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Biomedical subjects

H Bergman

Publications and source records attributed to H Bergman.

At least 73 records · Page 4Linked to original sources
PubMed1998

Aging-related clinical and health services research in Canada.

Research by Canadian geriatricians has grown significantly since the Canadian Society of Geriatric Medicine was founded in 1981. Most research has been clinical or related to health service use. More recently, the Canadian Study of Health and Aging (CSHA) has proved an important focus for population-based research, and research on dementia. An increasing number of Canadian geriatricians have undertaken formal research training, and the CSHA study team and other groups are providing opportunities for multicentre, multidisciplinary, collaborative studies. These developments point to continued growth in research by Canadian geriatricians, most likely research with a clinical and population focus and employing multicenter designs.

Aged↗
PubMed1998

Spatiotemporal structure of cortical activity: properties and behavioral relevance.

The study was designed to reveal occurrences of precise firing sequences (PFSs) in cortical activity and to test their behavioral relevance. Two monkeys were trained to perform a delayed-response paradigm and to open puzzle boxes. Extracellular activity was recorded from neurons in premotor and prefrontal areas with an array of six microelectrodes. An algorithm was developed to detect PFSs, defined as a set of three spikes and two intervals with a precision of +/-1 ms repeating significantly more than expected by chance. The expected level of repetition was computed based on the firing rate and the pairwise correlation of the participating units, assuming a Poisson distribution of event counts. Accordingly, the search for PFSs was corrected for rate modulations. PFSs were found in 24/25 recording sessions. Most PFSs (76%) were composed of spikes of more than one unit but usually not more than two units (67%). The PFSs spanned hundreds of milliseconds, and the average interval between two events within the PFSs was 200 ms. No traces of periodic oscillations were found in the PFS intervals. The bins of the matrix that were defined as PFSs were isolated temporally: the spikes that generated PFSs were not associated with high-frequency bursts or rapid coherent rate fluctuations. A given PFS tended to be correlated with the animal's behavior. Furthermore, for 19% of the PFS pairs that shared the same unit composition, each member of the pair was associated with a different type of behavior. The PFSs often appeared in clusters that were associated with particular phases of the behavior. The firing rate of single units did not provide a full explanation for the timing and structure of these clusters. A reduced spike train (RST) was defined for each unit by taking all spikes of that unit that were part of any PFS. In 88% of the cases the degree of modulation of the RST was higher than that of the complete spike train. The results suggest that relevant information is carried by the fine temporal structure of cortical activity. A coding scheme that involves such temporal structures is rich and sufficiently flexible to facilitate a rapid organization of cortical neurons into functional groups. The results can be accounted for by the synfire chain model, which suggests that cortical activity is mediated by synchronous activation of neural groups in a reverberatory mode.

Algorithms↗
PubMed1998

Incidence of temporomandibular joint changes after whiplash trauma: a prospective study using MR imaging.

OBJECTIVE: The purpose of this study was to describe the incidence of temporomandibular joint (TMJ) changes after a well-defined whiplash trauma. SUBJECTS AND METHODS: Sixty consecutively admitted patients with symptoms in the neck after rear-end traffic collisions underwent MR imaging of the TMJs within 3-14 days after the collisions. Fifty-three healthy volunteers constituted a control group. RESULTS: No statistically significant differences were found between the 60 patients and the 53 volunteers regarding frequency, stage, grade, or direction of TMJ disk displacement or joint effusion. MR imaging revealed that 45% of the control group and 53% of the patient group had a displaced disk in one or both TMJs (p = .393). Disk displacement was seen in 35% of TMJs in the control group and 40% of TMJs in the patient group. Effusion was seen in 8% of TMJs in the control group and 6% of TMJs in the patient group. No signs of bleeding or edema in the soft tissues were observed. In 15% of the patients, mild clinical symptoms in the TMJ or masticatory muscles developed in association with the trauma; in one third of these patients the symptoms were transient. CONCLUSION: This prospective study does not show any significantly increased incidence of disk displacement, joint effusion, or any other injury to the TMJ after whiplash trauma that could be revealed by MR imaging.

Adolescent↗
PubMed1997

[The Stockholm project: drunken drivers are given supervision instead of prison sentences].

