Showing papers by "Université de Montréal published in 1994"

Learning long-term dependencies with gradient descent is difficult

Abstract: Recurrent neural networks can be used to map input sequences to output sequences, such as for recognition, production or prediction problems. However, practical difficulties have been reported in training recurrent neural networks to perform tasks in which the temporal contingencies present in the input/output sequences span long intervals. We show why gradient based learning algorithms face an increasingly difficult problem as the duration of the dependencies to be captured increases. These results expose a trade-off between efficient learning by gradient descent and latching on information for long periods. Based on an understanding of this problem, alternatives to standard gradient descent are considered. >

Biodiversity and stability in grasslands

Abstract: One of the ecological tenets justifying conservation of biodiversity is that diversity begets stability. Impacts of biodiversity on population dynamics and ecosystem functioning have long been debated1–7, however, with many theoretical explorations2–6,8–11 but few field studies12–15. Here we describe a long-term study of grasslands16,17 which shows that primary productivity in more diverse plant communities is more resistant to, and recovers more fully from, a major drought. The curvilinear relationship we observe suggests that each additional species lost from our grasslands had a progressively greater impact on drought resistance. Our results support the diversity—stability hypothesis5,6,18,19, but not the alternative hypothesis that most species are functionally redundant19–21. This study implies that the preservation of biodiversity is essential for the maintenance of stable productivity in ecosystems.

Fidelity for Mixed Quantum States

Abstract: We propose a definition of fidelity for mixed quantum states in terms of Uhlmann's ‘transition probability’ formula F(ϱ1, ϱ2) = {trace [(√ϱ1ϱ2 × √ϱ1)1/2]}2 and give new elementary proofs of its essential properties.

A tabu search heuristic for the vehicle routing problem

Abstract: The purpose of this paper is to describe TABUROUTE, a new tabu search heuristic for the vehicle routing problem with capacity and route length restrictions. The algorithm considers a sequence of adjacent solutions obtained by repeatedly removing a vertex from its current route and reinserting it into another route. This is done by means of a generalized insertion procedure previously developed by the authors. During the course of the algorithm, infeasible solutions are allowed. Numerical tests on a set of benchmark problems indicate that tabu search out performs the best existing heuristics, and TABUROUTE often produces the best known solutions.

Distributed processing of pain and vibration by the human brain.

Abstract: Pain is a diverse sensory and emotional experience that likely involves activation of numerous regions of the brain. Yet, many of these areas are also implicated in the processing of nonpainful somatosensory information. In order to better characterize the processing of pain within the human brain, activation produced by noxious stimuli was compared with that produced by robust innocuous stimuli. Painful heat (47-48 degrees C), nonpainful vibratory (110 Hz), and neutral control (34 degrees C) stimuli were applied to the left forearm of right-handed male subjects. Activation of regions within the diencephalon and telencephalon was evaluated by measuring regional cerebral blood flow using positron emission tomography (15O-water-bolus method). Painful stimulation produced contralateral activation in primary and secondary somatosensory cortices (SI and SII), anterior cingulate cortex, anterior insula, the supplemental motor area of the frontal cortex, and thalamus. Vibrotactile stimulation produced activation in contralateral SI, and bilaterally in SII and posterior insular cortices. A direct comparison of pain and vibrotactile stimulation revealed that both stimuli produced activation in similar regions of SI and SII, regions long thought to be involved in basic somatosensory processing. In contrast, painful stimuli were significantly more effective in activating the anterior insula, a region heavily linked with both somatosensory and limbic systems. Such connections may provide one route through which nociceptive input may be integrated with memory in order to allow a full appreciation of the meaning and dangers of painful stimuli. These data reveal that pain-related activation, although predominantly contralateral in distribution, is more widely dispersed across both cortical and thalamic regions than that produced during innocuous vibrotactile stimulation. This distributed cerebral activation reflects the complex nature of pain, involving discriminative, affective, autonomic, and motoric components. Furthermore, the high degree of interconnectivity among activated regions may account for the difficulty of eliminating pathological pain with discrete CNS lesions.

