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183 nips-2013-Mapping paradigm ontologies to and from the brain


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Author: Yannick Schwartz, Bertrand Thirion, Gael Varoquaux

Abstract: Imaging neuroscience links brain activation maps to behavior and cognition via correlational studies. Due to the nature of the individual experiments, based on eliciting neural response from a small number of stimuli, this link is incomplete, and unidirectional from the causal point of view. To come to conclusions on the function implied by the activation of brain regions, it is necessary to combine a wide exploration of the various brain functions and some inversion of the statistical inference. Here we introduce a methodology for accumulating knowledge towards a bidirectional link between observed brain activity and the corresponding function. We rely on a large corpus of imaging studies and a predictive engine. Technically, the challenges are to find commonality between the studies without denaturing the richness of the corpus. The key elements that we contribute are labeling the tasks performed with a cognitive ontology, and modeling the long tail of rare paradigms in the corpus. To our knowledge, our approach is the first demonstration of predicting the cognitive content of completely new brain images. To that end, we propose a method that predicts the experimental paradigms across different studies. 1

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Summary: the most important sentenses genereted by tfidf model

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1 Mapping cognitive ontologies to and from the brain Yannick Schwartz, Bertrand Thirion, and Gael Varoquaux Parietal Team, Inria Saclay Ile-de-France Saclay, France firstname. [sent-1, score-0.739]

2 fr Abstract Imaging neuroscience links brain activation maps to behavior and cognition via correlational studies. [sent-3, score-0.719]

3 To come to conclusions on the function implied by the activation of brain regions, it is necessary to combine a wide exploration of the various brain functions and some inversion of the statistical inference. [sent-5, score-0.789]

4 Here we introduce a methodology for accumulating knowledge towards a bidirectional link between observed brain activity and the corresponding function. [sent-6, score-0.306]

5 We rely on a large corpus of imaging studies and a predictive engine. [sent-7, score-0.455]

6 Technically, the challenges are to find commonality between the studies without denaturing the richness of the corpus. [sent-8, score-0.229]

7 The key elements that we contribute are labeling the tasks performed with a cognitive ontology, and modeling the long tail of rare paradigms in the corpus. [sent-9, score-0.531]

8 To our knowledge, our approach is the first demonstration of predicting the cognitive content of completely new brain images. [sent-10, score-0.679]

9 1 Introduction Functional brain imaging, in particular fMRI, is the workhorse of brain mapping, the systematic study of which areas of the brain are recruited during various experiments. [sent-12, score-0.993]

10 To date, 33K papers on pubmed mention “fMRI”, revealing an accumulation of activation maps related to specific tasks or cognitive concepts. [sent-13, score-0.794]

11 From this literature has emerged the notion of brain modules specialized to a task, such as the celebrated fusiform face area (FFA) dedicated to face recognition [1]. [sent-14, score-0.466]

12 However, the link between the brain images and high-level notions from psychology is mostly done manually, due to the lack of co-analysis framework. [sent-15, score-0.35]

13 Beyond this lack of specificity, individual studies are seldom comprehensive, in the sense that they do not recruit every brain region. [sent-19, score-0.535]

14 Prior work on such large scale cognitive mapping of the brain has mostly relied on coordinate-based meta-analysis, that forgo activation maps and pool results across publications via the reported Talairach coordinates of activation foci [3, 4]. [sent-20, score-1.208]

15 Such large corpuses can be used to evaluate the occurrence of the cognitive and behavioral 1 terms associated with activations and formulate reverse inference as a Bayesian inversion on standard (forward) fMRI inference [2, 4]. [sent-22, score-0.802]

16 On the opposite end of the spectrum, [5] shows that using a machine-learning approach on studies with different cognitive content can predict this content from the images, thus demonstrating principled reverse inference across studies. [sent-23, score-0.975]

17 Two trends thus appear in the quest for explicit correspondences between brain regions and cognitive concepts. [sent-25, score-0.76]

18 One is grounded on counting term frequency on a large corpus of studies described by coordinates. [sent-26, score-0.39]

19 Our purpose here is to outline a strategy to accumulate knowledge from a brain functional image database in order to provide grounds for principled bidirectional reasoning from brain activation to behavior and cognition. [sent-29, score-1.01]

20 To increase the breadth in co-analysis and scale up from [5], which used only 8 studies with 22 different cognitive concepts, we have to tackle several challenges. [sent-30, score-0.561]

