Modified motor unit properties in residual muscle following transtibial amputation

Objective.Neural signals in residual muscles of amputated limbs are frequently decoded to control powered prostheses. Yet myoelectric controllers assume muscle activities of residual muscles are similar to that of intact muscles. This study sought to understand potential changes to motor unit (MU) properties after limb amputation.Approach.Six people with unilateral transtibial amputation were recruited. Surface electromyogram (EMG) of residual and intacttibialis anterior(TA) andgastrocnemius(GA) muscles were recorded while subjects traced profiles targeting up to 20% and 35% of maximum activation for each muscle (isometric for intact limbs). EMG was decomposed into groups of MU spike trains. MU recruitment thresholds, action potential amplitudes (MU size), and firing rates were correlated to model Henneman's size principle, the onion-skin phenomenon, and rate-size associations. Organization (correlation) and modulation (rates of change) of relations were compared between intact and residual muscles.Main results.The residual TA exhibited significantly lower correlation and flatter slopes in the size principle and onion-skin, and each outcome covaried between the MU relations. The residual GA was unaffected for most subjects. Subjects trained prior with myoelectric prostheses had minimally affected slopes in the TA. Rate-size association correlations were preserved, but both residual muscles exhibited flatter decay rates.Significance.We showed peripheral neuromuscular damage also leads to spinal-level functional reorganizations. Our findings suggest models of MU recruitment and discharge patterns for residual muscle EMG generation need reparameterization to account for disturbances observed. In the future, tracking MU pool adaptations may also provide a biomarker of neuromuscular control to aid training with myoelectric prostheses.

Ankle Torque Estimation With Motor Unit Discharges in Residual Muscles Following Lower-Limb Amputation

There has been increased interest in using residual muscle activity for neural control of powered lower-limb prostheses. However, only surface electromyography (EMG)-based decoders have been investigated. This study aims to investigate the potential of using motor unit (MU)-based decoding methods as an alternative to EMG-based intent recognition for ankle torque estimation. Eight people without amputation (NON) and seven people with amputation (AMP) participated in the experiments. Subjects conducted isometric dorsi- and plantarflexion with their intact limb by tracing desired muscle activity of the tibialis anterior (TA) and gastrocnemius (GA) while ankle torque was recorded. To match phantom limb and intact limb activity, AMP mirrored muscle activation with their residual TA and GA. We compared neuromuscular decoders (linear regression) for ankle joint torque estimation based on 1) EMG amplitude (aEMG), 2) MU firing frequencies representing neural drive (ND), and 3) MU firings convolved with modeled twitch forces (MUDrive). In addition, sensitivity analysis and dimensionality reduction of optimization were performed on the MUDrive method to further improve its practical value. Our results suggest MUDrive significantly outperforms (lower root-mean-square error) EMG and ND methods in muscles of NON, as well as both intact and residual muscles of AMP. Reducing the number of optimized MUDrive parameters degraded performance. Even so, optimization computational time was reduced and MUDrive still outperformed aEMG. Our outcomes indicate integrating MU discharges with modeled biomechanical outputs may provide a more accurate torque control signal than direct EMG control of assistive, lower-limb devices, such as exoskeletons and powered prostheses.

Finger Force Estimation using Motor Unit Discharges Across Forearm Postures

BACKGROUND

Myoelectric-based decoding has gained popularity in upper-limb neural-machine interfaces. Motor unit (MU) firings decomposed from surface electromyographic (EMG) signals can represent motor intent, but EMG properties at different arm configurations can change due to electrode shift and differing neuromuscular states. This study investigated whether isometric fingertip force estimation using MU firings is robust to forearm rotations from a neutral to either a fully pronated or supinated posture.

METHODS

We extracted MU information from high-density EMG of the extensor digitorum communis in two ways: (1) Decomposed EMG in all three postures (MU-AllPost); and (2) Decomposed EMG in neutral posture (MU-Neu), and extracted MUs (separation matrix) were applied to other postures. Populational MU firing frequency estimated forces scaled to subjects' maximum voluntary contraction (MVC) using a regression analysis. The results were compared with the conventional EMG-amplitude method.

