- Open Access
Hippocampal function is not required for the precision of remote place memory
© Kitamura et al; licensee BioMed Central Ltd. 2012
- Received: 11 January 2012
- Accepted: 2 February 2012
- Published: 2 February 2012
During permanent memory formation, recall of acquired place memories initially depends on the hippocampus and eventually become hippocampus-independent with time. It has been suggested that the quality of original place memories also transforms from a precise form to a less precise form with similar time course. The question arises of whether the quality of original place memories is determined by brain regions on which the memory depends.
To directly test this idea, we introduced a new procedure: a non-associative place recognition memory test in mice. Combined with genetic and pharmacological approaches, our analyses revealed that place memory is precisely maintained for 28 days, although the recall of place memory shifts from hippocampus-dependent to hippocampus-independent with time. Moreover, the inactivation of the hippocampal function does not inhibit the precision of remote place memory.
These results indicate that the quality of place memories is not determined by brain regions on which the memory depends.
- cAMP Response Element Binding
- Dorsal Hippocampus
- Contextual Fear Conditioning
- Freezing Behavior
- Hippocampal Function
The hippocampus is a key brain structure for learning and memory [1–3]. Recall of some associative and spatial memories initially depends on the hippocampus, but that hippocampal dependency progressively decays over time, a process that is associated with a gradual increase of neocortex-dependency [4–9]. It has been suggested that the quality of original memories also transforms from a precise (i.e., detailed) form to a less precise (i.e., more schematic or generic) form with similar time course [10–12]. The question arises of whether changes in the quality of the original memories depend on the shift in brain regions on which the recall of these memories relies, i.e., whether the hippocampus is always required for the precision of memories. This is an important question for understanding physiological significances of the hippocampal-cortical complementary memory systems.
There are several studies that address this issue in rodents. Using a contextual fear conditioning paradigm, which is an associative learning between a place and aversive experience, some studies demonstrated that the hippocampus is always necessary for the precision of place memories [13, 14], supporting the memory transformation view  in which the quality of place memory correlates with the brain region on which that memory depends. By contrast, another study demonstrated that the hippocampus is not required for memory precision after the passage of time , supporting the memory reorganization view  in which the quality of place memory does not correlate with the brain region. Importantly, this discrepancy can be attributed to differences in experimental protocols used for association with fear . Because association with fear modifies (i.e., strengthen or generalize) the precision [16, 17], we cannot rule out the possibility that fear association may mask the actual precision of place memory. Moreover, contextual fear conditioning indirectly evaluates the place memory by measuring fear responses. Analyses based on association procedures may not be suitable for evaluating the precision. A direct way to address this issue is to measure the place memory per se without association protocols. In this study, we introduced a new procedure: a one-trial and non-associative place recognition test in mice. The clear advantage is the absence of any explicit reinforcement. In this procedure, we simply placed mice in a previously experienced vs. novel place. In the previously experienced place, mice exhibited habituation (reduced motility). In the novel context, mice did not show this reduction in motility. Thus, we evaluated the adaptation level as an index of the successful retrieval of place memory. Mice quickly acquired place memory during a free exploration and clearly discriminate experienced place from novel place. Especially mice maintained these memories for one month, which is different from the case in rats . This procedure allows us to directly evaluate the precision of remote place memory. Using this procedure combined with genetic and pharmacological approaches, we examined the relationship between the precision of place memory and the brain region on which that memory depends.
All animal procedures were conducted in compliance with the guidelines of the National Institutes of Health and were approved by the Animal Care and Use Committee of the University of Toyama and the Mitsubishi Kagaku Institute of Life Sciences. For WT experiments, male C57BL/6JSLC mice at 8 weeks of age were purchased from Sankyo Laboratory (Japan). For experiments using inducible cAMP response element binding protein (CREB) repressor transgenic mice [19, 20] and α-Calcium-calmodulin kinase II heterozygous null mutant mice [21–23], the progeny for each line was produced using in vitro fertilization and embryo transfer techniques to produce a number of animals sufficient for behavioral testing. Age- and gender-matched littermates were used for the tests. All behavioral experiments were conducted and analyzed by scientists blind to the genotypes of the animals. Food and water were provided ad libitum.
