Lateralized auditory spatial perception and the contralaterality of cortical processing as studied with functional magnetic resonance imaging and magnetoencephalography

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were used to study the relationships between lateralized auditory perception in humans and the contralaterality of processing in auditory cortex. Subjects listened to rapidly presented streams of short FM-sweep tone bursts to detect infrequent, slightly deviant tone bursts. The stimulus streams consisted of either monaural stimuli to one ear or the other or binaural stimuli with brief interaural onset delays. The onset delay gives the binaural sounds a lateralized auditory perception and is thought to be a key component of how our brains localize sounds in space. For the monaural stimuli, fMRI revealed a clear contralaterality in auditory cortex, with a contralaterality index (contralateral activity divided by the sum of contralateral and ipsilateral activity) of 67%. In contrast, the fMRI activations from the laterally perceived binaural stimuli indicated little or no contralaterality (index of 51%). The MEG recordings from the same subjects performing the same task converged qualitatively with the fMRI data, confirming a clear monaural contralaterality, with no contralaterality for the laterally perceived binaurals. However, the MEG monaural contralaterality (55%) was less than the fMRI and decreased across the several hundred millisecond poststimulus time period, going from 57% in the M50 latency range (20-70 ms) to 53% in the M200 range (170-250 ms). These data sets provide both quantification of the degree of contralaterality in the auditory pathways and insight into the locus and mechanism of the lateralized perception of spatially lateralized sounds.     

Pallidal lesions. Structural and functional magnetic resonance imaging

OBJECTIVE: To study noninvasively the functional anatomy and pathophysiologic characteristics of the globus pallidus external (GPe) and internal (GPi) divisions. DESIGN: Structural and functional neuroimaging using high-resolution magnetic resonance imaging. SETTING: University medical center research facility. SUBJECTS. Seven patients with pallidal lesions, 4 with an akinetic-rigid syndrome and 3 with a dystonic syndrome, and 15 age-matched volunteers. MAIN OUTCOME MEASURES: T2-weighted anatomical magnetic resonance imaging and number of activated voxels in the GP during rapid supination and pronation of the hand. RESULTS: T2-weighted images showed hyperintense bilateral lesions in the GP of all patients. Patients with dystonic syndromes had isolated lesions in the GPi. Patients with signs of akinetic-rigid syndromes showed abnormalities in the GPe or in central portions of the GP (GPc). Patients with lesions in both parts of the GP had akinetic-rigid or dystonic syndromes. All patients showed activation in the areas of the lesions. The number of activated voxels in the GP was significantly smaller (P < .005, Wilcoxon signed rank test) in patients than in control subjects. Activation of the GP was predominantly contralateral to the moving hand. CONCLUSIONS: Lesions in the GPi result in a loss of inhibitory pallidal projections to the thalamus, which may explain the hyperkinetic signs. Lesions in the GPe lead to an increased inhibition of the thalamus, which may explain the hypokinetic signs. Neuronal activation in lesion sites suggests the presence of remaining functionally vital tissue.     

Use of functional magnetic resonance imaging

It has been the goal of this article to provide the reader with a brief background of fMRI, a basic understanding of the techniques of fMRI, and, more importantly, the potential for clinical and experimental studies using fMRI. In contrast to the limited number of installed PET and MEG units, the large installed base of MR imaging scanners (over 1000 installed at least at 1.5 T in the United States) makes fMRI potentially widely available. Initial studies (both clinical and experimental) have been validated and are reproducible in mapping the sensorimotor and visual cortices. The areas of language lateralization and memory are still preliminary at best. As methods to reduce the effects of head motion (due to both bulk head motion and physiologically induced motion) arise, the reliability of fMRI should improve, allowing for more definitive identification of task activation.     

