Marc Joliot

Cortical networks for working memory and executive functions sustain the conscious resting state in man

The cortical anatomy of the conscious resting state (REST) was investigated using a meta-analysis of nine positron emission tomography (PET) activation protocols that dealt with different cognitive tasks but shared REST as a common control state. During REST, subjects were in darkness and silence, and were instructed to relax, refrain from moving, and avoid systematic thoughts. Each protocol contrasted REST to a different cognitive task consisting either of language, mental imagery, mental calculation, reasoning, finger movement, or spatial working memory, using either auditory, visual or no stimulus delivery, and requiring either vocal, motor or no output. A total of 63 subjects and 370 spatially normalized PET scans were entered in the meta-analysis. Conjunction analysis revealed a network of brain areas jointly activated during conscious REST as compared to the nine cognitive tasks, including the bilateral angular gyrus, the left anterior precuneus and posterior cingulate cortex, the left medial frontal and anterior cingulate cortex, the left superior and medial frontal sulcus, and the left inferior frontal cortex. These results suggest that brain activity during conscious REST is sustained by a large scale network of heteromodal associative parietal and frontal cortical areas, that can be further hierarchically organized in an episodic working memory parieto-frontal network, driven in part by emotions, working under the supervision of an executive left prefrontal network.

Mapping numerical processing, reading, and executive functions in the developing brain: an fMRI meta‐analysis of 52 studies including 842 children

Tracing the connections from brain functions to childrens cognitive development and education is a major goal of modern neuroscience. We performed the first meta-analysis of functional magnetic resonance imaging (fMRI) data obtained over the past decade (1999-2008) on more than 800 children and adolescents in three core systems of cognitive development and school learning: numerical abilities, reading, and executive functions (i.e. cognitive control). We ran Activation Likelihood Estimation (ALE) meta-analyses to obtain regions of reliable activity across all the studies. The results indicate that, unlike results usually reported for adults, children primarily engage the frontal cortex when solving numerical tasks. With age, there may be a shift from reliance on the frontal cortex to reliance on the parietal cortex. In contrast, the frontal, temporo-parietal and occipito-temporal regions at work during reading in children are very similar to those reported in adults. The executive frontal regions are also consistent with the imaging literature on cognitive control in adults, but the developmental comparison between children and adolescents demonstrates a key role of the anterior insular cortex (AIC) with an additional right AIC involvement in adolescents.

The resting state questionnaire: An introspective questionnaire for evaluation of inner experience during the conscious resting state

We designed a semi-structured questionnaire for the introspective evaluation of inner experience of participants undergoing functional magnetic resonance imaging (fMRI) in the resting state. This resting state questionnaire (ReSQ) consists of 62 items organized by five main types of mental activity: visual mental imagery (IMAG); inner language (LANG), split into two subtypes, inner speech (SPEE) and auditory mental imagery (AUDI); somatosensory awareness (SOMA); inner musical experience (MUSI); and mental manipulation of numbers (NUMB). For IMAG and LANG, additional questions estimated association of such activities with ongoing learning, retrospective memories, or prospective thoughts. Using a 0-100% scale, the participant quantitatively rated the proportion of time spent in each mental activity during the resting state fMRI acquisition. A total of 180 healthy volunteers completed the ReSQ immediately after being scanned with fMRI while at rest. Of these, 66% exhibited dominance of a type of mental activity at rest (IMAG: 35%; LANG: 17%; SOMA: 7%; MUSI: 6%; NUMB: 1%). A majority of participants reported either retrospective memories (82%) or prospective thoughts (78%), with 58% of participants reporting both in at least one type of mental activity. Thoughts related to ongoing learning were low (37% of participants). The present results are consistent with those of previous studies investigating inner experience in a natural environment. In conclusion, we provide a robust and easy-to-implement tool for the exploration of mental activities during rest of healthy participants undergoing fMRI. This tool relies on normative data acquired from a 180-participant sample balanced for sex and handedness.

Gaussian Mixture Modeling of Hemispheric Lateralization for Language in a Large Sample of Healthy Individuals Balanced for Handedness

