Gray matter associations with extinction-induced neural activation in patients with anxiety disorders

The relationship between structural characteristics and extinction-induced brain activations in anxiety disorders (ANX) remains a space for greater exploration. In this study, we assessed gray matter volume (GMV) and its associated functional activations during fear extinction memory recall in an ANX cohort. We performed voxel-based morphometry analysis to examine GMVs from ANX (n = 92) and controls (n = 73). We further examined the correlation between GMVs and extinction-induced neural activations during recall across groups. In the patients' group, we observed decreased GMV in the anterior hippocampus and increased GMV in the dorsolateral prefrontal cortex (dlPFC). Hippocampal volume was positively correlated with ventromedial prefrontal cortex activation in healthy controls, while it was negatively correlated with dorsal anterior cingulate cortex (dACC) activation in ANX. The dlPFC volume was positively correlated with activations of dACC, pre- and post-central gyrus, and supramarginal gyrus only in healthy controls. Therefore, the link between structural and functional imbalance within the hippocampus and dlPFC might contribute to the pathophysiology of ANX. In the controls, the relationship between structural variance in the hippocampus and dlPFC and extinction-induced neural activations is consistent with a greater ability to regulate fear responding; associations that were absent in the ANX cohort. Furthermore, our findings of structure-function abnormalities within key nodes of emotional homeostasis in ANX point to dlPFC as a potential neural node to target using neuromodulation tools.

Longitudinal Increases in Cerebral Brain Activation During Working Memory Performance in Friedreich Ataxia: 24-Month Data from IMAGE-FRDA

Friedreich ataxia (FRDA) has been associated with functional abnormalities in cerebral and cerebellar networks, particularly in the ventral attention network. However, how functional alterations change with disease progression remains largely unknown. Longitudinal changes in brain activation, associated with working memory performance (N-back task), and grey matter volume were assessed over 24 months in 21 individuals with FRDA and 28 healthy controls using functional and structural magnetic resonance imaging, respectively. Participants also completed a neurocognitive battery assessing working memory (digit span), executive function (Stroop, Haylings), and set-shifting (Trail Making Test). Individuals with FRDA displayed significantly increased brain activation over 24 months in ventral attention brain regions, including bilateral insula and inferior frontal gyrus (pars triangularis and pars opercularis), compared with controls, but there was no difference in working memory (N-back) performance between groups. Moreover, there were no significant differences in grey matter volume changes between groups. Significant correlations between brain activations and both clinical severity and age at disease onset were observed in FRDA individuals only at 24 months. There was significant longitudinal decline in Trail Making Test (TMT) difference score (B-A) in individuals with FRDA, compared with controls. These findings provide the first evidence of increased longitudinal activation over time in the cerebral cortex in FRDA, compared with controls, despite comparable working memory performance. This finding represents a possible compensatory response in the ventral attention network to help sustain working memory performance in individuals with FRDA.

Detection of functional networks within white matter using independent component analysis

Spontaneous fluctuations in MRI signals from gray matter (GM) in the brain are interpreted as originating from variations in neural activity, and their inter-regional correlations may be analyzed to reveal functional connectivity. However, most studies of intrinsic neuronal activity have ignored the spontaneous fluctuations that also arise in white matter (WM). In this work, we explore spontaneous fluctuations in resting state MRI signals in WM based on spatial independent component analyses (ICA), a data-driven approach that separates signals into independent sources without making specific modeling assumptions. ICA has become widely accepted as a valuable approach for identifying functional connectivity within cortex but has been rarely applied to derive equivalent structures within WM. Here, BOLD signal changes in WM of a group of subjects performing motor tasks were first detected using ICA, and a spatial component whose time course was consistent with the task was found, demonstrating the analysis is sensitive to evoked BOLD signals in WM. Secondly, multiple spatial components were derived by applying ICA to identify those voxels in WM whose MRI signals showed similar temporal behaviors in a resting state. These functionally-related structures are grossly symmetric and coincide with corresponding tracts identified from diffusion MRI. Finally, functional connectivity was quantified by calculating correlations between pairs of structures to explore the synchronicity of resting state BOLD signals across WM regions, and the experimental results revealed that there exist two distinct groupings of functional correlations in WM tracts at rest. Our study provides further insights into the nature of activation patterns, functional responses and connectivity in WM, and support previous suggestions that BOLD signals in WM show similarities with cortical activations and are characterized by distinct underlying structures in tasks and at rest.

