Four experiments show that presentation of a synchronous premask frame within a 40-Hz, flickering premask matrix primes subsequent detection of a Kanizsa-type square by generation of a 40-Hz prime. Reaction time (RT) priming effects indicated a 150-200-ms prime duration following premask display. Kite were also found to be sensitive to the phase relationship between offset of the premask display relative to the onset time of the target: Priming effects were maximal when the target was presented out of phase with premask presentation (i.e., at interstimulus intervals displaced by 180° relative to the 40-Hz rhythm of premask-frame presentation). Taken together, these results demonstrate the existence of a very short-term visual memory that oscillates at 40 Hz. The findings are discussed in the context of complementary psychological and neurophysiological findings related to visual-object coding and the role of gamma-band activity in the brain.In order to represent the organization of separable feature elements as a single perceptual entity, the elements must be independently coded and then recombined or "bound" into a composite object representation. Neurophysiological studies have demonstrated that separate features of a stimulus object are coded by functionally specialized neurons, optimally tuned to particular stimulus attributes such as length, spatial frequency, spectral density, and orientation (e.g., Hubel & Wiesel, 1959;Livingstone & Hubel, 1988). In addition, recent single-cell recording studies have demonstrated that, although features belonging to the same object are coded by separate neurons, these neurons adjust their firing patterns to fire in synchrony. These findings have led to the hypothesis that synchronization of patterns of activity among featurecoding neurons is the most likely neurophysiological correlate of psychophysical "feature binding" (e.g., Gray, Konig, Engel, & Singer, 1989).The electrophysiological recordings of synchronized neuronal activity have typically been obtained from a series of

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The purpose of this study is to evaluate cardiac and respiratory modulations in the signals of arterial spin labeling (ASL) perfusion magnetic resonance imaging (MRI) using RETROICOR, an image domain based retrospective correction method. Systematic comparisons were conducted for tagging schemes, pulsed (PASL) versus frequency-modulated continuous (CASL) methods, and the use of background suppression (BGS). Results showed that cardiac pulsation accounted for more signal fluctuation in PASL than in CASL (two-tailed paired Student's t-test, p < 10(-3)), whereas no significant difference was found in the effect of respiratory motion ( p=0.55) on the two tagging schemes studied. For PASL, significantly more improvement was achieved by the inclusion of cardiac pulsation than respiratory motion in RETROICOR ( p < 0.01). On the contrary, the inclusion of respiratory motion offers more improvement for CASL ( p < 0.02). BGS effectively improved the temporal signal-to-noise ratio (tSNR) as previous studies reported, but no significant difference was measured in the spectral power of physiological modulations relative to the entire spectrum of PASL signals before and after the superimposition of BGS ( p=0.63 for cardiac component, p=0.67 for respiratory component). Thus, we conclude that BGS reduces noise without spectral selectivity, and the improvements of tSNR from RETROICOR and BGS are additive. CASL with a labeling duration at a multiple of an R-R interval can be used to minimize signal fluctuation originating from cardiac pulsation.

Nitric oxide (NO) has been implicated in the immunopathogenesis of MS as a potential mediator of neuronal loss. To investigate the role of.NO in the development of progressive disease we measured the NO metabolites (nitrate and nitrite) and neopterin, in the urine of 129 patients with demyelinating disease (DD): 23 with clinically isolated syndromes compatible with demyelination and in 46 relapsing remitting (RR) and 60 patients with progressive MS. Eighty-nine of these 129 patients underwent Gd-enhanced MRI. In addition 58 normal control subjects (NC), 19 AIDS and 35 rheumatoid arthritis (RA) patients were studied. Patients with DD, AIDS and RA had significantly elevated urinary nitrate plus nitrite (nit : creat. urine) and neopterin (neopt : creat.urine) to creatinine ratios compared to NC subjects. (Median[25th - 75th%] nit : creat.urine: NC=1183[962 - 1365] vs DD=1245[875 - 2403], AIDS=1686[1231 - 2531], and RA=1950[1214 - 2726] mumol/mol, P<0.001 and median[25th - 75th%] neopt : creat.urine: NC=99[76 - 151] vs DD=163[119 - 266], AIDS=972[653 - 1456], and RA=389[257 - 623] mu mol/mol, P<0.001). Patients with early DD and RR MS had significantly elevated nit : creat.urine compared to patients with progressive MS (nit : creat. urine: 1612[1020 - 2733] vs 1159[790 - 1641] mu mol/mol, P=0.006). The nit : creat.urine and neopt : creat.urine did not correlate with clinical relapse or MRI activity. Excretion of.NO metabolites is increased in patients with early or relapsing-remitting disease.NO appears to be a double-edged sword, mediating tissue damage and modulating complex immunological functions which may be protective in MS.

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