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Making Head or Tail of the Hippocampus: A Long-Axis Account of Episodic and Spatial Memory
Uppsala University, Disciplinary Domain of Humanities and Social Sciences, Faculty of Social Sciences, Department of Psychology.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

While episodic and spatial memory both depend on the hippocampus, opposite gender differences in these functions suggest they are partly separate, with different neural underpinnings. The anterior and posterior hippocampus differ  in structure and whole-brain connectivity, and studies point to the posterior hippocampus being more involved in spatial memory while the anterior hippocampus’ role in episodic memory is less clear. This thesis aims to explore the role of the anterior and posterior hippocampus, and associated brain regions, in episodic and spatial memory. Paper I studied gender differences in hippocampal activation underlying differences in spatial memory performance. Better performance in men was accompanied by greater right-lateralization of hippocampal activation compared to women. Paper II investigated regions of gray matter that covaried in volume with the anterior and posterior hippocampus, and whether these covariance patterns depended on gender and were related to behavior. The anterior and posterior hippocampus showed different patterns of covariance, with the anterior hippocampus covariance pattern observed in women and the posterior hippocampus covariance pattern primarily in men. Paper III considered whether the location of hippocampal recruitment in episodic memory depends on memory content. Verbal stimuli were associated with more anterior, and left-lateralized, encoding activations than pictorial stimuli, which in turn were associated with more posterior and bilateral encoding activations. This was not observed during retrieval. Paper IV investigated whether resting-state connectivity associated with the anterior and posterior hippocampus predicts episodic and spatial memory performance, respectively. Resting-state connectivity associated with the anterior, not posterior, hippocampus predicted episodic memory performance, while resting-state connectivity associated with the posterior, not anterior, hippocampus predicted spatial memory performance. This thesis lends further support to differences in function and structure between the anterior and posterior hippocampus suggesting that these two sub–segments play different roles in episodic and spatial memory. Further, it suggests that gender differences in anterior and posterior hippocampus function underlies gender differences in episodic and spatial memory, respectively. Considering the anterior and posterior hippocampus, as well as men and women, separately, is hence important when studying the effect of age and pathology on the hippocampus and associated memory functions.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 81 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Social Sciences, ISSN 1652-9030 ; 114
Keyword [en]
hippocampus, fMRI, episodic memory, spatial memory, gender differences
National Category
Psychology (excluding Applied Psychology) Neurosciences
Research subject
Psychology
Identifiers
URN: urn:nbn:se:uu:diva-261340ISBN: 978-91-554-9328-8 (print)OAI: oai:DiVA.org:uu-261340DiVA: diva2:850754
Public defence
2015-10-23, Auditorium Minus, Gustavianum, Akademigatan 3, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2015-09-28 Created: 2015-09-01 Last updated: 2015-10-01
List of papers
1. Remembering our origin: Gender differences in spatial memory are reflected in gender differences in hippocampal lateralization
Open this publication in new window or tab >>Remembering our origin: Gender differences in spatial memory are reflected in gender differences in hippocampal lateralization
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2013 (English)In: Behavioural Brain Research, ISSN 0166-4328, E-ISSN 1872-7549, Vol. 256, 219-228 p.Article in journal (Refereed) Published
Abstract [en]

Gender differences in spatial memory favoring men are frequently reported, and the involvement of the hippocampus in these functions is well-established. However, little is known of whether this behavioral gender difference is mirrored in a gender difference in hippocampal function. Here we assessed hippocampal activity, using functional MRI, while 24 men and women moved through three-dimensional virtual mazes (navigation phase) of varying length, and at the end-point estimated the direction of the starting-point (pointing phase). Men were indeed more accurate than women at estimating direction, and this was especially true in longer mazes. Both genders activated the posterior hippocampus throughout the whole task. During the navigation phase, men showed a larger activation in the right hippocampus than women, while in the pointing phase, women showed a larger activation in the left hippocampus than men. Right-lateralized activation during the navigation phase was associated with greater task performance, and may reflect a spatial strategy that is beneficial in this task. Left-sided activation during the pointing phase might reflect a less efficient post hoc verbal recapitulation of the route. This study is the first to identify neural correlates of the commonly observed male advantage in recalling one's original position, and points to hippocampal lateralization as a possible explanation for this behavioral gender difference.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:uu:diva-207612 (URN)10.1016/j.bbr.2013.07.050 (DOI)000328094100027 ()23938766 (PubMedID)
Available from: 2013-09-17 Created: 2013-09-17 Last updated: 2017-12-06Bibliographically approved
2. Sex differences in volume and structural covariance of the anterior and posterior hippocampus
Open this publication in new window or tab >>Sex differences in volume and structural covariance of the anterior and posterior hippocampus
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2014 (English)In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, no 99, 215-25 p.Article in journal (Refereed) Published
Abstract [en]