RESULTS

We found largely similar root-mean-square errors (RMSE) for the two MU-methods, indicating that MU decomposition was robust to postural differences. MU-methods demonstrated lower RMSE in the ring (EMG = 6.23, MU-AllPost = 5.72, MU-Neu = 5.64 %MVC) and pinky (EMG = 6.12, MU-AllPost = 4.95, MU-Neu = 5.36 %MVC) fingers, with mixed results in the middle finger (EMG = 5.47, MU-AllPost = 5.52, MU-Neu = 6.19% MVC).

CONCLUSION

Our results suggest that MU firings can be extracted reliably with little influence from forearm posture, highlighting its potential as an alternative decoding scheme for robust and continuous control of assistive devices.

Common Neural Input within and across Lower Limb Muscles: A Preliminary Study

Motor units (MUs) are the basic unit of motor control. MU synchronization has been evaluated to identify common inputs in neural circuitry during motor coordination. Recent studies have compared common inputs between muscles in the lower limb, but further investigation is needed to compare common inputs to MUs both within a muscle and between MUs of different muscle pairs. The goal of this preliminary study was to characterize levels of common inputs to MUs in three muscle groups: MUs within a muscle, between bilateral homologous pairs, and between agonist/antagonist muscle pairs. To achieve this, surface electromyography (EMG) was recorded during bilateral ankle dorsiflexion and plantarflexion on the right and left tibiales anterior (RTA, LTA) and gastrocnemii (RGA, LGA) muscles. After decomposing EMG into active MU firings, we conducted coherence analyses of composite MU spike trains (CSTs) in each muscle group in both the beta (13-30 Hz) and gamma (30-60 Hz) frequency bands. Our results indicate MUs within a muscle have the greatest levels of common input, with decreasing levels of common input to bilateral and agonist/antagonist muscle pairs, respectively. Additionally, each muscle group exhibited similar levels of common input between the beta and gamma bands. This work may provide a way to unveil mechanisms of functional coordination in the lower limb across motor tasks.

Screening for second malignancies in mycosis fungoides: non-Hodgkin lymphoma, Hodgkin lymphoma, lung cancer, bladder cancer and melanoma

BACKGROUND

Patients with mycosis fungoides (MF) are at increased risk of developing non-Hodgkin lymphoma (NHL), Hodgkin lymphoma (HL), lung cancer, bladder cancer and melanoma. The characteristics of patients developing these malignancies have not been specifically delineated. In addition, there are no established guidelines for screening MF patients for second malignancies.

MATERIALS/METHODS

We identified 742 patients with MF who developed second malignancies in the Surveillance Epidemiology and End Result-18 database.

RESULTS

The majority of second malignancy patients were white and male, mean age 55-67 years at diagnosis of MF, and mean age 61-72 years at diagnosis of second malignancy. The majority of patients diagnosed with second malignancies had early stage MF. MF patients with NHL, lung cancer, and bladder cancer tended to be diagnosed at earlier stages of the second malignancy than patients without MF and demonstrated better 5-year overall survival. There was no improvement in stage at diagnosis or survival for MF patients who were diagnosed with melanoma compared to patients without MF.

CONCLUSIONS

Improvements in survival in MF/NHL, MF/lung cancer and MF/bladder cancer patients may reflect differences in disease biology secondary to having MF or the importance of increased contact with the healthcare system. MF/melanoma data suggest that patients require regular pigmented-lesion-focused skin examinations. Tools for screening include regular lymph node examinations, pigmented-lesion-focused examinations and detailed review of systems questions. Smoking cessation counseling is key intervention in this population, as is ensuring that all age- and sex-specific cancer screenings are up-to-date (e.g. lung cancer screening, mammography, and colonoscopy). The utility of regular imaging for second malignancy screening and lab testing such as routine urinalysis requires additional study and expert consensus.

Demonstrating a Continuous Set of Two-Qubit Gates for Near-Term Quantum Algorithms

Quantum algorithms offer a dramatic speedup for computational problems in material science and chemistry. However, any near-term realizations of these algorithms will need to be optimized to fit within the finite resources offered by existing noisy hardware. Here, taking advantage of the adjustable coupling of gmon qubits, we demonstrate a continuous two-qubit gate set that can provide a threefold reduction in circuit depth as compared to a standard decomposition. We implement two gate families: an imaginary swap-like (iSWAP-like) gate to attain an arbitrary swap angle, θ, and a controlled-phase gate that generates an arbitrary conditional phase, ϕ. Using one of each of these gates, we can perform an arbitrary two-qubit gate within the excitation-preserving subspace allowing for a complete implementation of the so-called Fermionic simulation (fSim) gate set. We benchmark the fidelity of the iSWAP-like and controlled-phase gate families as well as 525 other fSim gates spread evenly across the entire fSim(θ,ϕ) parameter space, achieving a purity-limited average two-qubit Pauli error of 3.8×10^{-3} per fSim gate.

