Helmet Karim

Functional near-infrared spectroscopy (fNIRS) of brain function during active balancing using a video game system

Functional near-infrared spectroscopy (fNIRS) is a portable, non-invasive, brain imaging technology that uses low levels of non-ionizing light to record changes in cerebral blood flow in the brain through optical sensors placed on the surface of the scalp. These signals are recorded via flexible fiber optic cables, which allow neuroimaging experiments to be conducted on participants while performing tasks such as standing or walking. FNIRS has the potential to provide new insights into the evolution of brain activation during ambulatory motor learning tasks and standing tasks to probe balance and vestibular function. In this study, a 32 channel fNIRS system was used to record blood flow changes in the frontal, motor, sensory, and temporal cortices during active balancing associated with playing a video game simulating downhill skiing (Nintendo Wii™; Wii-fit™). Using fNIRS, we found activation of superior temporal gyrus, which was modulated by the difficulty of the balance task. This region had been previously implicated in vestibular function from other animal and human studies.

Functional brain imaging of multi-sensory vestibular processing during computerized dynamic posturography using near-infrared spectroscopy

Functional near-infrared spectroscopy (fNIRS) is a non-invasive brain imaging method that uses light to record regional changes in cerebral blood flow in the cortex during activation. fNIRS uses portable wearable sensors to allow measurements of brain activation during tasking. In this study, fNIRS was used to investigate how the brain processes information from multiple sensory modalities during dynamic posturography. Fifteen healthy volunteers (9M/6F; ages 28+/-9 yrs) participated in the posturography study while undergoing fNIRS brain imaging. Four standard conditions from the sensory organization test (SOT) were performed and a bilateral fNIRS probe was used to examine the cortical brain responses from the frontal, temporal, and parietal brain regions. We found that there was bilateral activation in the temporal-parietal areas (superior temporal gyrus, STG, and supramarginal gyrus, SMG) when both vision and proprioceptive information were degraded; forcing reliance on primarily vestibular information in the control of balance. This is consistent with previous reports of the role of these regions in vestibular control and demonstrates the potential utility of fNIRS in the study of cortical control of vestibular function during standing balance tasks.

Intrinsic functional connectivity in late-life depression: trajectories over the course of pharmacotherapy in remitters and non-remitters

Previous studies in late-life depression (LLD) have found that patients have altered intrinsic functional connectivity in the dorsal default mode network (DMN) and executive control network (ECN). We aimed to detect connectivity differences across a treatment trial among LLD patients as a function of remission status. LLD patients (N=37) were enrolled into a 12-week trial of venlafaxine and underwent five functional magnetic resonance imaging resting state scans during treatment. Patients had no history of drug abuse, psychosis, dementia/neurodegenerative diseases or medical conditions with known effects on mood. We investigated whether there were differences in three networks: DMN, ECN and anterior salience network connectivity, as well as a whole brain centrality measure (eigenvector centrality). We found that remitters showed increases in ECN connectivity in the right precentral gyrus and decreases in DMN connectivity in the right inferior frontal gyrus and supramarginal gyrus. The ECN and DMN had regions (middle temporal gyrus and bilateral middle/inferior temporal/fusiform gyrus, respectively) that showed reversed effects (decreased ECN and increased DMN, respectively). Early changes in functional connectivity can occur after initial medication exposure. This study offers new data, indicating that functional connectivity changes differ depending on treatment response and can occur shortly after exposure to antidepressant medication.

Neuroimaging to detect cortical projection of vestibular response to caloric stimulation in young and older adults using functional near-infrared spectroscopy (fNIRS)

Functional near-infrared spectroscopy (fNIRS) is a non-invasive and portable neuroimaging technique. The method uses non-ionizing laser light in the range of red to near-infrared to detect changes in cerebral blood oxygenation. In this study, we used fNIRS to investigate cortical hemodynamic changes in the temporo-parietal and frontal regions during caloric vestibular stimulation. Caloric stimulation has previously been investigated using functional magnetic resonance imaging (fMRI) and positron emission tomography (PET), which serves as a validation of the fNIRS imaging modality toward the measurement of vestibular related brain regions. To date, only a single study has used fNIRS during caloric irrigations, which observed blood volume changes in the temporal-parietal area in healthy younger subjects. In this current study, fNIRS was used to measure cortical vestibular activation in 10 right-handed younger subjects (5 male and 5 female, age 25+/-6 years) and 10 right-handed older subjects (6 male and 4 female, age 74+/-5 years). We investigated both warm (44 °C) and cool (30 °C) unilateral caloric vestibular stimulation. Consistent with previous reports, we found that warm (44 °C) caloric irrigation caused a bilateral activation. In addition, we found that cool (30 °C) caloric irrigation caused contralateral activation of the temporo-parietal area. This study is the first to investigate age effects of the caloric stimulation on brain activity. We found that the older subjects had stronger bilateral effects than the younger subjects. Our results confirm previous fMRI and PET studies that showed cortical activation during caloric vestibular irrigation is dependent on side of irrigation, and temperature of irrigation. Furthermore, our results demonstrate that fNIRS is a viable technique in measuring cortical effects during vestibular tasks.