21 For this very reason we choose to describe studies with terms that come from a cognitive paradigm ontology instead of a high-level cognitive process one. [sent-32, score-1.106]

22 This setting enables not only to span the terms across all the studies, but also to use atypical studies that do not clearly share cognitive processes. [sent-33, score-0.624]

23 A second challenge is that of diminishing statistical power with increasing number of cognitive terms under study. [sent-34, score-0.332]

24 We perform a brain mapping experiment across these studies, in which we consider both forward and reverse inference. [sent-37, score-0.659]

25 In section 2, we introduce our methodology for establishing correspondence between studies and performing forward and reverse inference across them. [sent-40, score-0.679]

26 In section 3, we present our data, a corpus of studies and the corresponding paradigm descriptions. [sent-41, score-0.384]

27 In section 4 we show empirically that our approach can predict these descriptions in unseen studies, and that it gives promising maps for brain mapping. [sent-42, score-0.459]

28 1 Methodology: annotations, statistics and learning Labeling activation maps with common terms across studies A standard task-based fMRI study results in activation maps per subject that capture the brain response to each experimental condition. [sent-45, score-1.258]

29 They are combined to single out responses to high-level cognitive functions in so-called contrast maps, for which the inference is most often performed at the group level, across subjects. [sent-46, score-0.492]

30 For example, to highlight computation processes, one might contrast visual calculation with visual sentences, to suppress the effect of the stimulus modality (visual instructions), and the explicit stimulus (reading the numbers). [sent-48, score-0.508]

31 When considering a corpus of different studies, finding correspondences between the effects highlighted by the contrasts can be challenging. [sent-49, score-0.243]

32 Indeed, beyond classical localizers, capturing only very wide cognitive domains, each study tends to investigate fairly unique questions, such as syntactic structure in language rather than language in general [8]. [sent-50, score-0.332]

33 Indeed, there are important ongoing efforts in cognitive science and neuroscience to organize the scientific concepts into formal ontologies [9]. [sent-53, score-0.47]

34 2 Forward inference: which regions are recruited by tasks containing a given term? [sent-56, score-0.228]

35 Armed with the term labels, we can use the standard fMRI analysis framework and ask using a General Linear Model (GLM) across studies for each voxels of the subject-level activation images if it is significantly-related to a term in the corpus of images. [sent-57, score-0.823]

36 If x ∈ Rp is the observed activation map with p voxels, the GLM tests P(xi = 0|T ) for each voxel i and term T . [sent-58, score-0.299]

37 The benefit of the GLM formulation is that it estimates the effect of each term partialing out the effects of the other terms, and thus imposes some form of functional specificity in the results. [sent-61, score-0.24]

38 3 Reverse inference: which regions are predictive of tasks containing a given term? [sent-64, score-0.234]

39 Poldrack 2006 [2] formulates reverse inferences as reasoning on P(T |x), the probability of a term T being involved in the experiment given the activation map x. [sent-65, score-0.471]

40 Approaches to build a reverse inference framework upon this description have relied on Bayesian inversion to go from P(xi = 0|T ), as output by the GLM, to P(T |xi = 0) [2, 4]. [sent-67, score-0.269]

41 Learning voxels-level parameters independently is a limitation as it makes it harder to capture distributed effects, such as large-scale functional networks, that can be better predictors of stimuli class than localized regions [6]. [sent-69, score-0.23]

42 The choice of linear models is crucial to our brain-mapping goals, as their decision frontier is fully represented by a brain map1 β ∈ Rp . [sent-73, score-0.306]

43 2 Reducing even further down to 2K parcels does not impact the classification performance, however the brain maps β are then less spatially resolved. [sent-88, score-0.459]

44 1 An image database Studies We need a large collection of task fMRI datasets to cover the cognitive space. [sent-93, score-0.399]

45 The datasets include risk-taking tasks [13, 14], classification tasks [15, 16, 17], language tasks [18, 8, 19], stop-signal tasks [20], cueing tasks [21], object recognition tasks [22, 23], functional localizers tasks [24, 25], and finally a saccades & arithmetic task [26]. [sent-96, score-0.761]

46 The database accounts for 486 subjects, 131 activation map types, and 3 826 individual maps, the number of subjects and map types varying across the studies. [sent-97, score-0.508]

47 To avoid biases due to heterogeneous data analysis procedures, we re-process from scratch all the studies with the SPM (Statistical Parametric Mapping) software. [sent-98, score-0.229]