Predicting post-transarterial chemoembolization outcomes: A comparison of direct and total bilirubin serums levels

PURPOSE

To retrospectively review the ability of direct bilirubin serum level to predict mortality and complications in patients undergoing transarterial chemoembolization (TACE) for hepatocellular carcinoma (HCC) and compare it to the predictive value of the currently utilized total bilirubin serum level.

MATERIALS AND METHODS

A total of 219 patients who underwent TACE for 353 hepatocelluar carcinomas (HCC) at a single institution were included. There were 165 men and 54 women, with a mean age of 61.4±7.6 (SD) [range: 27-86 years]. The patients' electronic medical records were evaluated and they were divided into cohorts based on total bilirubin (<2, 2-3, and >3mg/dL) as well as direct bilirubin (<1 and 1-2mg/dL).

RESULTS

Direct bilirubin serum level was significantly greater in the cohort of patients who did not survive as compared to those who survived 6 months ([0.58±0.46 (SD) mg/dL; range: <0.1-1.8mg/dL] vs. [0.40±0.31 (SD) mg/dL; range: <0.1-1.6mg/dL], respectively) (P=0.04) and 12 months ([0.49±0.38 (SD) mg/dL; range: <0.1-1.8mg/dL] vs. [0.38±0.32 (SD) mg/dL; range: <0.1-1.6mg/dL], respectively) (P=0.03). While total bilirubin serum level was not significantly different in those who did not and did survive 6 months ([1.54±0.99 (SD) mg/dL; range: 0.3-3.9mg/dL] vs. [1.27±0.70 (SD) mg/dL; range: 0.3-3.75mg/dL], respectively) (P=0.16), it was significantly different when evaluating 12 months survival ([1.46±0.87 (SD)mg/dL; range: 0.3-3.9mg/dL] vs. [1.22±0.65 (SD) mg/dL; range: 0.3-3.9mg/dL]) (P=0.03). Akaike information criterion (AIC) analysis revealed that direct bilirubin level more accurately predicted overall survival (AIC=941.19 vs. 1000.51) and complications (AIC=352.22 vs. 357.42) than total bilirubin serum levels.

CONCLUSION

Direct bilirubin serum level appears to outperform total bilirubin concentration for predicting complications and overall survival in patients undergoing TACE. Patients with relatively maintained direct bilirubin levels should be considered for TACE, particularly in the setting of bridging to transplant.

Mycosis fungoides: developments in incidence, treatment and survival

BACKGROUND

Prior studies have demonstrated improved disease-specific survival of mycosis fungoides (MF) patients over the last 50 years.

OBJECTIVE

To analyse patterns of survival and incidence from 1973 to 2016 and determine whether apparent improvements in MF-specific survival are due to lead-time bias rather than improvements in treatment.

METHODS

We performed an analysis of 10 155 patients diagnosed with MF from 1973 to 2016 in the United States cancer registries of SEER-18. We also performed a literature review of papers including stage data for unselected populations of MF patients prior to 2000.

RESULTS

Incidence of MF increased from 3.0 per million person-years in the 1970s to 5.9 in the 2010s. For all cohorts, non-Hodgkin lymphoma (including MF) was the leading cause of death. Survival analysis demonstrated marked improvement in disease-specific and overall survival from the 1970s to 2010s. Based on systematic review of the literature, 32%-73% of patients diagnosed prior to 2000 were diagnosed with early-stage disease, as opposed to 81% of patients in the SEER 2000-2016 cohort (P < 0.035 for all cohorts).

CONCLUSIONS

Although there have been improvements in MF-related survival over the last 50 years, these may reflect improvements in our ability to diagnose early-stage disease rather than improved treatment.

