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M Abeles

Publications and source records attributed to M Abeles.

At least 37 records · Page 2Linked to original sources
PubMed1996

Spatio-temporal firing patterns in the frontal cortex of behaving monkeys.

Recording the activity of several neurons in parallel in the frontal cortex of behaving monkeys reveals that firing times of neurons can maintain +/- 1 ms accuracy even after delays of over 400 ms. The accurate firing structures were associated with behavior. Neural networks that can sustain such accuracy can learn 'learn' to bind with each other and thus may serve as building blocks for cognitive processes.

Action Potentials↗
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

Patients with type IV Ehlers-Danlos syndrome may be predisposed to atlantoaxial subluxation.

OBJECTIVE: To determine if atlantoaxial subluxation is a complication of Ehlers-Danlos Syndrome (EDS). METHODS: Observational study of a selected cohort of patients with EDS attending a national meeting. Twenty-six patients with EDS (19 with type III; 3 with type IV; 1 each with types II and I; 2 with undefined subtypes) were radiologically evaluated. Lateral flexion-extension views of the cervical spine in each patient were read in blinded fashion by a radiologist and compared to unblinded interpretations made by a separate radiologist. Measurement was taken from the most inferior aspect of the anterior arch of C1 to the dens along a horizontal plane. The remainder of the radiograph was examined for abnormalities. RESULTS: Two patients with EDS type IV had radiographic evidence of atlantoaxial subluxation (p = 0.013 Fisher's exact test). Evidence of horizontal translation between vertebral bodies below C2 was noted in 3 patients. Cervical arthrosis was present in 9. CONCLUSIONS: Atlantoaxial subluxation may be a more common finding in persons with type IV EDS than previously thought. Examination of the cervical spine radiographically should be considered before administering general anesthesia to these patients.

Adult↗
PubMed1994

Population responses to multifrequency sounds in the cat auditory cortex: one- and two-parameter families of sounds.

Population responses to multi-frequency sounds were recorded in primary auditory cortex of anesthetized cats. The sounds consisted of single-tone stimuli; two-tone stimuli; and nine-tone stimuli, with the tones evenly spaced on a linear frequency scale. The stimuli were presented through a sealed, calibrated sound delivery system. Single units, cluster activity (CA) and the short-time mean absolute value of the envelope of the neural signal (MABS) were recorded extracellularly from six microelectrodes simultaneously. The CA and MABS were interpreted as measures of the activity of large populations of neurons, in contrast with the single unit activity which is presumably recorded from single neurons. The responses of the MABS signal to simple stimuli were generally similar to those of the CA, but were more stable statistically. Thus, the MABS is better suited for studying the activity of populations of neurons. The responses to tones near the best frequency were strongly influenced by a second tone, even when the second tone was outside the single-tone response area. These influences could be both facilitatory and suppressory. They could not be predicted from the responses to single tones. The responses to the nine-tone stimuli could be explained qualitatively by the responses to the two-tone stimuli. It is concluded that the population responses in primary auditory cortex are shaped by the contributions of the individual frequencies appearing in the stimulus and by the interactions between pairs of frequencies. Interactions between stimulus components are therefore a necessary component of any attempt to explain the processing of complex sounds in the auditory cortex. They may play a role in a global representation of the stimulus spectrum in the primary auditory cortex. The presence of higher-order interactions cannot be excluded by the results presented here.

Acoustic Stimulation↗
PubMed1994

Population responses to multifrequency sounds in the cat auditory cortex: four-tone complexes.

