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M Laubach

Publications and source records attributed to M Laubach.

11 recordsLinked to original sources
PubMed2000

Real-time prediction of hand trajectory by ensembles of cortical neurons in primates.

Signals derived from the rat motor cortex can be used for controlling one-dimensional movements of a robot arm. It remains unknown, however, whether real-time processing of cortical signals can be employed to reproduce, in a robotic device, the kind of complex arm movements used by primates to reach objects in space. Here we recorded the simultaneous activity of large populations of neurons, distributed in the premotor, primary motor and posterior parietal cortical areas, as non-human primates performed two distinct motor tasks. Accurate real-time predictions of one- and three-dimensional arm movement trajectories were obtained by applying both linear and nonlinear algorithms to cortical neuronal ensemble activity recorded from each animal. In addition, cortically derived signals were successfully used for real-time control of robotic devices, both locally and through the Internet. These results suggest that long-term control of complex prosthetic robot arm movements can be achieved by simple real-time transformations of neuronal population signals derived from multiple cortical areas in primates.

Animals↗
PubMed2000

Cortical ensemble activity increasingly predicts behaviour outcomes during learning of a motor task.

When an animal learns to make movements in response to different stimuli, changes in activity in the motor cortex seem to accompany and underlie this learning. The precise nature of modifications in cortical motor areas during the initial stages of motor learning, however, is largely unknown. Here we address this issue by chronically recording from neuronal ensembles located in the rat motor cortex, throughout the period required for rats to learn a reaction-time task. Motor learning was demonstrated by a decrease in the variance of the rats' reaction times and an increase in the time the animals were able to wait for a trigger stimulus. These behavioural changes were correlated with a significant increase in our ability to predict the correct or incorrect outcome of single trials based on three measures of neuronal ensemble activity: average firing rate, temporal patterns of firing, and correlated firing. This increase in prediction indicates that an association between sensory cues and movement emerged in the motor cortex as the task was learned. Such modifications in cortical ensemble activity may be critical for the initial learning of motor tasks.

Analysis of Variance↗
PubMed1999

Independent component analyses for quantifying neuronal ensemble interactions.

The goal of this study was to compare how multivariate statistical methods for dimension reduction account for correlations between simultaneously recorded neurons. Here, we describe applications of principal component analysis (PCA) and independent component analysis (ICA) (Cardoso J-F, Souloumiac A. IEE-Proc F 1993;140:362-70; Hyvarinen A, Oja E. Neural Comput 1997;9:1483-92; Lee TW, Girolami M, Sejnowski TJ. Neural Comp 1999;11:417-41) to neuronal ensemble data. Simulated ensembles of neurons were used to compare how well the methods above could account for correlated neuronal firing. The simulations showed that 'population vectors' defined by PCA were broadly distributed over the neuronal ensembles; thus, PCA was unable to identify independent groupings of neurons that shared common sources of input. By contrast, the ICA methods were all able to identify groupings of neurons that emerged due to correlated firing. This result suggests that correlated neuronal firing is reflected in higher-order correlations between neurons and not simply in the neurons' covariance. To assess the significance of these methods for real neuronal ensembles, we analyzed data from populations of neurons recorded in the motor cortex of rats trained to perform a reaction-time task. Scores for PCA and ICA were reconstructed on a bin-by-bin basis for single trials. These data were then used to train an artificial neural network to discriminate between single trials with either short or long reaction-times. Classifications based on scores from the ICA-based methods were significantly better than those based on PCA. For example, scores for components defined with an ICA-based method, extended ICA (Lee et al., 1999), classified more trials correctly (80.58+/-1.25%) than PCA (73.14+/-0.84%) for an ensemble of 26 neurons recorded in the motor cortex (ANOVA: P < 0.005). This result suggests that behaviorally relevant information is represented in correlated neuronal firing and can be best detected when higher-order correlations between neurons are taken into account.

Action Potentials↗
PubMed1998

Simultaneous encoding of tactile information by three primate cortical areas.

We used simultaneous multi-site neural ensemble recordings to investigate the representation of tactile information in three areas of the primate somatosensory cortex (areas 3b, SII and 2). Small neural ensembles (30-40 neurons) of broadly tuned somatosensory neurons were able to identify correctly the location of a single tactile stimulus on a single trial, almost simultaneously. Furthermore, each of these cortical areas could use different combinations of encoding strategies, such as mean firing rate (areas 3b and 2) or temporal patterns of ensemble firing (area SII), to represent the location of a tactile stimulus. Based on these results, we propose that ensembles of broadly tuned neurons, located in three distinct areas of the primate somatosensory cortex, obtain information about the location of a tactile stimulus almost concurrently.

Action Potentials↗
PubMed1998

Selective feticide in twin pregnancies with very early preterm premature rupture of membranes.

Nine consecutive multichorionic multiple gestations with early second-trimester (< or =20 weeks) preterm premature rupture of the membranes (PPROM) of the lower gestational sac were managed expectantly. Mean gestational age at PPROM was 17.5 weeks (13-20 weeks), and the mean PPROM delivery time interval was 6.2 weeks (0-11 weeks). A fetal loss of 63% (12 of 19), and a subsequent neonatal loss of 57% (4 of 7) were observed. Of the four pregnancies evolving beyond 25 weeks, three delivered before 30 weeks. The baby take-home rate was 16% (3 of 19). Histologic evidence of chorioamnionitis was present in 5 of 7 (71%) investigated pregnancies. Three other consecutive twin pregnancies were complicated by PPROM of the precervical gestational sac at 13 to 16 weeks of gestation (mean: 15 weeks). In the absence of clinical chorioamnionitis and amniotic fluid, selective feticide with potassium chloride was performed. Pregnancy was successfully prolonged beyond 33 weeks in two cases. The overall PPROM delivery time interval was 21 weeks (20-22 weeks). No neonatal losses were encountered. The baby take-home rate was 66% (2 of 3). Selective feticide of the fetus with early midtrimester PROM in the absence of maternal signs of infection may improve the former unfavorable pregnancy outcome.