Functional MR imaging of a simulated balance task.

Human postural control, which relies on information from vestibular, visual, and proprioceptive inputs, degrades with aging, and falls are the leading cause of injury in older adults. In the last decade, functional neuroimaging studies have been performed in order to gain a greater understanding of the supraspinal control of balance and walking. It is known that active balancing involves cortical and subcortical structures in the brain, but neuroimaging of the brain during these tasks has been limited. The study of the effect of aging on the functional neuroimaging of posture and gait has only recently been undertaken. In this study, an MRI-compatible force platform was developed to simulate active balance control. Eleven healthy participants (mean age 75±5 yr) performed an active balance simulation task by using visual feedback to control anterior-posterior center of pressure movements generated by ankle dorsiflexor (DF) and plantarflexor (PF) movements, in a pattern consistent with upright stance control. An additional ankle DF/PF exertion task was performed. During both the active balance simulation and the ankle DF/PF tasks, the bilateral fusiform gyrus and middle temporal gyrus, right inferior, middle, and superior frontal gyrii were activated. No areas were found to be more active during the ankle DF/PF task when compared with the active balance simulation task. When compared to the ankle DF/PF task, the active balance simulation task elicited greater activation in the middle and superior temporal gyrii, insula, and a large cluster that covered the corpus callosum, superior and medial frontal gyrii, as well as the anterior cingulate and caudate nucleus. This study demonstrates the utility in using a force platform to simulate active balance control during MR imaging that elicits activity in cortical regions consistent with studies of active balance and mental imagery of balance.

Motor sequence learning-induced neural efficiency in functional brain connectivity.

&NA; Previous studies have shown the functional neural circuitry differences before and after an explicitly learned motor sequence task, but have not assessed these changes during the process of motor skill learning. Functional magnetic resonance imaging activity was measured while participants (n = 13) were asked to tap their fingers to visually presented sequences in blocks that were either the same sequence repeated (learning block) or random sequences (control block). Motor learning was associated with a decrease in brain activity during learning compared to control. Lower brain activation was noted in the posterior parietal association area and bilateral thalamus during the later periods of learning (not during the control). Compared to the control condition, we found the task‐related motor learning was associated with decreased connectivity between the putamen and left inferior frontal gyrus and left middle cingulate brain regions. Motor learning was associated with changes in network activity, spatial extent, and connectivity. HIGHLIGHTSBrain activity was measured during motor sequence learning task.Posterior parietal and thalamus activated less during learning (vs. control).Putamen to frontal/mid. cingulate connectivity lower during learning (vs. control).Learning was associated with changes in brain activity/spatial extent/connectivity.

Reproducibility and Bias in Healthy Brain Segmentation: Comparison of Two Popular Neuroimaging Platforms

We evaluated and compared the performance of two popular neuroimaging processing platforms: Statistical Parametric Mapping (SPM) and FMRIB Software Library (FSL). We focused on comparing brain segmentations using Kirby21, a magnetic resonance imaging (MRI) replication study with 21 subjects and two scans per subject conducted only a few hours apart. We tested within- and between-platform segmentation reliability both at the whole brain and in 10 regions of interest (ROIs). For a range of fixed probability thresholds we found no differences between-scans within-platform, but large differences between-platforms. We have also found very large differences between- and within-platforms when probability thresholds were changed. A randomized blinded reader study indicated that: (1) SPM and FSL performed well in terms of gray matter segmentation; (2) SPM and FSL performed poorly in terms of white matter segmentation; and (3) FSL slightly outperformed SPM in terms of CSF segmentation. We also found that tissue class probability thresholds can have profound effects on segmentation results. We conclude that the reproducibility of neuroimaging studies depends on the neuroimaging software-processing platform and tissue probability thresholds. Our results suggest that probability thresholds may not be comparable across platforms and consistency of results may be improved by estimating a probability threshold correspondence function between SPM and FSL.

