Mental time travel and default-mode network functional connectivity in the developing brain Ylva Østbya, Kristine B. Walhovda,b, Christian K. Tamnesa, Håkon Grydelanda, Lars Tjelta Westlyea, and Anders M. Fjella,b,1 aCenter for the Study of Human Cognition, Department of Psychology, University of Oslo, 0373 Oslo, Norway; and bDepartment of Physical Medicine and Rehabilitation, Unit of Neuropsychology, Oslo University Hospital, 0424 Oslo, Norway Edited by Marcus E. Raichle, Washington University in St. Louis, St. Louis, MO, and approved September 10, 2012 (received for review June 22, 2012) A core brain network is engaged in remembering the past and construction is the process of mentally generating and main- envisioning the future. This network overlaps with the so-called taining a complex and coherent scene or event (12), according to default-mode network, the activity of which increases when de- which the hippocampus plays a critical role in imagination by mands for focused attention are low. Because of their shared brain binding together discrete elements of an event (4, 9, 12). Thus, substrates, an intriguing hypothesis is that default-mode activity, the common involvement of the core network does not need to be measured at rest, is related to performance in separate attention- related to future imagination but could just as well be imagina- focused recall and imagination tasks. However, we do not know how tion of experiences that are “not necessarily self-relevant, plau- functional connectivity of the default-mode network is related to sible or even possible” (12). individual differences in reconstruction of the past and imagination Properties of the default-mode network can be quantified in of the future. Here, we show that functional connectivity of the de- terms of functional connectivity, which may refer to the temporal fault-mode network in children and adolescents is related to the relationships between activity in spatially remote areas within the quality of past remembering and marginally to future imagination. network or between the default-mode network and other net- These results corroborate previous findings of a common neuronal works. Default-mode functional connectivity is often measured substrate for memory and imagination and provide evidence sug- at “rest” (i.e., with no specific demands for focused attention). In gesting that mental time travel is modulated by the task-indepen- contrast, memory and imagination performance are typically dent functional architecture of the default-mode network in the measured in attention-focused tasks, often cue-word tasks. developing brain. A further analysis showed that local cortical area- Importantly, brain networks identified in resting conditions show lization also contributed to explain recall of the past and imagination similarities with networks identified during specific cognitively de- fi of the future, underscoring the bene ts of studying both functional manding task sessions (13), demonstrating that the functional or- and structural properties to understand the brain basis for complex ganization of the brain remain relatively stable across a range of human cognition. psychological states. Because the default-mode network overlaps substantially with the core network implied in remembering and cortical area | development | fMRI | independent component analysis imagination, there is an intriguing possibility that default-network connectivity, as measured during a resting condition, is related to t is widely accepted that reconstruction and “re-experience” are performance on independent attention-demanding memory and Iimportant aspects of vivid episodic memory. Reconstruction of imagination tasks. However, it needs to be established how default- memories based on impoverished bits of information represents mode network functional connectivity is related to individual dif- an economical way of storing information and may also facilitate ferences in recall of the past and construction of the future (14, 15). anticipation of the future (1). A reconstructive memory system, This information is important for the understanding of the brain enables mental time travel by use of previous experiences as substrates for differences in subjective quality of memories. Thus, a basis for construction of imagined future situations (2). Thus, we tested how these abilities in children and adolescents were re- there is a theoretical and empirical connection between the ability lated to resting-state functional connectivity of the default-mode to reconstruct and re-experience our own personal past and the network. Furthermore, individual differences in brain activation ability to imagine new experiences (3). However, little is known during development can hardly be understood without taking about individual differences in the brain characteristics underlying possible differences in brain structure into account. To allow in- the ability to form rich representations of the past and future and, tegration of functional and structural aspects of the