Hemispheric lateralization for language production and its relationships with manual preference and manual preference strength were studied in a sample of 297 subjects, including 153 left-handers (LH). A hemispheric functional lateralization index (HFLI) for language was derived from fMRI acquired during a covert sentence generation task as compared with a covert word list recitation. The multimodal HFLI distribution was optimally modeled using a mixture of 3 and 4 Gaussian functions in right-handers (RH) and LH, respectively. Gaussian function parameters helped to define 3 types of language hemispheric lateralization, namely “Typical” (left hemisphere dominance with clear positive HFLI values, 88% of RH, 78% of LH), “Ambilateral” (no dominant hemisphere with HFLI values close to 0, 12% of RH, 15% of LH) and “Strongly-atypical” (right-hemisphere dominance with clear negative HFLI values, 7% of LH). Concordance between dominant hemispheres for hand and for language did not exceed chance level, and most of the association between handedness and language lateralization was explained by the fact that all Strongly-atypical individuals were left-handed. Similarly, most of the relationship between language lateralization and manual preference strength was explained by the fact that Strongly-atypical individuals exhibited a strong preference for their left hand. These results indicate that concordance of hemispheric dominance for hand and for language occurs barely above the chance level, except in a group of rare individuals (less than 1% in the general population) who exhibit strong right hemisphere dominance for both language and their preferred hand. They call for a revisit of models hypothesizing common determinants for handedness and for language dominance.

Atypical hemispheric specialization for language in right-handed schizophrenia patients.

BACKGROUNDnThe literature suggests that schizophrenia could be related to a failure in the setting up of left hemisphere dominance for language. We sought to determine hemispheric specialization for language in schizophrenic patients, using functional magnetic resonance imaging.nnnMETHODSnTwenty-one right-handed patients with DSM-IV schizophrenia and 21 right-handed control subjects matched by age, gender, and level of education were recruited. Fractional blood oxygen level dependent (BOLD) signal variations in anatomic regions of interest were compared between groups. Functional asymmetry indices (FAIs) were calculated in a region (LANG) resulting from the merging of activated regions showing a Group x Hemisphere interaction. The FAI difference between each patient and their matched control subject was computed.nnnRESULTSnWe found lower BOLD signal changes in patients as compared with their control subjects in a network comprising areas of the left middle temporal gyrus, the left angular gyrus, and the pars triangularis of the left inferior frontal gyrus, merged to constitute LANG. The intra-pair differences of FAIs in this area showed that 76% of the patients exhibited less leftward functional asymmetry than their matched control subjects, including six patients with a rightward asymmetry.nnnCONCLUSIONSnThese results demonstrated the existence of an anomaly in left hemisphere specialization for language in schizophrenic subjects.

Patterns of hemodynamic low-frequency oscillations in the brain are modulated by the nature of free thought during rest

During conscious rest, the mind switches into a state of wandering. Although this rich inner experience occupies a large portion of the time spent awake, how it relates to brain activity has not been well explored. Here, we report the results of a behavioral and functional magnetic resonance imaging (fMRI) study of the continuous resting state in 307 healthy participants. The analysis focused on the relationship between the nature of inner experience and the temporal correlations computed between the low-frequency blood oxygen level-dependent (BOLD) fluctuations (0.01-0.1 Hz) of five large-scale modules. The subjects self-reported time spontaneously spent on visual mental imagery and/or inner language was used as the behavioral variable. Decreased temporal correlations between modules were revealed when subjects reported more time spent thinking in mental images and inner language. These changes segregated the three modules supporting inner-oriented activities from those associated with sensory-related and externally guided activities. Among the brain areas associated with inner-oriented processing, the module including the lateral parietal and frontal regions (commonly described as being engaged in the manipulation and maintenance of internal information) was implicated in the majority of these effects. The preponderance of segregation appears to be the signature of the spontaneous sequence of thoughts during rest that are not constrained by logic, causality, or even a rigorous temporal organization. In other words, though goal-directed tasks have been demonstrated to rely on specific regional integration, mind wandering can be characterized by widespread modular segregation. Overall, the present study provides evidence that modulation of spontaneous low-frequency fluctuations in the brain is at least partially explained by spontaneous conscious cognition while at rest.

FMRI and PET of Self-Paced Finger Movement: Comparison of Intersubject Stereotaxic Averaged Data ☆

We compared the intersubject-averaged functional anatomy of self-paced right index finger movement as revealed by (15)O water positron emission tomography (PET) and blood oxygen level-dependent functional magnetic resonance imaging (FMRI) at 1.5 T. Image data sets were acquired with both techniques on a group of eight subjects, spatially normalized in the stereotaxic space and subsequently processed in order to get identical smoothness and degrees of freedom. Intersubject-averaged PET and FMRI activation maps were found congruent in the left primary sensorimotor area (PSM), bilateral supplementary motor area, bilateral supra marginalis gyri, left operculum, left inferior parietal lobule, right middle frontal gyrus, and right cerebellum. In those regions the mean distance between PET and FMRI local maxima was 7.4 mm. FMRI detected additional activations in the right precentral gyrus, right rolandic operculum, right inferior parietal lobule, and bilateral insula, whereas PET demonstrated a higher detection sensitivity at the deep nuclei level. PET and FMRI percentage signal variations were found linearly related by a factor around 10, both within the PSM and across a set of distributed local extrema. However, in most cases, FMRI was more sensitive than PET, as assessed by t values. Finally the pattern of deactivations was markedly dissimilar between the two techniques, possibly due to differences in the Rest control task.