A method for functional magnetic resonance imaging of olfaction

A method for generating olfactory stimuli for humans within a functional magnetic resonance imaging (fMRI) experimental design is described. The system incorporates a nasal-mask in which the change from odorant to no-odorant conditions occurs in less than 500 ms and is not accompanied by visual, auditory, tactile, or thermal cues. The mask provides an ordorant-free environment following prolonged ordorant presence. Specific imaging parameters that are conducive to the study of the human olfactory system are described. In a pilot study performed using these methods, the specific patterns of activation observed converged with published experimental and clinical findings.     

Experiences with functional magnetic resonance imaging at 1 tesla

Functional magnetic resonance imaging (fMRI) has been performed on a standard 1 T system using a pulse sequence developed to utilize blood oxygen level dependent (BOLD) contrast and an off-line analysis routine using correlation techniques. The sequence and the data analysis routine have been validated by reproducing the conventional hand movement paradigm studies reported by numerous other workers. Our work has then been extended to investigate cerebral foci for a tonic pain stimulus and the cortical representation of oesophageal stimulation. Both these studies relate to paradigms where the expected BOLD signal is significantly less than that encountered for motor or visual cortex paradigms. The results show good agreement with other modalities (positron emission tomography, magnetoencephalography and cortical evoked potentials). Performing fMRI at 1 T is slightly controversial. However, our successful study of demanding paradigms, using a standard clinical 1 T imaging system, has important implications for many other users operating at this field strength.     

Striatopallidal and thalamic dystonia. A magnetic resonance imaging anatomoclinical study

The effects of manual and a new mechanical chest compression device (Heartsaver 2000) during prolonged CPR with respect to haemodynamics and outcome were tested in a prospective, randomized, controlled experimental trial during ventricular fibrillation in 12 dogs of 9-13 kg body weight after 1 min of cardiac arrest. During the first 10 min of CPR the dogs were resuscitated according to the Basic Life Support (BLS) algorithm, followed by 20 min of Advanced Life Support (ALS) algorithm. After 30 min of CPR both manual and mechanical CPR groups were resuscitated following a standardized ALS protocol. During CPR, coronary perfusion pressure and end tidal CO2 were greater with mechanical CPR. All animals were successfully resuscitated and neurological deficit scores were not different. The CPR trauma score was less in the mechanical group. Mechanical external chest compression provided better haemodynamics than the manual technique, though outcome did not differ. Both optimally performed manual and mechanical techniques produce flow sufficient to maintain organ viability for 30 min of CPR after a 1 min arrest interval.     

Spatial and temporal resolution of functional magnetic resonance imaging

Functional magnetic resonance imaging has become an invaluable tool for cognitive neuroscience, despite the fact that many of the physiological mechanisms giving rise to the effect are not well understood. We review the known biochemical and physiological basis of the technique and discuss how, within the noted limits, one might fully exploit the spatial and temporal resolution that is intrinsic to the very high magnetic fields that we use for human studies. This noninvasive brain mapping technique relies on the changes in blood oxygenation, blood volume, and blood flow, and we discuss some of the issues influencing the effects of these hemodynamic parameters on image intensity.     

Probabilistic analysis of functional magnetic resonance imaging data

Probability theory is applied to the analysis of fMRI data. The posterior distribution of the parameters is shown to incorporate all the information available from the data, the hypotheses, and the prior information. Under appropriate simplifying conditions, the theory reduces to the standard statistical test, including the general linear model. The theory is particularly suited to handle the spatial variations in the noise present in fMRI, allowing the comparison of activated voxels that have different, and unknown, noise. The theory also explicitly includes prior information, which is shown to be critical in the attainment of reliable activation maps.     

Procedural learning in first episode schizophrenia investigated with functional magnetic resonance imaging.