Identification of epsilon toxin-producing Clostridium perfringens strains in American retail food

Food samples (n = 216) from New York city were tested for the presence of C. perfringens via PCR for specific toxin genes. Thirty-four (16%) samples were positive for C. perfringens. Of these 34, 31 (91.2%) were type A or E, one (2.9%) was type B, and two (5.9%) were type D.

The Role of Junctions in Surface Completion and Contour Matching

It has been suggested that contour junctions may be used as cues for occlusion. Ecologically, T-junctions and L-junctions are concurrent with situations of occlusion: they arise when the bounding contour of the occluding surface intersects with that of the occluded surface. However, there are other image properties that can be used as cues for occlusion. Here the role of junctions is directly compared with other occlusion cues—specifically, relatability and surface-similarity—in the emergence of amodal completion and illusory contour perception. Stimuli have been constructed that differ only in the junction structure, with the other occlusion cues kept unchanged. L-junctions and T-junctions were eliminated from the image or manipulated so as to be locally inconsistent with the (still valid) global occlusion interpretation. Although the other occlusion cues of relatability and surface similarity still existed in the image, subjects reported not perceiving illusory contours or amodal completion in junction-manipulated images. Junction manipulation also affected the perceived stereoscopic depth and motion of image regions, depending on whether they were perceived to amodally complete with a disjoint region in the image. These results are interpreted in terms of the role of junctions in the processes of surface completion and contour matching. It is proposed that junctions, being a local cue for occlusion, are used to launch completion processes. Other, more global occlusion cues, such as relatability, play a part at a later stage, once completion processes have been launched.

Abstract 3979: In vitro modeling of pharmacodynamics of resveratrol-induced anti-proliferation in breast cancer cells

We and others have shown that resveratrol, a naturally-occurring stilbene, induces p53-dependent apoptosis in human and animal cancer cell lines. The molecular basis of induction of apoptosis by resveratrol includes activation and nuclear translocation of mitogen-activated protein kinase (MAPK; ERK1/2) and MAPK-mediated Ser-15 phosphorylation of p53 (pSer15-p53). In this study, we used a newly developing perfusion bellows cell culture system to investigate resveratrol-induced apoptosis in the human estrogen receptor (ER)-negative breast cancer MDA-MB-231 cells. The cell culture system is a disposable bioreactor capable of high density cell culture for studies of anti-cancer drugs. Bellows-induced alternate flow of culture medium and air through porous matrices where cells are grown provides a relatively low shear, high aeration, foam-free culture environment. Medium level is raised and lowered to submerge and expose matrices to create a dynamic interface between air and media on the cell surface. Anchorage-dependent cells are grown on plastic flakes in the system; the flakes facilitate harvesting of whole cells for analysis. After 6 days incubation, the IC50 of resveratrol-induced apoptosis was 0.1 μM. Short term incubation with 10 μM resveratrol for 6 days inhibited cell proliferation by 75%. Using an injection system to pump media with different concentrations of resveratrol (0.5 μM to 100 μM), we were able to reproduce the resveratrol-induced anti-proliferation effect in the perfusion bellows culture system. Incubating the cells in either acidic or alkaline condition did not affect anti-proliferation induced by resveratrol. The effect of resveratrol-induced apoptosis is based on increasing transcription of pro-apoptotic p53-dependent genes such as PIG3, c-fos, c-jun and BAD. The aim of the present study is to establish the pharmacodynamics of resveratrol in the suppression or elimination of human breast cancer cells. With the use of the perfusion bellows cell culture system we will provide an efficient, convenient and financially beneficial method for determining optimal regimens for the effective suppression and elimination of these cancer cells.

Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3979.

Segmentation in structure from motion: modeling and psychophysics

Much work has been done on the question of how the visual system extracts the three-dimensional (3D) structure and motion of an object from two-dimensional (2D) motion information, a problem known as 'Structure from Motion', or SFM. Much less is known, however, about the human ability to recover structure and motion when the optic flow field arises from multiple objects, although observations of this ability date as early as Ullman's well-known two-cylinders stimulus [The interpretation of visual motion (1979)]. In the presence of multiple objects, the SFM problem is further aggravated by the need to solve the segmentation problem, i.e. deciding which motion signal belongs to which object. Here, we present a model for how the human visual system solves the combined SFM and segmentation problems, which we term SSFM, concurrently. The model is based on computation of a simple scalar property of the optic flow field known as def, which was previously shown to be used by human observers in SFM. The def values of many triplets of moving dots are computed, and the identification of multiple objects the image is based on detecting multiple peaks in the histogram of def values. In five experiments, we show that human SSFM performance is consistent with the predictions of the model. We compare the predictions of our model to those of other theoretical approaches, in particular those that use a rigidity hypothesis, and discuss the validity of each approach as a model for human SSFM.