brain, volume especially, how these characteristics support episodic recall and of the hippocampus and local arealization of the cerebral cortex imagination during development. The purpose of the present were included in an additional analysis. Local arealization was study was to delineate both functional and structural brain cor- chosen because this measure has received much recent attention relates of vividness in recall and future imagination in children and has shown to be of great interest as a metric of cortical struc- and adolescents. ture (16–19). Brain lesion (4, 5) and functional magnetic resonance imaging A total of 103 children and adolescents (age, 9.1–21.9 y) were (fMRI) studies (3, 6) have yielded evidence for a common core tested with a recall–imagination cue-word task. Children’s ability network of brain areas involved in recall of episodic memories to imagine the future has been subject of several recent studies and imagination of future scenarios. This network includes the (20–23). Episodic remembering and the ability to envision the medial temporal cortex, posterior cingulate/retrosplenial cortex/ precuneus, lateral parietal (inferior parietal lobule, temporo-pa- rietal junction), medial prefrontal, and lateral temporal cortices Author contributions: Y.Ø., K.B.W., C.K.T., H.G., L.T.W., and A.M.F. designed research; Y.Ø., (3), although the role played by the hippocampus in imagination K.B.W., C.K.T., H.G., L.T.W., and A.M.F. performed research; L.T.W. and A.M.F. analyzed is debated (7–9). These areas overlap to a substantial degree with data; and K.B.W. and A.M.F. wrote the paper. the default-mode network (10) and may, in a more general sense, The authors declare no conflict of interest. support self-projection, whether to the future, the past, or the This article is a PNAS Direct Submission. viewpoint of others (11). An alternative view to the self-pro- 1To whom correspondence should be addressed. E-mail: [email protected]. jection hypothesis on the relationship between the memory and This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10. imagination is based on the notion of scene construction. Scene- 1073/pnas.1210627109/-/DCSupplemental. 16800–16804 | PNAS | October 16, 2012 | vol. 109 | no. 42 www.pnas.org/cgi/doi/10.1073/pnas.1210627109 Downloaded by guest on September 26, 2021 − future emerge at the same time during development, approxi- score was −0.46 (P < 10 5), partialling out age and sex. The in- mately between the ages of 3 and 5 y (3, 24). Although it is clusion of participant movement as an additional covariate did not − known that much younger children have memories of their past affect the results (r = −0.45; P < 10 5), nor did inclusion of full- (25), there is controversy regarding the degree to which these scale intelligence quotient (IQ) from Wechsler Abbreviated Scale − memories are truly episodic in the autonoetic, “self-knowing,” of Intelligence (WASI) (r = −0.44; P < 10 4). No interaction with sense described by Tulving (2), or are more semantic in nature, age was found (P = 0.86), and running the analysis in the younger representing “knowledge” of the past (3, 24). In any case, the and older part of the sample split by median age (16.5 y) yielded ability to form episodic memories and to engage in episodic future similar correlations (r = −0.50 vs. −0.48, respectively; both P val- thinking should be undisputed in the age range sampled in the ues, <0.001). Because these correlations are based on already- present study, although compared with adults, relatively little is identified significant voxels, they should not be interpreted as an known about children’s autobiographical memory formation and estimate of the strength of the correlation in the population (26) ability to imagine the future (9). On a separate day from the but as a convenient way of testing the effect of including additional completion of the recall-imagination task, participants underwent covariates. Follow-up analyses were also run for the three sub- multimodal neuroimaging with resting-state fMRI and structural scales of the autonoetic score, with none showing larger correla- MRI. Based on the previous research reviewed above, we hy- tions than the total autonoetic score (r = −0.37 for experiential pothesized that the degree of detail and self-awareness in the score; r = −0.25 for perspective; r = −0.23 for coherence). subjective reports of past and future scenarios (i.e., the level of There was also a significant correlation between mean con- autonoetic consciousness) would be reflected in the default-mode nectivity in this cluster and imagination of the future (r = −0.25; network functional-connectivity pattern, local cortical arealization P < 0.05; age and sex partialled out). An analysis with future score in the memory network, and, possibly, hippocampal volume. as an independent variable and age and sex as covariates was therefore run across all voxels. The results revealed a cluster Results within the precuneus (t > 2, uncorrected; cluster size, 31 voxels; Descriptive Results.