There is a need to compile a national database on drunken driving, since experience from other countries is not necessarily applicable to Swedish conditions. Legislation, drinking habits, and public attitudes to drinking and driving differ markedly from country to country. Since 1990, the driving licence unit of the Magnus Huss Clinic has been collaborating with a probation office unit of the National Prisons and Probation Administration and the Offender Aid Society on a non-institutional drunk driving program of at least one year's duration, often linked with several years' follow-up. The article outlines experience and results derived from this program. Among other things, blood alcohol content is questioned as an indicator of the severity of a drinking problem.

Adult↗
PubMed1997

Care for Canada's frail elderly population: fragmentation or integration?

Budget constraints, technological advances and a growing elderly population have resulted in major reforms in health care systems across Canada. This has led to fewer and smaller acute care hospitals and increasing pressure on the primary care and continuing care networks. The present system of care for the frail elderly, who are particularly vulnerable, is characterized by fragmentation of services, negative incentives and the absence of accountability. This is turn leads to the inappropriate and costly use of health and social services, particularly in acute care hospitals and long-term care institutions. Canada needs to develop a publicly managed community-based system of primary care to provide integrated care for the frail elderly. The authors describe such a model, which would have clinical and financial responsibility for the full range of health and social services required by this population. This model would represent a major challenge and change for the existing system. Demonstration projects are needed to evaluate its cost-effectiveness and address issues raised by its introduction.

Aged↗
PubMed1997

HM-PAO (CERETEC) SPECT brain scanning in the diagnosis of Alzheimer's disease.

OBJECTIVE: To evaluate the accuracy of Single Photon Emission Computed Tomography (SPECT) scanning in the diagnosis of Alzheimer's Disease (AD) and its capacity to improve the diagnostic accuracy of conventional clinical evaluation. DESIGN: Comparison of SPECT scanning of AD and normal subjects with the criterion standard of clinical diagnosis confirmed by 1-year repeated evaluation. SETTING: A memory clinic in a tertiary care university hospital. PATIENTS: One hundred twenty patients were evaluated upon entering the Jewish General Hospital (McGill University) Memory Clinic. Fifty-eight patients were diagnosed as having AD and 17 as having vascular dementia. Twenty unmatched controls (recruited mainly through newspaper advertisements) were normal, and 25 had cognitive impairment without dementia (not included in the statistical analysis). MAIN OUTCOME MEASURES: Comparison of visual inspection of SPECT, based on the system of classification developed by Holman et al., using B pattern alone as positive or B (bilateral posterior temporal and/or parietal cortex deficits) or C (bilateral posterior temporal and/or parietal deficits with additional defects) pattern and B or C or D (unilateral posterior temporal and/or parietal defects with or without additional defects) as positive compared with clinical diagnosis after repeated evaluations. Sensitivity and specificity, as well as positive predictive value (PPV) and negative predictive value (NPV) based on the prevalence of AD in a memory clinic setting of 30% or 50%, were calculated. RESULTS: With B pattern as positive, the sensitivity of SPECT was 21% whereas the specificity was 80%. With B or C as positive, the sensitivity was 29% and the specificity was 75%. With B or C or D as positive, the sensitivity was 55% and the specificity was 65%. With a 30% prevalence, the PPV with B pattern as positive was 31% whereas the NPV was 30%. The PPV with B or C as positive was 33% while the NPV was 29%, and the PPV with B or C or D as positive was 40% whereas the NPV was 23%. With a 50% prevalence, the PPV with B pattern as positive was 51% and the NPV 49.6%; the PPV with B or C as positive was 54% and the NPV 48.6%; the PPV with B or C or D as positive was 61% while NPV was 41%. CONCLUSION: The sensitivity and specificity were too low for SPECT to be useful as a diagnostic test for AD. The poor positive and negative predictive values in our tertiary care clinic mean that SPECT is not useful in "ruling-in" or "ruling-out" AD in that setting. In fact, clinical evaluation is more accurate.

Aged↗
PubMed1997

A geriatric consultation team in the emergency department.