Female↗
PubMed1996

Early prenatal diagnosis of oculoauriculovertebral dysplasia or the Goldenhar syndrome.

We report a case of the sonographic detection of oculoauriculovertebral dysplasia in a fetus at 15 weeks' gestation. An early diagnosis was suggested by observation of a maxillar cleft in association with unilateral microphthalmia. In the presence of microphthalmia the syndrome is likely to include mental retardation. When the diagnosis is made in the perinatal period, management generally involves cosmetic surgery. If, however, the condition is recognized in the early stages of gestation, termination of pregnancy may be an option.

Adult↗
PubMed1995

Postoperative hypercoagulability and deep-vein thrombosis after laparoscopic cholecystectomy.

Patients who undergo laparoscopic cholecystectomy (LC) are operated on under general anesthesia, in a reverse Trendelenburg position, with 12-15-mmHg pneumoperitoneum. All of these factors can induce venous stasis of the legs, which may lead to postoperative deep-vein thrombosis (DVT). The objectives of this study were to assess the degree of hypercoagulability and to determine the rate of postoperative DVT in a group of 100 patients in whom LC was completed. Whole-blood thrombelastography (TEG) and plasma-activated partial thromboplastin time (PTT) determination were carried out preoperatively and on the 1st postoperative day. All patients received pre-, intra-, and postoperative graduated compression stockings and sequential pneumatic compression devices until fully ambulatory. Twenty-six percent of the patients with a risk score > 4, or a post-operative TEG index > +5.0, received subcutaneous heparin (5,000 units b.i.d.), beginning in the postoperative period and continuing for 4 weeks as an outpatient. A complete venous duplex scan of both legs was performed on the 7th postoperative day, at the time of their office visit. Our results revealed significant postoperative hypercoagulability for the TEG index (P < 0.005) and for PTT (P < 0.05). One patient had an asymptomatic DVT (1%), and no side effects from the mechanical or pharmacological prophylaxis occurred in this series. These data suggest that the low incidence of thrombosis in the face of theoretical and laboratory evidence of postoperative hypercoagulability may reflect an effective prophylactic regime.(ABSTRACT TRUNCATED AT 250 WORDS)

Bandages↗
PubMed1995

Venous duplex imaging follow-up of acute symptomatic deep vein thrombosis of the leg.

PURPOSE: The purpose of this study was to evaluate the rate of resolution of deep vein thrombosis (DVT) in the leg, by means of duplex imaging, in patients with symptoms during a 6-month period after initial diagnosis. METHODS: Seventy-three limbs in 69 patients with acute DVT diagnosed by duplex imaging received conventional heparin and warfarin treatment and underwent subsequent duplex studies 1, 4, 12, and 24 weeks after the initial diagnosis. The objectives of the study were to document (1) the rate or complete resolution of DVT, (2) the proportion of unstable, floating thrombi, and (3) the development of chronic damage as a result of vessel wall scarring. RESULTS: The rate of normalization of DVT 6 months after diagnosis was 78% in the common femoral vein, 70% in the superficial femoral vein, 75% in the popliteal vein, and 70% in the calf veins examined at the scheduled intervals. Twenty-six percent of thrombi were considered unstable on the baseline examination. The average number of days necessary for these thrombi to become stable was 10.7 days. Damage to the vessel wall or valves was documented in 44% of the patients. CONCLUSIONS: Rates of resolution of DVT were similar for the different veins of the leg studied. There was a high proportion of unstable thrombi, which present a high potential risk of embolization. Serial duplex scanning after DVT renders important information with regard to thrombus resolution, propagation, and attachment to the vein wall.

Acute Disease↗
PubMed1994

Prevention of venous thromboembolism in North America: results of a survey among general surgeons.

PURPOSE: The purpose of this study was to analyze current attitudes toward the prevention of postoperative venous thromboembolism among North American general surgeons. METHODS: A survey regarding awareness of the problem of venous thromboembolism and preferred modalities of prophylaxis was sent to 3500 randomly selected Fellows of the American College of Surgeons. RESULTS: A total of 1018 (29.1%) surveys was returned. Most of the responding surgeons consider venous thromboembolism a serious health problem. Ninety percent of the surgeons use prophylaxis against venous thromboembolism routinely. The most frequently used modalities are intermittent pneumatic compression, low-dose heparin, and elastic stocking. A combination of physical and pharmacologic methods is used by one fourth of respondents, and only 50% start pharmacologic prophylaxis before the surgical procedure. The thrombosis risk factors that are most frequently considered by surgeons when deciding about using prophylaxis are history of venous thromboembolism, immobility, and length of operation. CONCLUSIONS: North American surgeons who responded to this survey are well aware of the problem of venous thromboembolism and their approach to prevention has been significantly modified in the last 10 years. Compared with similar European surveys this survey reveals a higher implementations of physical methods such as intermittent pneumatic compression and elastic stockings. Because of the limited response rate and possibility of sampling bias, these findings should be interpreted with caution.

Adult↗