Effect of Familial Sinistrality on Planum Temporale Surface and Brain Tissue Asymmetries

The impact of having left-handers (LHs) among ones close relatives, called familial sinistrality (FS), on neuroanatomical markers of left-hemisphere language specialization was studied in 274 normal adults, including 199 men and 75 women, among whom 77 men and 27 women were positive for FS. Measurements of the surface of a phonological cortical area, the planum temporale (PT), and gray and white matter hemispheric volumes and asymmetries were made using brain magnetic resonance images. The size of the left PT of subjects with left-handed close relatives (FS+) was reduced by 10%, decreasing with the number of left-handed relatives, and lowest when the subjects mother was left-handed. Such findings had no counterparts in the right hemisphere, and the subjects handedness and sex were found to have no significant effect or interaction with FS on the left PT size. The FS+ subjects also exhibited increased gray matter volume, reduced hemispheric gray matter leftward asymmetry, and, in LHs, reduced strength of hand preference. These results add to the increasing body of evidence suggesting multiple and somewhat independent mechanisms for the inheritance of hand and language lateralization.

Descriptive anatomy of Heschl's gyri in 430 healthy volunteers, including 198 left-handers.

This study describes the gyrification patterns and surface areas of Heschl’s gyrus (HG) in 430 healthy volunteers mapped with magnetic resonance imaging. Among the 232 right-handers, we found a large occurrence of duplication (64xa0%), especially on the right (49 vs. 37xa0% on the left). Partial duplication was twice more frequent on the left than complete duplication. On the opposite, in the right hemisphere, complete duplication was 10xa0% more frequent than partial duplication. The most frequent inter-hemispheric gyrification patterns were bilateral single HG (36xa0%) and left single-right duplication (27xa0%). The least common patterns were left duplication-right single (22xa0%) and bilateral duplication (15xa0%). Duplication was associated with decreased anterior HG surface area on the corresponding side, independently of the type of duplication, and increased total HG surface area (including the second gyrus). Inter-hemispheric gyrification patterns strongly influenced both anterior and total HG surface area asymmetries, leftward asymmetry of the anterior HG surface was observed in all patterns except double left HG, and total HG surface asymmetry favored the side of duplication. Compared to right-handers, the 198 left-handers exhibited lower occurrence of duplication, and larger right anterior HG surface and total HG surface areas. Left-handers’ HG surface asymmetries were thus significantly different from those of right-handers, with a loss of leftward asymmetry of their anterior HG surface, and with significant rightward asymmetry of their total HG surface. In summary, gyrification patterns have a strong impact on HG surface and asymmetry. The observed reduced lateralization of HG duplications and anterior HG asymmetry in left-handers highlights HG inter-hemispheric gyrification patterns as a potential candidate marker of speech lateralization.

AICHA: An atlas of intrinsic connectivity of homotopic areas.

BACKGROUNDnAtlases of brain anatomical ROIs are widely used for functional MRI data analysis. Recently, it was proposed that an atlas of ROIs derived from a functional brain parcellation could be advantageous, in particular for understanding how different regions share information. However, functional atlases so far proposed do not account for a crucial aspect of cerebral organization, namely homotopy, i.e. that each region in one hemisphere has a homologue in the other hemisphere.nnnNEW METHODnWe present AICHA (for Atlas of Intrinsic Connectivity of Homotopic Areas), a functional brain ROIs atlas based on resting-state fMRI data acquired in 281 individuals. AICHA ROIs cover the whole cerebrum, each having 1-homogeneity of its constituting voxels intrinsic activity, and 2-a unique homotopic contralateral counterpart with which it has maximal intrinsic connectivity. AICHA was built in 4 steps: (1) estimation of resting-state networks (RSNs) using individual resting-state fMRI independent components, (2) k-means clustering of voxel-wise group level profiles of connectivity, (3) homotopic regional grouping based on maximal inter-hemispheric functional correlation, and (4) ROI labeling.nnnRESULTSnAICHA includes 192 homotopic region pairs (122 gyral, 50 sulcal, and 20 gray nuclei). As an application, we report inter-hemispheric (homotopic and heterotopic) and intra-hemispheric connectivity patterns at different sparsities.nnnCOMPARISON WITH EXISTING METHODnROI functional homogeneity was higher for AICHA than for anatomical ROI atlases, but slightly lower than for another functional ROI atlas not accounting for homotopy.nnnCONCLUSIONnAICHA is ideally suited for intrinsic/effective connectivity analyses, as well as for investigating brain hemispheric specialization.