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PubMed2000

A new submicroscopic deletion that refines the 9p region for sex reversal.

Male to female sex reversal has been described in patients with deletions of chromosome 9p, and a region critical for sex reversal has been localized to p24.3, at the tip of the chromosome (TD9). It was proposed that the sex reversal may arise by haploinsufficiency for a gene localized to the minimum deletion. The 9p24.3 genes DMRT1 and DMRT2 are the favorite TD9 candidates to date, in virtue of their sequence similarity to doublesex and mab-3, sexual regulators in Drosophila and Caenorhabditis elegans, respectively. The hypothesis of sex reversal by combined haploinsufficiency for the two genes was put forward to explain the lack of mutations in either gene in XY sex-reversed females. Here we describe a XY sex-reversed patient carrying a novel 9p deletion that extends over less than 700 kb of genomic DNA. This region defines the smallest interval for sex reversal found to date. DMRT1 and DMRT2 map outside this region. Our data do not support the hypothesis of combined haploinsufficiency for DMRT1 and DMRT2. Nevertheless, DMRT1 localizes very close to the deletion breakpoint and has a pattern of expression compatible with a role in sex determination. It therefore remains a candidate gene for 9p sex reversal.

Amino Acid Sequence↗
PubMed2001

Catalytic Activity of Hexokinase in Reversed Micelles.

Reversed micelles can control the size of water pools and the physical property of water by changing W(0)(=[water]/[surfactant]). Hexokinase (HK) activity seems to be easily affected by the microenvironment in the neighborhood of the enzyme because it is assumed that HK binds to the outer mitochondrial membrane by insertion of its hydrophobic NH(2) tail. The catalytic activity of HK was examined in reversed micelles in order to study the effect of the microenvironment in the neighborhood of HK on the activity. Sodium bis(2-ethylhexyl)sulfosuccinate (AOT), hexadecyltrimethyl ammonium chloride (HTAC), and octaoxyethylene dodecyl ether (C(12)E(8)) were used as anionic, cationic, and nonionic surfactants, respectively. HK activity was obtained by measuring ATP and ADP amounts with HPLC. The high electrostatic inner surfaces of AOT and HTAC reversed micelles were not favorable for HK to exhibit the catalytic activity, but the activity in HTAC reversed micelles was 2-3 times higher than that in AOT reversed micelles and the activities in both reversed micelles revealed an optimum at W(0)=10. The phenomenon was discussed in connection with the location of HK, nonuniform distribution of substrates, and the size and physical properties of the water pools. On the other hand, HK activity was much higher in C(12)E(8) reversed micelles than in AOT and HTAC reversed micelles and increased with the concentration of C(12)E(8). This suggests that HK activity is easily revealed in hydrated ethylene oxide chains. In conclusion, it was demonstrated that HK activity depends on the microenvironment such as the electrostatic field, the physical properties of water, and the hydrophobicity. Copyright 2001 Academic Press.

Journal Article↗
PubMed2002

Human immunodeficiency virus type 1 reverse transcription is stimulated by tat from other lentiviruses.

The tat gene is required by HIV-1 for efficient reverse transcription and this function of Tat can be distinguished from its role in transcription by RNA polymerase II using tat point mutations that abrogate each function independently. The mechanism of Tat's role in reverse transcription, however, is not known, nor is it known whether this role is conserved among trans-activating factors in other retroviruses. Here we examine the abilities of heterologous viral trans-activating proteins from jembrana disease virus (jTat), HIV-2 (Tat2), and equine infectious anemia virus (eTat) to substitute for HIV-1 Tat (Tat1) and restore reverse transcription in HIV-1 carrying an inactivated tat gene. Natural endogenous reverse transcription assays showed that trans-activators from some retroviruses (Tat2 and jTat, but not eTat) could substitute for Tat1 in complementation of HIV-1 reverse transcription. Finally, we show that Y47 is critical for Tat1 to function in reverse transcription, but not HIV-1 gene expression. We mutated the homologous position in jTat to H62Y and found it did not improve its ability to stimulate reverse transcription, but an H62A mutation did inhibit jTat complementation. These data highlight the finding that the role of Tat in reverse transcription is not related to trans-activation and demonstrate that other tat genes conserve this function.