Laparoscopic pylorus-preserving pancreatoduodenectomy

Abstract: A case of chronic pancreatitis localized in the head of the pancreas with pancreas divisum was treated by laparoscopic pylorus-preserving pancreatoduodenectomy. The laparoscopic technique of resection and reconstruction with a gastrojejunostomy, hepaticojejunostomy, and pancreaticojejunostomy is described. The postoperative period was complicated by a jejunal ulcer and delayed gastric emptying necessitating a prolonged hospitalization and intravenous hyperalimentation. No fistulas occurred, a follow-up CT scan revealed no pancreatic abnormalities, and the patient was discharged in good condition on the 30th postoperative day. Although technically feasible, the laparoscopic Whipple procedure may not improve the postoperative outcome or shorten the postoperative recovery period.

Restless legs syndrome and sleep bruxism : prevalence and association among Canadians

Abstract: A survey conducted through personal interviews was done in Canada to estimate the prevalence of subjective symptoms related to restless legs syndrome (RLS) and to sleep bruxism. Of the 2,019 respondents, all over 18 years of age, 15% reported leg restlessness at bedtime; 10% reported unpleasant leg muscle sensations associated with awakening during sleep and with the irresistible need to move or walk. Both these complaints are related to RLS. The prevalence of RLS-related symptoms increased linearly with age. Tooth grinding, a symptom related to sleep bruxism, was reported by 8% of the subjects; in contrast to RLS-related symptoms, the prevalence of tooth grinding decreased linearly with age. RLS-related symptoms were reported more frequently in Eastern provinces than in Ontario and Western Canada, and more frequently in Roman Catholic and French-speaking responders. This was not the case for sleep bruxism; between 14.5% and 17.3% of the subjects who reported subjective RLS-related symptoms also reported tooth grinding. Conversely, 9.6-10.9% of the tooth grinders reported RLS-related symptoms. These data suggest that both sleep movement disorders can be concomitant and that socio-geographic and age characteristics influence the prevalence of reports.

Major expansion of CD8+ T cells with a predominant V beta usage during the primary immune response to HIV.

Abstract: A SIGNIFICANT proportion (up to 70%) of individuals experience an acute clinical syndrome of varying severity associated with primary infection with the human immunodeficiency virus (HIV). We report here studies on six individuals who showed an acute HIV syndrome which generally resolved within four weeks, concomitant with a dramatic downregulation of viraemia. To characterize the T-cell-mediated primary immune response to HIV, we used combined semiquantitative polymerase chain reaction assay and cytofluorometry to analyse the T-cell antigen receptor repertoire in sequential peripheral blood mononuclear cells from the patients. We found major oligoclonal expansions in a restricted set of variable-domain beta-chain (V beta) families. Cells expressing the expanded V beta s predominantly expressed the CD8 T-cell differentiation antigen and mediated HIV-specific cytotoxicity. Major oligoclonal expansions of these CD8+ T lymphocytes may represent an important component of the primary immune response to viral infections and may help to clarify both the immunopathogenic and the protective mechanisms of HIV infection.

Foreign Branding and Its Effects on Product Perceptions and Attitudes

Abstract: With three experiments, the authors examine the notion that foreign branding—the strategy of pronouncing or spelling a brand name in a foreign language—triggers cultural stereotypes and influences ...

Predicting Early Onset of Male Antisocial Behavior From Preschool Behavior

Abstract: Methods: Data from a large longitudinal study of boys who were between kindergarten and age 13 years were used to (1) test whether Gray's and Cloninger's personality dimensions measured in kindergarten predicted the early onset of stable, highly delinquent behavior; (2) test whether 1, 2, or 3 dimensions were needed; and (3) test the predictive value of a categorical approach. Results: The impulsivity dimension was the best predictor of the early onset of stable, highly delinquent behavior. Anxiety and reward dependence made significant but weaker contributions. The categorical approach corroborated Cloninger's suggestion that boys who are high in impulsivity, low in anxiety, and low in reward dependence would be more at risk for delinquent involvement. Boys who were high in impulsivity and low in anxiety but high in reward dependence were much less at risk for delinquency. Differences in antisocial behavior among extreme kindergarten personality groups were stable from ages 11 to 13 years. Conclusions: The behavioral activating system appears to be the major dimension underlying the propensity toward early onset of antisocial behavior, but both the behavioral inhibition system and the need for social rewards play important roles. The behavioral style (personality) that results from the interplay of these systems is clearly in place by the kindergarten year. Preventive efforts should target preschool children with at-risk behavior profiles. However, longitudinal-experimental studies with at least yearly assessments between birth and school-entry age are needed to understand the extent to which the behavioral styles are antecedent to preschool disruptive behavior disorders.