Condom use and first-time urinary tract infection

We evaluated the effects of condom use, lubricated condom use, and spermicide use on risk of acquiring first urinary tract infection in a case-control study of sexually active college women ages 18-39 years. Cases (N = 144) were women with first urinary tract infection that was confirmed by culture recruited at the student health service; controls (N = 286) were women without a history of urinary tract infection who were randomly sampled from all women enrolled at the university. Participants completed a self-administered questionnaire regarding type and frequency of condom use during the previous 2 weeks. Condoms and spermicides usually were used in combination with each other or oral contraceptives. After adjusting for frequency of vaginal intercourse, using unlubricated condoms compared with using no birth control method strongly increased the risk of first urinary tract infection (odds ratio = 29.1; 95% confidence interval = 3.1-1,335). Using a lubricated condom (with or without spermicide in the lubricant) or a spermicidal cream or gel with an unlubricated condom was associated with two- to eightfold risk of first urinary tract infection. Unlubricated condom use was strongly associated with risk of first urinary tract infection, but this effect was largely neutralized by using a spermicidal cream or gel with the unlubricated condom or by using a lubricated condom.

Pharmacokinetics and pharmacodynamics of remifentanil in persons with renal failure compared with healthy volunteers

BACKGROUND

Remifentanil is an opioid analgesic for use in anesthesia. An ester linkage renders it susceptible to rapid metabolism by blood and tissue esterases. Thus it was hypothesized that remifentanil elimination would be independent of renal function. Because its principal metabolite (GR90291) is eliminated renally, it would depend on renal function. This study was designed to evaluate the pharmacokinetics and pharmacodynamics of remifentanil and its metabolite in persons with and without renal failure.

METHODS

Two groups of volunteers received two-stage infusions of remifentanil: low dose with 0.0125 microg x kg(-1) x min(-1) for 1 h followed by 0.025 microg x kg(-1) x min(-1) for 3 h; and high dose with 0.025 microg x kg(-1) x min(-1) for 1 h followed by 0.05 microg x kg(-1) x min(-1) for 3 h. Blood samples were collected for analysis of remifentanil and GR90291 concentrations. The pharmacokinetics of remifentanil were fit using a one-compartment pharmacokinetic model. Remifentanil's effect was determined intermittently using minute ventilation during a hypercapnic (7.5% CO2) challenge.

RESULTS

Fifteen patients with renal failure and eight control participants were enrolled. The clearance and volume of distribution of remifentanil were not different between those with renal failure and the controls. Patients with renal failure showed a marked reduction in the elimination of GR90291; the half-life of the metabolite increased from 1.5 h in the controls to more than 26 h in patients with renal failure. The steady-state concentration of GR90291 is likely to be more than 25 times higher in persons with renal failure. There were no obvious differences in opioid effects on minute ventilation in the controls and in patients with renal failure.

CONCLUSIONS

The pharmacokinetics and pharmacodynamics of remifentanil were not altered in patients with renal disease, but the elimination of its principal metabolite, GR90291, was markedly reduced. Based on simulations, the concentration of GR90291 at the end of a 12-h remifentanil infusion of 2 microg x kg(-1) x min(-1) is not likely to produce significant opioid effects.

Abrupt learning and retinal size specificity in illusory-contour perception

BACKGROUND

In behavioral studies of learning, a distinction is commonly made between gradual and abrupt improvements in performance. The learning of perceptual and motor skills is often characterized by gradual, incremental improvement, and is found not to generalize over stimulus manipulations such as changes in the size or location of the retinal image. In contrast, marked improvement in performance can occur suddenly - a phenomenon which has been termed 'insight'. Consequently, the brain mechanisms subserving the two types of learning are commonly thought of as distinct. Here, we examine learning of a perceptual task in which improvement appears to exhibit characteristics of both gradual and abrupt learning.

