Brain imaging in a patient with hemimicropsia.

Hemimicropsia is an isolated misperception of the size of objects in one hemifield (objects appear smaller) which is, as a phenomenon of central origin, very infrequently reported in literature. We present a case of hemimicropsia as a selective deficit of size and distance perception in the left hemifield without hemianopsia caused by a cavernous angioma with hemorrhage in the right occipitotemporal area. The symptom occurred only intermittently and was considered the consequence of a local irritation by the hemorrhage.

Human cortical areas underlying the perception of optic flow: brain imaging studies.

In summary, we have reviewed electrophysiological and brain imaging studies of motion and optic-flow processing. Single-unit studies indicate that MST (V5a) is a site of optic-flow extraction and that this information can be used to guide pursuit eye movements and to estimate heading. The EEG and MEG studies point to a localized electrical dipole in occipitotemporal cortex evoked by visual motion.

Dicationic 2-fluorenonylcarbapenems: potent anti-MRS agents with improved solubility and pharmacokinetic properties.

The synthesis and biological evaluation of a series of dicationic-substituted 2-fluorenonylcarbapenems is described. This class of compounds showed enhanced water solubility while maintaining potent activity against MRS. Introduction of a 1-beta-methyl substituent was found to improve pharmacokinetics.

The synthesis and anti-MRSA activity of amidinium-substituted 2-dibenzofuranylcarbapenems.

A series of amidinium-substituted 2-dibenzofuranylcarbapenems with potent activity against MRSA has been synthesized via a Stille cross-coupling reaction. These new carbapenems show reduced serum protein binding and improved in vivo efficacy as a consequence of the positively charged amidinium substituent.

2-Naphthylcarbapenems: broad spectrum antibiotics with enhanced potency against MRSA.

A regioisomeric set of 2-naphthylcarbapenems featuring cationic substituents was synthesized. Optimal placement of the cationic group was found to markedly improve activity against methicillin-resistant staphylococci while maintaining a good spectrum of gram-negative activity.

Inhibition of IMP-1 metallo-beta-lactamase and sensitization of IMP-1-producing bacteria by thioester derivatives.

IMP-1 metallo-beta-lactamase is a transferable carbapenem-hydrolyzing enzyme found in some clinical isolates of Pseudomonas aeruginosa, Serratia marcescens and Klebsiella pneumoniae. Bacteria that express IMP-1 show significantly reduced sensitivity to carbapenems and other beta-lactam antibiotics. A series of thioester derivatives has been shown to competitively inhibit purified IMP-1.

Synthesis and SAR of thioester and thiol inhibitors of IMP-1 metallo-beta-lactamase.

Potent thioester and thiol inhibitors of IMP-1 metallo-beta-lactamase have been synthesized employing a solid-phase Mitsunobu reaction as the key step.

The psychophysics of perceptual memory.

Psychophysical studies of short-term memory for attributes or dimensions of the visual stimulus known to be important in early visual processing--spatial frequency, orientation, contrast, motion--identify an early perceptual memory system. The proposed system, which may be part of the Schacter-Tulving perceptual representation system (PRS), is located early in the visual processing stream, prior to the structural description system responsible for shape priming but beyond primary visual cortex (V1), and consists of a series of parallel special-purpose perceptual mechanisms with independent but limited processing resources, where each mechanism is devoted to the analysis of a single stimulus dimension and is coupled to a memory store. The experimental evidence for this hypothesis is reviewed.

MR-eyetracker: a new method for eye movement recording in functional magnetic resonance imaging.

We present a method for recording saccadic and pursuit eye movements in the magnetic resonance tomograph designed for visual functional magnetic resonance imaging (fMRI) experiments. To reliably classify brain areas as pursuit or saccade related it is important to carefully measure the actual eye movements. For this purpose, infrared light, created outside the scanner by light-emitting diodes (LEDs), is guided via optic fibers into the head coil and onto the eye of the subject.

Spatial-frequency discrimination, brain lateralisation, and acute intake of alcohol.

The effect of alcohol (breath-alcohol level of 0.1%) on perceptual discrimination of low (1.5 cycles deg-1) and high (8 cycles deg-1) spatial frequencies in the left and right visual field was measured in eighteen right-handed males, in a double-blind, balanced placebo design.

Impairment in preattentive visual processing in patients with Parkinson's disease.

We explored the possibility of whether preattentive visual processing is impaired in Parkinson's disease. With this aim, visual discrimination thresholds for orientation texture stimuli were determined in two separate measurement sessions in 16 patients with idiopathic Parkinson's disease. The results were compared with those of 16 control subjects age-matched and 16 young healthy volunteers.

Electrophysiological localization of brain regions involved in perceptual memory.

Event-related potentials (ERP) were recorded during perceptual discrimination and short-term memory, varying the interstimulus interval (1-10 s) in delayed spatial frequency discrimination. Accuracy of discrimination remained unimpaired across this time interval, but choice reaction times increased. A brain source localization (BESA) model showed that the activity of the parietal and right temporal sources increased with long retention intervals in a sequential activation pattern where a long-latency component of the parietal source specific to the memory condition was observed, the latency of which matched a memory-related increase in choice reaction times in the cognitive task.

The processing of first- and second-order motion in human visual cortex assessed by functional magnetic resonance imaging (fMRI).

We have examined the activity levels produced in various areas of the human occipital cortex in response to various motion stimuli using functional magnetic resonance imaging (fMRI) methods. In addition to standard luminance-defined (first-order) motion, three types of second-order motion were used. The areas examined were the motion area V5 (MT) and the following areas that were delineated using retinotopic mapping procedures: V1, V2, V3, VP, V3A, and a new area that we refer to as V3B.

