Therapeutic success of treatment of cerebral diseases must be assessed in terms of functional outcome. In experimental stroke studies, this has been limited to behavioral studies combined with morphological evaluations and single time point functional magnetic resonance imaging (fMRI) measurements but lacking the access to understanding underlying mechanisms for alterations in brain activation. Using a recently developed blood oxygenation level-dependent fMRI protocol to study longitudinal and intraindividual profiles of functional brain activation in the somatosensory system, we have demonstrated activation reemergence in the original representation field as the basic principle of functional recovery from experimental stroke. No plastic reorganization has been observed at any time point during 7 weeks after stroke induction. Applying combined recording of fMRI and somatosensory evoked potentials, we observed a tight coupling of electrical brain activity and hemodynamic response at all times, indicating pe...

In this study we were interested in the hypothesis that different task sets would influence both behavior and prefrontal cortex (PFC) activation during performance of a memory task. Specifically, participants were asked to remember a list of words over a short delay, and then respond to a probe word, indicating whether or not the probe was present in the list of words. In one condition, participants were encouraged to use an active maintenance strategy by presenting short lists of words (1 to 6 words per list). In the other condition, participants were encouraged to use a retrieval-based strategy by presenting long lists of words (6 to 11 words per list). The critical comparison is between the 6-word trials, since the memory load, trial duration, and perceptual input are identical across the two conditions. To test our hypothesis that activation in PFC would correlate with task set, we conducted an event-related functional magnetic resonance imaging (fMRI) study on 25 younger adults. Behavioral results con...

Functional magnetic resonance imaging (fMRI) was used to monitor spinal cord mediated activation of sensory motor cortex by measuring changes of blood oxygenation level-dependent (BOLD) contrast during electric stimulation of forepaw, hindpaw or tail. Single or multi-slice gradient echo images were collected using gradient echo fast imaging or spiral gradient imaging. Stimulation of fore- or hindpaws repeatedly lead to robust activation of contralateral sensorimotor cortex. The center of the main cortical representation was situated 3.4 mm lateral to the midline and 5 mm posterior to the rhinal fissure (prf) for the forepaw and 2.0 mm lateral to the midline and 6 mm prf for the hindpaw. Tail stimulation gave rise to an extended bilateral cortical activation, along the midline in medial frontal and cingulate gyrus 4 and 5 mm prf. Axonal regeneration in peripheral nerves has been obtained using degradable tubes made of polyglycolic acid (PGA) and collagen (Kiyotani et al., 1996 Brain Res, 740:66-74). To obta...

Correction: In the article “A Comparative Magnetic Resonance Imaging Study of the Anatomy, Variability, and Asymmetry of Broca's Area in the Human and Chimpanzee Brain” by Simon S. Keller, Neil Roberts, and William Hopkins, which appeared on pages [14607–14616][1] of the November 18, 2009

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...

Experimental data up to 7.0 T show that the blood oxygenation level-dependent (BOLD) signal of functional magnetic resonance imaging (fMRI) increases with higher magnetic field strength. Although several studies at 11.7 T report higher BOLD signal compared with studies at 7.0 T, no direct comparison at these two field strengths has been performed under the exact same conditions. It therefore remains unclear whether the expected increase of BOLD effect with field strength will still continue to hold for fields >7.0 T. To examine this issue, we compared the BOLD activation signal at 7.0 and 11.7 T with the two common sequences, spin-echo (SE) and gradient-echo (GE) echo planar imaging (EPI). We chose the physiologically well controlled rat model of electrical forepaw stimulation under medetomidine sedation. While a linear to superlinear increase in activation with field strengths up to 7.0 T was reported in the literature, we observed no significant activation difference between 7.0 and 11.7 T with either SE...

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...

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...

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...