RESULTS

We describe experiments on illusory-contour perception in which the observers underwent an abrupt, dramatic improvement in performance, resembling an incident of insight. At the same time, however, the phenomenon showed a degree of stimulus-specificity that was previously thought to characterize incremental, gradual learning. The improvement was triggered only by specific visual stimuli, whereas other, quite similar, stimuli were found to be ineffective for training; the learning did not generalize to a new retinal image size, and re-training was necessary for different-sized images.

CONCLUSIONS

The juxtaposition of abrupt and stimulus-specific learning that we observed suggests that the distinction between the two forms of learning needs to be revised. Rather than postulating two distinct mechanisms, incremental and insightful learning need to be addressed within a single framework. In particular, the findings suggest that learning may involve interactions between multiple levels of representations of the stimulus.

The cost-effectiveness of placing urinary tract infection treatment over the counter

We use cost-effectiveness analysis to estimate the economic and health implications of approving the over-the-counter sale of oral antibiotics for treatment of urinary tract infection (UTI). We consider two alternatives for over-the-counter availability and examine the reduced economic cost from avoided doctors' visits, along with the potential additional costs associated with higher over-the-counter treatment prices or increased use due to greater access. We also consider important noneconomic costs such as reduced symptom days, restricted activity days, and growing resistance to antibiotics. Our analysis covers a 20-year time horizon to capture the long-term effects, from a societal perspective, of a policy decision to place UTI treatment over the counter today. In addition, we present sensitivity analyses to test the effects of the assumptions in our model. We estimate that the economic costs of placing UTI treatment over the counter outweigh the benefits, unless there is extensive patient education and a mechanism for allowing patients to properly self-diagnose to reduce markedly the number of doctors' visits, mistreated symptoms, and threat of resistance to antibiotics. Only if doctors' visits were reduced to 64.6% of current levels would the economic benefits of over-the-counter treatment begin to be realized. UTI is one of the most common complaints among women and accounts for a large number of doctor visits each year. However, the costs of over-the-counter distribution of UTI treatment, particularly those due to the risk of decreasing the time until standard treatments become ineffective due to bacterial resistance, outweigh the short-term gains of decreased symptom days and increased access to treatment.

The difficult patient: creation of a curriculum by third-year family practice residents

BACKGROUND AND OBJECTIVES

Family practice residents tend to perceive psychosocial problems as less important than other factual aspects of their curriculum. To address this, we developed a problem-based learning (PBL) approach to the biopsychosocial model of medical care.

METHODS

Third-year residents presented current problematic patients at a PBL advanced psychiatry conference. Data were collected on topics generated, resident attendance, and conference evaluation.

RESULTS

The residents generated a topic list that closely matched a prior faculty-generated list. Some topics were discussed on multiple occasions; others not on the faculty list were also generated. Topics omitted were mental health in the physician's home, crisis prevention/intervention, and troubled marriages. In 1992-1995, resident attendance ranged from 56%-79%. A minority (0-5 residents) consistently attended fewer than 50% of the conferences. Residents evaluated the conference from "good" to "very good."

CONCLUSIONS

By employing a PBL format and allowing residents to present current patients, conferences were better attended and covered almost all topics previously identified as important. PBL promoted efficient use of residents' time since residents were only required to research the literature about group knowledge deficits. This provided good training for the residents and excellent continuing medical education for faculty.

Abrupt Transitions in the Perception of Illusory Contours Triggered by Specific Visual Stimuli

Two forms of learning have been identified in previous studies. Gradual improvement is observed for many perceptual tasks; it is often stimulus-specific and is consequently thought to involve synaptic modifications in early visual cortical areas. In contrast, sudden transitions, either cognitive (‘insight’) or perceptual (eg in the Dalmatian dog picture) are generally thought to occur more centrally.

Here we report that a sudden transition in the perception of illusory-contour stimuli can be triggered by specific visual stimuli, rather than by verbal instructions, leading to an abrupt improvement in psychophysical performance.

