Min Retention Interval Research Articles

Spatial working memory over long retention intervals: Dependence on sustained cholinergic activation in the septohippocampal or nucleus basalis magnocellularis-cortical pathways?

Previous direct neurochemical studies of the temporal dynamics of cholinergic activation in the septohippocampal and nucleus basalis magnocellularis-cortical pathways at various stages during repeated testing of mice with selective spatial reference or working memory protocols [Durkin and Toumane (1992), Behav. Brain Res. 50,43–52] showed that the post-test durations of cholinergic activation in each pathway varied as a function of the type of memory tested and the level of task mastery. Since (i) the hippocampal formation is considered to constitute a critical component of a temporary memory buffer, and (ii) working memory items are not thought to be submitted to consolidation and permanent storage, we postulated that the duration of testing-induced cholinergic activation in the septohippocampal pathway may govern the maintenance of the working memory trace over the retention interval. In order to test directly this hypothesis C57 B1/6 mice were extensively trained (one trial/day, 25–30 days) on an identical selective working memory task to attain high levels of retention (> 80% correct), but using either 5 min (Group 1), or 60 min (Group 2) retention intervals. At various times (30s–75min) following the initial acquisition phase of the test, cholinergic activity in the hippocampus and frontal cortex was quantified using measures of high-affinity choline uptake. Whereas cholinergic activation was observed in both pathways at 30 s post-acquisition and throughout the 5 min retention interval in Group 1, the situation in Group 2 is different, activation of the septohippocampal pathway being maintained for only 15 min, while activation in the nucleus basalis magnocellularis-cortical pathway is maintained for the totality of the 1 h retention interval. The nucleus basalis magnocellularis-cortical cholinergic pathway, in addition to its role in long-term reference memory storage processes may, thus, via an intervention in the temporal encoding of information, also subsume a complementary intermediate-term buffer storage role in working memory situations requiring retention intervals in excess of 15min in mice. This secondary, “backup”, function of the nucleus basalis magnocellularis-cortical pathway would thus liberate the septohippocampal complex from its primary active role in the temporary maintenance and/or accessibility of the working memory trace in these particular cases requiring long retention intervals.

Memory for spatial and local cues: A comparison of a storing and a nonstoring species

Two passerine species, black-capped chickadees (Parus atricapillus, a food-storing bird) and darkeyed juncos (Junco hyemalis, a nonstoring bird) were compared in a task in which they inspected four feeders in an aviary. Different feeders and different spatial locations were used on each trial. One of the feeders was baited. The subjects returned after a 5-min retention interval to find the baited feeder. Tests with transformations of the feeder array made it possible to determine what cues controlled the food-finding behavior. Chickadees responded to spatial cues preferentially over local color and pattern cues associated with the feeder (Experiments 2–4). The same ordering of responding was found in Experiment 1, a food-storing version of the food-finding task outlined above. Experiment 5 tested juncos on the food-finding task. Juncos responded to all types of information equally. The results are discussed in relation to the notion that because of their food-storing lifestyle, chickadees may need to rely more heavily on spatial cues than do juncos.

Accessing related events increases retroactive interference in a matching recognition test.

Why is memory for a target event impaired by learning related events? Do related events change the trace for the target or hinder retrieval? Target names (e,g., Robert Harris) were shown; experimental items were followed by related names (e. g., Robert Knight) but control items were not. The given names and surnames of the targets were then provided for matching. At short (5-15 min) retention intervals, the control items were matched more accurately than were the experimental items. This retroactive interference (RI) decreased over a 30-min retention interval (Experiment 2), suggesting that the related names did not cause a permanent change in the target trace. More RI occurred at the 30-min retention interval when the related names appeared just before the test (Experiment 3)

Effects of response strategy and retention interval on performance of Clark's nutcrackers in a radial maze analogue.

Two groups of Clark's nutcrackers (Nucifraga columbiana) were trained to use either a stay or shift response strategy in a radial maze analogue. Each trial had a preretention stage, a retention interval, and a postretention test. In Experiment 1, acquisition with a 5-min retention interval was studied. Response strategy did not affect the rate at which the task was learned. Performance following longer retention intervals was tested in Experiments 2-4. Changes in retention intervals were presented in trial blocks of increasing duration in Experiment 2 and were randomly presented between trials in Experiment 3. Experiment 4 extended the retention interval to 24 hr. No difference in performance was found between the 2 groups in any of these experiments. These results suggest a flexible relationship between spatial memory and response requirement in food-hoarding birds for at least 1 spatial memory task.