Cannulation and drug infusion
We used a surgical procedure described previously [24, 25]. Briefly, mice were implanted bilaterally with stainless steel guide cannulae (Eicom) using the following stereotactic coordinates: AP = -2.0 mm, ML = ± 1.5 mm, V = -2.1 mm from the bregma. Mice were allowed to recover for at least 14 days in individual home cages. To transiently inactivate hippocampus, a fluorescently-labeled γ-aminobutyric acid subtype A receptor agonist (FCM, fluorophore-conjugated muscimol; Molecular Probe) was used. Mice were briefly anesthetized with isoflurane to facilitate the insertion of the injection cannula. FCM (0.8 mM, 0.5 ul) or PBS alone was infused into the dorsal hippocampus at a rate of 0.20 μl/min 60 min before the retrieval test. The fluorescent signals of FCM were distributed in the dorsal hippocampus bilaterally. To inhibit protein synthesis in the hippocampus, anisomycin (ANI, 100 μg/μl, 0.75 μl; Sigma) was infused into the dorsal hippocampus bilaterally at a rate of 0.25 μl/min 10 minutes after the learning. For the i.p. injection of ANI, ANI (150 mg/kg, i.p.) was dissolved in PBS (pH adjusted to 7.0-7.4) and administered to mice 10 minutes after the learning. At this dose, ANI inhibits 90% of protein synthesis in the brain during the first 2 hours . For the i.p. injection of (R)-CPP (10 mg/kg, i.p.; Tocris), an antagonist of N-methyl-D-aspartate receptors, (R)-CPP was dissolved in PBS and administered to mice 4.5 hours before the learning. To examine the effects of disrupting CREB function on place memory formation, we used the transgenic mice that express an inducible CREB repressor in the forebrain, where a dominant-negative CREB protein is fused with the ligand binding domain of a mutant estrogen receptor . Tamoxifen (4-hydroxytamoxifen; 16 mg/kg, i.p. TAM; Sigma), which was dissolved in 10 ml of peanut oil (Sigma), or peanut oil only (OIL) was administered to WT or transgenic mice 6 hours before the learning session.
Place memory test
Contextual fear conditioning
Contextual fear conditioning was carried out as described previously [24, 27, 28]. Briefly, during the training session, mice were placed in the conditioning chamber (S) in Room A. After 3 minutes, animals were subjected to three unsignaled footshocks (2 sec duration, 0.5 mA, a min apart). After the last shock, mice remained in the chamber for 1 minute and were then returned to their home cages. During the testing session, mice were placed back into the conditioning chamber (S) or the novel chamber (C) for 3 minutes in Room A at 1 day or 28 days after training. At the end of each session, mice were returned to their home cages and the chambers were cleaned with water and 80% ethanol. All experiments were conducted using a video tracking system (Muromachi Kikai; Japan) to measure the freezing behavior of the animals. Freezing was defined as a complete absence of movement, except for respiration. Scoring of the duration of the freezing responses was started after 1 sec of sustained freezing behavior.
All data are presented as mean ± SEM. The number of animals used is indicated by "n". Comparisons between two-group data were analyzed by unpaired Student's t-tests or paired t-tests. Multiple group comparisons were assessed using a one-way, two-way, or repeated measures analysis of variance (ANOVA), followed by the post-hoc Scheffe's test when significant main effects or interactions were detected. The null hypothesis was rejected at the P < 0.05 level.
Mice were exposed to a novel square-type (S) chamber to learn this place (Figure 1A, B). One day later, mice were again exposed to the same chamber or a novel circle-type (C) chamber to test memory retrieval (Figure 1A, C). We monitored the motility of mice in the chambers and evaluated the adaptation level for the experienced or novel chamber as an index of the successful retrieval of place memory (Figure 1C, D). Mice showed a reduction in their motility when exposed to the same S chamber (paired t-test; t6 = 9.96, P < 0.001) (Figure 1D). By contrast, a six-minute exposure to the S chamber did not induce adaptation in the novel C chamber (paired t-test; t6 = -0.07, P > 0.9) (Figure 1C, D). We obtained a similar result when we changed the sequence (C-C paired t-test: t5 = 8.39, P < 0.001; C-S paired t-test: t6 = 1.16, P > 0.2) (Figure 1D). These results indicate that mice quickly learn the place and completely discriminate the experienced place from the novel place one day after learning. Thus, the adaptation can be used to index place memory.
