Conceptual disorganization and redistribution of resting-state cortical hubs in untreated first-episode psychosis: A 7T study

Network-level dysconnectivity has been studied in positive and negative symptoms of schizophrenia. Conceptual disorganization (CD) is a symptom subtype that predicts impaired real-world functioning in psychosis. Systematic reviews have reported aberrant connectivity in formal thought disorder, a construct related to CD. However, no studies have investigated whole-brain functional correlates of CD in psychosis. We sought to investigate brain regions explaining the severity of CD in patients with first-episode psychosis (FEPs) compared with healthy controls (HCs). We computed whole-brain binarized degree centrality maps of 31 FEPs, 25 HCs, and characterized the patterns of network connectivity in the 2 groups. In FEPs, we related these findings to the severity of CD. We also studied the effect of positive and negative symptoms on altered network connectivity. Compared to HCs, reduced centrality of a right superior temporal gyrus (rSTG) cluster was observed in the FEPs. In patients exhibiting high CD, increased centrality of a medial superior parietal (mSPL) cluster was observed, compared to patients exhibiting low CD. This cluster was strongly correlated with CD scores but not with other symptom scores. Our observations are congruent with previous findings of reduced but not increased centrality. We observed increased centrality of mSPL suggesting that cortical reorganization occurs to provide alternate routes for information transfer. These findings provide insight into the underlying neural processes mediating the presentation of symptoms in untreated FEP. Longitudinal tracking of the symptom course will be useful to assess the mechanisms underlying these compensatory changes.

Sahaj Samadhi meditation vs a Health Enhancement Program in improving late-life depression severity and executive function: study protocol for a two-site, randomized controlled trial

Background

Recent estimates suggest an 11% prevalence of current late-life depression (LLD) and a lifetime prevalence of 16–20%. LLD leads to cognitive disturbance as well as a nearly two to three times increased risk of dementia. We conducted a recent randomized controlled trial (RCT) which demonstrated that Sahaj Samadhi meditation (SSM), an easy-to-implement, meditation-based augmentation strategy, led to higher rates of symptom remission when compared to treatment as usual (40.0 vs 16.3%; odds ratio, 3.36; 95% CI 1.06–10.64; p = 0.040). Here we present a protocol describing a two-site, blinded, RCT, comparing an SSM arm to an active-control arm – a Health Enhancement Program (HEP) intervention – in their ability to reduce depressive symptoms and improve executive functioning, among several other exploratory outcomes.

Methods/design

One hundred and ninety-two (n = 192) participants with LLD will be recruited at two sites (London, ON, Canada, and Montreal, QC, Canada). Participants will undergo stratified randomization with regards to site and the presence of treatment-resistant-LLD (TR-LLD) or not, to either SSM or HEP. We will assess change in (1) depression severity using the Hamilton Depression Rating Scale (HAM-D), (2) executive functioning, and (3) other exploratory physiological and mood-based measures, at baseline (0 weeks), post intervention (12 weeks), and 26 weeks after baseline. Raters, clinicians, and care providers will be blinded to group allocation while participants will be blinded to the study hypotheses.

Discussion

This study should more definitively assess whether SSM can be used as an augmentation strategy in routine clinical care for patients suffering from LLD and TR-LLD. If the effects of SSM are significantly better than HEP, it will offer support for the routine use of this intervention to manage LLD/TR-LLD and comorbid declines in executive dysfunction. The results of this study could also inform whether SSM can improve/prevent cognitive decline in LLD.

Trial registration

ClinicalTrials.gov, ID: NCT03564041. Registered on 20 June 2018.

Association between muscle hydration measures acquired using bioelectrical impedance spectroscopy and magnetic resonance imaging in healthy and hemodialysis population

Establishing the effect of fluctuating extracellular fluid (ECF) volume on muscle strength in people with end-stage renal disease (ESRD) on hemodialysis (HD) is essential, as inadequate hydration of the skeletal muscles impacts its strength and endurance. Bioelectrical impedance spectroscopy (BIS) has been a widely used method for estimating ECF volume of a limb or calf segment. Magnetic resonance imaging (MRI)-acquired transverse relaxation times (T2) has also been used for estimating ECF volumes of individual skeletal muscles. The purpose of this study was to determine the association between T2 (gold standard) of tibialis anterior (TA), medial (MG), and lateral gastrocnemius (LG), and soleus muscles and calf BIS ECF, in healthy and in people with ESRD/HD. Calf BIS and MRI measures were collected on two occasions before and after HD session in people with ESRD/HD and on a single occasion for the healthy participants. Linear regression analysis was used to establish the association between these measures. Thirty-two healthy and 22 participants on HD were recruited. The association between T2 of TA, LG, MG, and soleus muscles and ratio of calf BIS-acquired ECF and intracellular fluids (ICF) were: TA: β = 0.30, P > 0.05; LG: β = 0.37, P = 0.035; MG: β = 0.43, P = 0.014; soleus: β = 0.60, P < 0.001. For the HD group, calf ECF was significantly associated with T2 of TA (β = 0.44, P = 0.042), and medial gastrocnemius (β = 0.47, P = 0.027) following HD only. Hence BIS-acquired measures cannot be used to measure ECF volumes of a single muscle in the ESRD/HD population; however, BIS could be utilized to estimate ratio of ECF: ICF in healthy population for the LG, MG, and soleus muscles.