Amino Acid Sequence↗
PubMed1995

Reversible dementia: more than 10% or less than 1%? A quantitative review.

Dementia is reversible in some cases and these should be diagnosed without over-investigating the many others with irreversible disease. To estimate how often dementia can be reversed, we carried out a quantitative review of studies reported between 1972 and 1994 in which reversible dementia was diagnosed and outcome after treatment was assessed. We found 16 studies comprising 1551 patients. The percentages of reversed dementia varied widely: from 0 to 23% for partial and from 0 to 10% for full reversal. Depression and drug intoxication were the most frequent causes of reversible dementia, followed by metabolic and neurosurgical disorders. The percentage of both partial and full reversal of dementia has fallen in recent years, to less than 1% for both in the four most recent studies. This decrease could be associated with the change from an inpatient to an outpatient setting and the use of stricter diagnostic methods. We conclude that reversible dementia is very rare in an outpatient setting when using strict diagnostic methods. This has important implications for the diagnostic strategy in patients with dementia: major procedures should be performed selectively. In patients with clinical characteristics of Alzheimer's disease, CT of the brain is unlikely to detect a treatable cause of dementia.

Aged↗
PubMed2005

In situ expression of the GmNMH7 gene is photoperiod-dependent in a unique soybean (Glycine max [L.] Merr.) flowering reversion system.

Soybean is a short-day plant and its flowering process can be reversed when switching from short-day to long-day conditions. Flowering reversion provides a useful system to study the flowering process in both forward and backward directions. In this study, we optimized a soybean flowering reversion system using a photoperiod-sensitive cultivar Zigongdongdou. Three types of terminal structures were found during flowering reversion: reversed terminal raceme (RTR), short terminal raceme (STR), and vegetative terminal (VT). The relative frequency of these terminal structures during flowering reversion under long day was dependent on the duration of the prior short day (SD) pretreatment. This process is phytochrome dependent and young plants were more susceptible to flowering reversion. Leaf removal increased the minimal SD period needed for the induction of STR. To demonstrate the application of this system, we studied the patterns of in situ expression of the GmNMH7 gene during flowering development and reversion. NMH7 family members encode MADS-box proteins and are unique in legume families since their expression can be detected in both developing flowers and nodules. In situ hybridization experiments using plants grown under different photoperiod cycles provided several lines of evidence supporting a close relationship between GmNMH7 gene expression and floral development in soybean. Furthermore, it seems that GmNMH7 may participate in flower development at different stages. Interestingly, the expression pattern of GmNMH7 in root nodules was also found to be regulated by photoperiod. These results support the notion that the photoperiod sensitive GmNMH7 gene may play multiple roles in growth and development in soybean.

Amino Acid Sequence↗
PubMed1999

Methods for improving performance under reverse alignment conditions during endoscopic surgery.

BACKGROUND: There are times during endoscopic procedures when the surgeon has to operate ahead of the camera/telescope assembly. As a result, the image displayed on the monitor will be an inverted mirror image of the operative field (reverse alignment). The present study addresses the extent of these difficulties and suggests some techniques that may be used to overcome the problem. METHODS: Eight specialist registrars participated in experiments involving the execution of a simulated dissection task under 12 different imaging conditions. These conditions included normal alignment, reverse alignment, total or partial digital correction of reverse alignment (about the horizontal and vertical axes independently and together), and a simple rotation of the camera through 180 degrees. Normal, reverse, and corrected reverse alignment were also tested with optical axes of 45 degrees and 60 degrees. The endpoints were the task execution and the errors rate. RESULTS: A marked deterioration in execution time was observed when the surgeons worked under reverse alignment rather than under normal viewing (p = 0.036). Significant improvement in execution-time errors rate was found when both the horizontal and vertical axes were digitally corrected simultaneously (p = 0.27) and when the camera was rotated 180 degrees with respect to the telescope during reverse alignment (p = 0.28). CONCLUSIONS: The effect on performance produced by reverse alignment of the endoscope and instruments can be overcome by means of digital electronic processing, or simply by turning the camera through 180 degrees.

