Imagined Event Detail is Associated with BOLD Signal in Anterior-Medial Hippocampus: A Mega-Analysis
Poster No:
768
Submission Type:
Late-Breaking Abstract Submission
Authors:
Reece Roberts1, Ying Dai1, Yukta Madan1, Donna Rose Addis2
Institutions:
1The University of Auckland, Auckland, New Zealand, 2Baycrest Academy of Research and Education, Toronto, Ontario
First Author:
Co-Author(s):
Introduction:
Remembering the past and imagining the future engages a common network of brain regions, including the medial temporal lobes. However, the right anterior hippocampus has been found to be differentially activated during future imagination relative to remembering [4]. This finding has led to considerable interest in the attributes of imagined events that might be associated with differential future-related activity in the hippocampus, including the amount of detail imagined [e.g., 2,3,6]. Results have been mixed, owing in part to small sample sizes. In this study, we conducted a mega-analysis that combined raw data from seven fMRI studies on future imagination in which we collected subjective detail ratings [1,2,4-6,9,10]. We also utilized a hippocampal parcellation [7] to better characterize where in the hippocampus any significant effects of detail are evident.
Methods:
A total of 130 healthy, right-handed adults (52 male; aged 18-35 years) contributed data to this mega-analysis. In the original studies, BOLD data was collected on 1.5T or 3T scanners during a future simulation condition in which participants imagined novel future events. The future event conditions had between 16 and 90 trials, resulting in 6201 trials available for this analysis.
The future simulation paradigms varied in some ways. Future events were imagined in response to word cues that either referenced a generic noun (e.g., ENGINE), a common event (e.g., New Year's Eve), or a combination of personally-relevant people, places and objects. The duration of the imagination phase ranged from 8 s to 28 s. In all paradigms, the imagination phase was followed by a rating for the amount of detail imagined, however the Likert scale varied across studies; to harmonize ratings across studies, ratings were rescaled as a detail ratio score between 0 and 1.
Raw fMRI data from the 7 studies were re-preprocessed using a standard pipeline in SPM12. The GLMsingle toolbox [8] was then used to estimate voxelwise single-trial BOLD response amplitudes. GLMsingle identifies the optimal HRF that best explains the data in a given voxel on a given trial and returns a single beta weight for each trial, making this method ideal for harmonizing data from across experimental paradigms that vary in trial length. Plachti et al.'s 5-cluster hippocampal parcellation [7] was used to mask voxelwise maps, enabling us to extract and compute mean beta weights for each of the five regions in the left and right hippocampus.
To test the relationship between beta values and detail ratio scores, we computed for each hippocampal subregion a multilevel model (using lme4 in R) that accounted for the nested structure of the data. Studies and participants (nested in study) were specified as random effects, beta values were fixed effects, and detail ratio scores the dependent variable.
The future simulation paradigms varied in some ways. Future events were imagined in response to word cues that either referenced a generic noun (e.g., ENGINE), a common event (e.g., New Year's Eve), or a combination of personally-relevant people, places and objects. The duration of the imagination phase ranged from 8 s to 28 s. In all paradigms, the imagination phase was followed by a rating for the amount of detail imagined, however the Likert scale varied across studies; to harmonize ratings across studies, ratings were rescaled as a detail ratio score between 0 and 1.
Raw fMRI data from the 7 studies were re-preprocessed using a standard pipeline in SPM12. The GLMsingle toolbox [8] was then used to estimate voxelwise single-trial BOLD response amplitudes. GLMsingle identifies the optimal HRF that best explains the data in a given voxel on a given trial and returns a single beta weight for each trial, making this method ideal for harmonizing data from across experimental paradigms that vary in trial length. Plachti et al.'s 5-cluster hippocampal parcellation [7] was used to mask voxelwise maps, enabling us to extract and compute mean beta weights for each of the five regions in the left and right hippocampus.
To test the relationship between beta values and detail ratio scores, we computed for each hippocampal subregion a multilevel model (using lme4 in R) that accounted for the nested structure of the data. Studies and participants (nested in study) were specified as random effects, beta values were fixed effects, and detail ratio scores the dependent variable.
Results:
The mega-analysis revealed significant trial-level associations of detail ratio scores and beta weights in three hippocampal regions (Fig. 1): the right anterior hippocampus (p < .006), and the intermediate rostral medial hippocampus bilaterally (left: p < .003; right: p < .002). In all cases, higher BOLD response amplitudes were associated with higher detail ratings.
