Impact Factor 2.512 | CiteScore 4.1
More on impact ›

General Commentary ARTICLE

Front. Behav. Neurosci., 13 October 2014 |

Please keep calm: investigating hippocampal function without stress

  • Neurobiology Group, Institute of Medical Psychology, Otto-von-Guericke University Magdeburg, Magdeburg, Germany

A commentary on
Topographical disorientation after ischemic mini infarct in the dorsal hippocampus: whispers in silence

by Faraji, J., Soltanpour, N., Moeeini, R., Roudaki, S., Soltanpour, N., Abdollahi, A.-A., et al. (2014). Front. Behav. Neurosci. 8:261. doi: 10.3389/fnbeh.2014.00261

Please keep calm: investigating hippocampal function without stress

The article “Topographical disorientation after ischemic mini infarct in the dorsal hippocampus: whispers in silence” by Faraji et al. published in “Frontiers in Behavioral Neuroscience” is remarkable for three reasons:

• The behavioral “Ziggurat Test” used in this work is one of the most sensitive assessments available for detecting deficits in hippocampal function [because behavioral effects of such minor hippocampal lesions could not be detected so far (Driscoll et al., 2008)].

• Artifacts by stress or fear are avoided (as no aversive stimuli is used during the operant behavior).

• In conjunction with the model of micro brain lesions the depth of understanding brain function is surpassing (as the test goes far beyond a simple binary evaluation (function/no function) toward a multi-parameter assessment of the quality of behavioral changes).

Scientific methods are often used just as tools to quantify a chosen parameter. The aim is to apply a reliable test which gives a clear-cut result to proof a hypothesis. However, the interpretation of the numbers usually is not clear-cut: one should always have in mind that it is a substantial simplification to use scientific methods as mere tools: they are inevitably the subject of the research, too.

This issue is especially important when performing behavioral studies. The Morris Water Maze test (MWMT) since its publication (Morris, 1981) has been extremely helpful to investigate changes/deficits in spatial navigation in rodents and it has become a standard for such spatial learning and memory research. However, as in any behavioral tests, there are confounding factors, and here especially the stress rodents experience when they are placed into the water need to be considered. Therefore, it is not possible to know for sure whether the effects detected with a paradigm involving stress can be attributed to the concept of hippocampus-dependent spatial navigation or emotional components. That stress or fear may lead to confusing results has been demonstrated before, e.g., when it was described that lesions of the dorsal hippocampus induced rather emotional dysregulation than deficits in a context-dependent memory task (Henrich-Noack et al., 2011). Unfortunately, such stress and fear confounders are a drawback for most spatial navigation tasks (MWMT, fear conditioning, elevated mazes) and an appropriate model to detect early signs of vascular dementia has been missing so far. This is also the case because some of the behavioral tests avoiding stress and fear (e.g., variants of the t-maze or y-maze) have a rather simple conceptual design with restricted variables to be measured.

In their very elegant study Faraji et al. addressed this problem by using a newly developed behavioral test where the animals are trying to find baits on top of 16 pyramids which are equally distributed in a chamber. Importantly, here the rodents do not experience emotional stress during the task like it is the case when e.g., swimming in a water tank (and mild food restriction necessary for the task has only a negligible impact; Belda et al., 2005).

Other established spatial learning tests using appetitive motivation (e.g., the hole board) may also have the potential to detect behavioral effects of micro brain lesions, but it seem they have not yet reached such high sensitivity (Gordan et al., 2012). However, there have been studies recently presenting other new ways/techniques to overcome the problems of the standard tests: in addition to the reports introducing and applying the Ziggurate Test (Faraji et al., 2008, 2010, 2011); Sauvage et al. (2008, 2010) for example described innovative behavioral set-ups where one main aspect is also to investigate spatial and object recognition in rodents without the drawback of strong emotional components.

Beer et al. (2014) from this group have published data indicating that the dorsal CA1 shows higher activation for (non-spatial) object recognition tasks than the ventral CA1. The current work from Farajii et al. suggests that micro lesions in the dorsal hippocampus affect the performance in the Ziggurat Test more than ventral lesions: the number of returns was significantly higher than in unlesioned controls or after damage in the ventral hippocampal CA1 region. If the object recognition is more affected in animals with dorsal lesions (as Beer et al., 2014 suggest) it can be speculated that this failure may play a role in the increase in corrections (returns) in the Ziggurat Test. According to this interpretation these animals—which have this dorsal-CA1-lesion-induced specific deficit of object recognition—change, as a consequence, their strategy (i.e., more returns) in order to rely predominantly on creating a new spatial relation for a new, promising route.

Establishing new behavioral tasks is labor intensive, time consuming and risky—but the brain can only be understood by analyzing its function. Therefore, it is definitely worth the effort—as shown by the Faraji et al. publication. In addition, such work about new behavioral paradigms does not only answer many questions, it provides ample food for thoughts, lively discussions, thrilling ideas and new hypotheses, too. For example:

(i) As sex differences influence reliance on environmental cues (Tropp and Markus, 2001; Faraji et al., 2010) it would be interesting to see how (proestrous) female rats behave with such micro lesions in the dorsal CA1.

