Podokinetic circular vection: characteristics and interaction with optokinetic circular vection.

Stabilising horizontal body orientation in space without sight on a rotating platform by holding to a stationary structure and circular 'treadmill' stepping in the opposite direction can elicit an illusion of self-turning in space (Bles and Kapteyn in Agressologie 18:325-328, 1977). Because this illusion is analogous to the well-known illusion of optokinetic circular vection (oCV), we call it 'podokinetic circular vection' (pCV) here. Previous studies using eccentric stepping on a path tangential to the rotation found that pCV was always contraversive relative to platform rotation. In contrast, when our subjects stepped at the centre of rotation about their vertical axis, we observed an inverted, ipsiversive pCV as a reproducible trait in many of our subjects. This ipCV occurred at the same latency as the pCV of subjects reporting the actually expected contraversive direction, but had lower gain. In contrast to pCV, the nystagmus accompanying circular treadmill stepping had the same direction in all individuals (slow phase in the direction of platform motion). The direction of an individual's pCV predicted the characteristics of the CV resulting from combined opto- and podokinetic stimulation (circular treadmill stepping while viewing a pattern rotating together with the platform): in individuals with contraversive pCV, latency shortened and both gain and felt naturalness increased in comparison with pure oCV, whereas the opposite (longer latency, reduced gain and naturalness) occurred in individuals with ipCV. Taken together, the reproducibility of ipCV, the constant direction of nystagmus and the fact that pCV direction predicts the outcome of combined stimulation suggest that ipCV is an individual trait of many subjects during compensatory stepping at the centre of rotation. A hypothetical model is presented of how ipCV possibly could arise.

Optokinetic circular vection: a test of visual-vestibular conflict models of vection nascensy.

The propensity to experience circular vection (the illusory perception of self-turning evoked by a rotating scene, CV) as reflected by its onset latency exhibits considerable interindividual variation. Models of CV nascensy have linked this delay to the time it takes the visual-vestibular conflict to disappear. One line of these "conflict models" (Zacharias and Young in Exp Brain Res 41:159-171, 1981) predicts that, across individuals, CV latency (CVL) correlates positively with the vestibular time constant (TC) and negatively with the vestibular motion detection threshold (vTHR). A second type of models (Mergner et al. in Arch Ital Biol 138:139-166, 2000) predicts only an increase in CVL with TC. We here examine which of these predictions can be experimentally substantiated. Also, we ask whether the relative weight W O of the optokinetic contribution to the perception of real self-turning could also be a factor influencing CVL. We conducted 5 experiments in 29 subjects measuring: (1) CVL, (2) the TCs of velocity perception and of accompanying nystagmus during rotation in darkness and (3) likewise for displacement perception, (4) vTHR, and (5) W O as revealed by discordant visual-vestibular stimulation. CVL correlated with the nystagmus TC recorded during velocity estimation but with none of the other vestibular TCs nor with vTHR. Confirming earlier findings, CVL shortened with rising scene velocity. Finally, CVL correlated inversely with W O: the larger an individual's optokinetic weight, the shorter was his CVL. Taken together, our data favour the second type of models which invoke an antagonism between CV inhibition by the optokinetic-vestibular conflict and disinhibition by optokinetic stimulation. Idiosyncratic factors appear to strongly modulate the balance between inhibition and disinhibition, thus increasing CVL variability and obscuring the expected relation between CVL and TC.

Overcoming obstacles to late presentation for HIV infection in Europe.