Altered Functional Magnetic Resonance Imaging Markers of Affective Processing During Treatment of Late-Life Depression

OBJECTIVE This study investigated neural substrate changes in affective processing among late-life depression (LLD) patients undergoing antidepressant treatment and determined if these changes correlated with remission status. METHODS Thirty-three LLD patients were enrolled in a 12-week venlafaxine treatment course. During treatment functional magnetic resonance imaging (fMRI) scans, paired with an affective task that assessed emotional reactivity and regulation, were performed on days 1, 2, 3, and 7 and at week 12. Following treatment patients were classified as remitters or non-remitters. A voxel-wise two-way repeated-measures ANOVA was performed to assess the fMRI data at a significance level of α = 0.05, corrected. RESULTS The emotional reactivity contrast demonstrated a significant interaction between remission status and scan time in the right middle temporal gyrus (MTG) (F = 24.1, df = 1,112, k = 102). Further analysis showed increased emotional reactivity-induced activity among non-remitters, and decreased activity among remitters, which significantly differed from baseline at day 7 (95% CI: 0.027, 0.540; Cohens d = -1.35) and week 12 (95% CI: -0.171, -0.052; Cohens d = 0.68), respectively. No significant interaction was observed with the emotional regulation contrast, but multiple regions had significant main effects of scan time, including the cuneus, occipital lobe, insula, lingual gyrus, posterior cingulate cortex, and MTG. CONCLUSIONS During treatment of LLD patients, affective processing-induced activity in the right MTG shows changes based on remission status. This alteration becomes evident early during the course of treatment, suggesting that antidepressant pharmacotherapy may acutely affect the neural basis of emotional reactivity in a differential manner that is relevant to illness remission.

Neurodevelopmental maturation as a function of irritable temperament

Few studies have investigated the neural systems involved in decreasing behavioral reactivity to emotional stimuli as children age. It has been suggested that this process may interact with temperament‐linked variations in neurodevelopment to better explain individual differences in the maturation of emotion regulation. In this investigation, children ages 4 to 12 (n = 30, mean age = 7.62 years, SD = 1.71 years) and adults (n = 21, mean age = 26.67 years) watched clips from popular childrens films containing positive, negative, or neutral emotional content during functional magnetic resonance imaging. Compared to adults, children demonstrated greater activation in subcortical and visual regions (hippocampus, thalamus, visual cortex, fusiform) during negative clips and greater activation of subcortical and prefrontal regions during positive clips (hippocampus, thalamus, caudate, ACC, OFC, superior frontal cortex). In children only, we found an age by temperament interaction in frontal and subcortical regions indicating that activation increased as a function of age in the most irritable children, but decreased as a function of age in the least irritable children. Findings were not present in the temperament domain of fear. Findings replicate and extend the existing irritability literature, indicating that healthy children highest in irritability may develop comparatively greater activation of the lateral prefrontal cortex in order to support adaptive regulation during emotional challenges. These results are discussed within the context of the emerging literature on the utility of complex, multidimensional, and naturalistic stimuli, which present a complementary alternative to understanding ecologically valid and sustained neural responses to emotionally evocative stimuli. Hum Brain Mapp 38:5307–5321, 2017.

Brain Activation and Psychomotor Speed in Middle-Aged Patients with Type 1 Diabetes: Relationships with Hyperglycemia and Brain Small Vessel Disease

Slower psychomotor speed is very common in patients with type 1 diabetes mellitus (T1D), but the underlying mechanisms are not clear. We propose that hyperglycemia is associated with slower psychomotor speed via disruption of brain activation. Eighty-five adults (48% women, mean age: 49.0 years, mean duration: 40.8) with childhood onset T1D were recruited for this cross-sectional study. Median response time in seconds (longer = worse performance) and brain activation were measured while performing a psychomotor speed task. Exposure to hyperglycemia, measured as glycosylated hemoglobin A1c, was associated with longer response time and with higher activation in the inferior frontal gyrus and primary sensorimotor and dorsal cingulate cortex. Higher activation in inferior frontal gyrus, primary sensorimotor cortex, thalamus, and cuneus was related to longer response times; in contrast, higher activation in the superior parietal lobe was associated with shorter response times. Associations were independent of small vessel disease in the brain or other organs. In this group of middle-aged adults with T1D, the pathway linking chronic hyperglycemia with slower processing speed appears to include increased brain activation, but not small vessel disease. Activation in the superior parietal lobe may compensate for dysregulation in brain activation in the presence of hyperglycemia.