Internalizing symptoms in intractable pediatric epilepsy: Structural and functional brain correlates

Internalizing disorders (i.e., depression and anxiety) are common comorbidities in people with epilepsy. In adults with epilepsy, comorbid depression or anxiety is associated with worse seizure control and reduced quality of life, and may be linked to specific neural biomarkers. Less is known about brain correlates of internalizing symptoms in pediatric populations. In the current study, we performed a retrospective analysis of 45 youth between the ages of 6 and 18 years old with intractable epilepsy. Individuals were evaluated for internalizing symptoms on the Child Behavior Checklist (CBCL) and underwent magnetic resonance (MR) and fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging as part of the clinical evaluation for surgical treatment of epilepsy. Forty-two percent of patients experienced clinically significant internalizing symptoms based on parent report. Compared with individuals who scored in the normal range, youth with clinical levels of internalizing problems showed overall reductions in cortex volume, as well as widespread reductions in cortical thickness and functional activation in the bilateral occipital/parietal lobe, left temporal regions, and left inferior frontal cortex on MR and PET scans. There were no group differences in amygdala or hippocampus volumes, nor other patient- or illness-related variables such as age, sex, or the type, lateralization, or duration of epilepsy. Results suggest that high rates of internalizing disorders are present in youth with refractory epilepsy. Multifocal reductions in cortical thickness and function may be nonspecific risk factors for clinically meaningful internalizing symptoms in youth with chronic epilepsy. As such, the presence of broad cortical thinning and reduced glucose uptake upon radiological examination may warrant more focused clinical evaluation of psychological symptoms.

Changes of functional response in sensorimotor cortex of preterm and full-term infants during the first year: An fNIRS study

BACKGROUND

Motor impairments are frequently associated with preterm birth and interfere in acquisition of essential skills to global development. Using Near Infrared Spectroscopy (NIRS), the study of neural correlates of motor development in early stages of life are feasible in an ecological assessment.

AIMS

To evaluate changes in cortical activity in response to a sensorimotor stimulation in preterm and full-term infants at 6 and 12 months of age.

STUDY DESIGN

A longitudinal study was conducted with 22 infants (12 preterm and 10 full-term). Hemodynamic activity during sensorimotor task (8 blocks of 8 s of vibration applied to infant's right hand) was measured by Functional Near Infrared Spectroscopy (fNIRS). The optical probe consisted of 84 channels positioned according to the international 10-20 system coordinates, covering the frontal (38 channels), parietal (16 channels), temporal (22 channels) and occipital (8 channels) lobes of both hemispheres.

RESULTS

Preterm and full-term infants exhibited differences of location of the activation as well on the hemodynamic response in both the evaluated age groups.

CONCLUSIONS

Group differences in activation of sensorimotor cortex observed in this study demonstrate the potential of fNIRS application for preterm evaluation of motor development in children. Overall, the present work contributes to our understanding of cortical activation of cerebral motor skills spanning early ages in preterm-born children.

Voxel-wise detection of functional networks in white matter

Functional magnetic resonance imaging (fMRI) depicts neural activity in the brain indirectly by measuring blood oxygenation level dependent (BOLD) signals. The majority of fMRI studies have focused on detecting cortical activity in gray matter (GM), but whether functional BOLD signal changes also arise in white matter (WM), and whether neural activities trigger hemodynamic changes in WM similarly to GM, remain controversial, particularly in light of the much lower vascular density in WM. However, BOLD effects in WM are readily detected under hypercapnic challenges, and the number of reports supporting reliable detections of stimulus-induced activations in WM continues to grow. Rather than assume a particular hemodynamic response function, we used a voxel-by-voxel analysis of frequency spectra in WM to detect WM activations under visual stimulation, whose locations were validated with fiber tractography using diffusion tensor imaging (DTI). We demonstrate that specific WM regions are robustly activated in response to visual stimulation, and that regional distributions of WM activation are consistent with fiber pathways reconstructed using DTI. We further examined the variation in the concordance between WM activation and fiber density in groups of different sample sizes, and compared the signal profiles of BOLD time series between resting state and visual stimulation conditions in activated GM as well as activated and non-activated WM regions. Our findings confirm that BOLD signal variations in WM are modulated by neural activity and are detectable with conventional fMRI using appropriate methods, thus offering the potential of expanding functional connectivity measurements throughout the brain.