A thalamic nucleus specific for pain and temperature sensation

Abstract: THE existence of a posterolateral thalamic relay nucleus for pain and temperature sensation was postulated in 1911, on the basis of the stroke-induced analgesia and thermanaesthesia found paradox-ically in patients with thalamic pain syndrome1. Pain or tempera-ture sensations can be evoked in humans by electrical stimulation in a vaguely defined region of the posterolateral thalamus2'3. Here we use anterograde tracing and single unit recordings to demon-strate that there is a distinct nucleus in the posterior thalamus of the macaque monkey that receives a dense, topographic input from spinothalamic lamina I neurons and in which almost all neurons are nociceptive- or thermoreceptive-specific. Immunohistochemical staining showed that this nucleus is defined by a dense calbindin-positive fibre plexus in the macaque, so we applied the same stain-ing method to sections of human thalamus. We found a nearly identical fibre plexus localized within a distinct nucleus that is cytoarchitectonically homologous to the lamina I relay nucleus in the macaque thalamus. The stereotaxic coordinates of this nucleus and its location relative to the main somatosensory representation fit clinical descriptions of the pain-producing region in humans. We conclude that this is a specific thalamic nucleus for pain and temperature sensation in both monkey and human.

Convergence Properties of the K-Means Algorithms

Abstract: This paper studies the convergence properties of the well known K-Means clustering algorithm. The K-Means algorithm can be described either as a gradient descent algorithm or by slightly extending the mathematics of the EM algorithm to this hard threshold case. We show that the K-Means algorithm actually minimizes the quantization error using the very fast Newton algorithm.

Modeling brain evolution from behavior: a permutational regression approach.

Abstract: This paper has two complementary purposes: first, to present a method to perform multiple regression on distance matrices, with permutation testing appropriate for path-length matrices representing evolutionary trees, and then, to apply this method to study the joint evolution of brain, behavior and other characteristics in marsupials. To understand the computation method, consider that the dependent matrix is unfolded as a vector y; similarly, consider X to be a table containing the independent matrices, also unfolded as vectors. A multiple regression is computed to express y as a function of X. The parameters of this regression (R2 and partial regression coefficients) are tested by permutations, as follows. When the dependent matrix variable y represents a simple distance or similarity matrix, permutations are performed in the same manner as the Mantel permutational test. When it is an ultrametric matrix representing a dendrogram, we use the double-permutation method (Lapointe and Legendre 1990, 1991). When it is a path-length matrix representing an additive tree (cladogram), we use the triple-permutation method (Lapointe and Legendre 1992). The independent matrix variables in X are kept fixed with respect to one another during the permutations. Selection of predictors can be accomplished by forward selection, backward elimination, or a stepwise procedure. A phylogenetic tree, derived from marsupial brain morphology data (28 species), is compared to trees depicting the evolution of diet, sociability, locomotion, and habitat in these animals, as well as their taxonomy and geographical relationships. A model is derived in which brain evolution can be predicted from taxonomy, diet, sociability and locomotion (R2 = 0.75). A new tree, derived from the "predicted" data, shows a lot of similarity to the brain evolution tree. The meaning of the taxonomy, diet, sociability, and locomotion predictors are discussed and conclusions are drawn about the evolution of brain and behavior in marsupials.

The thermal grill illusion: unmasking the burn of cold pain

Abstract: In Thunberg's thermal grill illusion, first demonstrated in 1896, a sensation of strong, often painful heat is elicited by touching interlaced warm and cool bars to the skin. Neurophysiological recordings from two classes of ascending spinothalamic tract neurons that are sensitive to innocuous or noxious cold showed differential responses to the grill. On the basis of these results, a simple model of central disinhibition, or unmasking, predicted a quantitative correspondence between grill-evoked pain and cold-evoked pain, which was verified psychophysically. This integration of pain and temperature can explain the thermal grill illusion and the burning sensation of cold pain and may also provide a basis for the cold-evoked, burning pain of the classic thalamic pain syndrome.