Effect of eye movements on the magnitude of functional magnetic resonance imaging responses in extrastriate cortex during visual motion perception.

We have studied the effects of pursuit eye movements on the functional magnetic resonance imaging (fMRI) responses in extrastriate visual areas during visual motion perception. Echoplanar imaging of 10-12 image planes through visual cortex was acquired in nine subjects while they viewed sequences of random-dot motion. Images obtained during stimulation periods were compared with baseline images, where subjects viewed a blank field.

Limited-capacity mechanisms of visual discrimination.

Discrimination thresholds of spatial frequency and choice reaction times (RT) were measured in three subjects who performed a dual-judgment delayed discrimination task. Two reference gratings were presented side-by-side with a 0-800 msec stimulus onset asynchrony (SOA), which were followed after a 5-sec retention interval by two test gratings. Subjects judged which component changed and which interval had the higher spatial frequency (SF).

Contrast detection, discrimination and adaptation in patients with Parkinson's disease and multiple system atrophy.

Visual spatial contrast thresholds and suprathreshold contrast matches were measured before and after adaptation to high-contrast sinewave gratings in patients with Parkinson's disease (n = 27), patients with multiple system atrophy (n = 6) and a group of age-matched control patients without CNS disease (n = 27). Contrast thresholds were higher in the Parkinson's disease patients than in either the multiple system atrophy patients or control patients. The effect of contrast adaptation on both contrast thresholds and matches was approximately equal in the three groups.

Competition and sharing of processing resources in visual discrimination.

Discrimination thresholds for spatial frequency and contrast tested individually were compared with dual discrimination of contrast and spatial frequency, and dual discrimination of 2 contrast or spatial frequency components. The components were presented overlapping, forming a compound grating or as side-by-side simple gratings. When observers had to judge contrast and spatial frequency simultaneously, discrimination thresholds increased by an amount predicted by a model of stimulus uncertainty for orthogonal dimensions (1.

Visual discrimination and short-term memory for random patterns in patients with a focal cortical lesion.

Visual discrimination and short-term recognition memory for computer-generated random patterns were explored in 23 patients with a postsurgical lesion in one of the cortical hemispheres. Their results are compared with those of 23 age-matched volunteers. In a same-different forced-choice discrimination task, d' and log beta (measures of sensitivity and bias), as well as reaction time (RT) were determined.

Detection and discrimination of first- and second-order motion in patients with unilateral brain damage.

The present investigation explored the extent to which extrastriate cortex is necessary for various aspects of motion processing and whether the processing of first-order (Fourier) and second-order (non-Fourier) motion involves the same extrastriate cortical regions. Orientation, direction, and speed discrimination thresholds were measured in 21 patients with unilateral damage to the lateral occipital, temporal, or posterior parietal cortex. Their results were compared with those of 14 age-matched control subjects.

Postnatal development and the differential expression of presynaptic terminal-associated proteins in the developing retina of the Brazilian opossum, Monodelphis domestica.

In the present study we have characterized the postnatal (PN) development of the retina in the Brazilian opossum, Monodelphis domestica. Monodelphis, a small, pouchless marsupial, undergoes a protracted period of postnatal development. Using bromodeoxyuridine immunohistochemistry, we have investigated postnatal neurogenesis of the retina.

Parallel processing in visual short-term memory.

Visual short-term memory for the contrast and spatial frequency of sinusoidal gratings was measured in a delayed discrimination task in which the 2 stimuli to be compared were separated in time by 1-10 s interstimulus intervals (ISIs). Delayed discrimination thresholds for spatial frequency and contrast were compared, both when the 2 types of thresholds were measured in separate blocks of trials and when the 2 types of measures were randomly intermixed in an uncertainty paradigm, which required participants to process information about both dimensions on each trial. In both cases, accuracy of memory for spatial frequency was independent of ISI, but memory for contrast decreased as ISI increased.

Human colour discrimination based on a non-parvocellular pathway.

Background: Traditionally, colour information is assumed to be carried by neural channels in the parvocellular pathway and to be encoded in an opponent manner, while other, non-parvocellular, spectrally non-opponent channels are thought to play no part in colour vision. But is the parvocellular pathway the only way that colours can be discriminated in human vision? We studied two patients with cerebral achromatopsia, who lack conscious colour perception but are nevertheless able to make use of colour information. In particular, we investigated whether, in these patients, colour discrimination is mediated by the parvocellular pathway.

Visual short-term memory of stimulus velocity in patients with unilateral posterior brain damage.

Neurophysiological studies indicate the existence of an area in the extrastriate monkey cortex specialized for the processing of stimulus motion. The present investigation was conducted to determine whether a homologous area exits in the human cortex that underlies the processing and short-term storage of velocity information. Contrast detection and velocity discrimination thresholds were measured in a group of 23 patients with unilateral focal damage to either the lateral occipital, temporal, or posterior parietal cortex.

Comparison of two mechanical carotid baroreceptor stimulation techniques.

We compared two mechanical carotid baroreceptor stimulation techniques, the phase related external suction (PRES) method and the conventional neck suction techniques concerning their effects on blood pressure and heart rate responses in a group of 10 normotensive men. The cuff pressure using the PRES method was phase-locked in time to the R-wave of the ECG. During the conventional neck suction technique the cuff pressure changes were not related to the cardiac cycle, it was either negative or positive.

Effect of contrast and adaptation on the perception of the direction and speed of drifting gratings.

Three experiments were conducted to analyse the effect of contrast and adaptation state on the ability of human observers to discriminate the motion of drifting gratings. In the first experiment, subjects judged the direction of briefly presented gratings, which slowly drifted leftward or rightward. The test gratings were enveloped in space by a raised cosine function and in time by a Gaussian.