Adult↗
PubMed1991

Absence of complement-mediated events after protamine reversal of heparin anticoagulation.

Protamine reversal of heparin anticoagulation is associated with adverse hemodynamic effects that may be attenuated with protamine pretreatment (PP). This study assesses the role of complement activation during these phenomena in adult cardiac surgery patients. Sixteen individuals undergoing cardiopulmonary bypass were given intravenous normal saline or protamine (2 mg/kg) as a randomized pretreatment prior to undergoing heparin anticoagulation (400 IU/kg), coronary artery revascularization, and subsequent reversal of the anticoagulated state with protamine (4 mg/kg). Blood pressure, pulmonary artery diastolic pressure (PAD), heart rate, and cardiac output (CO) were measured during and after pretreatment, prior to heparin reversal by protamine, and for 10 min after reversal. Total hemolytic complement (CH50), C3 conversion to C3b, C3a/C5a, platelet count, and white blood cell count (WBC) were also measured at the same time periods. No significant correlation existed between complement activation and hemodynamic events, as might have been evident by decreased CH50, increased C3 conversion to C3b, or elevations in C3a/C5a levels. PP significantly prevented the CO decrease occurring at 1 and 3 min following heparin reversal by protamine (-0.8 and -1.4 liters/min vs 0.1 and -0.2 liters/min, P less than 0.05 and P less than 0.01, respectively). Reversal hypotension was less with PP, although PAD fell equally in both groups. WBC decreases after heparin reversal were less after PP (-25% vs -7%, P = 0.06). These data support the conclusion that, contrary to earlier reports, adverse hemodynamic and hematologic responses accompanying protamine reversal of heparin anticoagulation do not appear to be correlated with activation of complement. In fact, those patients having the greatest C3a generation exhibited the least hemodynamic changes.

Adult↗
PubMed1993

Structural and catalytic properties of enzymes in reverse micelles.

Structural and catalytic properties of two enzymes--alpha-chymotrypsin and horse liver alcohol dehydrogenase (LADH)--are studied in bis(2-ethylhexyl) sodium sulfosuccinate (AOT)-isooctane reverse-micelle solutions. Circular dichroism (CD) and electron paramagnetic resonance spectroscopy (EPR) studies show little change in alpha-chymotrypsin structure upon incorporation into reverse micelles. These structural properties explain, in part, the observed activity of these two enzymes in reverse micelles. alpha-Chymotrypsin retains activity in reverse micelles and, in some cases, displays enhanced activity. A sixfold increase in the turnover number was observed in w0 = 10 reverse micelles. LADH has low activity in reverse micelles compared to that in aqueous solution. At w0 = 70, the turnover number of LADH is 18% of the aqueous value. Active-site titrations show a decrease in active enzyme concentration for both enzymes upon incorporation into reverse micelles. Little change in the structure of both LADH and alpha-chymotrypsin is observed with change of water content in the reverse-micelle system.

Alcohol Dehydrogenase↗
PubMed1990

The effects of excitotoxic lesions of the basal forebrain on the acquisition, retention and serial reversal of visual discriminations in marmosets.

The effects of N-methyl-D-aspartate-induced lesions of the basal forebrain (which included the cholinergic cells of the nucleus basalis of Meynert) were studied on three aspects of visual discrimination; learning, retention and reversal performance, in the marmoset. Neurobiological investigations revealed that the lesion produced large reductions in choline acetyltransferase activity within anterior regions of cortex, particularly prefrontal. In Experiment 1 lesioned animals showed impaired retention, one week after surgery, of a visual discrimination learned immediately prior to surgery and subsequently showed impaired performance over a series of reversals. The reversal deficit could be characterized as a tendency to perseverate on the previously correct stimulus on the first reversal and as a failure to show serial reversal learning on subsequent reversals. Acquisition of a novel discrimination was not impaired five weeks after surgery. As time of testing may have been a confounding factor, in Experiment 2 the effects of the same lesion on new learning were examined immediately following surgery and the effects on retention a month later. The lesion was found to disrupt new learning but did not affect retention. From the two experiments it is clear that, whereas disruption of retention and new learning was relatively transient, the impairments in reversal performance were more long lasting. In addition, lesioned animals exhibited behavioural hyperactivity and elevations in consummatory and schedule-controlled licking. The disinhibitory and preservative effects observed following lesions of the basal forebrain in this study are similar to those following lesions of the orbitofrontal cortex while the disruption of serial reversal learning is commonly seen following damage to the amygdala. Therefore, these results are consistent with the hypothesis that the range of behavioural effects of the lesion result from damage to the cholinergic afferents to orbitofrontal cortex and to the amygdala, two structures intimately connected to one another.

