Imaging the where and when of tic generation and resting state networks in adult Tourette patients

It is commonly assumed that functional brain connectivity reflects structural brain connectivity. The exact relationship between structure and function, however, might not be straightforward. In this review we aim to examine how our understanding of the relationship between structure and function in the 'resting' brain has advanced over the last several years. We discuss eight articles that directly compare resting-state functional connectivity with structural connectivity and three clinical case studies of patients with limited white matter connections between the cerebral hemispheres. All studies examined show largely convergent results: the strength of resting-state functional connectivity is positively correlated with structural connectivity strength. However, functional connectivity is also observed between regions where there is little or no structural connectivity, which most likely indicates functional correlations mediated by indirect structural connections (i.e. via a third region). As the methodologies for measuring structural and functional connectivity continue to improve and their complementary strengths are applied in parallel, we can expect important advances in our diagnostic and prognostic capacities in diseases like Alzheimer's, multiple sclerosis, and stroke.

Functional connectivity analyses of resting-state fMRI data are rapidly emerging as highly efficient and powerful tools for in vivo mapping of functional networks in the brain, referred to as intrinsic connectivity networks (ICNs). Despite a burgeoning literature, researchers continue to struggle with the challenge of defining computationally efficient and reliable approaches for identifying and characterizing ICNs. Independent component analysis (ICA) has emerged as a powerful tool for exploring ICNs in both healthy and clinical populations. In particular, temporal concatenation group ICA (TC-GICA) coupled with a back-reconstruction step produces participant-level resting state functional connectivity maps for each group-level component. The present work systematically evaluated the test-retest reliability of TC-GICA derived RSFC measures over the short-term (<45 min) and long-term (5-16 months). Additionally, to investigate the degree to which the components revealed by TC-GICA are detectable via single-session ICA, we investigated the reproducibility of TC-GICA findings. First, we found moderate-to-high short- and long-term test-retest reliability for ICNs derived by combining TC-GICA and dual regression. Exceptions to this finding were limited to physiological- and imaging-related artifacts. Second, our reproducibility analyses revealed notable limitations for template matching procedures to accurately detect TC-GICA based components at the individual scan level. Third, we found that TC-GICA component's reliability and reproducibility ranks are highly consistent. In summary, TC-GICA combined with dual regression is an effective and reliable approach to exploratory analyses of resting state fMRI data. Copyright (c) 2009 Elsevier Inc. All rights reserved.

Assessments of anterior cingulate cortex in experimental animals and humans have led to unifying theories of its structural organization and contributions to mammalian behaviour. The anterior cingulate cortex forms a large region around the rostrum of the corpus callosum that is termed the anterior executive region. This region has numerous projections into motor systems, however, since these projections originate from different parts of anterior cingulate cortex and because functional studies have shown that it does not have a uniform contribution to brain functions, the anterior executive region is further subdivided into 'affect' and 'cognition' components. The affect division includes areas 25, 33 and rostral area 24, and has extensive connections with the amygdala and periaqueductal grey, and parts of it project to autonomic brainstem motor nuclei. In addition to regulating autonomic and endocrine functions, it is involved in conditioned emotional learning, vocalizations associated with expressing internal states, assessments of motivational content and assigning emotional valence to internal and external stimuli, and maternal-infant interactions. The cognition division includes caudal areas 24' and 32', the cingulate motor areas in the cingulate sulcus and nociceptive cortex. The cingulate motor areas project to the spinal cord and red nucleus and have premotor functions, while the nociceptive area is engaged in both response selection and cognitively demanding information processing. The cingulate epilepsy syndrome provides important support of experimental animal and human functional imaging studies for the role of anterior cingulate cortex in movement, affect and social behaviours. Excessive cingulate activity in cases with seizures confirmed in anterior cingulate cortex with subdural electrode recordings, can impair consciousness, alter affective state and expression, and influence skeletomotor and autonomic activity. Interictally, patients with anterior cingulate cortex epilepsy often display psychopathic or sociopathic behaviours. In other clinical examples of elevated anterior cingulate cortex activity it may contribute to tics, obsessive-compulsive behaviours, and aberrent social behaviour. Conversely, reduced cingulate activity following infarcts or surgery can contribute to behavioural disorders including akinetic mutism, diminished self-awareness and depression, motor neglect and impaired motor initiation, reduced responses to pain, and aberrent social behaviour. The role of anterior cingulate cortex in pain responsiveness is suggested by cingulumotomy results and functional imaging studies during noxious somatic stimulation. The affect division of anterior cingulate cortex modulates autonomic activity and internal emotional responses, while the cognition division is engaged in response selection associated with skeletomotor activity and responses to noxious stimuli. Overall, anterior cingulate cortex appears to play a crucial role in initiation, motivation, and goal-directed behaviours.(ABSTRACT TRUNCATED AT 400 WORDS)