OBJECTIVE: The central goal of the HIV in Europe Initiative is to promote testing and treatment throughout Europe and Central Asia in order to decrease the number of people living with HIV presenting late for care. This article summarizes the results from the HIV in Europe 2009 Conference and the early results of the projects set up by the initiative, and discusses their implications for the future. METHODS: In November 2009, 100 key stakeholders from 25 countries met in Stockholm at the HIV in Europe Conference. The focus was to address five key issues that contribute to the barriers to testing identified in 2007 at an innovative HIV conference. The conference discussed barriers to testing and other reasons for late presentation and outlined concrete recommendations to address the problem. RESULTS: An early result of the initiative has been stimulation of the process of reaching a consensus definition of what is meant by a 'late presenter', with this definition to be implemented at the European level. Steps are being taken to advocate for appropriate health policies and surveillance data related to HIV throughout Europe. Also, the initiative has set up projects related to the barriers to testing, i.e. criminalization law, stigmatization and lack of offering of testing for people presenting with certain indicator diseases. CONCLUSIONS: The final results of ongoing projects will be published and widely disseminated in 2010 and beyond. The HIV in Europe Initiative will continue to reinforce collaboration, advocacy and networking activities in the field throughout Europe.

Radar scattering from venus at large angles of incidence and the question of polar ice caps.

Spectrum analysis of radar waves backscattered from an anulus near the limb of Venus shows that a uniform scattering model applies over regions extending from the equator to within approximately 15 degrees of the poles. These observations indicate that large polar ice caps extending to latitudes as low as 60 degrees are very unlikely.

Evidence for highly reflecting materials on the surface and subsurface of vensus.

Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas.

Topography of the lunar poles from radar interferometry: a survey of cold trap locations.

Detailed topographic maps of the lunar poles have been obtained by Earth-based radar interferometry with the 3.5-centimeter wavelength Goldstone Solar System Radar. The interferometer provided maps 300 kilometers by 1000 kilometers of both polar regions at 150-meter spatial resolution and 50-meter height resolution. Using ray tracing, these digital elevation models were used to locate regions that are in permanent shadow from solar illumination and may harbor ice deposits. Estimates of the total extent of shadowed areas poleward of 87.5 degrees latitude are 1030 and 2550 square kilometers for the north and south poles, respectively.

Radar detection of phobos.

Radar echoes from the martian satellite Phobos provide information about that object's surface properties at scales near the 3.5-cm observing wavelength. Phobos appears less rough than the moon at centimeter-to-decimeter scales. The uppermost few decimeters of the satellite's regolith have a mean bulk density within 20% of 2.0 g cm(-3). The radar signature of Phobos (albedo, polarization ratio, and echo spectral shape) differs from signatures measured for small, Earth-approaching objects, but resembles those of large (>/=100-km), C-class, mainbelt asteroids.

Radar interferometric observations of venus at 70-centimeter wavelength.

A radar interferometer was used to map unambiguously the surface reflectivity of Venus in the polarized mode at a wavelength of 70 centimeters. The observed region extended from 260 degrees to 30 degrees in longitude and from -60 degrees to 50 degrees in latitude with a surface resolution of approximately 3 degrees by 3 degrees . The result agrees well in most respects with earlier maps made elsewhere at shorter wavelengths and, in addition, discloses a number of new "features."

The case for the radar radius of venus.

The Venus radius of 6085 +/- 10 kilometers, deduced from combining observations made with the Venera 4 and Mariner V space probes is incompatible with the value of 6050 +/- kilometers determined from Earth-based radar mesurements.

Eye-head coordination in moderately affected Huntington's Disease patients: do head movements facilitate gaze shifts?

In addition to many other symptoms, Huntington's Disease (HD) also causes an impairment of oculomotor functions. In particular, saccadic eye movements become progressively slower and more difficult to initiate; ultimately, patients are forced to recur to large head thrusts as means to initiate gaze shifts. We wondered whether, as a precursor of this condition, head movements would facilitate gaze shifts already in early stages of the disease. We studied horizontal head movements and eye-head coordination in 29 early stage HD patients (Ps) and 24 age matched controls (Cs). Subjects tracked random horizontal steps of visual or auditory targets while their heads were either stabilised (saccade amplitudes

Cerebral glucose metabolism in the course of subacute sclerosing panencephalitis.

