Demonstration of tuning to stimulus orientation in the human visual cortex: a high-resolution fMRI study with a novel continuous and periodic stimulation paradigm.

Cells in the animal early visual cortex are sensitive to contour orientations and form repeated structures known as orientation columns. At the behavioral level, there exist 2 well-known global biases in orientation perception (oblique effect and radial bias) in both animals and humans. However, their neural bases are still under debate. To unveil how these behavioral biases are achieved in the early visual cortex, we conducted high-resolution functional magnetic resonance imaging experiments with a novel continuous and periodic stimulation paradigm. By inserting resting recovery periods between successive stimulation periods and introducing a pair of orthogonal stimulation conditions that differed by 90° continuously, we focused on analyzing a blood oxygenation level-dependent response modulated by the change in stimulus orientation and reliably extracted orientation preferences of single voxels. We found that there are more voxels preferring horizontal and vertical orientations, a physiological substrate underlying the oblique effect, and that these over-representations of horizontal and vertical orientations are prevalent in the cortical regions near the horizontal- and vertical-meridian representations, a phenomenon related to the radial bias. Behaviorally, we also confirmed that there exists perceptual superiority for horizontal and vertical orientations around horizontal and vertical meridians, respectively. Our results, thus, refined the neural mechanisms of these 2 global biases in orientation perception.

Processing of infant-directed speech by adults.

Adults typically address infants in a special speech mode called infant-directed speech (IDS). IDS is characterized by a special prosody (i.e., higher pitched, slower and hyperarticulated) and a special lexicon ("baby talk"). Here we investigated which areas of the adult brain are involved in processing IDS, which aspects of IDS (prosodic or lexical) are processed, to what extent the experience of being a parent affects the way adults process IDS, and the effects of gender and personality on IDS processing. Using functional magnetic resonance imaging, we found that mothers with preverbal infants showed enhanced activation in the auditory dorsal pathway of the language areas, regardless of whether they listened to the prosodic or lexical component of IDS. We also found that extroverted mothers showed higher cortical activation in speech-related motor areas than did mothers with lower extroverted personality scores. Increased cortical activation levels were not found for fathers, non-parents, or mothers with older children.

Correction of 3D rigid body motion in fMRI time series by independent estimation of rotational and translational effects in k-space.

In functional magnetic resonance imaging (fMRI), even subvoxel motion dramatically corrupts the blood oxygenation level-dependent (BOLD) signal, invalidating the assumption that intensity variation in time is primarily due to neuronal activity. Thus, correction of the subject's head movements is a fundamental step to be performed prior to data analysis. Most motion correction techniques register a series of volumes assuming that rigid body motion, characterized by rotational and translational parameters, occurs. Unlike the most widely used applications for fMRI data processing, which correct motion in the image domain by numerically estimating rotational and translational components simultaneously, the algorithm presented here operates in a three-dimensional k-space, to decouple and correct rotations and translations independently, offering new ways and more flexible procedures to estimate the parameters of interest. We developed an implementation of this method in MATLAB, and tested it on both simulated and experimental data. Its performance was quantified in terms of square differences and center of mass stability across time. Our data show that the algorithm proposed here successfully corrects for rigid-body motion, and its employment in future fMRI studies is feasible and promising.

A temporal frequency-dependent functional architecture in human V1 revealed by high-resolution fMRI.

Although cortical neurons with similar functional properties often cluster together in a columnar organization, only ocular dominance columns, the columnar structure representing segregated anatomical input (from one of the two eyes), have been found in human primary visual cortex (V1). It has yet to be shown whether other columnar organizations that arise only from differential responses to stimulus properties also exist in human V1. Using high-resolution functional magnetic resonance imaging, we have found such a functional architecture containing domains that respond preferentially to either low or high temporal frequency.

Contrast adaptation and representation in human early visual cortex.