Functional NIRS Measurement of Cytochrome-C-Oxidase Demonstrates a More Brain-Specific Marker of Frontal Lobe Activation Compared to the Haemoglobins

Functional near-infrared spectroscopy (fNIRS) is an increasingly common neuromonitoring technique used to observe evoked haemodynamic changes in the brain in response to a stimulus. The measurement is typically in terms of concentration changes of oxy- (∆HbO₂) and deoxy- (∆HHb) haemoglobin. However, noise from systemic fluctuations in the concentration of these chromophores can contaminate stimulus-evoked haemodynamic responses, leading to misinterpretation of results. Short-separation channels can be used to regress out extracerebral haemodynamics to better reveal cerebral changes, significantly improving the reliability of fNIRS. Broadband NIRS can be used to additionally monitor concentration changes of the oxidation state of cytochrome-c-oxidase (∆oxCCO). Recent studies have shown ∆oxCCO to be a depth-dependent and hence brain-specific signal. This study aims to investigate whether ∆oxCCO can produce a more robust marker of functional activation. Continuous frontal lobe NIRS measurements were collected from 17 healthy adult volunteers. Short 1 cm source-detector separation channels were regressed from longer separation channels in order to minimise the extracerebral contribution to standard fNIRS channels. Significant changes in ∆HbO₂ and ∆HHb were seen at 1 cm channels but were not observed in ∆oxCCO. An improvement in the haemodynamic signals was achieved with regression of the 1 cm channel. Broadband NIRS-measured concentration changes of the oxidation state of cytochrome-c-oxidase has the potential to be an alternative and more brain-specific marker of functional activation.

A validation study of the use of near-infrared spectroscopy imaging in primary and secondary motor areas of the human brain

The electroencephalographically measured Bereitschafts (readiness)-potential in the supplementary motor area (SMA) serves as a signature of the preparation of motor activity. Using a multichannel, noninvasive near-infrared spectroscopy (NIRS) imager, we studied the vascular correlate of the readiness potential. Sixteen healthy subjects performed a self-paced or externally triggered motor task in a single or repetitive pattern, while NIRS simultaneously recorded the task-related responses of deoxygenated hemoglobin (HbR) in the primary motor area (M1) and the SMA. Right-hand movements in the repetitive sequence trial elicited a significantly greater HbR response in both the SMA and the left M1 compared to left-hand movements. During the single sequence condition, the HbR response in the SMA, but not in the M1, was significantly greater for self-paced than for externally cued movements. Nonetheless, an unequivocal temporal delay was not found between the SMA and M1. Near-infrared spectroscopy is a promising, noninvasive bedside tool for the neuromonitoring of epileptic seizures or cortical spreading depolarizations (CSDs) in patients with epilepsy, stroke, or brain trauma because these pathological events are associated with typical spatial and temporal changes in HbR. Propagation is a characteristic feature of these events which importantly supports their identification and characterization in invasive recordings. Unfortunately, the present noninvasive study failed to show a temporal delay during self-paced movements between the SMA and M1 as a vascular correlate of the readiness potential. Although this result does not exclude, in principle, the possibility that scalp-NIRS can detect a temporal delay between different regions during epileptic seizures or CSDs, it strongly suggests that further technological development of NIRS should focus on both improved spatial and temporal resolution. This article is part of a Special Issue entitled Status Epilepticus.

Somatosensory evoked changes in cerebral oxygen consumption measured non-invasively in premature neonates

The hemodynamic functional response is used as a reliable marker of neuronal activity in countless studies of brain function and cognition. In newborns and infants, however, conflicting results have appeared in the literature concerning the typical response, and there is little information on brain metabolism and functional activation. Measurement of all hemodynamic components and oxygen metabolism is critical for understanding neurovascular coupling in the developing brain. To this end, we combined multiple near infrared spectroscopy techniques to measure oxy- and deoxy-hemoglobin concentrations, cerebral blood volume (CBV), and relative cerebral blood flow (CBF) in the somatosensory cortex of 6 preterm neonates during passive tactile stimulation of the hand. By combining these measures we estimated relative changes in the cerebral metabolic rate of oxygen consumption (rCMRO2). CBF starts increasing immediately after stimulus onset, and returns to baseline before blood volume. This is consistent with the model of pre-capillary arteriole active dilation driving the CBF response, with a subsequent CBV increase influenced by capillaries and veins dilating passively to accommodate the extra blood. rCMRO2 estimated using the steady-state formulation shows a biphasic pattern: an increase immediately after stimulus onset, followed by a post-stimulus undershoot due to blood flow returning faster to baseline than oxygenation. However, assuming a longer mean transit time from the arterial to the venous compartment, due to the immature vascular system of premature infants, reduces the post-stimulus undershoot and increases the flow/consumption ratio to values closer to adult values reported in the literature. We are the first to report changes in local rCBF and rCMRO2 during functional activation in preterm infants. The ability to measure these variables in addition to hemoglobin concentration changes is critical for understanding neurovascular coupling in the developing brain, and for using this coupling as a reliable functional imaging marker in neonates.