Bihemispheric transcranial direct current stimulation (tDCS) is thought to upregulate excitability of the primary motor cortex (M1) using anodal stimulation while concurrently downregulating contralateral M1 using cathodal stimulation. This “dual” tDCS method enhances motor learning in healthy subjects and facilitates motor recovery after stroke. However, its impact on motor system activity and connectivity remains unknown. Therefore, we assessed neural correlates of dual and unihemispheric anodal tDCS effects in 20 healthy older subjects in a randomized, sham-controlled study using a cross-over design. Participants underwent tDCS and simultaneous functional magnetic resonance imaging during a choice reaction time task and at rest. Diffusion tensor imaging (DTI) allowed us to relate potential functional changes to structural parameters. The resting-state analysis demonstrated that, compared with sham, both dual and anodal tDCS decreased connectivity of right hippocampus and M1 (contralateral to the anode p...

Alterations in motivated behavior are a hallmark of attention-deficit/hyperactivity disorder (ADHD), one of the most common psychiatric disorders in children and adolescents. The orbitofrontal cortex (OFC) plays a key role in controlling goal-directed behavior, but the link between OFC dysfunction and behavioral deficits in ADHD, particularly in adolescence, remains poorly understood. Here we used advanced high-resolution functional magnetic resonance imaging (fMRI) of the human OFC in adolescents with ADHD and typically developing (TD) controls ( N = 39, age 12–16, all male except for one female per group) to study reward-related OFC responses and how they relate to behavioral dysfunction in ADHD. During fMRI data acquisition, participants performed a simple decision-making task, allowing us to image expectation-related responses to small and large monetary outcomes. Across all participants, we observed significant signal increases to large versus small expected rewards in the OFC. These responses were si...

Past investigations on stem cell-mediated recovery after stroke have limited their focus on the extent and morphological development of the ischemic lesion itself over time or on the integration capacity of the stem cell graft ex vivo . However, an assessment of the long-term functional and structural improvement in vivo is essential to reliably quantify the regenerative capacity of cell implantation after stroke. We induced ischemic stroke in nude mice and implanted human neural stem cells (H9 derived) into the ipsilateral cortex in the acute phase. Functional and structural connectivity changes of the sensorimotor network were noninvasively monitored using magnetic resonance imaging for 3 months after stem cell implantation. A sharp decrease of the functional sensorimotor network extended even to the contralateral hemisphere, persisting for the whole 12 weeks of observation. In mice with stem cell implantation, functional networks were stabilized early on, pointing to a paracrine effect as an early suppo...

The feeling of “body ownership” may be experimentally investigated by perceptual illusions. The “rubber hand illusion” (RHI) leads human subjects to experience an artificial hand as their own. According to functional imaging, the ventral premotor cortex (PMv) plays a key role in the integration of multisensory inputs allowing the “incorporation” of the rubber hand into body representation. However, causal structure–function relationships can only be obtained by lesion studies. Here, we tested the RHI in 70 stroke patients and in 40 age-matched healthy controls. Additionally, asomatognosia, the unawareness of one's own body parts, was assessed in a subgroup of 64 stroke patients. Ischemic lesions were delineated on diffusion-weighted magnetic resonance images and normalized. Right-hemispheric lesions were mirrored across the midline. Voxels that might be essential for RHI and/or somatognosia were defined by voxel-based lesion-symptom mapping. Probabilistic diffusion tractography was used to identify tracts...

Neuroimaging studies in autism spectrum disorders (ASD) have provided inconsistent evidence of cortical abnormality. This is probably due to the small sample sizes used in most studies, and important differences in the sample characteristics, particular...

Young healthy participants spontaneously use different strategies in a virtual radial maze, an adaptation of a task typically used with rodents. Functional magnetic resonance imaging confirmed previously that people who used spatial memory strategies showed increased activity in the hippocampus, whereas response strategies were associated with activity in the caudate nucleus. Here, voxel based morphometry was used to identify brain regions covarying with the navigational strategies used by individuals. Results showed that spatial learners had significantly more gray matter in the hippocampus and less gray matter in the caudate nucleus compared with response learners. Furthermore, the gray matter in the hippocampus was negatively correlated to the gray matter in the caudate nucleus, suggesting a competitive interaction between these two brain areas. In a second analysis, the gray matter of regions known to be anatomically connected to the hippocampus, such as the amygdala, parahippocampal, perirhinal, entor...

Single-unit recordings have identified a region in the posterior parietal cortex (PPC) of the monkey that represents and updates visual space in a gaze-centered frame. Here, using event-related functional magnetic resonance imaging, we identified an analogous bilateral region in the human PPC that shows contralateral topography for memory-guided eye movements and arm movements. Furthermore, when eye movements reversed the remembered horizontal target location relative to the gaze fixation point, this PPC region exchanged activity across the two cortical lobules. This shows that the human PPC dynamically updates the spatial goals for action in a gaze-centered frame.

Degradation of white matter fibers can affect the transmission of signals in brain circuits that normally enable integration of highly lateralized visual and motor processes. Here, we used diffusion tensor imaging tractography in combination with functional magnetic resonance imaging to examine the specific contributions of interhemispheric and intrahemispheric white matter fibers to functional measures of hemispheric transfer and parallel information processing using bilateral and unilateral left and right visual field stimulation in normal and compromised systems. In healthy adults, a greater degree of bilateral processing advantage with the left (nondominant) hand correlated with higher integrity of callosal fibers connecting occipital cortices, whereas less unilateral processing advantage with the right hand correlated with higher integrity of left-hemispheric posterior cingulate fibers. In contrast, alcoholics who have compromised callosal integrity showed less bilateral processing advantage than cont...

Aging is associated with an increased risk for stroke and enhanced injury with reperfusion, although the aging-specific mechanisms underlying these observations are not known. Stroke studies in aged (>20 month old) transgenic mice are needed to address these questions, including potential alterations in cerebral blood flow (CBF). The purpose of this study was to utilize perfusion MRI to determine the effects of hypoxia-ischemia (H/I) on cerebral blood volume (CBV) as a measure of CBF, as well as post-ischemic structural changes, in young (3 month) and aged (24 month) mice. Male C57Bl/6 mice were subjected to unilateral carotid artery ligation (isoflurane anesthesia), recovered 2 hours, injected ip with gadolinium pentate (10mmol/Kg), and positioned in a small bore 9.4 tesla vertical Brucker magnet for multiple whole brain T2 images. Following baseline, 8% O2/bal N2 was delivered to obtain H/I images as depicted below. Top panel are CBV maps with corresponding structural images below, ligated(ischemic) hemi...

Systemic drug delivery produces off target effects which limits the ability to pharmacologically treat or investigate region specific brain function. Furthermore, side effects can often outweigh clinical treatment potential and confound preclinical resu...