Animals↗
PubMed1994

Surgical treatment of threatened reversed infrainguinal vein grafts.

PURPOSE: Current information concerning the results of surgical revision of threatened infrainguinal vein grafts is largely limited to in situ conduits. Infrainguinal grafts may be threatened by intrinsic graft lesions or significant stenosis in the adjacent inflow or outflow arteries. To assess the results of operative revision of infrainguinal reversed vein grafts, we reviewed our experience with surgical revision of threatened infrainguinal reversed vein grafts identified through a program of postoperative clinical and vascular laboratory graft surveillance. METHODS: All patients who underwent surgical revision of a threatened but patent infrainguinal reversed vein graft from January 1987 through April 1993 were identified through review of our vascular registry. Data were analyzed for type of vein used, date of original reversed vein graft, clinical and vascular laboratory findings leading to reversed vein graft revision, results of preoperative angiography, patient risk factors, operative techniques and complications, and long-term assisted primary graft patency and limb salvage. RESULTS: Ninety-six patients with 100 infrainguinal reversed vein grafts (69) femoral-popliteal, 31 femoral-tibial) underwent 117 surgical vein graft revisions or inflow procedures during the study period. Eighty-one percent of the original reversed vein grafts consisted of a single segment of greater saphenous vein. All revised grafts had at least a 50% stenosis in the graft itself or the proximal or distal artery. A single revision was performed in 85 grafts, two revisions in 13 grafts, and three revisions in two grafts. There were nine (8%) isolated inflow procedures, eight (7%) vein patch angioplasties, 62 (53%) interposition vein grafts, and 29 (25%) vein graft extensions to a new distal anastomotic site. The remaining nine (8%) procedures consisted of combinations of the above. Median time to primary graft revision after initial graft implantation was 15 months (range 2 days to 316 months). Mean time to secondary revision after primary revision was 21 months. Operative mortality was 0.9%. Cumulative assisted primary patency of the original grafts revised for stenotic lesions was 99%, 96%, and 92% at 1, 3, and 5 years, respectively. Limb salvage was 99%, 97%, and 97% at 1, 3, and 5 years, respectively. CONCLUSIONS: Although surgical revision of reversed vein graft requires much use of alternative vein sources, these procedures can be performed with minimum mortality and provide excellent assisted primary graft patency and limb salvage.

Adult↗
PubMed2005

Evaluating the utility and accuracy of a reverse telephone directory to identify the location of survey respondents.

PURPOSE: To investigate the utility and positional accuracy of a reverse telephone directory to enhance geocoding using self-reported street addresses. METHODS: This cross-sectional study used 2001 self-reported survey data from 2636 participants in three Missouri areas. When available, street addresses were appended to participant telephone numbers using a reverse telephone directory. The odds of finding a telephone number in the reverse directory and the positional accuracy between self-reported addresses and those obtained from the reverse directory were calculated. We also determined the quality of self-reported address information and that obtained by means of the reverse telephone directory. RESULTS: Rural respondents, younger respondents, women, African Americans, and respondents with less than a high school education were less likely to have their telephone number present in the reverse directory. Using the reverse directory increased the overall percentage of respondents whose addresses were geocoded from 51.5% to 72.0%. Eighty-one percent of addresses were geocoded to the same US Census Block Group and 89% were geocoded to the same Census Tract as the self-reported addresses. CONCLUSIONS: The street address of survey participants obtained through the reverse directory can be used to augment the unknown location of telephone survey respondents but specific groups of people are less likely to be found in the directory.