Equivalent forgetting rates in long-term memory for diencephalic and medial temporal lobe amnesia

Amnesia can result from damage to either the midline diencephalon or the medial temporal lobe. An important related question has been whether these two forms of amnesia result in similar or different kinds of memory impairment. Earlier studies raised the possibility that differences might exist in the rate of forgetting within long-term memory, specifically, that the forgetting rate is normal in diencephalic amnesia but abnormally rapid in medial temporal lobe amnesia. In the present study, forgetting was studied in five amnesic patients with damage to the medial temporal lobe, six amnesic patients with damage to the diencephalon, and 10 normal subjects. One hundred twenty pictures were presented to the control subjects for 1 sec each and to the amnesic patients for 8 sec each. Retention was then tested after 10 min, 2 hr, and 30-32 hr using four different procedures for testing recognition memory. The different exposure times for the pictures succeeded in matching the performance scores of both groups of amnesic patients and the control subjects at the 10 min retention interval. Both groups of amnesic patients also performed similarly to control subjects at retention delays of 2 hr and 30-32 hr. In addition, performance was nearly identical, regardless whether recognition memory was assessed by asking subjects to select the new items or the old items. The findings emphasize the similarities between medial temporal lobe and diencephalic amnesia.

Septo-hippocampal and nBM-cortical cholinergic neurones exhibit differential time-courses of activation as a function of both type and duration of spatial memory testing in mice

We previously showed that the initial acquisition session of a spatial discrimination (mixed reference/working memory) test in an 8-arm radial maze induced differential activations in the ascending cholinergic septo-hippocampal and nBM-cortical pathways in mice. This data showed that the duration of post-test cholinergic activation was longer in the nBM-cortical pathway than in the septo-hippocampal projection. Moreover, the post-test durations but not the immediate post-test amplitudes of activation in each pathway decreased progressively as a function of repeated daily acquisition sessions. In the present study we have thus tested the hypotheses that the time-courses of post-test cholinergic activation in the septo-hippocampal and nBM-cortical pathways may vary both as a function of the type of memory used (working vs. reference) and according to the duration of repeated daily testing. Cholinergic activity in vivo in the hippocampus or frontal cortex of mice was quantified using measures of sodium-dependent high-affinity choline uptake at two different times (30 s and 15 min) following specific spatial working or reference memory testing in an 8-arm radial maze. The memory tests were administered daily over a 13-day period to attain high levels of performance in each type of task. In comparison to control groups both types of memory testing induced significant post-test cholinergic activations in each brain region on Day 15. However, cholinergic activity remained elevated in frontal cortex at 15 min post-test following reference memory testing, whereas significantly shorter durations of cortical and hippocampal cholinergic activation were observed following working memory testing using short (1 min) retention intervals. The possible significance of these differential modifications to the time-course of the post-test activations in these cholinergic pathways in working and reference memory processes and the putative transsynaptic mechanisms involved are discussed.

One-trial associative memory in black-capped chickadees.

Black-capped chickadees (Parus atricapillus), birds that store food, inspected feeders in an aviary, 1 of which was baited, and returned after a 5-min retention interval to consume the then-hidden food. In Experiment 1, Ss quickly learned this task but only if different feeders were used on each trial. In Experiment 2, memory for the baited feeder decayed substantially after 24 hr but not after 30 min. In Experiments 3 and 4, there were 4 alternatives to the baited feeder

Differential susceptibility to anterograde and retrograde amnesia treatments in preweanling rats.

Although there have been several reports that preweanling rats and mice are relatively resistant to experimentally induced retrograde amnesia, there is virtually no information concerning susceptibility to anterograde amnesia in subjects of this age. Therefore, in the present experiment, 23-day-old rats received hypothermia either prior to, or immediately after, punishment training in an attempt to induce anterograde and retrograde amnesia, respectively. When tested 24 hr later, only those subjects given hypothermia prior to training exhibited any loss of retention. Thus these results confirmed previous evidence of resistance to retrograde amnesia in preweanling rats and further demonstrated that substantial anterograde amnesia could be obtained in these subjects. Performance of subjects tested after a 5-min retention interval revealed that the poor retention performance in subjects cooled prior to training and tested 24 hr later was not due to a learning deficit. These results are also discussed with respect to the issue of the independence of anterograde and retrograde amnesia.