(ii) An adapted version of the Ziggurat Test may be very helpful to investigate (early) behavioral deficits in other models of vascular dementia or in transgenic Alzheimer mice (Schneider et al., 2014) without the need for aversive stimuli.

As a conclusion, keeping the rats calm may induce motivation, emotions and enthusiasm in neuroscientists.

Conflict of Interest Statement

The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


Beer, Z., Chwiesko, C., and Sauvage, M. M. (2014). Processing of spatial and non-spatial information reveals functional homogeneity along the dorso-ventral axis of CA3, but not CA1. Neurobiol. Learn. Mem. 111, 56–64.

Pubmed Abstract | Pubmed Full Text | Google Scholar

Belda, X., Ons, S., Carrasco, J., and Armario, A. (2005). The effects of chronic food restrictions on hypothalamic-pituitary-adrenal activity depend on morning versus evening availability of food. Pharmacol. Biochem. Behav. 81, 41–46. doi: 10.1016/j.pbb.2005.02.009

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Driscoll, I., Hong, N. S., Craig, L. A., Sutherland, R. J., and McDonald, R. J. (2008). Enhanced cell death and learning deficits after a mini-stroke in aged hippocampus. Neurobiol. Ageing 29, 1847–1858. doi: 10.1016/j.neurobiolaging.2007.04.025

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Faraji, J., Ejaredar, M., Metz, G. A., and Sutherland, R. J. (2011). Chronic stress prior to hippocampal stroke enhances post-stroke spatial deficits in the ziggurat task. Neurobiol. Learn. Mem. 95, 335–345. doi: 10.1016/j.nlm.2011.01.006

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Faraji, J., Lehmann, H., Metz, G. A., and Sutherland, R. J. (2008). Rats with hippocampal lesion show impaired learning and memory. Behav. Brain Res. 189, 17–31. doi: 10.1016/j.bbr.2007.12.002

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Faraji, J., Metz, G. A., and Sutherland, R. J. (2010). Characterization of spatial performance in male and female Long-Evans rats by means of the Morris water task and the ziggurat task. Brain Res. Bull. 81, 164–172. doi: 10.1016/j.brainresbull.2009.10.017

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Gordan, M. L., Jungwirth, B., Ohl, F., Kellermann, K., Kochs, E. F., and Blobner, M. (2012). Evaluation of neurobehavioural deficits following different severities of cerebral ischemia in rats: a comparison between the modified hole board test and the Morris water maze test. Behav. Brain Res. 235, 7–20. doi: 10.1016/j.bbr.2012.07.027

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Henrich-Noack, P., Krautwald, K., Reymann, K. G., and Wetzel, W. (2011). Effects of transient global ischaemia on freezing behaviour and activity in a context-dependent fear conditioning task – implications for memoty investigations. Brain Res. Bull. 85, 346–353. doi: 10.1016/j.brainresbull.2011.04.001

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Morris, R. G. M. (1981). Spatial localization does not require the presence of local cues. Learn. Motiv. 12, 239–260. doi: 10.1016/0023-9690(81)90020-5

CrossRef Full Text | Google Scholar

Sauvage, M. M., Beer, Z., Ekovich, M., Ho, L., and Eichenbaum, H. (2010). The caudal medial entorhinal cortex: a selective role in recollection-based recognition memory. J. Neurosci. 30, 15695–15699. doi: 10.1523/JNEUROSCI.4301-10.2010

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Sauvage, M. M., Fortin, N. J., Owens, C. B., Yonelinas, A. P., and Eichenbaum, H. (2008). Recognition memory: opposite effects of hippocampal damage on recollection and familiarity. Nat. Neurosci. 11, 16–18. doi: 10.1038/nn2016

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Schneider, F., Baldauf, K., Wetzel, W., and Reymann, K. G. (2014). Behavioral and EEG changes in male 5xFAD mice. Physiol. Behav. 135C, 25–33. doi: 10.1016/j.physbeh.2014.05.041

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Tropp, J., and Markus, E. J. (2001). Sex differences in the dynamics of cue utilization and exploratory behaviour. Behavi. Brain Res. 119, 143–154. doi: 10.1016/S0166-4328(00)00345-4

Pubmed Abstract | Pubmed Full Text | CrossRef Full Text | Google Scholar

Keywords: spatial behavior, hippocampal lesion, rat models, stress induced artifacts, dorsal CA1, vascular dementia, micro infarct

Citation: Henrich-Noack P (2014) Please keep calm: investigating hippocampal function without stress. Front. Behav. Neurosci. 8:356. doi: 10.3389/fnbeh.2014.00356

Received: 25 July 2014; Accepted: 25 September 2014;
Published online: 13 October 2014.

Edited by:

Nuno Sousa, University of Minho, Portugal

Reviewed by:

João J. Cerqueira, University of Minho, Portugal
Jukka Jolkkonen, University of Eastern Finland, Finland

Copyright © 2014 Henrich-Noack. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.