Finally, we examined whether hippocampal function is required for the precision of remote place memory retrieval. In the retrieval test for 28-day memory, FCM-infused mice were placed in the experienced S chamber or novel C chamber (Figure 4E). FCM-infused mice showed adaptation for the experienced S chamber (paired t-test: t9 = 12.06, P < 0.001), whereas FCM-infused mice did not show adaptation for the novel C chamber (paired t-test: t9 = -0.68, P > 0.5) (Figure 4E). We further examined the variable-rooms/constant-chamber condition 28 days after learning (Figure 4E). Similar to naive mice (Figure 3A), FCM-infused mice did not show adaptation for the experienced S chamber in the novel room B (paired t-test: t11 = -0.84, P > 0.4) (Figure 4E). These results indicate that the pharmacological inactivation of hippocampal function does not inhibit the precision of remote place memory.
In this study, we carried out the contextual fear conditioning test and the non-associative place recognition test under the same experimental condition (same chambers and same exposure time to chamber) (Figure 3). These results clearly indicate that the association with fear masks the actual precision of place memory. Moreover, in contextual fear conditioning mice showed the freezing responses even for unconditioned place in recent memory test (Figure 3B) [13, 15, 24, 32–34], whereas in our non-associative place recognition test mice did not show any adaptation behavior even for similar place in remote memory test (Figure 3A). Therefore, the conclusions of previous studies using contextual fear conditioning [13–15] need to be validated by non-associative protocol. Thus, we examined the contribution of hippocampal function on the precision of remote place memory by non-associative place recognition test.
Using this procedure, we found that the place memory is precisely maintained for 28 days, which may require α-CaMKII-dependent plasticity in the cortex, and that the retrieval of remote place memory (not recent memory) does not require hippocampal function. These results indicate that the quality of a place memory does not correlate with the brain region on which that memory depends. Moreover, we found that the inactivation of hippocampal function does not inhibit the precision of remote place memory. These results indicate that the hippocampal function is not required for the precision of remote place memory. This is consistent with a human case study in which a patient with bilateral extensive hippocampal damage showed intact memories for places learned long ago, but not intact recent place memory . Eight patients with bilateral hippocampal damage were able to recall their remote autobiographical memories . Thus, the quality of original place memories is not determined by brain regions on which the memory depends.
We thank S. Kamijo, M. Matsuo and H. Hidaka for the care of the animals. We also thank B. Wiltgen and N. Ohkawa for reading the manuscript and for discussions, and all members of the Inokuchi laboratory for daily discussions. This work was supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST) to K.I., a Grant-in-Aid for Scientific Research (S) to K.I., the Mitsubishi Foundation to K.I., the Uehara Memorial Foundation to K.I., a Grant-in-Aid for Young Scientists (B) to T.K., and the Sasagawa Scientific Research Grant to T.K.
