Individual subject approaches to mapping sensory-biased and multiple-demand regions in human frontal cortex
Introduction
The accurate mapping of the functional architecture of the frontal lobes presents a number of scientific challenges. In the human brain, frontal cortex appears to consist of many small functional regions that exhibit substantial anatomical variation across individuals. Recent work has uncovered an increasingly fractionated architecture, with many functionally distinct regions lying within the larger regions defined by early fMRI studies [1,2]. Unlike primary sensory or motor areas, these regions typically exhibit modest levels of functional MRI activation for a variety of cognitive tasks. Because of the low activation levels, frontal lobe researchers traditionally average together the results from many subjects and spatially smooth data in hopes of observing statistically significant activation [3, 4, 5]. While that strategy provides advantages in terms of statistical power, it may come at the cost of obscuring fine-scale organization. In particular, small, functionally distinct regions could potentially be obscured and misinterpreted as large functionally homogenous regions. ‘Deep imaging,’ or the practice of collecting a sizable amount of data on individual subjects, offers significant advantages in revealing fine-scale aspects of functional organization [6•,7••,8, 9, 10, 11]. In this paper, we discuss deep imaging approaches to mapping sensory-biased and multiple-demand regions within human lateral frontal cortex.
Section snippets
Sensory-biased frontal lobe regions
Sensory modality preference plays a fundamental role in the functional organization of occipital, temporal, and parietal cortex [12, 13, 14, 15]; however, investigations of human frontal lobe have long reported no specificity for sensory modality [4,5,16, 17, 18, 19]. This amodal view of human frontal cortex contrasts with substantial non-human primate evidence for strong sensory modality influences in lateral frontal cortex [20,21••,22]. Through the use of deep imaging fMRI methods and
Multiple-demand versus sensory-biased representations
Prior studies, including some that have emphasized within-subject analyses, have reported that lateral frontal cortex contains ‘multiple-demand’ regions that are recruited by a broad range of cognitive task-demands [4,25, 26, 27]. At first glance, the ‘sensory-biased’ account might be viewed as contradictory to the ‘multiple-demand’ account of lateral frontal cortical organization. In order to examine the relationship between sensory-biased regions and multiple-demand regions, we [11] scanned
Resting-state functional connectivity networks
Resting-state functional MRI (rs-fMRI) scans, in which participants are not given explicit cognitive tasks to perform (other than ‘keep your eyes open and let your mind wander’), are effective in revealing brain networks across groups of individuals [2,30, 31, 32], but also can reveal fine-scale individual differences in functional organization [6•,7••,33]. We advocate for routinely including rs-fMRI as part of deep imaging protocols. Here, we discuss 3 potential uses: network-level validation
Connectome fingerprinting – connectivity predicts function
The localization of small functional cortical regions in individual subjects presents logistical and financial challenges. Although the deep imaging methods described above and in other articles in this special issue can identify small cortical regions effectively, deep imaging requires collection of a substantial amount of task-fMRI data per subject. This not only places a high price tag on functional localization, in terms of scanner time, but also the prolonged scan sessions required for
Best practices in deep imaging
Deep imaging has the potential to reveal fine-scale functional architecture that can be obscured by group-level analyses. There are notable trade-offs implicit in deep imaging approaches, since investing resources into collecting ample amounts of data per subject implies a potential cost in terms of the number of subjects and/or number of task contrasts studied. We consider four ‘best practices’ considerations for deep imaging fMRI experiments: Cognitive Task Design; Resting-State fMRI;
Conflict of interest statement
Nothing declared.
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
•• of outstanding interest
CRediT authorship contribution statement
David C Somers: Conceptualization, Writing - original draft. Samantha W Michalka: Investigation, Writing - review & editing, Visualization. Sean M Tobyne: Investigation, Writing - review & editing, Visualization. Abigail L Noyce: Investigation, Writing - review & editing, Visualization.
Acknowledgements
This work was supported by National Science Foundation grant BCS-1829394 to D.C.S. as well as by National Institutes of Health grants R01-EY022229 to D.C.S., F31-MH101963 to S.W.M., F31-NS103306 to S.M.T., F32-EY026796 to A.L.N. The views expressed in this article do not necessarily represent the views of the NSF, NIH, or the United States Government.
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