Functional brain imaging studies - including position emission tomography (Fias, Lammertyn, Reynvoet, Dupont, & Orban, 2003; Pesenti, Thioux, Seron, & De Volder, 2000), functional magnetic resonance imaging (Bugden, Price, McLean, & Ansari, 2012; Dehaen...

Neuronal activity induces transient magnetic fields, and previous works have attempted to directly measure such magnetic field changes using MRI. The feasibility of various MR techniques for detecting neuronal oscillations and related MR signal dephasin...

Neuroimaging is increasingly taking on a significant role in assessment of progression and outcome of neurotrauma, including magnetic resonance imaging (MRI). The fluid percussion model (FPI) was used for the induction of brain injury. FPI animals were imaged on a Bruker 4.7 T MRI (3, 24, 48 hr; 3, 4, 7 day) using: 1) T2-weighted-, 2) diffusion weighted, and 3) MR spectroscopy (MRS). A new gradient echo method, susceptibility weighted imaging (SWI), for visualization of extravascular blood was also assessed. Quantitative data analysis was obtained; T2 values (ms), apparent diffusion coefficients (ADC). MRS metabolites were quantified for: choline; creatine; N-acetyl aspartate; and lactate. SWI images were generated by minimum intensity projections. FPI resulted in an increase in T2 values over the course of 7 days. The largest increases were found in the cortical regions, then hippocampus and thalamus. Increased ADC values in the cortical regions progressed over 7 days, and were accentuated on the side of ...

Speech production requires the precise timing of around 100 muscles involved in articulation. The neural basis of the exact coordination of these movements is not entirely clear. Here we investigated brain activation associated with overt sub-lexical articulations using event-related fMRI with compressed image acquisition. Nine young healthy volunteers (right-handed, fluent speakers of English; 5 men) were included. Subjects were asked to repeat acoustically presented speech sounds of different complexity and to perform non-verbal oral movements. The required responses were the vowel /a/, a consonant-vowel (CV) syllable (either /pa/, /ka/, or /ta/), a three-syllabic utterance (/pataka/), and oral movements (opening the mouth or protruding the lips). All instructions were delivered and all responses were made within the silent interval between the acquisition of the fMR images. Functional imaging was performed on a 3 Tesla MRI system with a standard head coil using a T2*-weighted spiral-in/out sequence. The...

One of the most remarkable abilities of bilinguals is to produce and/or to perceive a switch from one language to the other without any apparent difficulty. However, several psycholinguistic studies indicate that producing, recognizing, and integrating a linguistic code different from the one in current use may entail a processing cost for the speaker/listener. Up to now, the underlying neural substrates of perceiving language switches are unknown. In the present study, we investigated the neural mechanisms of language switching during auditory perception in bilinguals. Event-related functional magnetic resonance imaging was performed in 12 early, highly proficient Italian/French bilinguals, who were more exposed to their second language. Subjects had to listen to narratives containing “switched passages” that could either respect (i.e., regular switches) or violate (i.e., irregular switches) the constituents of sentence structure. The results indicate that switching engages an extensive neural network, in...

Although the non-invasive measurement of visually evoked responses has been extensively studied, the structural basis of variabilities in latency in healthy humans is not well understood. We investigated how tissue properties of optic radiation could predict interindividual variability in the latency of the initial visually evoked component (C1), which may originate from the primary visual cortex (V1). We collected C1 peak latency data using magnetoencephalography (MEG) and checkerboard stimuli, and multiple structural magnetic resonance imaging (MRI) data from 20 healthy subjects. While we varied the contrast and position of the stimuli, the C1 measurement was most reliable when high-contrast stimuli were presented to the lower visual field (LVF). We then attempted to predict interindividual variability in C1 peak latency in this stimulus condition with a multiple regression model using MRI parameters along the optic radiation. We found that this model could predict >20% of variance in C1 latency, when th...

Comparisons of neural activity between humans and monkeys have usually relied on techniques using very different spatial and temporal scales. We report a method for scanning behaving macaques in a horizontal human 3 Tesla MR scanner to investigate neural processes involved in perception and to compare them to that of humans. Specifically, we have developed an apparatus for the animal to lie prone in the scanner bore, training procedures to minimize body movements while maintaining long periods of eye fixation (> 10 s), a mock training environment to acclimate the animal to the sights and sounds of the MRI, and surgical head-bolt implants for rigid head fixation that are MR-compatible. With the use of a 12 cm surface coil placed above the animal’s head, high-resolution functional (1.5 x 1.5 x 2.0 mm) and anatomical (0.5 mm3) scans are acquired in awake animals. Ongoing studies are exploring the organization of inferior temporal cortex with direct comparisons to human cortex. Other studies map retinotopicall...

Previous neuroimaging studies in the visual domain have shown that neurons along the perceptual processing pathway retain the physical properties of written words, faces, and objects. The aim of this study was to reveal the existence of similar neuronal properties within the human auditory cortex. Brain activity was measured using functional magnetic resonance imaging during a repetition priming paradigm, with words and pseudowords heard in an acoustically degraded format. Both the amplitude and peak latency of the hemodynamic response (HR) were assessed to determine the nature of the neuronal signature of spoken word priming. A statistically significant stimulus type by repetition interaction was found in various bilateral auditory cortical areas, demonstrating either HR suppression and enhancement for repeated spoken words and pseudowords, respectively, or word-specific repetition suppression without any significant effects for pseudowords. Repetition latency shift only occurred with word-specific repeti...

Activation resembling ocular dominance or orientation columns has been mapped with high-resolution functional magnetic resonance imaging (fMRI). However, the neuronal interpretation of these functional maps is unclear because of the poor sensitivity of fMRI, unknown point spread function (PSF), and lack of comparison with independent techniques. Here we show that cerebral blood volume (CBV)-weighted fMRI with a blood plasma contrast agent (monocrystalline iron oxide nanoparticles), in combination with continuous temporally encoded stimulation, can map columnar neuronal activity in the cat primary visual cortex with high sensitivity, selectivity, and reproducibility. We examined hemodynamic response PSF by comparing these CBV-based signals with oxygen metabolism-based negative blood oxygenation level-dependent signals. A significant positive correlation exists between CBV- and metabolism-based iso-orientation maps, suggesting that the hemodynamic PSF is narrower than intercolumn distances. We also compared ...

Cerebral amyloid angiopathy (CAA) is a common feature of Alzheimer's disease (AD). More advanced stages are accompanied by microhemorrhages and vasculitis. Peripheral blood-borne macrophages are intimately linked to cerebrovascular pathology coincident with AD. Magnetic resonance imaging (MRI) was used to noninvasively study microvascular lesions in amyloid precursor protein transgenic mouse AD models. Foci of signal attenuation were detected in cortical and thalamic brain regions of aged APP23 mice. Their strength and number was considerably enhanced by intravenous administration of iron oxide nanoparticles, which are taken up by macrophages through absorptive endocytosis, 24 h before image acquisition. The number of cortical sites displaying signal attenuation increased with age. Histology at these sites demonstrated the presence of iron-containing macrophages in the vicinity of CAA-affected blood vessels. A fraction of the sites additionally showed thickened vessel walls and vasculitis. Consistent with ...