- Scoville WB, Milner B: Loss of recent memory after bilateral hippocampal lesions. J Neurol Neurosurg Psychiatry. 1957, 20: 11-21.PubMed CentralView ArticlePubMedGoogle Scholar
- Squire LR, Stark CE, Clark RE: The medial temporal lobe. Annu Rev Neurosci. 2004, 27: 279-306.View ArticlePubMedGoogle Scholar
- The Hippocampus Book. Edited by: Andersen P, Morris R, Amaral D, Bliss T, O'Keefe J. 2007, (New York: Oxford University Press)Google Scholar
- Kim JJ, Fanselow MS: Modality-specific retrograde amnesia of fear. Science. 1992, 256: 675-677.View ArticlePubMedGoogle Scholar
- McClelland JL, McNaughton BL, O'Reilly RC: Why there are complementary learning systems in the hippocampus and neocortex: insights from the successes and failures of connectionist models of learning and memory. Psychol Rev. 1995, 102: 419-457.View ArticlePubMedGoogle Scholar
- Dudai Y: The neurobiology of consolidations, or, how stable is the engram?. Annu Rev Psychol. 2004, 55: 51-86.View ArticlePubMedGoogle Scholar
- Wiltgen BJ, Brown RA, Talton LE, Silva AJ: New circuits for old memories: the role of the neocortex in consolidation. Neuron. 2004, 44: 101-108.View ArticlePubMedGoogle Scholar
- Frankland PW, Bontempi B: The organization of recent and remote memories. Nat Rev Neurosci. 2005, 6: 119-130.View ArticlePubMedGoogle Scholar
- Squire LR, Bayley PJ: The neuroscience of remote memory. Curr Opin Neurobiol. 2007, 17: 185-196.PubMed CentralView ArticlePubMedGoogle Scholar
- Nadel L, Moscovitch M: Memory consolidation, retrograde amnesia and the hippocampal complex. Curr Opin Neurobiol. 1997, 7: 217-227.View ArticlePubMedGoogle Scholar
- Moscovitch M, Nadel L, Winocur G, Gilboa A, Rosenbaum RS: The cognitive neuroscience of remote episodic, semantic and spatial memory. Curr Opin Neurobiol. 2006, 16: 179-190.View ArticlePubMedGoogle Scholar
- McKenzie S, Eichenbaum H: Consolidation and reconsolidation: two lives of memories?. Neuron. 2011, 71: 224-233.PubMed CentralView ArticlePubMedGoogle Scholar
- Winocur G, Moscovitch M, Sekeres M: Memory consolidation or transformation: context manipulation and hippocampal representations of memory. Nat Neurosci. 2007, 10: 555-557.View ArticlePubMedGoogle Scholar
- Wiltgen BJ, Zhou M, Cai Y, Balaji J, Karlsson MG, Parivash SN, Li W, Silva AJ: The hippocampus plays a selective role in the retrieval of detailed contextual memories. Curr Biol. 2010, 20: 1336-1344.PubMed CentralView ArticlePubMedGoogle Scholar
- Wang SH, Teixeira CM, Wheeler AL, Frankland PW: The precision of remote context memories does not require the hippocampus. Nat Neurosci. 2009, 12: 253-255.View ArticlePubMedGoogle Scholar
- Houston FP, Stevenson GD, McNaughton BL, Barnes CA: Effects of age on the generalization and incubation of memory in the F344 rat. Learn Mem. 1999, 6: 111-119.PubMed CentralPubMedGoogle Scholar
- Balogh SA, Radcliffe RA, Logue SF, Wehner JM: Contextual and cued fear conditioning in C57BL/6J and DBA/2J mice: context discrimination and the effects of retention interval. Behav Neurosci. 2002, 116: 947-957.View ArticlePubMedGoogle Scholar
- Izquierdo I, da Cunha C, Rosat R, Jerusalinsky D, Ferreira MB, Medina JH: Neurotransmitter receptors involved in post-training memory processing by the amygdala, medial septum, and hippocampus of the rat. Behav Neural Biol. 1992, 58: 16-26.View ArticlePubMedGoogle Scholar
- Kida S, Josselyn SA, Pena de Ortiz S, Kogan JH, Chevere I, Masushige S, Silva AJ: CREB required for the stability of new and reactivated fear memories. Nat Neurosci. 2002, 5: 348-355.View ArticlePubMedGoogle Scholar
- Kim R, Moki R, Kida S: Molecular mechanisms for the destabilization and restabilization of reactivated spatial memory in the Morris water maze. Mol Brain. 2011, 4: 9-PubMed CentralView ArticlePubMedGoogle Scholar
- Silva AJ, Wang Y, Paylor R, Wehner JM, Stevens CF, Tonegawa S: Alpha calcium/calmodulin kinase II mutant mice: deficient long-term potentiation and impaired spatial learning. Cold Spring Harb Symp Quant Biol. 1992, 57: 527-539.View ArticlePubMedGoogle Scholar