Objective: The present investigation assessed the severity, course, and cerebral implications of serial reaction time (SRT) procedural learning deficits in schizophrenia. Method: Hemodynamic changes on fMRI were assessed during an SRT task in 17 unmedicated first episode psychosis (FEP) patients and matched healthy controls. Results: The groups demonstrated comparable procedural learning and associated activation of anterior cingulate cortex, subcortical structures, and many left frontal structures. The groups also demonstrated comparable increased activation of right parietal structures on trials with demands for spatial localization without procedural memory. Relative to healthy controls, the schizophrenia sample showed less activation of one region of the left middle frontal cortex and more activation of left superior temporal cortex on procedural trials, but more activation of right medial frontal cortex on localization trials. Conclusions: Intact SRT procedural learning and normal or enhanced hemodynamic response in subcortical and right cortical structures diverges from prior results with medicated samples, suggesting a more focal cerebral dysfunction in the left middle frontal cortex before the onset of treatment. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Brain mechanisms for reading and language processing in spina bifida meningomyelocele: A combined magnetic source- and structural magnetic resonance imaging study.

Objective: The development of the ability to process spoken and written language depends upon a network of left hemisphere temporal, parietal, and frontal regions. The present study explored features of brain organization in children with spina bifida meningomyelocele (SBM) and shunted hydrocephalus, who commonly present with precocious development of word reading skills and preservation of vocabulary and grammar skills. Method: Eight children with SBM were compared with 15 IQ and reading-level matched, typically developing controls on MRI-based morphometric and Magnetic Source Imaging-derived neurophysiological profiles. Results: Children with SBM showed reduced magnetic activity in left inferior parietal regions during spoken word recognition and pseudoword reading tasks. We also noted reduced surface area/volume in inferior parietal and posterior temporal regions in SBM and increased gray matter volumes in left middle frontal regions and gyral complexity in left posterior temporal and inferior parietal regions. Conclusions: A complex pattern of changes in cortical morphology and activation may serve as evidence for structural and functional brain reorganization ensuring preservation of language and decoding abilities in children with SBM. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Relation of reward from food intake and anticipated food intake to obesity: A functional magnetic resonance imaging study.

The authors tested the hypothesis that obese individuals experience greater reward from food consumption (consummatory food reward) and anticipated consumption (anticipatory food reward) than lean individuals using functional magnetic resonance imaging (fMRI) with 33 adolescent girls (mean age = 15.7, SD = 0.9). Obese relative to lean adolescent girls showed greater activation bilaterally in the gustatory cortex (anterior and mid insula, frontal operculum) and in somatosensory regions (parietal operculum and Rolandic operculum) in response to anticipated intake of chocolate milkshake (vs. a tasteless solution) and to actual consumption of milkshake (vs. a tasteless solution); these brain regions encode the sensory and hedonic aspects of food. However, obese relative to lean adolescent girls also showed decreased activation in the caudate nucleus in response to consumption of milkshake versus a tasteless solution, potentially because they have reduced dopamine receptor availability. Results suggest that individuals who show greater activation in the gustatory cortex and somatosensory regions in response to anticipation and consumption of food, but who show weaker activation in the striatum during food intake, may be at risk for overeating and consequent weight gain. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Static functional study with magnetic resonance of anterior shoulder instability

We studied the glenohumeral joint, in its different components, with cine MRI. Ten asymptomatic volunteers and 6 patients with recurrent shoulder instability were examined with T2-weighted GE MR sequences on the axial plane with the subjects' arms rotated in different positions. The sections corresponding to the subcoracoid space and bicipital groove were recorded in closed-loop video format for cine display. Normal morphological glenoid labrum changes were demonstrated in different degrees of humerus rotation. The subscapularis tendon and the capsule were redundant and infolded toward the joint on internal rotation in 4/6 patients. We found capsular detachment in 2 patients, humeral head subluxation in 3 and subcoracoid impingement in 2 patients. Cine MRI permitted the accurate study of the changes in the glenoid labrum, capsule and subscapularis tendon in all patients and it also showed narrowed coracohumeral distance (< 11 mm) on internal rotation.     