Adult↗
PubMed2005

Simulated nystagmus reduces pattern-reversal more strongly than pattern-onset multifocal visual evoked potentials.

OBJECTIVE: In patients with nystagmus conventional pattern-reversal visual evoked potentials are severely degraded, while sizeable pattern-onset VEPs can often still be obtained. We tested whether this differential effect of retinal image motion on pattern-reversal and pattern-onset responses also applies to multifocal VEPs (mfVEPs). METHODS: In eight subjects with normal oculomotor behaviour and vision we recorded pattern-reversal and pattern-onset mfVEPs from an occipital electrode pair to 60 locations of a scaled dartboard-pattern, and to 64 locations of a uniform checkerboard-pattern. Subjects viewed the stimulus monocularly via a mirror, which was placed close to the eye and driven by a scanner with a 4 Hz sawtooth waveform at an amplitude of 2 degrees to simulate horizontal jerk nystagmus and of 0 degrees for the reference condition. RESULTS: For the scaled dartboard-stimulus we observed an eccentricity-dependent effect of induced retinal image motion on mfVEP responses: in the central visual field (0-0.5 degrees), pattern-reversal and pattern-onset responses were reduced by 73 and 42%, respectively. In the periphery (10-16 degrees), only pattern-reversal responses were reduced (by 27%), while pattern-onset responses were enhanced by 39%. Pattern-onset responses to the uniform checkerboard stimulus were enhanced by 17%, while pattern-reversal responses were reduced by 27%. CONCLUSIONS: Pattern-onset mfVEPs are more efficient than pattern-reversal mfVEPs, if retinal image motion is superimposed onto the stimulus. This is in close correspondence to previous reports on conventional VEPs. SIGNIFICANCE: This study demonstrates a differential effect of retinal image motion on pattern-reversal and pattern-onset mfVEPs and thus suggests stimulus conditions to enhance the efficiency of mfVEP recordings in patients with moderate nystagmus.

Adult↗
PubMed2006

Sperm harvesting and cryopreservation during vasectomy reversal is not cost effective.

OBJECTIVE: To determine whether sperm harvesting and cryopreservation at the time of vasectomy reversal is cost-effective. DESIGN: Model of actual costs and results at five institutions. SETTING: Multicenter study comprising five centers, including university hospitals and private practices. PATIENT(S): Men undergoing vasectomy reversal. INTERVENTION(S): We established two models for vasectomy reversal. The first model was sperm harvesting and cryopreservation at the time of vasectomy reversal. The second model was sperm harvesting at the time of IVF only if the patient remained azoospermic after vasectomy reversal. Vasectomy reversal procedures modeled included bilateral vasovasostomy and bilateral epididymovasostomy. The costs for each procedure at the five institutions were collated and median costs determined. MAIN OUTCOME MEASURE(S): Median cost of procedure and calculated financial comparisons. RESULT(S): The median cost of testicular sperm extraction/cryopreservation performed at the time of bilateral vasovasostomy was $1,765 (range, $1,025-$2,800). The median cost of microsurgical epididymal sperm aspiration or testicular sperm extraction with cryopreservation performed at the time of epididymovasostomy was $1,209 (range, $905-$2,488). The average of the median costs for percutaneous sperm aspiration or testicular sperm aspiration for those patients with a failed vasectomy reversal was $725 (range, $400-$1,455). CONCLUSION(S): Sperm retrieval with cryopreservation at the time of vasectomy reversal is not a cost-effective management strategy.

Cost-Benefit Analysis↗
PubMed2005

Characterization of reversed micelles of Cibacron Blue F-3GA modified Span 85 for protein solubilization.