The effect of home cage stimuli on acquisition and retention of an active avoidance response in previsual rats.

The effect of home cage environmental stimuli on learning and the effects on retention of the presence or absence of these familiar contextual training stimuli during the retention test (Experiment 1) or during the retention interval (Experiment 2) were examined using 10-day-old rats, a multidirectional active avoidance task, and a 30-min retention interval. Home cage environmental stimuli were found to improve learning. A change in stimuli immediately after training, during the 30-min retention interval, was found to have a greater impact on retention performance than stimulus change introduced at the time of the retention test. The implications of these findings are discussed in relation to ontogenetic differences in retention performance and theories of forgetting.

Postacquisition unexpected footshock disrupts appetitively motivated instrumental performance based on short-term retention

Water-deprived rats were trained to run for water in an E-maze on a delayed-alternation task with a 5-min retention interval. Each day, long before encountering and again long after having encountered the delayed-alternation task, all subjects consistently experienced weak footshock in Context A and no footshock in Context B. Contexts A and B were highly dissimilar to each other and to the E-maze. On delayed-alternation probe trials, subjects were exposed to Context A or Context B for the middle 30 sec of the delayed-alternation retention interval. Performance on these trials was unaffected when weak footshock occurred in Context A or no footshock occurred in Context B. However, when weak footshock occurred in Context B, retention was impaired. An absence of footshocks in Context A produced a nonsignificant tendency towards impairment. Thus, the disruptive effects of unexpected events that occur during the retention interval do not appear to depend upon the target and unexpected events’ having similar reinforcers or even having reinforcers of the same valence. The results are interpreted in terms of unexpected events’ recruiting more of the limited information-processing capacity of the subject than do otherwise similar expected events. Moreover, the tendency of unexpected shock to interfere with performance more than does unexpected nonshock suggests that the degree to which an unexpected event recruits processing capacity depends on the affective value of the event as well as on its unexpectedness.

Amnesia and memory for visual location

Short-term memory and long-term memory for visual stimuli not readily verbalisable were studied in amnesic patients. Decay functions for recall of the location of a single dot stimulus over retention intervals of 0–60 sec were measured in a group of 7 amnesic subjects and 6 matched controls. Recall of the location of 5 randomly positioned dots after 10 learning trials was tested using a 2 min retention interval. It was found that the amnesic patients' performance was not significantly worse on the former, S.T.M. task but showed a significant deficit on the latter, L.T.M. task. in addition, three patients with a selective impairment of auditory verbal S.T.M. were tested. The findings are discussed in relation to comparable tasks of verbal S.T.M. and L.T.M.

A similarity between amnesic memory and normal forgetting

Warrington and Weiskrantz reported a significant interaction between method of testing and subject group when amnesics' and controls' memory was tested after a 1 min retention interval. An attempt was made to duplicate this finding without using any amnesic subjects but substituting for them a group of normal subjects with a presumably weak memory trace and comparing them with a group of normal subjects with a presumably strong memory trace. The attempt succeeded. Each subject learned a list of 100 words and was then tested on half the words after 1 min and on the other half after one week. A separate group of six subjects was used for each of the following methods of testing: yes-no recognition; cueing with initial letters; cueing with a fragmented form of the words. The statistic corresponding to the interaction between method of testing and retention interval was significant. Also normal performance on yes-no recognition at one week was (like amnesic performance significantly inferior to normal performance at 1 min; and normal performance on each of the methods of partial information at one week (like amnesic performance) did not differ significantly from normal performance at 1 min. Certain reservations and implications are discussed but it is concluded that Warrington and Weiskrantz's experiment can no longer be regarded as providing support for the theory that the amnesic syndrome is limited to a defect of retrieval.

The extent of the verbal encoding ability of Korsakoff patients

Four experiments were designed to determine the extent of Korsakoff patients' ability to encode semantically meaningful verbal material. The first experiment demonstrated that these patients are aided by category cues following a one min retention interval. The remaining experiments, which also employed cueing techniques demonstrated that Korsakoff patients, with instructions, can encode on acoustic, associative, and semantic levels. When left to their own preferences, however, the Korsakoff patients rely upon acoustic and associative encoding. This failure to employ semantic encoding strategies spontaneously may underlie their overall inability to retain verbal material.