previously entered arms. These data are analogous to previous animal research. Overall, the human hippocampus is necessary for spatial memory and navigation in a virtual radial arm maze task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory of radial maze behavior in pigeons after ablations of the presumed equivalent of mammalian prefrontal cortex.

Pigeons were trained and postoperatively tested in an 8-arm radial maze in which 1 arm was always used for start, 3 were never baited, and 4 were always baited. Of 2 groups of pigeons, 1 (n = 6) received ablations of the postero-dorso-lateral neostriatum (PDLNS) as well as the corticoid, and the other (n = 8) was sham operated. After the surgery, in the PDLNS group the number of reference memory errors (entering the never-baited arms) was significantly increased, but the number of working memory errors (entering previously visited baited arms) was not. Two of 6 pigeons with PDLNS ablations did not show any impairment, 3 were impaired in the reference memory, and 1 was impaired in working memory. This outcome resembles behavioral effects obtained in rats with prefrontal lesions. In pigeons and rats, the lesion seems to "release" the normal "win-shift" tendency and/or impair the ability to choose correctly in simultaneous multiple-choice situations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Central-place foraging by Rattus norvegicus on a radial maze.

We studied central-place foraging in rats (Rattus norvegicus) by placing food items that varied in size and weight at the ends of a 4-arm radial maze. In Experiments 1–3, rats increasingly tended to carry food to the center of the maze as the size of those items increased. Very large food items often were hoarded in the center. Rats consumed food faster on the arms than in the center, and rats traveled faster when carrying food than when not. Blocking arm entrances increased travel time between the center and the arms and decreased food carrying at every item weight except the largest. In Experiments 4–6, important conditions that influence the degree of food-carrying behavior were discovered; these were the intersection of maze arms, the presence of a conspecific, and the use of open vs. closed maze arms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of retroactive interference in the spatial memory of normal rats and rats with hippocampal lesions.

Studied the importance of retroactive interference (RI) in memory for spatial locations by using a 12-arm radial maze and a standard RI paradigm. 26 male albino Sprague-Dawley rats in the RI condition first learned to choose 4 of the 12 arms, followed by training to a 2nd set of 4 arms. In the control condition for interference, Ss learned the 1st set of arms but were not trained to approach the 2nd set. Thereafter, Ss in each interference condition were assigned to groups (hippocampal, cortical control, or unoperated control), the operations were carried out, and then all Ss were tested for retention of the set of arms learned first. Contrary to predictions of the cognitive map theory (J. O'Keefe and L. Nadel, 1978), RI was found in control Ss. The severe memory deficit found in hippocampals was not influenced by the interference variable. In addition to impaired performance early in relearning, Ss with hippocampal lesions continued to make many errors throughout the 10 wks of testing, including choices to unbaited arms and repeated entries into baited arms. However, hippocampals eventually learned not to reenter unbaited arms. Data indicate a deficit in the selection and utilization of sets of responses and are interpreted as implicating the hippocampus in retrieval processes. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory and N-methyl-D-aspartate receptor antagonists APV and MK-801: Memory impairments depend on familiarity with the environment, drug dose, and training duration.

Rats given N-methyl-D-aspartate (NMDA) antagonists were tested in the radial maze in spatial working memory (WM) and reference memory (RM) tasks. 16 female rats given (+)-10,11-dihydro-5-methyl-5H-dibenzo [a,d] cycloheptene-5,10 imine (MK-801; 0.0625 mg/kg intraperitoneal/ly (ip)) before daily testing in an 8-arm WM task were impaired even after 70 days. Control rats learned quickly, were assigned to a group given MK-801 or saline, and were trained to avoid 4 of the 8 arms. MK-801 impaired this reversal learning but did not affect WM performance. 15 male rats were trained on an 8-arm WM task for 19 days and then given intracranial aminophosphonovaleric acid (APV; 33 mM), which impaired both WM and motor behavior. 24 male rats were trained for 65 days to enter 4 of 8 arms and then given intracranial APV (20 or 30 mM). WM and RM were normal in the familiar environment but were both impaired in an unfamiliar environment. Results suggest that the mnemonic effects of NMDA antagonists depend on environmental familiarity, dose, and training duration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of Fimbria-Fornix, Hippocampus, and Amygdala Lesions on Discrimination Between Proximal Locations.

The conditioned cue preference (CCP) task was used to study the information required to discriminate between spatial locations defined by adjacent arms of an 8-arm radial maze. Normal rats learned the discrimination after 3 unreinforced preexposure (PE) sessions and 4 food paired-unpaired training trials. Fimbria-fornix lesions made before, but not after, PE, and hippocampus lesions made at either time, blocked the discrimination, suggesting that the 2 structures processed different information. Lateral amygdala lesions made before PE facilitated the discrimination. This amygdala-mediated interference with the discrimination was the result of a conditioned approach response that did not discriminate between the 2 arm locations. A hippocampus/fimbria-fornix system and an amygdala system process different information about the same learning situation simultaneously and in parallel. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

3,4 Methylenedioxymethamphetamine (ecstasy) impairs eight-arm radial maze performance and arm entry pattern in rats.

The recreational use of 3,4 methylenedioxymethamphetamine (ecstasy) in humans has been associated with memory impairment. The present study examined whether ecstasy impairs short- and long-term working memory and the pattern of arm entries in rats tested in the 8-arm radial maze with a 2-hr delay. After completing the training session, the rats were given a single dose of ecstasy (1, 2, or 3 mg/kg ip) 20 min before the test. The highest dose slightly affected short-term working memory. Under conditions of delay, there was a progressive deficit in long-term working memory, starting from I mg/kg. Under both test conditions, 2 and 3 mg/kg flattened the pattern of arm entry. None of the doses caused hyperlocomotion or stereotypy in the radial maze. These findings suggest that acute ecstasy mainly affects the long-term components of working memory and disrupts the pattern of arm entry in a way similar to serotonergic agents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial memory: A Rosetta stone for rat and human hippocampal discourse: Theoretical comment on Goodrich-Hunsaker and Hopkins (2010).

The article by Goodrich-Hunsaker and Hopkins (2010, this issue) takes up an important place among in the recent contributions on the role of the hippocampus in memory. They evaluate the effect of bilateral damage to the hippocampus on performance by human participants in a virtual 8-arm radial maze. The hippocampal damage appears to be highly selective and nearly complete. Exactly as with selective hippocampal damage in rats, the human participants showed a deficit in accurately choosing rewarded versus never-rewarded arms and a deficit in avoiding reentering recently visited arms. The results are triply significant: (1) They provide good support for the idea that the wealth of neurobiological information, from network to synapse to gene, on spatial memory in the rat may apply as a whole to the human hippocampal memory system; (2) They affirm the utility of human virtual task models of rat spatial memory tasks; (3) They support one interpretation of the dampening of the hippocampal functional MRI (fMRI) blood oxygen level-dependent (BOLD) signal during performance of the virtual radial arm maze observed by Astur et al. (2005). (PsycINFO Database Record (c) 2010 APA, all rights reserved)