BACKGROUND: The proportion and absolute number of older patients presenting to emergency departments (EDs) are increasing. Older ED patients tend to have multiple medical and psychosocial problems that make their care in the ED problematic. Despite this, there have been no previous descriptions of geriatric ED consultative services. SETTING: The Sir Mortimer B. Davis Jewish General Hospital is a 628-bed tertiary care McGill University teaching hospital. It serves a population of about 160,000, of which 23% are aged 65 and older. In response to the special needs of this group, the Division of Geriatric Medicine at the Jewish General Hospital has developed, among its clinical and teaching services, an ED consultation team. PROGRAM DESCRIPTION: The consultation team is composed of a geriatrician, a full-time nurse clinician, and part-time physical and occupational therapists. Consultations are received from referring, primarily Ed physicians and encompass all aspects of medical and psychosocial issues. Geriatric assessment is geared toward decision making for rapid disposition: discharge home or admission to acute geriatrics ward or other services. Thus, the service functions as a gatekeeper for admission to the acute geriatrics ward, as well as coordinating geriatric follow-up both in-hospital (for patients admitted to other services) and in the community (for patients discharged home), via the outpatient geriatric clinic, home visits, or linkage to other community resources.

Aged↗
PubMed1996

Do consensus conferences influence their participants?

OBJECTIVE: To determine whether participation in a consensus conference on the assessment of dementia would influence conference participants with respect to their recommendations to primary care physicians for the assessment of dementia. DESIGN: Questionnaire before and after the conference. SETTING: Canadian Consensus Conference on the Assessment of Dementia, held in Montreal, Oct. 5 and 6, 1989. PARTICIPANTS: All 38 experts representing relevant health disciplines who participated in the consensus conference; 36 completed both questionnaires. OUTCOME MEASURES: Participants' opinion before and after the conference as to how frequently each of 28 manoeuvres (12 blood tests, 4 neurologic imaging procedures, 4 types of consultation and 8 "other" tests) should be ordered by primary care physicians as part of an assessment of a patient with dementia suspected in clinical grounds. RESULTS: For 18 (64%) of the 28 manoeuvres (10 of the 12 blood tests, 3 of the 4 neurologic imaging procedures and 5 of the 8 "other" tests), there was a shift in opinion after the conference toward recommending that primary care physicians order them less often; for 10 of these 18 (5 blood tests and 5 "other" tests) the shift was statistically significant. For the remaining 10 manoeuvres (36%) the shift in opinion was toward a recommendation that primary care physicians order them more often; the shift was not statistically significant for any of these 10 manoeuvres. CONCLUSION: Expert members of a consensus conference are influenced by the process of having participated in such a conference and are capable and willing to chance their initial recommendations when confronted with relevant data.

Clinical Laboratory Techniques↗
PubMed1996

Simultaneously recorded single units in the frontal cortex go through sequences of discrete and stable states in monkeys performing a delayed localization task.

To test whether spiking activity of six to eight simultaneously recorded neurons in the frontal cortex of a monkey can be characterized by a sequence of discrete and stable states, neuronal activity is analyzed by a hidden Markov model (HMM). Using the HMM method, we are able to detect distinct states of neuronal activity within which firing rates are approximately stationary. Transitions between states, as expressed by concomitant changes in the firing rates of several units, occur quite abruptly. The significance and consistency of the states are confirmed by comparison with simulated data. The detected states are specific to a monkey's response in a delayed localization task, allowing correct prediction of the response in approximately 90% of the trials. Similar predictive power is achieved by a model based simply on the response histograms (PSTH) of the units. The two models reach this predictive ability with different time courses: the PSTH model gains predictive power with a higher rate in the first second of the delay, and the HMM gains predictive power with higher rate in the next 3 sec. In this later period, conventional methods such as the PSTH cannot detect any firing rate modulations, but the HMM successfully captures transitions between distinct states that are specific to the monkey's behavioral response and occur at highly variable times from trial to trial. Our results suggest that neuronal activity in this later period is described best as transitions among distinct states that may reflect discrete steps in the monkey's mental processes.

Animals↗
PubMed1996

Neuronal synchronization of tonically active neurons in the striatum of normal and parkinsonian primates.