- Yamasaki N, Maekawa M, Kobayashi K, Kajii Y, Maeda J, Soma M, Takao K, Tanda K, Ohira K, Toyama K, et al: Alpha-CaMKII deficiency causes immature dentate gyrus, a novel candidate endophenotype of psychiatric disorders. Mol Brain. 2008, 1: 6-PubMed CentralView ArticlePubMedGoogle Scholar
- Hasegawa S, Furuichi T, Yoshida T, Endoh K, Kato K, Sado M, Maeda R, Kitamoto A, Miyao T, Suzuki R, et al: Transgenic up-regulation of alpha-CaMKII in forebrain leads to increased anxiety-like behaviors and aggression. Mol Brain. 2009, 2: 6-PubMed CentralView ArticlePubMedGoogle Scholar
- Kitamura T, Saitoh Y, Takashima N, Murayama A, Niibori Y, Ageta H, Sekiguchi M, Sugiyama H, Inokuchi K: Adult neurogenesis modulates the hippocampus-dependent period of associative fear memory. Cell. 2009, 139: 814-827.View ArticlePubMedGoogle Scholar
- Kitamura T, Saitoh Y, Murayama A, Sugiyama H, Inokuchi K: LTP induction within a narrow critical period of immature stages enhances the survival of newly generated neurons in the adult rat dentate gyrus. Mol Brain. 2010, 3: 13-PubMed CentralView ArticlePubMedGoogle Scholar
- Flood JF, Rosenzweig MR, Bennett EL, Orme AE: The influence of duration of protein synthesis inhibition on memory. Physiol Behav. 1973, 10: 555-562.View ArticlePubMedGoogle Scholar
- Hayashi F, Takashima N, Murayama A, Inokuchi K: Decreased postnatal neurogenesis in the hippocampus combined with stress experience during adolescence is accompanied by an enhanced incidence of behavioral pathologies in adult mice. Mol Brain. 2008, 1: 22-PubMed CentralView ArticlePubMedGoogle Scholar
- Inoue N, Nakao H, Migishima R, Hino T, Matsui M, Hayashi F, Nakao K, Manabe T, Aiba A, Inokuchi K: Requirement of the immediate early gene vesl-1S/homer-1a for fear memory formation. Mol Brain. 2009, 2: 7-PubMed CentralView ArticlePubMedGoogle Scholar
- Lee YS, Bailey CH, Kandel ER, Kaang BK: Transcriptional regulation of long-term memory in the marine snail Aplysia. Mol Brain. 2008, 1: 3-PubMed CentralView ArticlePubMedGoogle Scholar
- Leutgeb S, Leutgeb JK, Barnes CA, Moser EI, McNaughton BL, Moser MB: Independent codes for spatial and episodic memory in hippocampal neuronal ensembles. Science. 2005, 309: 619-623.View ArticlePubMedGoogle Scholar
- Fyhn M, Hafting T, Treves A, Moser MB, Moser EI: Hippocampal remapping and grid realignment in entorhinal cortex. Nature. 2007, 446: 190-194.View ArticlePubMedGoogle Scholar
- Wiltgen BJ, Silva AJ: Memory for context becomes less specific with time. Learn Mem. 2007, 14: 313-317.View ArticlePubMedGoogle Scholar
- Biedenkapp JC, Rudy JW: Context preexposure prevents forgetting of a contextual fear memory: implication for regional changes in brain activation patterns associated with recent and remote memory tests. Learn Mem. 2007, 14: 200-203.PubMed CentralView ArticlePubMedGoogle Scholar
- Ruediger S, Vittori C, Bednarek E, Genoud C, Strata P, Sacchetti B, Caroni P: Learning-related feedforward inhibitory connectivity growth required for memory precision. Nature. 2011, 473: 514-518.View ArticlePubMedGoogle Scholar
- Frankland PW, O'Brien C, Ohno M, Kirkwood A, Silva AJ: Alpha-CaMKII-dependent plasticity in the cortex is required for permanent memory. Nature. 2001, 411: 309-313.View ArticlePubMedGoogle Scholar
- Allen TA, Narayanan NS, Kholodar-Smith DB, Zhao Y, Laubach M, Brown TH: Imaging the spread of reversible brain inactivations using fluorescent muscimol. J Neurosci Methods. 2008, 171: 30-38.PubMed CentralView ArticlePubMedGoogle Scholar
- Teng E, Squire LR: Memory for places learned long ago is intact after hippocampal damage. Nature. 1999, 400: 675-677.View ArticlePubMedGoogle Scholar
- Bayley PJ, Hopkins RO, Squire LR: Successful recollection of remote autobiographical memories by amnesic patients with medial temporal lobe lesions. Neuron. 2003, 38: 135-144.View ArticlePubMedGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.