Fabrice Crivello

Automated Anatomical Labeling of Activations in SPM Using a Macroscopic Anatomical Parcellation of the MNI MRI Single-Subject Brain

An anatomical parcellation of the spatially normalized single-subject high-resolution T1 volume provided by the Montreal Neurological Institute (MNI) (D. L. Collins et al., 1998, Trans. Med. Imag. 17, 463-468) was performed. The MNI single-subject main sulci were first delineated and further used as landmarks for the 3D definition of 45 anatomical volumes of interest (AVOI) in each hemisphere. This procedure was performed using a dedicated software which allowed a 3D following of the sulci course on the edited brain. Regions of interest were then drawn manually with the same software every 2 mm on the axial slices of the high-resolution MNI single subject. The 90 AVOI were reconstructed and assigned a label. Using this parcellation method, three procedures to perform the automated anatomical labeling of functional studies are proposed: (1) labeling of an extremum defined by a set of coordinates, (2) percentage of voxels belonging to each of the AVOI intersected by a sphere centered by a set of coordinates, and (3) percentage of voxels belonging to each of the AVOI intersected by an activated cluster. An interface with the Statistical Parametric Mapping package (SPM, J. Ashburner and K. J. Friston, 1999, Hum. Brain Mapp. 7, 254-266) is provided as a freeware to researchers of the neuroimaging community. We believe that this tool is an improvement for the macroscopical labeling of activated area compared to labeling assessed using the Talairach atlas brain in which deformations are well known. However, this tool does not alleviate the need for more sophisticated labeling strategies based on anatomical or cytoarchitectonic probabilistic maps.

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.

Evaluation of the dual route theory of reading: a metanalysis of 35 neuroimaging studies

Numerous studies concerned with cerebral structures underlying word reading have been published during the last decade. A few controversies, however, together with methodological or theoretical discrepancies between laboratories, still contribute to blurring the overall view of advances effected in neuroimaging. Carried out within the dual route of reading framework, the aim of this metanalysis was to provide an objective picture of these advances. To achieve this, we used an automated analysis method based on the inventory of activation peaks issued from word or pseudoword reading contrasts of 35 published neuroimaging studies. A first result of this metanalysis was that no cluster of activations has been found more recruited by word than pseudoword reading, implying that the first steps of word access may be common to word and word-like stimuli and would take place within a left occipitotemporal region (previously referred to as the Visual Word Form Area-VWFA) situated in the ventral route, at the junction between inferior temporal and fusiform gyri. The results also indicated the existence of brain regions predominantly involved in one of the two routes to access word. The graphophonological conversion seems indeed to rely on left lateralized brain structures such as superior temporal areas, supramarginal gyrus, and the opercular part of the inferior frontal gyrus, these last two regions reflecting a greater load in working memory during such an access. The lexicosemantic route is thought to arise from the coactivation of the VWFA and semantic areas. These semantic areas would encompass a basal inferior temporal area, the posterior part of the middle temporal gyrus, and the triangular part of inferior frontal gyrus. These results confirm the suitability of the dual route framework to account for activations observed in nonpathological subjects while they read.

Neural Correlates of Simple and Complex Mental Calculation

Some authors proposed that exact mental calculation is based on linguistic representations and relies on the perisylvian language cortices, while the understanding of proximity relations between numerical quantities implicates the parietal cortex. However, other authors opposed developmental arguments to suggest that number sense emerges from nonspecific visuospatial processing areas in the parietal cortex. Within this debate, the present study aimed at revealing the functional anatomy of the two basic resolution strategies involved in mental calculation, namely arithmetical fact retrieval and actual computation, questioning in particular the respective role of language and/or visuospatial cerebral areas. Regional cerebral blood flow was measured with positron emission tomography while subjects were at rest (Rest), read digits (Read), retrieved simple arithmetic facts from memory (i.e., 2 x 4, Retrieve), and performed mental complex calculation (i.e., 32 x 24, Compute). Compared to Read, Retrieve engaged a left parieto-premotor circuit representing a developmental trace of a finger-counting representation that mediates, by extension, the numerical knowledge in adult. Beside this basic network, Retrieve involved a naming network, including the left anterior insula and the right cerebellar cortex, while it did not engage the perisylvian language areas, which were deactivated as compared to Rest. In addition to this retrieval network, Compute specifically involved two functional networks: a left parieto-frontal network in charge of the holding of the multidigit numbers in visuospatial working memory and a bilateral inferior temporal gyri related to the visual mental imagery resolution strategy. Overall, these results provide strong evidence of the involvement of visuospatial representations in different levels of mental calculation.

Neural correlates of woman face processing by 2-month-old infants.

The age of 2 months marks a turn in the development of face processing in humans with the emergence of recognition based on internal feature configuration. We studied the neural bases of this early cognitive expertise, critical for adaptive behavior in the social world, by mapping with positron emission tomography the brain activity of 2-month-old alert infants while looking at unknown woman faces. We observed the activation of a distributed network of cortical areas that largely overlapped the adult face-processing network, including the so-called fusiform face area. We also evidenced the activation of left superior temporal and inferior frontal gyri, regions associated, in adults, with language processing. These findings demonstrates that cognitive development proceeds early in functionally active interconnected cortical areas despite the fact they have not all yet reached full metabolic maturation.