48 The neuroscience community recognizes the value of such vocabularies and develops ontologies to cover the different aspects of the field such as protocols, paradigms, brain regions and cognitive processes. [sent-101, score-0.853]

49 Among the many initiatives, CogPO (The Cognitive Paradigm Ontology) [9] aims to represent the cognitive paradigms used in fMRI studies. [sent-102, score-0.399]

50 As an example a stimulus modality may be auditory or visual, the explicit stimulus a non-vocal sound or a shape. [sent-105, score-0.493]

51 For instance, we only have visual or auditory stimulus modalities. [sent-110, score-0.309]

52 While a handful of contrasts display both stimulus modalities, the fact that a stimulus is not auditory mostly amounts to it being visual. [sent-111, score-0.435]

53 For this reason, we exclude from our forward inference visual, which will be captured by negative effects on auditory, and digits, that amounts mainly to the instruction being count. [sent-112, score-0.321]

54 To evaluate the spatial layout of the different CogPO categories, we report the different term effects as outlines in the brain, and show the 5% top values for each term to avoid clutter in Figure 3. [sent-114, score-0.183]

55 Forward inference 4 outlines many regions relevant to the terms, such as the primary visual and auditory systems on the stimulus modality maps, or pattern and object-recognition areas in the ventral stream, on the explicit stimulus maps. [sent-115, score-0.734]

56 It can be difficult to impose a functional specificity in forward inference because of several phenomena: i) the correlation present in the design matrix, makes it hard to separate highly associated (often anti-correlated) factors, as can be seen in Fig. [sent-116, score-0.329]

57 This assumption ignores modulations and interactions effects that are very likely to occur; however their joint occurrence is related to the protocol, making it impossible to disentangle these factors with the database used here. [sent-119, score-0.19]

58 2 Reverse inference The promise of predictive modeling on a large statistical map database is to provide principled reverse inference, going from observations of neural activity to well-defined cognitive processes. [sent-123, score-0.814]

59 Figure 1 highlights some confounding effects that can captured by a predictive model: two statistical maps originating from the same study are closer than two maps labeled as sharing a same experimental condition in the sense of a Euclidean distance. [sent-125, score-0.517]

60 Second, we only test the classifiers on previously unseen studies and if possible subjects, using for example a leave-one-study out cross validation scheme. [sent-129, score-0.331]

61 We compare this approach to training independent predictive models for each term and use three types of classifiers: a naive Bayes, a logistic regression, and a weighted logistic regression. [sent-136, score-0.24]

62 It confirms the idea outlined in Figure 1, that an Euclidean distance alone is not appropriate to discriminate underlying brain functions because of overwhelming confounding effects4 . [sent-147, score-0.408]

63 On the contrary, the methods using a logistic regression show better results, and yield performance scores above the chance levels which are represented by the red horizontal bars for the leave-onestudy out cross validation scheme in Figure 2. [sent-149, score-0.243]

64 5 Nb of m a ps All Sa m e la be l Sa m e s tudy Sa m e c ontra s t 0 Dis ta nc e be twe e n two m a ps Figure 1: (Left) Histogram of the distance between maps owing to their commonalities: study of origin, functional labels, functional contrast. [sent-157, score-0.381]

65 We evaluate the spatial layout of maps representing CogPO categories for reverse inference as well, and report boundaries of the 5% top values from the weighted logistic coefficients. [sent-160, score-0.524]

66 Figure 3 reports the outlined regions that include motor cortex activations in the instructions category, and activations in the auditory cortex and FFA respectively for the words and faces terms in the explicit stimulus category. [sent-161, score-0.732]

67 Despite being very noisy, those regions report findings consistent with the literature and complementary to the forward inference maps. [sent-162, score-0.292]

68 For instance, the move instruction map comprises the motor cortex, unlike for forward inference. [sent-163, score-0.262]

69 Similarly, the saccades over response map segments the intra-parietal sulci and the frontal eye fields, which corresponds to the well known signature of saccades, unlike the corresponding forward inference map, which is very non specific of saccades5 . [sent-164, score-0.355]

70 5 Discussion and conclusion Linking cognitive concepts to brain maps can give solid grounds to the diffuse knowledge derived in imaging neuroscience. [sent-165, score-0.872]

71 Common studies provide evidence on which brain regions are recruited in given tasks. [sent-166, score-0.687]

72 However coming to conclusions on the tasks in which regions are specialized requires data accumulation across studies to overcome the small coverage in cognitive domain of the tasks assessed in a single study. [sent-167, score-0.909]

