Internal representation of hierarchical sequences involves the default network - PubMed (original) (raw)

Internal representation of hierarchical sequences involves the default network

Baxter P Rogers et al. BMC Neurosci. 2010.

Abstract

Background: The default network is a set of brain regions that exhibit a reduction in BOLD response during attention-demanding cognitive tasks, and distinctive patterns of functional connectivity that typically include anti-correlations with a fronto-parietal network involved in attention, working memory, and executive control. The function of the default network regions has been attributed to introspection, self-awareness, and theory of mind judgments, and some of its regions are involved in episodic memory processes.

Results: Using the method of psycho-physiological interactions, we studied the functional connectivity of several regions in a fronto-parietal network involved in a paired image discrimination task involving transitive inference. Some image pairs were derived from an implicit underlying sequence A>B>C>D>E, and some were independent (F>G, H>J, etc). Functional connectivity between the fronto-parietal regions and the default network regions depended on the presence of the underlying sequence relating the images. When subjects viewed learned and novel pairs from the sequence, connectivity between these two networks was higher than when subjects viewed learned and novel pairs from the independent sets.

Conclusions: These results suggest that default network regions were involved in maintaining the internal model that subserved discrimination of image pairs derived from the implicit sequence, and contributed to introspective access of an internal sequence model built during training. The default network may not be a unified entity with a specific function, but rather may interact with other functional networks in task-dependent ways.

PubMed Disclaimer

Figures

Figure 1

Figure 1

Cognitive task. Four tasks (P, IP, S, IS) were performed in 30-second blocks during fMRI scanning. Prior to scanning, subjects learned via feedback to discriminate the P and S pairs. During scanning, the subject had to indicate the correct stimulus in each pair via button press (no feedback was given). The pairs presented in the IP and IS conditions were novel and had to be inferred from the previously learned pairs in the P and S condition. For the sequenced set in S and IS, the underlying sequence A>B>C>D>E determined the correct response on all trained and novel pairs. There is no such relationship among pairs for the non-sequenced set in P and IP. Each image has an arbitrary letter label to assist in description; this was not shown to the subjects. For each pair, the correct response is indicated with an outlined letter.

Figure 2

Figure 2

Fronto-parietal connectivity and sequence representation. The fronto-parietal network interacted more strongly with the default network during tasks that used an internal sequence representation. During scanning, participants responded to learned and novel pairs from a sequenced set and a non-sequenced set (Figure 1). Connectivity depended on the presence or absence of the underlying sequence. (A) Midline areas showed increased connectivity with the right parietal seed during sequence tasks. Functional connectivity was higher during S and IS conditions than P and IP, a positive Sequence by Parietal Seed psycho-physiological interaction. The orange/yellow colored voxels exhibited this interaction in a second-level analysis (p < 0.01). (B) Midline areas also showed increased connectivity with the preSMA seed during sequence tasks. Colored voxels exhibited a positive Sequence by PreSMA Seed psycho-physiological interaction (p < 0.01). (C) Connectivity between the fronto-parietal network and the posterior cingulate was high during sequence tasks S and IS, low during non-sequence tasks P and IP. Right: connectivity between right parietal seed and posterior cingulate from (A). Left: connectivity between PreSMA seed and posterior cingulate from (B). Error bars indicate the standard error of the mean. (D) The midline areas are within the default mode network. The table gives cluster coordinates in the MNI atlas space, corresponding to maps in (A) and (C). Voxels individually were p < 0.001 uncorrected, and reported clusters were significant at p < 0.01 corrected for multiple voxel comparisons based on cluster extent (one-tailed tests). The clusters were located in anterior cingulate, medial frontal gyrus, posterior cingulate, and precuneus, areas associated with the default network.

Figure 3

Figure 3

Fronto-parietal connectivity and inference. Some cortical regions showed stronger connectivity with the fronto-parietal seed ROIs during responses to learned pairs, versus to novel pairs. The table shows clusters of voxels with a significant Inference by Seed psycho-physiological interaction (p < 0.01 corrected), all of which showed higher connectivity with the corresponding seed ROI during the S and P conditions compared to IS and IP.

Figure 4

Figure 4

Connectivity/behavior correlations. Individual differences in connectivity between the right parietal seed region and the motor network partially explained the behavioral transitive inference effect. The behavioral TI effect was calculated from the reaction times for the four conditions: (RTIS-RTS)-(RTIP-RTP), which is the additional response time for the novel sequence (transitive inference) pairs relative to the learned sequence pairs, above and beyond the portion attributable to novelty only as determined from the non-sequence pairs. The connectivity TI effect was the parameter estimate for the sequence by inference by seed psycho-physiological interaction, analogous to (CIS-CS)-(CIP-CP) with C the connectivity between each voxel and the seed. (A) The behavioral and right parietal connectivity transitive inference effects were correlated in the bilateral supplementary motor area and left precentral gyrus. Significant positive correlation between the sequence by inference by seed psycho-physiological interaction and the behavioral TI effect was present in the colored voxels in a second-level analysis (p < 0.05). (B) The areas of correlation were the bilateral supplementary motor area and left precentral gyrus. The table gives cluster coordinates in the MNI atlas space corresponding to the map in (A). Voxels were p < 0.001 uncorrected, and reported clusters were significant at p < 0.05 corrected for multiple comparisons based on cluster extent (one-tailed tests). The clusters were located in areas associated with motor planning and execution. (C) The relationship between connectivity and behavioral TI effects was approximately linear. The plot shows the values from the SMA.

Similar articles

Cited by

References

    1. Acuna BD, Eliassen JC, Donoghue JP, Sanes JN. Frontal and parietal lobe activation during transitive inference in humans. Cereb Cortex. 2002;12(12):1312–1321. doi: 10.1093/cercor/12.12.1312. - DOI - PubMed
    1. Heckers S, Zalesak M, Weiss AP, Ditman T, Titone D. Hippocampal activation during transitive inference in humans. Hippocampus. 2004;14(2):153–162. doi: 10.1002/hipo.10189. - DOI - PubMed
    1. Nagode JC, Pardo JV. Human hippocampal activation during transitive inference. Neuroreport. 2002;13(7):939–944. doi: 10.1097/00001756-200205240-00008. - DOI - PubMed
    1. Ongur D, Cullen TJ, Wolf DH, Rohan M, Barreira P, Zalesak M, Heckers S. The neural basis of relational memory deficits in schizophrenia. Archives of general psychiatry. 2006;63(4):356–365. doi: 10.1001/archpsyc.63.4.356. - DOI - PubMed
    1. Van Opstal F, Verguts T, Orban GA, Fias W. A hippocampal-parietal network for learning an ordered sequence. NeuroImage. 2008;40(1):333–341. doi: 10.1016/j.neuroimage.2007.11.027. - DOI - PubMed

Publication types

MeSH terms

LinkOut - more resources