In vivo normative atlas of the hippocampal subfields using multi-echo susceptibility imaging at 7 Tesla

OBJECTIVES

To generate a high-resolution atlas of the hippocampal subfields using images acquired from 7 T, multi-echo, gradient-echo MRI for the evaluation of epilepsy and neurodegenerative disorders as well as investigating R2* (apparent transverse relaxation rate) and quantitative volume magnetic susceptibility (QS) of the subfields.

EXPERIMENTAL DESIGN

Healthy control subjects (n=17) were scanned at 7 T using a multi-echo gradient-echo sequence and susceptibility-weighted magnitude images, R2* and QS maps were reconstructed. We defined a hippocampal subfield labeling protocol for the magnitude image produced from the average of all echoes and assessed reproducibility through volume and shape metrics. A group-wise diffeomorphic registration procedure was used to generate an average atlas of the subfields for the whole subject cohort. The quantitative MRI maps and subfield labels were then warped to the average atlas space and used to measure mean values of R2* and QS characterizing each subfield.

PRINCIPAL OBSERVATIONS

We were able to reliably label hippocampal subfields on the multi-echo susceptibility images. The group-averaged atlas accurately aligns these structures to produce a high-resolution depiction of the subfields, allowing assessment of both quantitative susceptibility and R2* across subjects. Our analysis of variance demonstrates that there are more apparent differences between the subfields on these quantitative maps than the normalized magnitude images.

CONCLUSION

We constructed a high-resolution atlas of the hippocampal subfields for use in voxel-based studies and demonstrated in vivo quantification of susceptibility and R2* in the subfields. This work is the first in vivo quantification of susceptibility values within the hippocampal subfields at 7 T.

Functional MRI as a tool to assess vision in dogs: the optimal anesthetic

Functional magnetic resonance imaging (fMRI) is a recent advance in neuroimaging that provides a picture of brain activity with excellent spatial resolution. Current methods used to evaluate canine vision are poorly standardized and vulnerable to bias. Functional MRI may represent a valuable method of testing vision in dogs if the impacts of anesthesia on fMRI are understood. Six dogs were scanned during visual stimulation, each under three different anesthetic protocols (isoflurane, propofol, fentanyl/midazolam) to address the questions: (1) Can visually evoked fMR signals be reliably recorded in anesthetized dogs? and (2) Which anesthetic agent permits the least suppression of visually induced fMR signal in dogs? This study confirms that visual stimuli reliably elicit neural activity and fMR signal change in anesthetized dogs. No significant differences in images acquired under the three anesthetics were found, and there was no significant relationship between anesthetic dose and brain activity, within the range of doses used in this study. Images obtained during isoflurane anesthesia were more consistent between dogs than those obtained with the other two agents. This reduced variation may reflect the fact that inhalant anesthesia is more easily controlled than intravenous anesthesia under conditions associated with high field fMRI.

fMRI-derived cortical maps for haptic shape, texture, and hardness

We used functional magnetic resonance imaging (fMRI) to investigate the neural substrates involved in haptic processing of texture, shape, and hardness. Subjects performed haptic classification tasks on a set of 27 silicone objects having parametrically defined shape, texture, and hardness. The objects were ellipsoids of revolution in which the ratio of the long to the short axis was varied, producing three different shapes. Three surface textures and three hardness levels were used. In three separate experiments, the same subjects classified each object along the three levels of one of the object properties (shape, texture, or hardness). Texture, shape, and hardness processing led to contralateral activation in the postcentral gyrus (PCG). A common region located within relatively posterior portions of the PCG was observed during shape and texture identification whereas a separate and more anterior region was activated during the hardness identification task. The hardness identification task also produced bilateral activation within the parietal operculum.

Functional MRI activity in the thalamus and occipital cortex of anesthetized dogs induced by monocular and binocular stimulation

The neuroanatomy of the mammalian visual system has received considerable attention through electrophysiological study of cats and non-human primates, and through neuroimaging of humans. Canine neuroanatomy, however, has received much less attention, limiting our understanding of canine vision and visual pathways. As an early step in applying blood oxygenation level dependant (BOLD) functional magnetic resonance imaging (fMRI) for veterinary use, we compared visual activity in the thalamus and occipital cortex of anesthetized dogs presented with binocular and monocular visual stimuli. Activity in the left and right thalamus and occipital cortex during monocular stimulation was also compared. Six beagles were presented with a vertical grating visual stimulus and scanned at 4 Tesla. Each dog was scanned twice under each of 3 anesthetic protocols (isoflurane, propofol, and fentanyl/midazolam). We found: 1) significant BOLD activation in the lateral geniculate nucleus (LGN) of the thalamus and the occipital cortex; 2) a significantly larger area of activation in the LGN during monocular stimulation than during binocular stimulation; and 3) that activity in the hemisphere contralateral to the stimulus was not significantly greater than that ipsilateral to it.

fMRI evidence for an inverted face representation in human somatosensory cortex

We provide evidence that the face component of the somatosensory homunculus is actually upside down rather than right-side up along the central sulcus of the human brain. We pneumatically stimulated the forehead or chin of neurologically intact humans while acquiring fMRI images of somatosensory cortex. During forehead stimulation cortical regions along relatively inferior portions of the postcentral gyrus were most active whereas during chin stimulation relatively superior regions were most active. These data are consistent with an inverted face representation along the central sulcus of the human brain.