Population responses to two-tone and four-tone sounds were recorded in primary auditory cortex of anesthetized cats. The stimuli were delivered through a sealed, calibrated sound delivery system. The envelope of the neural signal (short time mean absolute value, MABS) was recorded extracellularly from six microelectrodes simultaneously. A new method was developed to describe the responses to the four-tone complexes. The responses were represented as sums of contributions of different orders. The first order contributions described the effect of the single frequencies appearing in the stimulus. The second order contributions described the modulatory effect of the pairs of frequencies. Higher order contributions could in principle be computed. This paper concentrates on the mean onset responses. The extent to which the first and second order contributions described the onset responses was assessed in two ways. First, the actual responses to two-tone stimuli were compared with those predicted using the contributions computed from the four-tone stimuli. Second, the residual variance in the responses, after the subtraction of the first and second order contributions, was computed and compared with the variability in the responses to repetitions of the same stimulus. The first type of analysis showed good quantitative agreement between the predicted and the measured two-tone responses. The second type of analysis showed that the first and second order contributions were often sufficient to predict the responses to four-tone stimuli up to the level of the variability in the responses to repetitions of a single stimulus. In conjunction with the results of the companion paper (Nelken et al., 1994a) it is concluded that the onset responses to multifrequency sounds are shaped mainly by the single frequency content of the sound and by two-tone interactions, and that higher order interactions contribute much less to the responses. It follows that single-tone effects and two-tone interactions are necessary and sufficient to explain the mean population onset responses to the four-tone stimuli. More information can be coded in the temporal evolution of the responses.

Acoustic Stimulation↗
PubMed1994

In search of the best stimulus: an optimization procedure for finding efficient stimuli in the cat auditory cortex.

Units in the auditory cortex of cats respond to a large variety of stimuli: pure tones, AM- and FM-modulated signals, clicks, wideband noise, natural sounds, and more. However, no single family of sounds was found to be optimal (in the sense that oriented lines are optimal in the visual cortex). The search for optimal complex sounds is hard because of the high dimensionality of the space of interesting sounds. In an effort to overcome this problem, an automatic search procedure for finding efficient stimuli in high-dimensional sound spaces was developed. This procedure chooses the stimuli to be presented according to the responses to past stimuli, trying to increase the strength of the response. The results of applying this method to recordings of population activity in the primary auditory cortex of cats are described. The search was applied to single tones, two-tone stimuli, four-tone stimuli and to a two-dimensional subset of nine-tone stimuli, parametrized by the center frequency and the fixed difference between adjacent frequencies. The method was able to find efficient stimuli, and its performance improved with the dimension of the sound spaces. Efficient stimuli, found in different optimization runs using population activity recorded from the same electrode, often shared similar frequencies and pairs of frequencies, and tended to evoke similar levels of activity. This result indicates that a global analysis of the location of spectral peaks is performed at the level of the auditory cortex.

Acoustic Stimulation↗
PubMed1994

Alpha-delta sleep in patients with a chief complaint of chronic fatigue.

Our prospective, standardized cohort study was designed to assess the presence of alpha wave intrusions during non-rapid eye movement sleep (alpha-delta sleep) and its relationship to fibromyalgia, major depression, and chronic fatigue syndrome (CFS) in patients with a chief complaint of chronic fatigue. The study group comprised 30 consecutive patients seen at a university hospital referral clinic for evaluation of chronic fatigue. All patients had nocturnal polysomnography, dolorimetric tender point assessment for fibromyalgia, a comprehensive history, physical, and laboratory evaluation, and a structured psychiatric interview. Alpha-delta sleep was identified in 8 of the 30 patients (26%), major depression in 20 (67%), CFS in 15 (50%), and fibromyalgia in 4 (13%). Ten of the 30 patients (33%) had a primary sleep disorder (sleep apnea, periodic limb movements, or narcolepsy). Alpha-delta sleep was not significantly correlated with fibromyalgia, CFS, major depression, or primary sleep disorders, but was significantly more common among patients who had chronic fatigue without major depression. We conclude that primary sleep disorders are relatively common among patients with chronic fatigue and must be diligently sought and treated. Alpha-delta sleep is not a marker of fibromyalgia or CFS, but may contribute to the illness of nondepressed patients with these conditions.

Adolescent↗
PubMed1994

A 2 year, open ended trial of methotrexate in systemic lupus erythematosus.