The human visual system can distinguish variations in image contrast over a much larger range than measurements of the static relationship between contrast and response in visual cortex would suggest. This discrepancy may be explained if adaptation serves to re-center contrast response functions around the ambient contrast, yet experiments on humans have yet to report such an effect. By using event-related fMRI and a data-driven analysis approach, we found that contrast response functions in V1, V2, and V3 shift to approximately center on the adapting contrast. Furthermore, we discovered that, unlike earlier areas, human V4 (hV4) responds positively to contrast changes, whether increments or decrements, suggesting that hV4 does not faithfully represent contrast, but instead responds to salient changes. These findings suggest that the visual system discounts slow uninformative changes in contrast with adaptation, yet remains exquisitely sensitive to changes that may signal important events in the environment.

Consistent and precise localization of brain activity in human primary visual cortex by MEG and fMRI.

The tomographic localization of activity within human primary visual cortex (striate cortex or V1) was examined using whole-head magnetoencephalography (MEG) and 4-T functional magnetic resonance imaging (fMRI) in four subjects. Circular checkerboard pattern stimuli with radii from 1.8 to 5.2 degrees were presented at eccentricity of 8 degrees and angular position of 45 degrees in the lower quadrant of the visual field to excite the dorsal part of V1 which is distant from the V1/V2 border and from the fundus of the calcarine sulcus. Both fMRI and MEG identified spatially well-overlapped activity within the targeted area in each subject. For MEG, in three subjects a very precise activation in V1 was identified at 42 ms for at least one of the two larger stimulus sizes (radii 4.5 and 5.2 degrees ). When this V1 activity was present, it marked the beginning of a weak wave of excitations in striate and extrastriate areas which ended at 50 ms (M50). The beginning of the next wave of activations (M70) was also marked by a brief V1 activation, mainly between 50 and 60 ms. The mean separation between V1 activation centers identified by fMRI and the earliest MEG activation was 3-5 mm.

Human ocular dominance columns as revealed by high-field functional magnetic resonance imaging.

We mapped ocular dominance columns (ODCs) in normal human subjects using high-field (4 T) functional magnetic resonance imaging (fMRI) with a segmented echo planar imaging technique and an in-plane resolution of 0.47 x 0.47 mm(2). The differential responses to left or right eye stimulation could be reliably resolved in anatomically well-defined sections of V1. The orientation and width ( approximately 1 mm) of mapped ODC stripes conformed to those previously revealed in postmortem brains stained with cytochrome oxidase. In addition, we showed that mapped ODC patterns could be largely reproduced in different experiments conducted within the same experimental session or over different sessions. Our results demonstrate that high-field fMRI can be used for studying the functions of human brains at columnar spatial resolution.

Cerebral polyopia with extrastriate quadrantanopia: report of a case with magnetic resonance documentation of V2/V3 cortical infarction.

This is a case report of the occurrence of cerebral diplopia with right-side superior homonymous quadrantanopia in a young woman after chiropractic neck manipulation. Magnetic resonance imaging confirmed an infarct in the left inferior V2/V3 (extrastriate) cortex. The characteristics of the diplopia are illustrated with the patient's drawings, and persisting abnormalities in perception are described in the area of the initial field defect after static (computed) visual field testing yielded normal results.

Imaging lungs using inert fluorinated gases.

Rat lungs were imaged by 19F projection MRI of hexafluoroethane, mixed with 20% oxygen to form the inhaled gas. The 3D image had 700 microm resolution, and the data took 4.3 h to acquire. Free induction decays were collected in the presence of steady magnetic field gradients in 686 different directions. To take advantage of fast relaxation (T1 = 5.9 +/- 0.2 ms), the repetition time was 5 ms. To eliminate signal loss from magnetic field inhomogeneities, data were collected within 2 ms of spin excitation (from 80 micros to 2 ms after the 42-micros pi/2 pulses). The singular value decomposition of the transform from frequency to time domain was used to obtain projections despite the absence of data during and immediately after the RF pulses. Inert fluorinated gas imaging may be less expensive than polarized noble gas imaging and is appropriate for imaging steady-state rather than transient gas concentrations.

Harmonic interactions in health care facilities, Part II: Practical handling of harmonic interactions.

This is part two in a two-part series aimed at helping the reader understand and prepare for a world of electrical peculiarities. Part one offered an introduction to harmonics. This document covers practical issues involving the handling and mitigation of harmonic distortion.