The use of alternative medicine by children

Abstract: Objective. Alternative medicine (AM) is of growing interest to the general public. Although several studies have been published concerning its use in adults, the use by children is less well known. The purpose of this study is to determine the frequency with which alternative medicine is employed in a pediatric population that also uses conventional medicine. A second goal is to investigate the sociodemographic factors that influence the choice of these forms of therapy. Methods. Parents of children consulting the general outpatient clinic of a university hospital completed a self-administered questionnaire asking about previous use of AM for themselves or their children. Results. Based on 1911 completed questionnaires, 208 children (11%) previously consulted one or more AM practitioners. Chiropractic, homeopathy, naturopathy, and acupuncture together accounted for 84% of use. Children who used AM differed significantly from those who only used conventional medicine in that they were older than the nonusers, their mothers were better educated, and their parents also tended to use AM. Conclusion. The findings indicate that AM is an aspect of child health care that no longer can be ignored. Being aware of these practices will enable physicians to discuss alternative therapies with parents in order to ensure the continuity of essential conventional treatments.

Inverse agonist activity of beta-adrenergic antagonists.

Abstract: Agonist-independent properties of the human beta 2-adrenergic receptor (beta 2AR) were studied using the baculovirus expression system in Sf9 cells. In the absence of agonist but in the presence of GTP, membranes from cells expressing the beta 2AR exhibited higher levels of cAMP production than did membranes from uninfected cells or from cells infected with wild-type baculovirus. The increase in cAMP production was proportional to the number of beta 2AR expressed, up to 40 pmol/mg of membrane protein, and it could be inhibited in a dose-dependent manner by beta AR antagonists. The increase and its reversal both were independent of the possible presence of contaminating catecholamines in the culture medium and thus appear to reflect spontaneous beta 2AR activity and direct antagonist-receptor interactions, respectively. The maximal level of inhibition varied among the beta AR ligands tested, to yield the following rank order of "inverse efficacy"; timolol > or = propranolol > alprenolol > or = pindolol > labetalol > dichloroisoproterenol. The same rank order was observed using membranes prepared from Chinese hamster fibroblasts expressing beta 2AR. The effect of timolol was partly blocked by labetalol and dichloroisoproterenol, in an apparently competitive manner. The intracellular cAMP content of Sf9 cells cultured in serum-free medium was also increased by the expression of beta 2AR, and that increase was reversed by timolol and propranolol, consistent with observations in membrane preparations. The properties revealed by the expression of the beta 2AR in Sf9 cells suggest two agonist-independent traits of G protein-linked receptors, i.e., 1) that unliganded receptors are able to activate G proteins both in membrane preparations and in whole cells and 2) that antagonists may mediate their effects not only by preventing the binding of agonists but also by decreasing the propensity of the receptor to assume an active state.

An Input Output HMM Architecture

Abstract: We introduce a recurrent architecture having a modular structure and we formulate a training procedure based on the EM algorithm. The resulting model has similarities to hidden Markov models, but supports recurrent networks processing style and allows to exploit the supervised learning paradigm while using maximum likelihood estimation.

Comparison of amitriptyline, cyclobenzaprine, and placebo in the treatment of fibromyalgia

Abstract: Objective. To compare the relative efficacy and tolerability of amitriptyline, cyclobenzaprine, and placebo in the treatment of fibromyalgia, and to identify predictors of response to amitriptyline and cyclobenzaprine. Methods, Two hundred eight patients who fulfilled the American College of Rheumatology criteria for the classification of fibromyalgia were entered into a 6-month prospective, double-blind, multicenter trial and were randomized to 1 of 3 treatment groups: amitriptyline, cyclobenzaprine, or placebo. Results. After 1 month, 21%, 12%, and 0% of the amitriptyline, cyclobenzaprine, and placebo patients, respectively, had significant clinical improvement (amitriptyline versus placebo P = 0.002, cyclobenzaprine versus placebo P = 0.02, amitriptyline versus cyclobenzaprine P not significant). These percentages increased to 36%, 33%, and 19%, respectively, at the 6-month assessment (P not significant). The nature and frequency of side effects reported by patients treated with amitriptyline and those reported by patients treated with cyclobenzaprine were similar. A normal Minnesota Multiphasic Personality Inventory (MMPI) profile at baseline was predictive of clinical improvement at the 1-month evaluation (odds ratio 3.3, 95% confidence interval 1.2—9.0). However, neither the MMPI profile nor any of the demographic, clinical, or functional parameters evaluated at baseline predicted long-term response. Conclusion. Our data confirm the short-term efficacy of amitriptyline and cyclobenzaprine in a small percentage of patients with fibromyalgia. Long-term efficacy could not be demonstrated because of a higher-than-expected placebo response. Predictors of response to these drugs could not be determined.