Subjects discriminated between two classes of Kanizsa-like shapes where the (illusory) edges were slightly curved into ‘thin’ or ‘fat’ figures (D L Ringach, R Shapley, 1993 Perception22 Supplement, 51). In the first (‘test’) block, only small amounts of curvature (1° – 3°) were given; subjects performed poorly in that block. In the second (‘training’) block, stimuli with larger curvature (4° – 6°) were added to the set. Performance for the 1° – 3° stimuli improved abruptly—often within seconds—compared to the first block: the pooled responses of eight naive subjects showed a marked jump, followed by maintained elevation, of the fraction-correct responses as a function of time. Good performance was retained in a third (re-test) block, with a stimulus set identical to that of the first block. Control experiments verified that the subjects understood the task from the beginning. Furthermore, the learned performance did not transfer to a different (smaller) retinal size. Thus the jump in performance is a perceptual, stimulus-specific phenomenon (rather than a cognitive one), although it exhibits characteristics of ‘insightful’ understanding.

Enhanced perception of illusory contours in the lower versus upper visual hemifields

The visual world consciously perceived is very different from the spatial array of photo-receptor activation present on our retinae; it is composed of segregated surfaces, organized into distinct objects. An important component of this organizational process, the segmentation of an image into figures and background, is shown to be performed much better in the lower visual field. This finding is demonstrated by the performance in two tasks that involve the perception of illusory contours. This asymmetry indicates a neural specialization that may be related to the anatomical discontinuity along the representation of the horizontal meridian in extrastriate visual cortex.

Illusory contours activate specific regions in human visual cortex: evidence from functional magnetic resonance imaging

The neural basis for perceptual grouping operations in the human visual system, including the processes which generate illusory contours, is fundamental to understanding human vision. We have employed functional magnetic resonance imaging to investigate these processes noninvasively. Images were acquired on a GE Signa 1.5T scanner equipped for echo planar imaging with an in-plane resolution of 1.5 x 1.5 mm and slice thicknesses of 3.0 or 5.0 mm. Visual stimuli included nonaligned inducers (pacmen) that created no perceptual contours, similar inducers at the corners of a Kanizsa square that created illusory contours, and a real square formed by continuous contours. Multiple contiguous axial slices were acquired during baseline, visual stimulation, and poststimulation periods. Activated regions were identified by a multistage statistical analysis of the activation for each volume element sampled and were compared across conditions. Specific brain regions were activated in extrastriate cortex when the illusory contours were perceived but not during conditions when the illusory contours were absent. These unique regions were found primarily in the right hemisphere for all four subjects and demonstrate that specific brain regions are activated during the kind of perceptual grouping operations involved in illusory contour perception.

Restricted ability to recover three-dimensional global motion from one-dimensional motion signals: psychophysical observations

We tested human ability to recover the 3D structure and motion information from time-varying images where only 1D motion cues were available. Under these conditions, observers exhibit poor performance in discriminating between two perpendicular axes of rotation, or discriminating between rigid and non-rigid 3D motion. This behavior of the visual system is to be contrasted with the good depth from motion performance exhibited when 2D motion cues are given in the image, as was found previously in numerous studies, and also in the work presented here. In a related paper, we suggest a theoretical framework in which to understand this differential performance on the basis of the two types of motion cues (1D vs 2D). Our findings are consistent with those of previous studies of frontoparallel motion, where it was shown that in many cases, the 1D cues alone were not integrated by the visual system into the correct global motion percept. This accumulating evidence suggests that oriented (1D) motion detectors alone cannot account for observed human performance of global motion perception, and that the role of units such as point or endpoint detectors should be studied further.

Restricted ability to recover three-dimensional global motion from one-dimensional local signals: theoretical observations

Recovering 3D information from a 2D time-varying image is a vital task which human observers face daily. Numerous models exist which compute global 3D structure and motion on the basis of 2D local motion measurements of point-like elements. On the other hand, both experimental and computational research of early visual motion mechanisms emphasize the role of oriented (1D) detectors. Therefore, it is important to find out whether indeed 1D motion signals can serve as primary cues for 3D global motion computation. We have addressed this question by combining mathematical results and perceptual observations. We show that given the 2D-projected 1D instantaneous velocity field, it is mathematically impossible to discriminate rigid rotations from non-rigid transformations and/or to recover the rotation parameters. We relate this fact to existing results in cases where localized (point-like) cues are present, and to our own experiments on human performance in global motion perception when only 1D cues are given. Taken together, the data suggest a necessary role for localized information in early motion mechanisms and call for further physiological and psychophysical research in that direction.