1. Previous studies indicate that tonically active neurons (TANs) are the cholinergic interneurons of the striatum and predict that their activity is synchronized. To test whether TANs do fire synchronously, and whether dopamine depletion affects their synchronization, we recorded the simultaneous activity of several TANs in the putamens of two vervet monkeys before and after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. 2. Cross-correlation analysis revealed that most pairs of TANS (33 of 54; 61.1%) fire synchronously at +/- 60-ms delay. Correlated activity was more common between neurons with characteristic response to reward (17 of 19 pairs; 89.5%). 3. Cross-correlation study of 24 triplets of TANS showed synchronization of spiking activity of all 3 TANS in only 29.2% of cases (7 of 24 triplets). Correlated activity of two of three possible pairs was found in 25% of the cases. 4. After MPTP treatment and the development of parkinsonian symptoms, most TANS' auto- and cross-correlograms (22 of 28 units; 78.6%; and 23 of 28 pairs; 82.1%) became oscillatory. The number of correlated pairs was slightly increased (24 of 28; 85.7%). The strength of the synchronization was not significantly different from the normal values. 5. These findings support the notion that TANs function as distributed, partially overlapping synchronized networks. However, a normal dopaminergic system is not essential for synchronization of TANs; on the contrary, dopaminergic activity may even have a desynchronizing effect on the basal ganglia's system.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1995

Cortical activity flips among quasi-stationary states.

Parallel recordings of spike trains of several single cortical neurons in behaving monkeys were analyzed as a hidden Markov process. The parallel spike trains were considered as a multivariate Poisson process whose vector firing rates change with time. As a consequence of this approach, the complete recording can be segmented into a sequence of a few statistically discriminated hidden states, whose dynamics are modeled as a first-order Markov chain. The biological validity and benefits of this approach were examined in several independent ways: (i) the statistical consistency of the segmentation and its correspondence to the behavior of the animals; (ii) direct measurement of the collective flips of activity, obtained by the model; and (iii) the relation between the segmentation and the pair-wise short-term cross-correlations between the recorded spike trains. Comparison with surrogate data was also carried out for each of the above examinations to assure their significance. Our results indicated the existence of well-separated states of activity, within which the firing rates were approximately stationary. With our present data we could reliably discriminate six to eight such states. The transitions between states were fast and were associated with concomitant changes of firing rates of several neurons. Different behavioral modes and stimuli were consistently reflected by different states of neural activity. Moreover, the pair-wise correlations between neurons varied considerably between the different states, supporting the hypothesis that these distinct states were brought about by the cooperative action of many neurons.

Animals↗
PubMed1995

Dynamics of neuronal interactions in monkey cortex in relation to behavioural events.

It is possible that brain cortical function is mediated by dynamic modulation of coherent firing in groups of neurons. Indeed, a correlation of firing between cortical neurons, seen following sensory stimuli or during motor behaviour, has been described. However, the time course of modifications of correlation in relation to behaviour was not evaluated systematically. Here we show that correlated firing between single neurons, recorded simultaneously in the frontal cortex of monkeys performing a behavioural task, evolves within a fraction of a second, and in systematic relation to behavioural events. Moreover, the dynamic patterns of correlation depend on the distance between neurons, and can emerge even without modulation of the firing rates. These findings support the notion that neurons can associate rapidly into a functional group in order to perform a computational task, at the same time becoming dissociated from concurrently activated competing groups. Thus, they call for a revision of prevailing models of neural coding that rely solely on single neuron firing rates.

Animals↗
PubMed1995

Hypothalamic tissue stimulates hippocampal pyramidal neuron survival during development: evidence from intraocular double transplants.

The present study was undertaken to evaluate innervation and possible growth promotion by posterior hypothalamic tissue on different areas that are, or are not, interactive with this brain region during development. Posterolateral hypothalamus was dissected from embryonic day 17 rat fetuses, and inserted into the anterior chamber of the eye of adult rat hosts. Two weeks postgrafting, a second transplant consisting of either fetal hippocampal, cerebellar, or lung tissue was placed adjacent to the first graft. Growth of the intraocular double transplants was monitored weekly by measurements through the cornea. Fetal hippocampal tissue grew significantly larger when placed together with a hypothalamic graft, as compared to single hippocampal transplants. Cerebellar or lung tissue growth was not stimulated by a hypothalamic cograft. Pyramidal neuron cell counts demonstrated a significantly higher final number of these neurons in growth-stimulated hippocampal grafts, as compared to non-stimulated single hippocampal grafts. Immunohistochemistry with antibodies directed against histamine or histidine decarboxylase revealed that hippocampal transplants received the most dense histaminergic innervation. Cerebellar transplants contained occasional histaminergic neurites, and lung tissue never exhibited any histaminergic innervation from the adjacent hypothalamic graft. Taken together, these results demonstrate a growth-promoting effect of posterior hypothalamic tissue on developing hippocampal tissue, as well as target specificity of histaminergic innervation patterns.