Elevated dopa decarboxylase activity in living brain of patients with psychosis

Abstract: The hypofrontality theory of the pathogenesis of schizophrenia predicts that cortical lesions cause psychosis. During a search for abnormalities of catecholaminergic neurotransmission in patients with complex partial seizures of the mesial temporal lobe, we discovered an increase of the rate of metabolism of an exogenous dopa tracer (6-[18F]fluoro-L-dopa) in the neostriatum of a subgroup of patients with a history of psychosis. When specifically assayed for this abnormality, patients with schizophrenia revealed the same significant increase of the rate of metabolism in the striatum. The finding is consistent with the theory that a state of psychosis arises when episodic dopamine excess is superimposed on a trait of basic dopamine deficiency in the striatum. The finding is explained by the hypothesis that cortical insufficiency, a proposed pathogenetic mechanism of both disorders, causes an up-regulation of the enzymes responsible for dopa turnover in the neostriatum as well as the receptors mediating dopaminergic neurotransmission.

Using natural-language processing to produce weather forecasts

Abstract: Improved numerical weather prediction simulations have led weather services to examine how and where human forecasters add value to forecast production. The Forecast Production Assistant (FPA) was developed with that in mind. The authors discuss the Forecast Generator (FOG), the first application developed on the FPA. FOG is a bilingual report generator that produces routine and special purpose forecast directly from the FPA's graphical weather predictions. Using rules and a natural-language generator, FOG converts weather maps into forecast text. The natural-language issues involved are relevant to anyone designing a similar system. >

A new proof of the quantum noiseless coding theorem

Abstract: We give an account of the quantum noiseless coding theorem, including a new proof based on a simplified block coding scheme. We also discuss an illustrative example of quantum coding.

Functional dissociations following bilateral lesions of auditory cortex.

Abstract: We present two patients with bilateral lesions of the superior temporal cortex who manifested a number of functional dissociations in the auditory domain. The perception of speech and environmental sounds were preserved; yet, the perception of tunes, prosody and voice was impaired. As the processing of melodic but not rhythmic variations in musical sequences was selectively disturbed, the deficit cannot be attributed to a general impairment in auditory memory or sequential processing. These findings suggest that melody processing is not mediated by a general-purpose auditory architecture but by specialized cortical subsystems residing within the lesioned areas. Current taxonomies of auditory agnosia and models of normal music cognition are evaluated in light of the functional dissociations manifested by these patients.

A hormone-encoding gene identifies a pathway for cardiac but not skeletal muscle gene transcription.

Abstract: In contrast to skeletal muscle, the mechanisms responsible for activation and maintenance of tissue-specific transcription in cardiac muscle remain poorly understood. A family of hormone-encoding genes is expressed in a highly specific manner in cardiac but not skeletal myocytes. This includes the A- and B-type natriuretic peptide (ANP and BNP) genes, which encode peptide hormones with crucial roles in the regulation of blood volume and pressure. Since these genes are markers of cardiac cells, we have used them to probe the mechanisms for cardiac muscle-specific transcription. Cloning and functional analysis of the rat BNP upstream sequences revealed unexpected structural resemblance to erythroid but not to muscle-specific promoters and enhancers, including a requirement for regulatory elements containing GATA motifs. A cDNA clone corresponding to a member of the GATA family of transcription factors was isolated from a cardiomyocyte cDNA library. Transcription of this GATA gene is restricted mostly to the heart and is undetectable in skeletal muscle. Within the heart, GATA transcripts are localized in ANP- and BNP-expressing myocytes, and forced expression of the GATA protein in heterologous cells markedly activates transcription from the natural cardiac muscle-specific ANP and BNP promoters. This GATA-dependent pathway defines the first mechanism for cardiac muscle-specific transcription. Moreover, the present findings reveal striking similarities between the mechanisms controlling gene expression in hematopoietic and cardiac cells and may have important implications for studies of cardiogenesis.