The nonionic surfactant of sorbitan trioleate (Span 85) was modified with Cibacron Blue F-3GA (CB) as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. The reversed micelles formed by the mixture of Span 85 and CB-Span 85 conjugate were extensively characterized in water content, hydrodynamic radius, and aggregation number. The results show that the water content and hydrodynamic radius of the reversed micelles were significantly increased by the introduction of CB ligands (CB-Span 85 conjugate), and the reversed micelles with CB-Span 85 conjugate had a wider aggregation number distribution than the Span 85 reversed micelles. Using lysozyme as a model protein, protein solubilization by the reversed micelles was investigated. Lysozyme solubilization increased significantly with the coupled CB concentration, indicating that the extraction was based upon the affinity interactions between lysozyme molecules and the CB ligand. High solubilization of lysozyme was obtained by the affinity-based reversed micelles of 62.7 mmol/L Span 85 with coupled CB higher than 0.25 mmol/L. Lysozyme recovery was carried out using a stripping solution of high ionic strength. The recovered lysozyme exhibited an activity equivalent to the native lysozyme and its secondary structure was also unchanged. The results indicate that the reversed micellar system would find potential application in protein separation.

Hexanes↗
PubMed2005

Dioptric changes in eyes with reversed intraocular lenses.

PURPOSE: To theoretically calculate refractive changes in eyes with reversed intraocular lenses (IOLs). SETTING: Nara Medical University, Nara, Japan. METHODS: With the ray-tracing method, the refractive changes in a theoretical eye model with a reversed IOL in the capsular bag were calculated. Data for 3 models, anterior biconvex (MA60AC, Alcon), posterior biconvex (MA60BM, Alcon), and convex plano (UV2565T, Menicon), were provided by the manufacturer and used in the analysis. RESULTS: Using the assumption that the axial length varied from 22 to 27 mm, the anterior-biconvex IOLs elicited small refractive changes when reversed. The posterior-biconvex IOLs elicited a significant myopic shift (up to 0.90 diopter [D]) when reversed. The convex-plano IOLs elicited a significant hyperopic shift (up to 2.01 D) when reversed. CONCLUSIONS: Anterior-biconvex IOLs with similar anterior and posterior radii of curvature will not cause large diopter surprises when reversed. High-power posterior-convex IOLs will cause significant myopic diopter surprises when reversed. Both these changes shift toward myopic if the postoperative anterior chamber depth (ACD) becomes shallow. Medium- to high-power convex-plano IOLs will cause a large hyperopic shift when reversed. This hyperopic shift decreases if the postoperative ACD becomes shallower.

Humans↗
PubMed2004

Carotid angioplasty with internal carotid artery flow reversal is well tolerated in the awake patient.

OBJECTIVE: The purpose of this study was to evaluate the neurologic tolerance and changes in ipsilateral hemispheric oxygen saturation during transcervical carotid artery stenting with internal carotid artery (ICA) flow reversal for embolic protection. PATIENTS AND METHODS: This was a prospective study of 10 patients (mean age 68 years) undergoing transcervical carotid angioplasty and stenting. All ICA stenoses were greater that 70%. Seven patients had an ipsilateral hemispheric stroke (3) or transient ischemic attack (4), two patients had a contralateral stroke, and one patient was asymptomatic. Nine procedures were done under local anesthesia. Cerebral protection was established through a cervical common carotid (CCA) cutdown to create an external fistula between the ICA and the internal jugular vein with temporally CCA occlusion. Venous oxygen saturation (SVO(2)) was continuously monitored through a catheter placed in the distal internal jugular vein. Mental status and motor-sensory changes were categorized and assessed throughout and after the procedure. RESULTS: All procedures were technically successful without significant residual stenosis. Mean ICA flow reversal time was 22 minutes (range, 15 to 32). Common carotid artery (CCA) occlusion produced a slight (SVO(2) = 72.6%+/-9.4) but significant decrease (P =.012) in SVO(2), compared with baseline (SVO(2) = 77% +/-10.5). During ICA flow reversal (SVO(2) = 72.4% +/-10.1) cerebral oxygen saturation did not change compared with CCA occlusion alone (P =.85). Transient balloon occlusion during angioplasty of the ICA (SVO(2) = 64.6%+/-12.9) produced a significant decrease in cerebral SVO(2) compared with CCA occlusion (P =.015) and compared with CCA occlusion with ICA flow reversal (P =.018). No mental status changes or ipsilateral hemispheric focal symptoms occurred during CCA occlusion with ICA flow reversal. One patient with contralateral ICA occlusion sustained brief upper extremity weakness related to the contralateral hemisphere. Five patients sustained a vasovagal response during balloon dilatation, four did not require treatment, and one had asystole requiring atropine injection. Mean SVO(2) saturation was not different in these five patients compared with the five who did not sustain a vasovagal response. No deaths or neurologic deficits occurred within 30 days after the procedure. CONCLUSIONS: Our data suggest that transcervical carotid angioplasty and stenting with ICA flow reversal is well tolerated in the awake patient, even in the presence of symptomatic carotid artery disease. Cerebral oxygenation during ICA flow reversal is comparable to that during CCA occlusion. ICA angioplasty balloon inflation produces a decrease in cerebral SVO(2) significantly greater than that occurring during ICA flow reversal.