Conclusions:
This mega-analysis provides new insights into the regions of the hippocampus that contribute to the imagining of detailed future events. In particular, the bilateral nature of the findings suggests that the emphasis in the literature on the role of the right hippocampus may not be substantiated. The findings implicate multiple regions in the anterior hippocampus - including the head and the anterior (rostromedial) aspect of the body - in the generation of event detail. Finally, combining GLMsingle with a mega-analytic approach has provided robust findings that generalize not only across populations (US and NZ samples) and magnet strength (1.5 and 3T) but also experimental paradigms that use varying trial lengths.
Higher Cognitive Functions:
Higher Cognitive Functions Other 1
Learning and Memory:
Long-Term Memory (Episodic and Semantic) 2
Keywords:
FUNCTIONAL MRI
Memory
Other - future thinking; imagination; hippocampus
1|2Indicates the priority used for review
Abstract Information
By submitting your proposal, you grant permission for the Organization for Human Brain Mapping (OHBM) to distribute your work in any format, including video, audio print and electronic text through OHBM OnDemand, social media channels, the OHBM website, or other electronic publications and media.
The Open Science Special Interest Group (OSSIG) is introducing a reproducibility challenge for OHBM 2025. This new initiative aims to enhance the reproducibility of scientific results and foster collaborations between labs. Teams will consist of a “source” party and a “reproducing” party, and will be evaluated on the success of their replication, the openness of the source work, and additional deliverables. Click here for more information. Propose your OHBM abstract(s) as source work for future OHBM meetings by selecting one of the following options:
Please indicate below if your study was a "resting state" or "task-activation” study.
Healthy subjects only or patients (note that patient studies may also involve healthy subjects):
Was this research conducted in the United States?
Are you Internal Review Board (IRB) certified? Please note: Failure to have IRB, if applicable will lead to automatic rejection of abstract.
Were any human subjects research approved by the relevant Institutional Review Board or ethics panel? NOTE: Any human subjects studies without IRB approval will be automatically rejected.
Were any animal research approved by the relevant IACUC or other animal research panel? NOTE: Any animal studies without IACUC approval will be automatically rejected.
Please indicate which methods were used in your research:
For human MRI, what field strength scanner do you use?
Which processing packages did you use for your study?
Provide references using APA citation style.
[2] Addis, D.R., Roberts, R.P., & Schacter, D.L. (2011). Age-Related Neural Changes in Remembering and Imagining. Neuropsychologia, 49, 3656-3669.
[3] Addis, D.R., & Schacter, D.L. (2008). Effects of detail and temporal distance of past and future events on the engagement of a common neural network. Hippocampus, 18, 227-237.
[4] Addis, D.R., Wong, A.T., & Schacter, D. L. (2007). Remembering the past and imagining the future: Common and distinct neural substrates during event construction and elaboration. Neuropsychologia, 45, 1363–1377,
[5] Hach, S., Tippett, L.J., & Addis, D.R. (2014). Neural changes associated with the generation of specific past and future events in depression. Neuropsychologia, 65, 41–55.
[6] Martin, V.C., Schacter, D.L., Corballis, M.C., & Addis, D.R. (2011). A role for the hippocampus in encoding future simulations. Proceedings of the National Academy of Sciences USA, 108, 13858-13863.
[7] Plachti, A., Eickhoff, S.B., Hoffstaedter, F., Patil, K.R., Laird, A.R., Fox, P.T., Amunts, K., & Genon, S. (2019). Multimodal parcellations and extensive behavioral profiling tackling the hippocampus gradient. Cerebral Cortex, 29, 4595-4612.
[8] Prince, J. S., Charest, I., Kurzawski, J.W., Pyles, J.A., Tarr, M.J., & Kay, K.N. (2022). Improving the accuracy of single-trial fMRI response estimates using GLMsingle. Elife, 11, e77599.
[9] Roberts, R.P., Grady, C.L. Addis, D.R. (2020). Creative, internally-directed cognition is associated with reduced BOLD variability. NeuroImage, 219, 116758.
[10] van Mulukom, V., Schacter, D.L., Corballis, M.C., & Addis, D.R. (2013). Re-imagining the future: Repetition decreases hippocampal involvement in future simulation. PLoS ONE, 8, e69596.