Regional cerebral glucose metabolism was studied in a 15-year-old boy with subacute sclerosing panencephalitis before and after therapy with human interferon beta, using positron emission tomography of fluorine 18-2-fluoro-2-deoxyglucose. At first examination, metabolism was symmetrically decreased in the thalamus, cerebellum, and all cortical areas except prerolandic motor cortex, but increased in lentiform nucleus. A computed tomographic scan was normal. Six months later, bilateral focal necrosis centered in the previously hypermetabolic putamen was demonstrated by computed tomography and magnetic resonance imaging. The caudate nucleus and the superoposterior part of the putamen were spared, still showing increased metabolism. Corresponding with some clinical improvement, cortical glucose consumption rates had returned to a normal level.

Visually-guided saccadic eye movements in adolescents at genetic risk for schizophrenia.

Visually-guided saccades of 21 offspring of schizophrenic parents and 21 individually matched controls were compared with regard to the frequency of occurrence of saccadic hypometria and hypermetria, non-fixations, and omissions of target jumps. Target steps ranged from 10 to 60 degrees, and interstimulus intervals averaged 2.5 s; subjects were promised financial reward depending on performance. Recordings were carried out at the subjects' homes. To screen for cognitive abilities and psychopathological behavior, subjects were tested by means of an intelligence scale and a behavioral checklist. With large target steps (40-60 degrees), the high-risk group made significantly more grossly hypometric saccades (gain < or = 0.8) than the control group; responses to small target steps (10-30 degrees) exhibited a similar, albeit statistically not significant, trend. There were no significant differences with regard to the occurrence of hypermetria. Non-fixations scored marginally higher in the high-risks as compared to controls, but this was again not a significant difference. The incidence of omissions of saccades was very low in both groups. The results of the study suggest that subjects at genetic risk for schizophrenia may differ from controls by an increased incidence of conspicuously hypometric saccades. Clearly, this difference is not caused by a deficit of the saccadic motor circuitry proper; comparison to control data obtained with a similar experimental protocol suggests that it probably reflects an impaired internal control of saccades in the presence of distraction and stress. The relevance of saccades as indicators of a possible schizophrenic vulnerability is discussed.

Different effects involved in the interaction of saccades and the vestibulo-ocular reflex.

The accuracy of human goal-directed saccades during passive sinusoidal whole-body rotation is the same as that of normal saccades with the head still. Two mechanisms contribute to this accuracy: 1. There is an incomplete summation (70% on the average) of saccade and VOR velocities. 2. The duration of saccades during head rotation is lengthened if VOR and saccade velocities have the same direction, and is shortened if their direction is opposite. The latter finding supports the hypothesis that saccades are controlled by local feedback.

Locally synthesized antibodies in cerebrospinal fluid of patients with AIDS.

Twelve patients with AIDS were examined by enzyme-linked immunosorbent assay for antibody activity of IgG in serum and CSF. Two patients were only anti-HTLV III antibody carriers (stage I), two had lymphadenopathy syndrome (stage II) and eight had manifest AIDS (stage III). Eight of the 12 patients had 2- to 8-fold higher antibody titres in CSF than in serum, indicating that anti-HTLV III antibodies were produced in the nervous system. One of these patients with obviously locally synthesized anti-HTLV III antibodies in CSF belonged to stage I, two to stage II and five to stage III. Only four of these eight patients also showed locally synthesized IgG in CSF as measured by laser-nephelometry. In contrast, 61 controls with normal CSF (12), impaired blood-CSF barrier (12) multiple sclerosis (12) and various infections of the CNS other than HTLV III (25), the last two groups with locally synthesized IgG in CSF, all revealed negative results. It appears possible that locally synthesized anti-HTLV III antibodies in CSF are a sensitive and early indicator of an HTLV III infection of the nervous system.

Pragmatic-semantic and syntactic factors influencing ear differences in dichotic listening.

