Neural correlates of transmeatal cochlear laser (TCL) stimulation in healthy human subjects.

Transmeatal cochlear laser (TCL) treatment has recently been proposed as a therapeutic procedure for cochlear dysfunction such as chronic cochlear tinnitus or sensorineural hearing loss. The aim of this study was to investigate whether TLC has any influence on the central nervous system using functional MRI with healthy young adults. The laser stimulation device was placed on the tympanic membrane of both ears. A laser stimulation run and a placebo run were performed in random order. The participants were unable to differentiate between verum and placebo stimulation. In the comparison of verum to placebo runs, we observed significant activations within the left superior frontal gyrus, the right middle and medial frontal gyrus, the right superior parietal lobule, the left superior occipital gyrus, the precuneus and cuneus bilaterally, the right anterior and the left and right middle and posterior cingulate gyrus and the left thalamus. This network of brain areas corresponds well to results from previous PET studies of patients with tinnitus. Though TCL seems to have a clinically measurable effect on the central nervous system the neurophysiological mechanism leading to the observed activated neuronal network remains unknown.

Brain activation patterns during a selective attention test-a functional MRI study in healthy volunteers and patients with schizophrenia.

Functional magnetic resonance imaging was used to compare cortical activation patterns in healthy volunteers with those in patients with schizophrenia during a modified verbal Stroop task. Healthy subjects (n=13) and patients with schizophrenia (n=13) on stable antipsychotic treatment, matched on demographic variables, were included. Patients were preselected on the basis of good performance on a selective attention test. Patients with schizophrenia showed a significantly increased pattern of activation in the left and right inferior frontal cortex and the anterior cingulate cortex. A significant negative correlation between activation of the left prefrontal cortex and accuracy in the modified Stroop test was observed for healthy controls but not schizophrenia patients. Although both groups recruited the prefrontal cortex during the modified Stroop task, for the schizophrenia patients this activation was bilateral, whereas for the controls this activation was primarily in the left hemisphere, suggesting that patients with schizophrenia recruited more prefrontal regions to perform the task with the same accuracy as healthy controls. Our findings of increased activity across multiple areas of the brain, including dorsolateral frontal cortex and anterior cingulate, in patients with schizophrenia who perform relatively well on a task of selective attention give further evidence that task performance may be a confounding factor in the interpretation of neuroimaging results.

Caffeine and cognition in functional magnetic resonance imaging.

Caffeine has been consumed since ancient times due to its beneficial effects on attention, psychomotor function, and memory. Caffeine exerts its action mainly through an antagonism of cerebral adenosine receptors, although there are important secondary effects on other neurotransmitter systems. Recently, functional MRI (fMRI) entered the field of neuropharmacology to explore the intracerebral sites and mechanisms of action of pharmacological agents. However, as caffeine possesses vasoconstrictive properties it may interfere with the mechanisms underlying the functional contrast in fMRI. Yet, only a limited number of studies dealt with the effect of caffeine on measures in fMRI. Even fewer neuroimaging studies examined the effects that caffeine exerts on cognition: Portas and colleagues used fMRI in an attentional task under different levels of arousal (sleep deprivation or caffeine administration), concluding that the thalamus is involved in mediating the interaction of attention and arousal. Bendlin and colleagues found caffeine to stabilize the extent of neuronal activation in repetitive word stem completion, counteracting the general task practice effect. Recently, Koppelstaetter and colleagues assessed the effect of caffeine on verbal working memory demonstrating a modulatory effect of caffeine on brain regions (medial frontopolar and anterior cingulate cortex) that have been associated with attentional and executive functions. This review surveys and discusses neuroimaging findings on 1) how caffeine affects the contrast underlying fMRI techniques, particularly the blood oxygen level dependent contrast (BOLD fMRI), and 2) how caffeine operates on neuronal activity underlying cognition, to understand the effect of caffeine on behavior and its neurobiological underpinnings.

Contact force- and amplitude-controllable vibrating probe for somatosensory mapping of plantar afferences with fMRI.

PURPOSE: To study cerebral responses evoked from mechanoreceptors in the human foot sole using a computer-controlled vibrotactile stimulation system. MATERIALS AND METHODS: The stimulation system consisted of two stationary moving magnet actuators with indentors to gently contact and vibrate the foot sole during functional MRI (fMRI) experiments. To allow independent settings of contact force (0-20 N) and intensity of vibration (frequency range=20-100 Hz) the actuators were controlled by a digital servo loop. For fMRI experiments with complex stimulus protocols, both vibrating probes were further operated under supervisory control. RESULTS: The MR compatibility of this electromagnetic system was tested in a 1.5T scanner with an actively shielded magnet (Siemens Magnetom Sonata). Blood oxygenation level-dependent (BOLD) responses were detected in the contralateral left pre- and postcentral gyrus, bilaterally within the secondary somatosensory cortex, bilaterally within the supplementary motor cortex, and bilaterally within the anterior cingular gyrus. CONCLUSION: This stimulation device provides a new tool for identifying cerebral structures that convey sensory information from the foot region, which is of promising diagnostic value, particularly for assessing sensorimotor deficits resulting from brain lesions.