Prefrontal cortex involvement in selective letter generation: a functional magnetic resonance imaging study

Leech neurons exposed to salines containing inorganic Ca(2+)-channel blockers generate rhythmic bursts of impulses. According to an earlier model, these blockers unmask persistent Na+ currents that generate plateau-like depolarizations, each triggering a burst of impulses. The resulting increase in intracellular Na+ activates an outward Na+/K+ pump current that contributes to burst termination. We tested this model by examining systematically the effects of six transition metal ions (Co2+, Ni2+, Mn2+, Cd2+, La3+, and Zn2+) on the electrical activity of neurons in isolated leech ganglia. Each ion induced bursting activity, but the amplitude, form, and persistence of bursting differed with the ion used and its concentration relative to Ca2+. All ions tested suppressed chemical synaptic transmission between identified motor neurons, consistent with block of voltage-dependent Ca2+ currents in these cells. In addition, a strong correlation between suppression of synaptic transmission and burst amplitudes was obtained. Finally, burst duration was increased and the rate of repolarization decreased in reduced K+ saline, as expected for pump-dependent repolarization. These results provide further support for the hypothesis that a novel form of oscillatory electrical activity driven by persistent Na+ currents and the Na+/K+ pump occurs in leech ganglia exposed to Ca(2+)-channel blockers.     

Activation of the hippocampal formation by vestibular stimulation: a functional magnetic resonance imaging study

Functional MRI (f-MRI) is a non-invasive technique developed to permit functional mapping of the brain with a better temporal and spatial resolution than that offered by PET techniques. In our study, f-MRI was performed using blood oxygenation level dependent (BOLD) contrast imaging based on the magnetic properties of hemoglobin. This method relies on changes in the blood supply to the brain that accompany sensory stimulation or changes in cognitive state. All the images were obtained at 1.5 T on a Signa GEMS without ultrafast imaging. The vestibular stimulation was cold irrigation of the external auditory meatus (caloric stimulation). A population of normal healthy volunteers without a history of vestibular dysfunction was studied. The hippocampal formation as well as the retrosplenial cortex and the subiculum were activated by vestibular stimulation, suggesting that this activation may be related to spatial disorientation and a sensation of self-rotation experienced by the subjects during vestibular stimulation. The other results are similar to those obtained using PET.     

Lateralization of prefrontal activation during internal mental calculation: a functional magnetic resonance imaging study

We have reported previously that oxysterols inhibit astrogliosis and intracranial glioblastoma growth. To elucidate the mechanism of action of these molecules in vivo, we have investigated their effect on the cholesterol biosynthesis in the injured brain. In a bilateral lesion model, injection of liposomes containing 7 beta-hydroxy-cholesterol decreased [3H]acetate incorporation into neutral lipids and cholesterol by 30% and 40%, respectively. Structural analogues were tested using a unilateral lesion model. The injury did not significantly affect cholesterogenesis; injection of 7 beta-hydroxycholesterol or 7 beta-hydroxycholesteryl-3-oleate reduced acetate incorporation into cholesterol by 47% and 43%, respectively. Both 7-ketocholesteryl-3-oleate and 7 alpha-hydroxycholesteryl-3-oleate inhibited cholesterogenesis by 32%. As cholesterol and by-products of the cholesterol pathway play a key role in cell division, we have assessed the effect of oxysterols on reactive astrocyte proliferation. The incorporation of bromodeoxyuridine showed that up to 46% of astrocytes were proliferating 24 h after the injury. Injection of 12 nmol of 7 beta-hydroxycholesterol or 7 beta-hydroxycholesteryl-3-oleate reduced the labelling index to 26%, whereas the labelling index in the 7-keto-cholesteryl-3-oleate-treated cortex was 37%. These findings demonstrate that oxysterols are potent inhibitors of the endogenous cholesterol biosynthesis in brain and show a correlation between cholesterogenesis and reactive astrocyte proliferation.     