OBJECTIVE: To investigate a possible role for methotrexate (MTX) in the treatment of patients with systemic lupus erythematosus (SLE) who require unacceptably high doses of glucocorticosteroids (GCS) for control of their disease. METHODS: Twelve patients with SLE participated in this open ended prospective study. Patients with active renal or central nervous system (CNS) disease were excluded as were patients with liver disease. Serological variables, SLE disease activity index, joint count, and prednisone dose were serially evaluated. Data were analyzed using paired t test and contingency table analysis. RESULTS: Arthritis was the major persistent problem in 7 patients: 1 patient had recurrent pleuropericarditis, 2 patients had refractory cutaneous lupus rashes and 2 had vasculitis. Three patients discontinued MTX because of side effects. The remaining 9 patients have been treated from 7-26 months. In 6 patients the GCS dose was reduced by an average of 42%. In 1 patient symptoms subsided and joint count was reduced without change in the GCS dose. GCS dosage was increased in 2 patients: 1 with recurrent serositis, 1 with persistent vasculitis. No apparent effect on anti-dsDNA antibodies, complement or erythrocyte sedimentation rate (ESR) was noted. CONCLUSION: MTX appears to be useful in selected patients with SLE, especially those with persistent synovitis.

Adult↗
PubMed1994

Recurrent leukocytoclastic vasculitis as the initial manifestation of acute myelomonocytic leukemia.

The association between cutaneous and systemic leukocytoclastic vasculitis and myeloproliferative and lymphoproliferative malignancies has been reported. We describe a patient who developed recurrent episodes of leukocytoclastic vasculitis 10 months before the diagnosis of acute myelomonocytic leukemia. To our knowledge, this is the first documented case of leukocytoclastic vasculitis presenting as the initial manifestation of acute myelomonocytic leukemia, a subtype of acute myelogenous leukemia.

Female↗
PubMed1993

Spatiotemporal firing patterns in the frontal cortex of behaving monkeys.

1. Activity of up to 10 single units was recorded in parallel from frontal areas of behaving monkeys. 2. Spatiotemporal firing patterns were revealed by a method that detects all excessively repeating patterns regardless of their complexity or single-unit composition. 3. Excess of repeating patterns was found in 30-60% of the cases examined when timing jitter of 1-3 ms was allowed. 4. An independent test refuted the hypothesis that these patterns represented chance events. 5. In a given behavioral condition there were usually many different patterns, each repeating several times, and not one (or a few) pattern repeating many times. 6. In 13 out of 20 cases, when a single unit elevated its firing rate in association with an external event beyond 40/s, most of the spikes within that period were associated with excessively repeating spatiotemporal patterns. 7. Of 157 types of patterns whose excess was most marked, 107 were composed of spikes from one single unit, 45 of the patterns contained spikes from two single units, and only one was composed of spikes from three different single units. 8. These properties suggest that the patterns were generated by reverberations in a synfire mode within self-exciting cell assemblies.

Animals↗
PubMed1992

Dependence of cortical plasticity on correlated activity of single neurons and on behavioral context.

It has not been possible to analyze the cellular mechanisms underlying learning in behaving mammals because of the difficulties in recording intracellularly from awake animals. Therefore, in the present study of neuronal plasticity in behaving monkeys, the net effect of a single neuron on another neuron (the "functional connection") was evaluated by cross-correlating the times of firing of the two neurons. When two neurons were induced to fire together within a short time window, the functional connection between them was potentiated, and when simultaneous firing was prevented, the connection was depressed. These modifications were strongly dependent on the behavioral context of the stimuli that induced them. The results indicate that changes in the temporal contingency between neurons are often necessary, but not sufficient, for cortical plasticity in the adult monkey: behavioral relevance is required.

Acoustic Stimulation↗
PubMed1991

Evaluation of Social Security disability in claimants with rheumatic disease.

We compared the Social Security Administration's (SSA) judgment of disability with uninvolved rheumatologists' evaluations of ability to work. With the cooperation of the SSA, 52 new disability claimants who alleged rheumatoid arthritis, osteoarthritis, or systemic lupus erythematosus were identified at the beginning of their claim. At the same time that their claim was being formally reviewed, they had a standardized examination by an independent rheumatologist who was not involved with their care, and they had a standardized test of observed performance. Rheumatologists' judgments of ability to work were compared with the SSA judgments. Rheumatologist and SSA judgments were in agreement for 35 of the 52 claimants (67%). All 11 claimants who met or equaled the SSA medical evaluation criteria were judged work-disabled by the rheumatologist. Of 27 judged able to work by the SSA, the rheumatologist judged 11 to be unable. Agreement between the SSA judgment of residual functional capacity and observed performance was no more than would be expected by chance. Most SSA judgments agree with a clinician's evaluation but a standardized physical evaluation by a rheumatologist and performance-based tests appear to add important information.