Human brain structures related to plantar vibrotactile stimulation: a functional magnetic resonance imaging study.

The purpose of this study was to investigate the sensorimotor cortex response to plantar vibrotactile stimulation using a newly developed MRI compatible vibration device. Ten healthy subjects (20-45 years) were investigated. Vibrotactile stimulation of the sole of the foot with a frequency of 50 Hz and a displacement of 1 mm was performed during fMRI (echo-planar imaging sequence at 1.5 T) using an MRI compatible moving magnet actuator that is able to produce vibration frequencies between 0 and 100 Hz and displacement amplitudes between 0 and 4 mm. The fMRI measurement during vibrotactile stimulation of the right foot revealed brain activation contralaterally within the primary sensorimotor cortex, bilaterally within the secondary somatosensory cortex, bilaterally within the superior temporal, inferior parietal, and posterior insular region, bilaterally within the anterior and posterior cingular gyrus, bilaterally within the thalamus and caudate nucleus, contralaterally within the lentiform nucleus, and bilaterally within the anterior and posterior cerebellar lobe. The advantages of the new MRI compatible vibration device include effective transmission of the stimulus and controlled vibration amplitudes, frequencies, and intensities. The results indicate that plantar vibration can be a suitable paradigm to observe activation within the sensorimotor network in fMRI. Furthermore, the method may be used to determine the optimal responsiveness of the individual sensorimotor network.

Magnetic resonance in the differential diagnosis of dementia.

Magnetic resonance became an important tool for the differential diagnosis of dementia. Magnetic resonance imaging is the preferred method to exclude treatable entities accompanied by dementing symptoms. New techniques including diffusion and perfusion magnetic resonance imaging are helpful for the differentiation between vascular dementia and degenerative disorders. Magnetic Resonance spectroscopy evolves as a tool for the diagnosis of different forms of degenerative dementia. Multimodal magnetic resonance holds promise to diagnose Alzheimer's disease at early clinical stages and to monitor the progression of the disease.

Serial contrast-enhanced magnetic resonance imaging and spectroscopic imaging of acute multiple sclerosis lesions under high-dose methylprednisolone therapy.

To evaluate biochemical changes in contrast-enhancing multiple sclerosis (MS) lesions, we examined 14 patients with relapsing-remitting MS at acute clinical exacerbation with the help of contrast-enhanced magnetic resonance imaging (MRI) and 1H magnetic resonance spectroscopic imaging (1H MRSI). Using a 1.5-tesla MR system (Magnetom Vision, Siemens, Germany), we followed 29 contrast-enhancing and 24 nonenhancing MS lesions as well as normal-appearing white matter (NAWM) before and during high-dose methylprednisolone (HDMP) therapy. Metabolite ratios of N-acetylaspartate (NAA), choline (Cho), creatine (Cr), and lactate (Lac) were calculated. A transient decrease in contrast enhancement under HDMP therapy was observed. Both groups of MS lesions showed significantly decreased NAA to Cr ratios compared to NAWM with no changes in time. Baseline 1H MRSI revealed significantly increased Cho to Cr ratios in the contrast-enhancing MS lesions (1.13 +/- 0.25) compared to the nonenhancing MS lesions (0.85 +/- 0.26, P < 0.001) and NAWM (0.97 +/- 0.22, P = 0.015). Both the contrast-enhancing and the nonenhancing MS lesions exhibited a significant increase in Cho to Cr ratios from the second to the third 1H MRSI. We identified resonances of lactate in both groups of MS lesions and NAWM without any significant group differences or changes over time. 1H MRSI provides additional information that help to estimate macrophages' activity, cell membrane activation, and neuronal impairment within MS lesions. We believe that combined contrast-enhanced MRI and 1H MRSI may help to further investigate inflammatory processes within active MS lesions and should be employed more frequently to the research on therapy effects in MS.

Functional magnetic resonance imaging of the human sensorimotor cortex using a novel vibrotactile stimulator.

The purpose of this study was to investigate the fMRI response of the sensorimotor cortex to a vibration paradigm produced by a novel vibrotactile stimulator. Fifteen contiguous slices covering the sensorimotor cortex parallel to the anterior (AC) and posterior commissure (PC) line were obtained with echoplanar magnetic resonance imaging at 1.5T. Cortical activity in ten healthy subjects (20-45 years) was investigated during vibration (50 Hz) of the palm of the right hand and compared to a finger-to-thumb tapping paradigm. For the vibration paradigm a mechanically driven vibration head was mounted on the palm of the right hand. The new vibration device produces vibration frequencies (1-130 Hz) and displacement amplitudes (0.5-4 mm) suitable to elicit the tonic vibratory reflex. The fMRI measurement during vibratory stimulation revealed activation in the pre- and postcentral gyrus in all subjects. These activations were comparable to the finger-to-thumb tapping paradigm. The advantages of the new MR compatible vibration device include effective transmission of the stimulus and controlled vibration frequencies and intensities. These preliminary fMRI results indicate that vibration can be an alternative paradigm for the evaluation of sensory and motor functions in patients unable to perform active motor paradigms.