Functional anatomy of human auditory attention studied with PET.

Positron emission tomography was used to investigate the functional anatomy of selective auditory attention in 17 right-handed male volunteers who submitted to different tasks: silent rest (REST) listening to frequent low- or rare high-pitched tones (LIS) delivered randomly to the right or the left ear, selective auditory attention where subjects had to attend to deviants in one ear, right (ATTR) or left (ATTL). Six subjects had the series REST, LIS, ATTR twice, eight subjects the series REST, LIS, ATTL, and the last three subjects the sereis REST, ATTR, ATTL. Event-related potentials were simultaneously recorded with PET and showed significant task and electrode site effects on the N100 amplitude. When compared to REST, LIS elicited bilateral temporal activations of the Heschls gyri and the planum temporale, with a significant rightward asymmetry, and of the posterior part of the superior temporal gyrus. Significant right precentral and anterior cingulate gyri normalized regional cerebral blood flow increases were observed in the frontal lobe. Both the ATTR and the ATTL conditions, compared to LIS, activated the supplementary motor area, bilateral precentral, and left postcentral cortices without any temporal cortex activation. In addition, the ATTL condition resulted in a right prefrontal cortex activation. Pooling the 14 subjects revealed an asymmetry in the superior temporal gyrus favoring the cortex contralateral to the attended ear. Two major networks seem thus to be involved during selective auditory attention: (1) a local temporal network, on which selective attention produces a modulation of the functional lateralization, and (2) a frontal network that could mediate the temporal cortex modulation by attention.

Functional anatomy of dominance for speech comprehension in left handers vs right handers.

In order to study the functional anatomy of hemispheric dominance for language comprehension we compared the patterns of activations and deactivations with PET and H(2)15O during a story-listening task in two groups of normal volunteers selected on the basis of their handedness. The reference task was a silent rest. The results showed asymmetrical temporal activations favoring the left hemisphere in right handers (RH) together with Brocas area and medial frontal activations. A rightward lateralization of deactivations located in the parietal and inferior temporal gyrus was also observed. In left handers (LH) the temporal activations were more symmetrical as were the parietal and inferior frontal deactivations. Brocas area and medial frontal gyrus activations were present in LH. The direct comparison of RH and LH activations revealed larger activations in the left superior temporal, in particular in the left planum temporale and temporal pole of RH, while LH activated an additional right middle temporal region. Individual analysis of LH differences images superimposed on individual MRI planes demonstrated an important variability of functional dominance, with two LH leftward lateralized, two symmetrical, and one showing a rightward lateralization of temporal activations. There was no relationship between functional dominance and handedness scores. These results are in accordance with data from aphasiology that suggest a greater participation of the right hemisphere in language processing in LH. In addition, the presence of bilateral deactivations of the dorsal route could support the assumption that LH ambilaterality concerns, in addition to language, other cognitive functions such as visuospatial processing.

Mental calculation in a prodigy is sustained by right prefrontal and medial temporal areas

Calculating prodigies are individuals who are exceptional at quickly and accurately solving complex mental calculations. With positron emission tomography (PET), we investigated the neural bases of the cognitive abilities of an expert calculator and a group of non-experts, contrasting complex mental calculation to memory retrieval of arithmetic facts. We demonstrated that calculation expertise was not due to increased activity of processes that exist in non-experts; rather, the expert and the non-experts used different brain areas for calculation. We found that the expert could switch between short-term effort-requiring storage strategies and highly efficient episodic memory encoding and retrieval, a process that was sustained by right prefrontal and medial temporal areas.

Comparison of spatial normalization procedures and their impact on functional maps

The alignment accuracy and impact on functional maps of four spatial normalization procedures have been compared using a set of high resolution brain MRIs and functional PET volumes acquired in 20 subjects. Simple affine (AFF), fifth order polynomial warp (WRP), discrete cosine basis functions (SPM), and a movement model based on full multi grid (FMG) approaches were applied on the same dataset for warping individual volumes onto the Human Brain Atlas (HBA) template. Intersubject averaged structural volumes and tissue probability maps were compared across normalization methods and to the standard brain. Thanks to the large number of degrees of freedom of the technique, FMG was found to provide enhanced alignment accuracy as compared to the other three methods, both for the grey and white matter tissues; WRP and SPM exhibited very similar performances whereas AFF had the lowest registration accuracy. SPM, however, was found to perform better than the other methods for the intra‐cerebral cerebrospinal fluid (mainly in the ventricular compartments). Limited differences in terms of activation morphology and detection sensitivity were found between low resolution functional maps (FWHM ∼10 mm) spatially normalized with the four methods, which overlapped in 42.8% of the total activation volume. These findings suggest that the functional variability is much larger than the anatomical one and that precise alignment of anatomical features has low influence on the resulting intersubject functional maps. When increasing the spatial resolution to approximately 6 mm, however, differences in localization of activated areas appear as a consequence of the different spatial normalization procedure used, restricting the overlap of the normalized activated volumes to only 6.2%. Hum. Brain Mapping 16:228–250, 2002.

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.