Activities of Daily Living↗
PubMed1991

Neural interactions in the frontal cortex of a behaving monkey: signs of dependence on stimulus context and behavioral state.

In order to gain an understanding of the processes taking place within and between neuronal assemblies, we made simultaneous recordings of spike trains from groups of up to 11 neurons in the frontal cortex of a rhesus monkey, that was trained to perform a sensorimotor behavioral task. We report here on preliminary results from correlation analysis of these neuronal activities, with special emphasis on signs of behaviorally induced modifications of neural interaction, possibly due to rapid modulations of discharge synchronization among the neurons. Our findings suggest that different functional groups of neurons may co-exist within each small volume of cortex, and that neurons may be dynamically recruited into such a group to fulfil a specific function.

Animals↗
PubMed1990

Evidence for spatiotemporal firing patterns within the auditory thalamus of the cat.

Multiple spike trains were recorded in the auditory thalamus of cats. Each unit was studied before, during and after cooling of the ipsilateral primary auditory cortex, during spontaneous activity and acoustically evoked activity. The search for spatiotemporal firing patterns provided evidence that excess of patterns does exist and that the acoustical stimulation increased their number. Cortical cooling did not affect the probability of finding the firing pattern.

Acoustic Stimulation↗
PubMed1990

The American College of Rheumatology 1990 Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee.

To develop criteria for the classification of fibromyalgia, we studied 558 consecutive patients: 293 patients with fibromyalgia and 265 control patients. Interviews and examinations were performed by trained, blinded assessors. Control patients for the group with primary fibromyalgia were matched for age and sex, and limited to patients with disorders that could be confused with primary fibromyalgia. Control patients for the group with secondary-concomitant fibromyalgia were matched for age, sex, and concomitant rheumatic disorders. Widespread pain (axial plus upper and lower segment plus left- and right-sided pain) was found in 97.6% of all patients with fibromyalgia and in 69.1% of all control patients. The combination of widespread pain and mild or greater tenderness in greater than or equal to 11 of 18 tender point sites yielded a sensitivity of 88.4% and a specificity of 81.1%. Primary fibromyalgia patients and secondary-concomitant fibromyalgia patients did not differ statistically in any major study variable, and the criteria performed equally well in patients with and those without concomitant rheumatic conditions. The newly proposed criteria for the classification of fibromyalgia are 1) widespread pain in combination with 2) tenderness at 11 or more of the 18 specific tender point sites. No exclusions are made for the presence of concomitant radiographic or laboratory abnormalities. At the diagnostic or classification level, the distinction between primary fibromyalgia and secondary-concomitant fibromyalgia (as defined in the text) is abandoned.

Adult↗
PubMed1990

Does the acetyl group of aspirin contribute to the antiinflammatory efficacy of salicylic acid in the treatment of rheumatoid arthritis?

In a multicenter, double-blind, parallel-group study, 233 patients with classical or definite RA who demonstrated disease flare during a prestudy washout period were randomized to 12 weeks of treatment with either the nonacetylated salicylate, salsalate (salicylsalicylic acid), or aspirin. Of the 150 patients who completed the study, 83 received salsalate and 67 were treated with aspirin. Doses of the two drugs were calculated to provide equal amounts of bioavailable salicylic acid. The efficacy of salsalate and aspirin, as measured by all the usual variables, was equivalent but aspirin-treated patients had a higher incidence of severe gastrointestinal problems. Thus, this study demonstrated that the acetyl group of aspirin does not enhance the anti-inflammatory efficacy of salicylic acid in RA.

Anti-Inflammatory Agents, Non-Steroidal↗