Journal - Brain research bulletin (United States )

Abstract :

Positron tomography was used to investigate modulations of brain activity during the so-called resting state that may occur due to a concurrent cognitive training. Twelve subjects were repeatedly scanned during resting periods and while solving logical problems containing a bias causing them to make reasoning errors. At experiment mid-time, eight subjects were trained to inhibit the reasoning bias so that their performance in solving logical problems dramatically increased afterwards, while the other four subjects were trained to logical reasoning only which did not help improving their performance. In the subgroup of subjects who increased their performance after training, we found that during the post-training resting periods, as compared to pre-training resting periods, brain activity increases in areas not belonging to the classical resting network, namely the midbrain, thalamus, peristriate, inferior frontal, and ventromedial prefrontal cortices. Strikingly, in this subgroup of subjects, these same areas were found to be also more active during post-training successful execution of the logical task, as compared to pre-training erroneous execution of the task. Such findings were not observed in the subgroup of subjects who did not improve their performance after training to logic only. These results indicate that the brain default mode is a dynamic state during which context dependent local increases of cerebral blood flow may occur on a short-term, likely for the consolidation of newly acquired knowledge.

Journal - Human brain mapping (United States )

Journal - Neuroreport (England )

Abstract :

A classical developmental model for the left hemisphere specialization for language has been proposed based on the observation of a positive correlation coefficient between the value of an index of asymmetry between the left and right planum temporale surface areas and the size of the right planum temporale. Here, we demonstrate that such correlation is a mathematical artefact and thus should not serve as a basis for establishing models of language hemispheric dominance.

Journal - Brain research bulletin (United States )

Abstract :

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.

Journal - Philosophical Transactions of the Royal Society B: Biological Sciences

Abstract :

Motivated by the vast amount of information that is rapidlyaccumulating about the human brain in digital form, we embarkedupon a program in 1992 to develop a four–dimensional probabilisticatlas and reference system for the human brain. Through an InternationalConsortium for Brain Mapping (ICBM) a dataset is being collectedthat includes 7000 subjects between the ages of eighteen andninety years and including 342 mono– and dizygotic twins.Data on each subject includes detailed demographic, clinical,behavioural and imaging information. DNA has been collectedfor genotyping from 5800 subjects. A component of the programmeuses post–mortem tissue to determine the probabilisticdistribution of microscopic cyto– and chemoarchitecturalregions in the human brain. This, combined with macroscopicinformation about structure and function derived from subjectsin vivo, provides the first large scale opportunity to gainmeaningful insights into the concordance or discordance in micro–and macroscopic structure and function. The philosophy, strategy,algorithm development, data acquisition techniques and validationmethods are described in this report along with database structures.Examples of results are described for the normal adult humanbrain as well as examples in patients with Alzheimer's diseaseand multiple sclerosis. The ability to quantify the varianceof the human brain as a function of age in a large populationof subjects for whom data is also available about their geneticcomposition and behaviour will allow for the first assessmentof cerebral genotype–phenotype–behavioural correlationsin humans to take place in a population this large. This approachand its application should provide new insights and opportunitiesfor investigators interested in basic neuroscience, clinicaldiagnostics and the evaluation of neuropsychiatric disordersin patients.