A magnetic resonance imaging study of planum temporale asymmetry in men with developmental dyslexia

The influence of ionic strength and composition on the binding and inhibition of human leukocyte elastase by glycosaminoglycans with variable degree and position of sulfation was investigated. The kinetic mechanism of inhibition had a hyperbolic, mixed-type character with a competitive component that was promoted by low ionic strength, reduced by phosphate ions, and which also depended on the substrate and glycosaminoglycan structure. Enzyme binding was a cooperative phenomenon that varied with ionic strength and composition. The inhibition patterns correlated with the cationic character of elastase and with the distribution of arginines on its molecular surface, most notably with residues located in the vicinity of the substrate binding region. The order of affinity for elastase binding was chondroitin 4-sulfate < chondroitin 6-sulfate < dermatan sulfate, iduronate-containing derivatives being superior with respect to the glucuronate-containing counterparts. Additional sulfation at both the 4- and 6- positions or at the N- and 4-positions of the N-acetylgalactosamine moiety decidedly improved the inhibitory efficiency. The results highlight a fundamental physiological role of enzyme-glycosaminoglycan interactions. In the azurophil granule of the human polymorphonuclear neutrophil, elastase and other enzymes are bound to a matrix of chondroitin 4-sulfate because this is the only glycosaminoglycan that simultaneously offers good binding for enzyme compartmentalization together with prompt release from the bound state at the onset of phagocytosis.     

Cerebral structural abnormalities in obsessive-compulsive disorder. A quantitative morphometric magnetic resonance imaging study

BACKGROUND: A previous pilot study of only posterior brain regions found lower white-matter volume in patients with obsessive-compulsive disorder than in normal control subjects. We used new cohorts of patients and matched normal control subjects to study whole-brain volume differences between these groups with magnetic resonance imaging-based morphometry. METHODS: Ten female patients with obsessive-compulsive disorder and 10 female control subjects, matched for handedness, age, weight, education, and verbal IQ, underwent magnetic resonance imaging with a 3-dimensional volumetric protocol. Scans were blindly normalized and segmented by means of well-characterized semiautomated intensity contour mapping and differential intensity contour algorithms. Brain structures investigated included the cerebral hemispheres, cerebral cortex, diencephalon, caudate, putamen, globus pallidus, hippocampus amygdala, third and fourth ventricles, corpus callosum, operculum, cerebellum, and brain stem. Anterior to posterior neocortical regions, including precallosum, anterior pericallosum, posterior pericallosum, and retrocallosum, with adjacent white matter were also measured. Volumes found different between groups were correlated with Yale-Brown Obsessive Compulsive Scale score and Rey-Osterieth Complex Figure Test measures. RESULTS: Confirming results of our earlier pilot study and expanding the findings to the whole brain, patients with obsessive-compulsive disorder had significantly less total white matter but, in addition, significantly greater total cortex and opercular volumes. Severity of obsessive-compulsive disorder and nonverbal immediate memory correlated with opercular volume. CONCLUSIONS: Replication of volumetric white-matter differences suggests a widely distributed structural brain abnormality in obsessive-compulsive disorder. Whereas determining the etiogenesis may require research at a microscopic level, understanding its functional significance can be further explored via functional neuroimaging and neuropsychological studies.     

Functional magnetic resonance imaging evidence for right-hemisphere involvement in processing unusual semantic relationships.

Brain areas active in generating usual (typical) or unusual (atypical) noun–verb relations were examined using functional magnetic resonance imaging. Seven adults generated the 1st verb to come to mind (usual verb) in response to novel and repeated nouns (priming test) and then generated either an unusual verb or the 1st verb to come to mind in response to novel nouns (unusual test). The left inferior prefrontal cortex (LIPC) and right cerebellum were more active when generating usual verbs to novel nouns than to repeated nouns. When participants generated unusual verbs, there was no increased activation in LIPC, but there was increased activity in the right middle and superior frontal gyri, left middle frontal gyrus, and bilateral cerebellum. Results support theories that the right hemisphere is involved in the processing of distant associations that may be useful in creative thought and problem solving. (PsycINFO Database Record (c) 2010 APA, all rights reserved)