Animals↗
PubMed1995

Characterization of histaminergic H3 receptors in intraocular tuberomammillary transplants containing histaminergic neurons.

This study was performed to investigate the physicological properties of histaminergic neurons in intraocular hypothalamic transplants. Pieces of posterolateral hypothalamus containing the tuberomammillary nucleus were dissected from Embryonic Day 17 rat fetuses and transplanted into the anterior chamber of the eye of adult rat hosts. The hypothalamic transplants were left to mature for 2-5 months, after which in vivo electrophysiological recordings were performed. Extracellular recordings revealed spontaneously active neurons in the grafts, with a mean (+/- SEM) firing rate of 2.8 +/- 2.0 Hz and a mean action potential duration of 1.2 +/- 0.5 ms. When the surface of the grafts was superfused with histamine, the neuronal activity was depressed at concentrations above 30 microM. Superfusion with the H3 agonist (R)-alpha-methylhistamine also elicited depression of baseline firing rate, with an EC50 of 0.435 microM. This depression could be antagonized by superfusion with the H3-receptor antagonist thioperamide. In studies of histamine levels using a sensitive radioenzymatic assay, the mean (+/- SEM) level of histamine in the grafts was 73 +/- 28 ng/g tissue, i.e., about half the concentration of histamine in the adult rat hypothalamus in situ. Intracellular recordings in combination with biocytin labeling and histidine decarboxylase immunohistochemistry suggested that the grafted neurons from which recordings were made were histaminergic. Taken together, these data indicate that tuberomammillary neurons continue their development in intraocular transplants and develop physiological characteristics found in these neurons in situ.

Action Potentials↗
PubMed1995

Loss of frequencies in autocorrelations and a procedure to recover them.

We show that the standard methods, like the autocorrelation of a discrete time series, such as a spike train, can often miss prominent oscillation frequencies. In particular, if a phenomenon involves bursting and oscillations at two or more frequencies, the higher frequencies, with a lesser number of spikes per burst, can be often missed by the conventional methods. It is argued that on should separate the intraburst phenomena from the interburst phenomena by identifying bursts as single events. The distribution of oscillation frequencies should then computed by evaluating the autocorrelation of these events. A method is also developed for situations where intraburst and interburst time scales overlap significantly. It is shown that the correct estimate of strengths of various frequencies is found by using different thresholds for burst identification. The method is applied to data from a neuron in the subthalamic nucleus of a Parkinsonian (MPTP-treated) monkey. The conventional analysis shows that the neuron oscillates at only 6 Hz, whereas the new analysis reveals the presence of an additional, predominant, oscillation frequency of 18 Hz.

Animals↗
PubMed1995

Intracranial transplantation and survival of tuberomammillary histaminergic neurons.

Investigations were undertaken to determine whether fetal histaminergic neurons in the tuberomammillary nucleus of the posterior hypothalamus survive intracranial transplantation to adult hosts. Two methods of transplantation were utilized. Grafts were placed either into the delayed cavity of a fimbria-fornix lesion or directly into the hippocampus using stereotaxic techniques. The tissue was taken from rat fetuses at embryonic days 16-17 and grafted into adult rats of either the Sprague-Dawley or the Fischer 344 strain. Routine histology and immunohistochemistry were used to evaluate the grafts. All transplants to Sprague-Dawley rats showed signs of rejection, while no signs of rejection were seen in any of the Fischer 344 rats. Transplants placed directly into the delayed fimbria-fornix cavity did not grow as well or contain as many surviving neurons as the intraparenchymal grafts. The largest number of surviving histamine-positive neurons was obtained with grafts of posterolateral blocks of hypothalamus from fetal day 17 placed directly into the CA1 region of the rostral hippocampal formation of Fischer 344 hosts. Histamine-immunoreactive cell bodies with neuritic outgrowth were found in all Fischer 344 rats that received hypothalamic grafts. Cell bodies exhibited histamine immunoreactivity evenly throughout the cytoplasm and had morphological characteristics resembling histaminergic neurons in situ. Axonal outgrowth extended throughout the grafted hypothalamic tissue, and was sometimes seen in the host hippocampal tissue as well. It is concluded that fetal histaminergic neurons survive transplantation to the adult hippocampal formation, and that this allograft procedure can supplement current strategies to investigate the function of histaminergic tuberomamillary neurons in the central nervous system.

Animals↗