Harmonic interactions in health care facilities.

This document is the beginning of a two-part series that will help the reader understand and prepare for a world of electrical peculiarities. Part I offers an introduction to the problematic world of harmonics and their effects on medical equipment. Part II will take the subject a step further to cover the practical issues involving the handling and mitigation of harmonic distortion.

Velocity distribution of slow fluid flows in Bentheimer sandstone: an NMRI and propagator study.

This work addresses the special problems of measuring flow velocity distributions in rock by NMR methods. Specifically, these problems are to measure very slow flows as well as flows in the presence of background magnetic field gradients caused by heterogeneities of the rock. We modify a stimulated echo sequence for use in diffusion measurements, in order to maximize velocity sensitivity and minimize background gradient effects. Accurate velocity images of Soltrol 220 oil in sandstone were made for flow velocities up to around 0.04 mm/s with an imager that does not have echo-planar capability. Accurate velocity distributions by the propagator method can be obtained even with stimulated echo delays of 1.9 T1 by phase cycling combined with suitable crusher gradients.

Stabilization of spinal injury for early transfer.

We have reviewed the means of transport and type of stabilization used for all patients with acute spinal cord injuries (SCI) transferred to our center since 1985 to determine what effect these variables may have had on change in level of impairment and probability of neurologic improvement after arrival. Sixty-one patients were reviewed, 47 males and 14 females, with a mean age of 34 years. Twenty-five patients (41%) were transported by ground ambulance, 33 (54%) by helicopter, three (5%) by fixed-wing aircraft. Forty-three patients (70.5%) had cervical spine injuries, 11 (18%), thoracic spine injuries, and seven (11.5%), lumbar spine injuries. Fifty-one patients (84%) were transferred within 24 hours of injury. A variety of standard methods of stabilization were used during transport. No patient suffered ascending level of injury as a result of early transfer. Level of function improved before discharge in 26 of 61 patients (43%); patients transported within 24 hours were more likely to show improvement (25/51) than those transported after 24 hours (1/10). There was no significant difference in the probability of improvement between ground (8/25) or air (18/36) transport. Skeletal traction was used before transfer in only four of 43 patients with cervical spine injuries, and was maintained as a method of long-term stabilization in two patients. We conclude that acute SCI patients can be safely transported by air or ground using standard precautions. Distance and extent of associated injury are the best determinants of mode of transport. Skeletal traction does not appear to be a prerequisite for safe, early transfer of SCI patients.

Acquired resistance to rifampicin by Mycobacterium kansasii.

Two patients with Mycobacterium kansasii infection of the lung had organisms sensitive to rifampicin. Following treatment, essentially with rifampicin alone, the patients began to excrete organisms completely resistant to rifampicin. The ability of M. kansasii to acquire resistance to rifampicin during treatment has been clearly demonstrated. This reinforces the need to treat this infection with an adequate multiple drug regimen.

Isolation of mycobacteria from clinical specimens by use of selective 7H11 medium.

7H11 agar containing carbenicillin, amphotericin B, polymyxin B and trimethoprim lactate (selective 7H11 or S7H11) was used for the selective isolation of mycobacteria from clinical specimens. This medium as previously described contained 100 mug. carbenicillin per ml. It was found that reducing the concentration of carbenicillin to 50 mug. per ml. made S7H11 less inhibitory to certain strains of mycobacteria. However, some strains of M. kansaii, M. intracellulare, and M. gordonae still do not grow well on S7H11. Of 3,134 clinical specimens (mostly sputum) received, processed, and plated on 7H11 agar and the S7H11 medium, 508 positive specimens were isolated. Of these, 402 were positive on both types of media, 30 were positive on 7H11 only, 19 were positive on S7H11 only, 52 were contaminated on 7H11 but positive on S7H11, while only 5 were contaminated on S7H11 and positive on the plain medium. Thus, the total positive specimens on 7H11 was 437 and total positive specimens on the selective medium was 473. Used in conjunction with nonselective media, S7H11 agar appears to be a valuable culture medium for used in diagnostic mycobacteriology laboratories.