Incomplete processing of progastrin expressed by human colon cancer cells: role of noncarboxyamidated gastrins

Gastrin is mitogenic for several colon cancers. To assess a possible autocrine role of gastrin in colon cancers, we examined human colon cancer cell lines for expression of gastrin mRNA and various forms of gastrin. Gastrin mRNA was not detected in the majority of colon cancer cell lines by Northern hybridization but was detected in all human colon cancer lines by the sensitive method of reverse transcriptase-polymerase chain reaction (PCR). Gastrin mRNA was quantitated by the competitive PCR method. The majority of cell lines expressed very low levels of gastrin mRNA (< 1-5 copies/cell); only one cell line expressed > 20 copies/cell. The mature carboxyamidated form of gastrin was not detected in any of the cell lines by radioimmunoassay or immunocytochemistry. Results suggested that either gastrin mRNA expressed by colon cancer cells was altered (mutated) or posttranslational processing of progastrin was incomplete. Gastrin cDNA from all the colon cancer cell lines had an identical sequence to the published sequence of human gastrin cDNA. Specific antibodies against precursor forms of gastrin were used, and significant concentrations of nonamidated (glycine-extended) and prepro forms of gastrin were measured in tumor extracts of representative colon cancer cell lines. The presence of precursor forms of gastrin suggested a lack of one or more of the processing enzymes and/or cofactors. Significant concentrations of the processing enzyme (peptidylglycine alpha-amidating monooxygenase) were detected in colon cancer cells by immunocytochemistry. Therefore, lack of other cofactors or enzymes may be contributing to incomplete processing of precursor forms of gastrin, which merits further investigation. Since low levels of gastrin mRNA were expressed by the majority of human colon cancer cell lines and progastrin was incompletely processed, it seems unlikely that gastrin can function as a viable autocrine growth factor for colon cancer cells. High concentrations of glycine-extended gastrin-17 (GG) (> 10(-6) M) were mitogenic for a gastrin-responsive human colon cancer (DLD-1) cell line in vitro. It remains to be seen if GG or other precursor forms of gastrin are similarly mitogenic in vivo, which may then lend credibility to a possible autocrine role of gastrinlike peptides in colon cancers.

Insulinlike growth factors and binding proteins in colon cancer

Insulinlike growth factors (IGFs) express anabolic and mitogenic activity on wide variety of cells. Besides endocrine effects, IGFs have major autocrine and paracrine effects on many cellular functions. Two factors that significantly affect the extent of cellular response to IGFs include the membrane receptors for IGFs and the soluble binding proteins (BPs), which modulate the action of IGFs at the receptor level. IGFs, IGF receptors, and IGFs and their BPs (IGF-BPs) thus constitute three components of the IGF system. A role of IGFs in the transformation and proliferation of cancer cells has become increasingly evident in the past few years. Studies from several laboratories show that all three components of the IGF system may play an important role in the proliferation of colon cancers. It was recently shown that the relative expression of IGFs and IGF/BPs may critically control the metastatic potential of colon cancers. The purpose of this article is to summarize our current knowledge of the IGF system and to present support for a significant role of IGFs in the initiation and growth of colon cancers. The expression and structural aspects of IGFs, their receptors, and BPs are outlined first, followed by a discussion of the role of IGFs in gastrointestinal functions and in colon cancers.

Isolating the effect of one-dimensional motion signals on the perceived direction of moving two-dimensional objects

A considerable body of evidence suggests the existence of a two-stage mechanism for the detection of global motion. In the first stage the motion of elongated contours is extracted and then at the second stage these one-dimensional (1D) motion signals are combined. What is the nature of the computation carried out in combining the 1D motion signals towards forming a global motion percept? We devised a set of stimuli that differentiate between different possible computations. In particular, they distinguish between a velocity-space construction (such as intersection of constraints) and a linear computation such as vector averaging. In addition, these stimuli do not contain two-dimensional (2D) motion signals such as line intersections, that allow unambiguous determination of global velocity. Stimuli were presented in uncrossed disparity relative to the aperture through which they were presented, to reduce the effect of line terminator motion. We found that subjects are unable to detect the veridical global direction of motion for these stimuli. Instead, they perceive the stimulus pattern to be moving in a direction which reflects the average of its 1D motion components. Our results suggest that the visual system is not equipped with a mechanism implementing a velocity-space computation of global motion.