A common cortical metric for spatial, temporal, and social distance

1. A common cortical metric for spatial, temporal, and social distance A Journal of Neuroscience publication by Carolyn Parkinson, Shari Liu, and Thalia Wheatley of Dartmouth College. Presented by Nicco Reggente on 4/10/14 at Neuroimaging+ Journal Club

2. Motivation • Does distance carry a common psychological meaning? • Spatial: Franz is “closer” to Gonda than it is to SaMo beach. • Temporal: This moment is “closer” to HBM than it is to SfN. • Social: Tessa is “closer” to Rachel than she is to R. Kelly. • Construal Level Theory (CLT) says that distance in any domain signifies a common meaning: distance from current first-hand experience. Conceptual Metaphor theory(CMT) says that we use spatial language because we actually “plot” information spatially. • Does distance’s ubiquity across domains of thought serve a computationally efficient purpose in the brain?

3. Stimuli/Paradigm In scanner: “Yes” or “No” Response to Probe

4. Stimuli/Paradigm Outside Scanner: For soon/close/familiar  For late/far/familiar  (-1 * (opposite_metric))

5. Behavioral Methods • Formation of a behavioral representational dissimilarity matrices(bRDM) • Closer/more familiar should be more similar than closer/less familiar.

6. Support Vector Machine “Bait & Switch” • Train on Closer vs. Farther Trials • Test on Sooner vs. Later Trials & More vs. Less Familiar • “Apply Trained Classifier”/”Use the same decision boundary” in a pairwise fashion

7. RSA • Formation of neural representation dissimilarity matrices (nRDM) • In a pairwise fashion, calculate (1-Pearson’s r) for each trial type … Voxel n Voxel 1

8. bRDM and nRDM RSA • Correlate the BRDM and NRDM in an attempt to see the degree to which all pairs of experimental conditions are dissimilar to one another in accordance with both fMRI responses and behavioral ratings.   Spearman’s r  

9. Searchlight • Conduct both Support Vector Machine “bait and switch” and RSA of BRDM and NRDM in a searchlight mapping fashion (9mm/3voxel radius).  Classify or correlate

10. Statistics • For the SVM bait and switch to be considered significant… • Classification values (arcsine transformed( )) were submitted to a two-tailed, one-sample t-test against 50% correct. • Conjunction analysis of 6 t-test statistical maps(each possible training and testing scheme) with FDR correction and p <.05. • Clusters > 10 voxels • For the BRDM and NRDM RSA to be considered significant... • Shuffle BRDM scores and correlate with actual NRDM. 1000 permutations. • Actual BRDM and actual NRDM compared to this pseudo-population to yield z-scores. • One-sample t-test(against 0) on the z-scores at the group-level and p<.05 FDR corrected • Clusters>10 voxels

11. Bait and Switch Results • Regions in which psychological distance could be decoded across all distance domains.

12. bRDM and nRDMRSA RESULTS • Population codes within searchlights centered in these areas contain representations that reflect subjective perceptions of egocentric distance.

13. Interpretations/Discussion • Right IPL/ Right TPJ is part of the frontoparietal control network(FPCN) • FPCN is thought to selectively recruit the Default Mode Network(DMN) and the Dorsal Attention Network(DAN) • DMN – internally directed cognition • “proximal”/concrete/detailed information manipulation? • DAN – externally directed cognition • “distal” / decontexualized / abstract information manipulation? • IPL would be perfectly positioned to fulfill this role and serve as a “flexible hub” that has a common cortical metric / parsimonious coding scheme for the guidance of information processing….

14. Interpretations/Discussion

15. Interpretations/Discussion

16. Interpretations/Discussion

17. Interpretations/Discussion • Right IPL/ Right TPJ has been shown to: • Encode egocentric space • Support self-other distinctions • Lesions to Right IPL/ Right TPJ results in: • Deficits in representing space • Deficits in representing events along a mental timeline. • IPL circuitry is thought to have been originally devoted to sensorimotor transformations and representing one’s own body in space and was “recycled” to operate analogously on increasingly abstract contents via evolution.

18. Interpretations/Discussion • Medial occipital has been previously associated with mental imagery during relative distance comparisons • SMA/IFG are involved in retrieving spatial locations from memory and may be similarly involved in accessing temporal and social frames of reference….

19. Interpretations/Discussion “It would be inefficient for the brain to represent spatial, social, and temporal distances entirely separately if they carry a common psychological meaning.”