Sex differences in episodic and spatial memory are frequently observed, suggesting that there may be sex-related structural differences in the hippocampus (HC). Earlier findings are inconsistent, possibly due to a known variability along the hippocampal longitudinal axis. Here, we assessed potential sex differences in hippocampal volume and structural covariance with the rest of the brain in young men and women (N=76), considering the anterior (aHC) and posterior (pHC) hippocampus separately. Women exhibited a larger pHC than men adjusted for brain size. Using partial least squares, we identified two significant patterns of structural covariance of the aHC and pHC. The first included brain areas that covaried positively and negatively in volume with both the aHC and pHC in men, but showed greater covariance with the aHC than pHC in women. The second pattern revealed distinct structural covariance of the aHC and pHC that showed a clear difference between men and women: in men the pHC showed reliable structural covariance with the medial and lateral parietal lobes and the prefrontal cortex, whereas in women the aHC showed reliable structural covariance with the anterior temporal lobe bilaterally. This pattern converges with resting state functional connectivity of the aHC and pHC and suggests that these hippocampal sections interact with different brain regions, consistent with a division of labor with regards to episodic and spatial memory. Our findings lend support to a division of the HC into an anterior and posterior part and identify sex as a potential moderating factor when investigating hippocampal structure and connectivity.

National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:uu:diva-225425 (URN)10.1016/j.neuroimage.2014.05.038 (DOI)000339860000023 ()24857714 (PubMedID)
Available from: 2014-06-03 Created: 2014-06-03 Last updated: 2017-12-05Bibliographically approved
3. Hippocampal hemispheric and long-axis differentiation of stimulus content during episodic memory encoding and retrieval: An activation likelihood estimation meta-analysis
Open this publication in new window or tab >>Hippocampal hemispheric and long-axis differentiation of stimulus content during episodic memory encoding and retrieval: An activation likelihood estimation meta-analysis
2015 (English)In: Hippocampus, ISSN 1050-9631, E-ISSN 1098-1063, Vol. 25, no 12, 1614-1631 p.Article in journal (Refereed) Published
Abstract [en]

While there is ample evidence that the hippocampus is functionally heterogeneous along its longitudinal axis, there is still no consensus regarding its exact organization. Whereas spatial memory tasks frequently engage the posterior hippocampus, the regions engaged during episodic memory are more varying and may depend on the specific nature of the stimuli. Here, we investigate the effect of stimulus content on the location of hippocampal recruitment during episodic memory encoding and retrieval of pictorial and verbal material with a meta-analysis approach, using activation likelihood estimation and restricting the analysis to the hippocampus. Verbal material was associated with left-lateralized anterior activation, compared to pictorial material that recruited a more posterior aspect of the hippocampus, primarily within the right hemisphere. This effect held for encoding of both single items and item-item associations but was less clear during retrieval. The findings lend further support to a functional subdivision of the hippocampus along its longitudinal axis and indicate that the content of episodic memories is one factor that determines the location of hippocampal recruitment.

Keyword
meta-analysis; hippocampus; episodic memory; spatial memory; activation likelihood estimation; encoding; retrieval
National Category
Psychology
Identifiers
urn:nbn:se:uu:diva-259778 (URN)10.1002/hipo.22482 (DOI)000368281700012 ()26108671 (PubMedID)
Available from: 2015-08-11 Created: 2015-08-11 Last updated: 2017-12-04Bibliographically approved
4. Predicting episodic and spatial memory performance from hippocampal resting-state functional connectivity: evidence for an anterior-posterior division of function
Open this publication in new window or tab >>Predicting episodic and spatial memory performance from hippocampal resting-state functional connectivity: evidence for an anterior-posterior division of function
(English)Manuscript (preprint) (Other academic)
National Category
Psychology
Identifiers
urn:nbn:se:uu:diva-259780 (URN)
Available from: 2015-08-11 Created: 2015-08-11 Last updated: 2015-09-29

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