In a three-factorial experiment sequences of 3 words were presented dichotically. The sequences consisted of two uninflected nouns denoting a person or a group of persons and 1 verb denoting an interaction. The three factors were Ear, Syntactic Structuredness vs. Unstructuredness and Semantic-Pragmatic Structuredness vs. Unstructuredness. The sequences in the syntactic unstructuredness condition are spoken in staccato form without sentence intonation and the order of the 2 nouns and the verb was at random; in the syntactic structuredness condition the sequences were spoken fluently and with sentence intonation and the order was always N-V-N. Semantic-pragmatic structuredness of the sequences means that one of the two potential actor-object-relations between the two nouns of a sequence was more probable than the other. The results show that it is only the left hemisphere that is responsive to syntactic structuredness, while the two hemispheres seems to be equally responsive to semantic-pragmatic structuredness. But it is possible that the two hemispheres differ in the manner in which they make use of semantic structures: the left hemisphere in a selective manner, appropriate for the solution of a specific task, and the right hemisphere in a more diffuse and global manner.

Human oblique saccades: quantitative analysis of the relation between horizontal and vertical components.

Are the horizontal and vertical components of oblique saccades produced by two separate pulse generators or by a single, vectorial pulse generator? To investigate this question, purely horizontal and vertical ("cardinal") saccades as well as oblique saccades with a meridional direction of +/- 45 deg (horizontal and vertical components of equal size) were recorded in 10 human subjects using a magnetic search coil. The components of oblique saccades were slower than cardinal saccades of comparable size, yet the oblique vector velocity was slightly larger than the velocity along cardinal directions. The onset of the two components was always synchronized, but their times to peak velocity and their durations, although approximately equal on average, frequently were different in individual trials; the component velocities were weakly correlated only. Correspondingly, the trajectory of oblique saccades exhibited various types of curvature which often changed from trial to trial. There was no correlation between curvature and aiming accuracy. These results are discussed in terms of various models of saccade generation. It is suggested that each of the two components is generated by its own local feedback pulse generator; the two components would be coordinated by crosscoupling the two local feedback circuits at the level of their error signals. By contrast, the extraretinal feedback that prepares corrective saccades is apparently not evaluated componentwise but may use a vector representation, since the latency of oblique corrective saccades was a function of the vectorial error magnitude.

Color analysis of dextrose solutions using a color difference meter.

A method for quantitating color measurements in dextrose solutions by using a color difference meter is described. This method was shown to correlate well with standard American Public Health Association (APHA) color measurements. A mathematical relationship was developed relating yellowness index values to APHA numbers as described in the USP for dextrose solutions. This relationship was tested by comparing the results from standard APHA color tests on laboratory samples of autoclaved dextrose solutions to APHA numbers calculated from yellowness index values for the same samples.

[Brain involvement in acquired immunodeficiency syndrome (AIDS): computed tomography (CT) and magnetic resonance tomography (MR)]. / Zerebrale Beteiligung bei erworbenem Immunmangelsyndrom (AIDS). Computertomographie (CT) und Kernspintomographie (MR).

Involvement of the central nervous system in acquired immune deficiency syndrome (AIDS) is usually due to opportunistic infections; these frequently offer a difficult differential diagnostic problem. Imaging methods play an important part in the elucidation of symptoms. CT and MR findings were analysed in 13 patients with AIDS and neurological symptoms. Some infections of the central nervous system (encephalitis of unknown aetiology, cytomegalic encephalitis, meningitis) may show cerebral atrophy or even no morphological changes. Toxoplasmosis and PML are the most common opportunistic infections typical changes on CT and MR may lead to diagnosis. MR offers advantages compared with CT in its higher sensitivity for the demonstration even of small lesions.

First experiences with a multichannel software gradiometer recording normal and tangential components of MEG.

We describe a 28-channel magnetometer that operates as a 22-channel 'software gradiometer'. Gradiometer function is achieved by subtraction of weighted signals representing the noise field along three orthogonal axes as detected by six compensation channels. The instrument measures both normal and tangential field components; the user can select a total of 22 normal and/or tangential measuring sites from two arrays of 16 sites each. First experiences indicate that the combination of a shielded room with a software suppression of the residual field entering the room is amply sufficient to allow biomagnetic measurements in a hospital environment.