73 Indeed, finding correspondence between studies is a key step to going beyond idiosyncrasies of the experimental designs. [sent-171, score-0.229]

74 Yet the framework should not discard rare but repeatable features of the experiments as these provide richness to the description of brain function. [sent-172, score-0.362]

75 Previous work [5] showed high classification scores for several mental states across multiple studies, using cross-validation with a leave-one-subject out strategy. [sent-176, score-0.199]

76 As figure 1 shows, predicting studies is much easier albeit of little neuroscientific interest. [sent-179, score-0.229]

77 Interestingly, [5] also explores the ability of a model to be predictive on two different studies sharing the same cognitive task, and a few subjects. [sent-180, score-0.642]

78 When using the common subjects, their model performs worse than without these subjects, as it partially mistakes cognitive 5 This failure of forward inference is probably due to the small sample size of saccades. [sent-181, score-0.547]

79 To avoid this loophole, we included in our corpus only studies that had terms in common with at least on other study and performed cross-validation by leaving a study out, and thus predicting from completely new activation maps. [sent-187, score-0.51]

80 Our labeled corpus is riddled with very infrequent terms giving rise to class imbalance problems in which the rare occurrences are the most difficult to model. [sent-190, score-0.262]

81 Interestingly, though coordinates databases such as Neurosynth [4] cover a larger set of studies and a broader range of cognitive processes, they suffer from a similar imbalance bias, which is given by the state of the literature. [sent-191, score-0.625]

82 For instance, the reverse inference map corresponding to the term digits is empty, whereas the forward inference map is well defined 6 . [sent-194, score-0.671]

83 Neurosynth draws from almost 5K studies while our work is based on 19 studies; however, unlike Neurosynth, we are able to benefit from the different contrasts and subjects in our studies, which provides us with 3 826 training samples. [sent-195, score-0.37]

84 This paper shows the first demonstration of zero-shot learning for prediction of tasks from brain activity: paradigm description is given for images from unseen studies, acquired on different scanners, in different institutions, on different cognitive domains. [sent-197, score-0.809]

85 To minimize clutter, we set the outline so as to encompass 5% of the voxels in the brain on each figure, thus highlighting only the salient features of the maps. [sent-201, score-0.398]

86 In reverse inference, to reduce the visual effect of the parcellation, maps were smoothed using a σ of 2 voxels. [sent-202, score-0.392]

87 accumulation, combined with the predictive model can provide good proxies of reverse inference maps, giving regions whose activation supports certain cognitive functions. [sent-203, score-0.936]

88 These maps should, in principle, be better suited for causal interpretation than maps estimated from standard brain mapping correlational analysis. [sent-204, score-0.658]

89 In future work, we plan to control the significance of the reverse inference maps, that show promising results but would probably benefit from thresholding out non-significant regions. [sent-205, score-0.269]

90 In addition, we hope that further progress, in terms of spatial and cognitive resolution in mapping the brain to cognitive ontologies, will come from enriching the database with new studies, that will bring more images, and new low and high-level concepts. [sent-206, score-1.037]

91 Chun, “The fusiform face area: a module in human extrastriate cortex specialized for face perception. [sent-212, score-0.235]

92 Poldrack, “Can cognitive processes be inferred from neuroimaging data? [sent-217, score-0.377]

93 Hanson, “Decoding the large-scale structure of brain function by classifying mental states across individuals,” Psychological Science, vol. [sent-239, score-0.465]

94 Halchenko, “Brain reading using full brain support vector machines for object recognition: there is no face identification area,” Neural Computation, vol. [sent-244, score-0.366]

95 Laird, “The cognitive paradigm ontology: design and application,” Neuroinformatics, vol. [sent-266, score-0.383]

96 Thirion, “A supervised clustering approach for fMRI-based inference of brain states,” Pattern Recognition, vol. [sent-275, score-0.403]

97 Shimodaira, “Improving predictive inference under covariate shift by weighting the log-likelihood function,” Journal of statistical planning and inference, vol. [sent-279, score-0.178]

98 Milham, “Competition between functional brain networks mediates behavioral variability,” Neuroimage, vol. [sent-353, score-0.42]

99 Dehaene, “Fast reproducible identification and large-scale databasing of individual functional cognitive networks,” BMC neuroscience, vol. [sent-382, score-0.446]

100 Dehaene, “Genetic and environmental contributions to brain activation during calculation,” NeuroImage, vol. [sent-387, score-0.483]


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