Aged↗
PubMed2004

Illusory motion reversal is caused by rivalry, not by perceptual snapshots of the visual field.

In stroboscopic conditions--such as motion pictures--rotating objects may appear to rotate in the reverse direction due to under-sampling (aliasing). A seemingly similar phenomenon occurs in constant sunlight, which has been taken as evidence that the visual system processes discrete "snapshots" of the outside world. But if snapshots are indeed taken of the visual field, then when a rotating drum appears to transiently reverse direction, its mirror image should always appeared to reverse direction simultaneously. Contrary to this hypothesis, we found that when observers watched a rotating drum and its mirror image, almost all illusory motion reversals occurred for only one image at a time. This result indicates that the motion reversal illusion cannot be explained by snapshots of the visual field. The same result is found when the two images are presented within one visual hemifield, further ruling out the possibility that discrete sampling of the visual field occurs separately in each hemisphere. The frequency distribution of illusory reversal durations approximates a gamma distribution, suggesting perceptual rivalry as a better explanation for illusory motion reversal. After adaptation of motion detectors coding for the correct direction, the activity of motion-sensitive neurons coding for motion in the reverse direction may intermittently become dominant and drive the perception of motion.

Humans↗
PubMed1999

Dobutamine stress echocardiography at 7.5 mg/kg/min using color tissue Doppler imaging M-mode safely predicts reversible dysfunction early after reperfusion in patients with acute myocardial infarction.

Dobutamine stress echocardiography (DSE) is widely used to predict reversible left ventricular dysfunction, but evaluation by this method is subjective. The recently developed color tissue Doppler imaging (TDI) M-mode may permit objective and quantitative assessment of changes in wall motion induced by DSE. We tested the hypothesis that this new method can detect sensitively reversible dysfunction in the post-myocardial infarction setting. DSE with color TDI M-mode and conventional DSE were performed to predict reversible dysfunction in 53 patients at a mean of 3 days after infarction using 7.5 and 10 microg/kg/min of dobutamine. Follow-up regular echocardiography (4 weeks later) was used as the reference technique to define reversible dysfunction segments. To predict reversible dysfunction segments, the standard segmental wall motion score change on conventional DSE and the ratio of the segmental wall velocity difference at rest versus stress (7.5 and 10 microg/kg/ min) on DSE with color TDI M-mode (7.5-TDI-M and 10-TDI-M, respectively) were used. With 7.5 microg/kg/min of dobutamine, the sensitivity for predicting reversible dysfunction using color TDI M-mode (7.5-TDI-M) was significantly higher than that of conventional DSE (89% vs 73%, p <0.05) whereas specificities and predictive values were almost identical. With a 10-microg/kg/min dose, color TDI-M mode (10-TDI-M) and conventional DSE were not significantly different in predicting reversible dysfunction. With use of color TDI-M mode, regional wall motion during DSE was analyzed objectively and quantitatively. Moreover, combined TDI-M and conventional data were slightly superior to either mode alone. There were no arrhythmias during 7.5 microg/kg/min of dobutamine, but 9 arrhythmias occurred during the 10-microg/kg/min dose in patients with acute myocardial infarction. In conclusion, color TDI M-mode permits objective and quantitative assessment of regional ventricular wall motion and gives additional information for detecting reversible dysfunction in DSE. Improvement of sensitivity at a lower dose of dobutamine with color TDI-M mode may increase the safety of DSE in the post-myocardial infarction setting.

Angioplasty, Balloon, Coronary↗