Pierre Toulouse

Water phases in rat striated muscles as determined by T2 proton NMR relaxation times

The spin echo decay curve of NMR protons in in-vitro rat muscle is two or three exponential as Hazlewood demonstrated in 1974. This author hypothesized that the longer T2 component is extracellular water and that the medium T2 is intracellular water. Our purpose was to test the histological significance of these two T2. Variations of water contents in two types of rat muscles were induced by electrical stimulation and osmotic diuresis and their incidence on the decomposition of the proton spin echo signal analysed. Decomposition of signal in resting muscles revealed two phases with T2 values similar to the Hazlewoods: a short phase, S, with T2 of 40 ms (20 MHz, 276 degrees K) representing 90-97% of the total signal and a long one, L, with T2 of 100-120 ms representing 3-10% of the signal. Increasing vascular volume appeared to increase the percentage of phase (L) in the total signal. Osmotic diuresis decreased the volume of the phase (S) and increased the volume of the phase (L). The use of Gd-DTPA allowed to differentiate the vascular compartment: Gd DTPA decreased in a great extent the T2 values of phase (L) and in low extent the T2 values of phases (S). From these results, it appears that phase (L) could correspond to vascular volume and that phase (S) would be interstitial and intracellular water. Elements of comparison with classical methods for determination of water compartmentation in tissues are given.

Automatic classification of electromyographic signals

The results of the application of classification methods to electromyograph signals of weak contractions in normal and myopathic subjects are described. Methods of pattern recognition, previously presented, allow the selection of representative motor unit action potentials. The analysis is done with ordinal qualitative variables obtained by identification of shape descriptive parameters (amplitude, duration, number of phases, number of extrema). From this analysis, characteristic classes for normality and myopathy appear, from which a diagnostic aid by assignment can be made.

Non-linear Local Registration of Functional Data

Within the scope of three-dimensional brain imaging we propose an inter-individual fusion scheme to register functional activations relatively to anatomical cortical structures, the sulci. This approach is local and non-linear. It relies on a statistical sulci shape model accounting for the inter-individual variability of a population of subjects, and providing deformation modes relatively to a reference shape (a mean sulcus). The deformation field obtained between a given sulcus and the reference sulcus is extended to a neighborhood of the given sulcus by using the thin-plate spline interpolation. It is then applied to the functional activations associated with this sulcus. This approach is compared with other classical matching methods.

Magnetoencephalographic studies of two cases of diffuse subcortical laminar heterotopia or so-called double cortex.

Two cases (a young male and a girl, suffering intractable epilepsy) of diffuse subcortical laminar heterotopia, or so-called double cortex (DC) have been investigated using magnetoencephalography (MEG). MEG confirmed involvement of both cortices (hetero- and normocortex) in the genesis of interictal spikes, and, according to the heterogeneity of DC syndrome, some differences were observed: spike initiation in the normocortex and latter involvement of the heterotopic cortex in the man, and rather a cancellation in both cortices in the girl. In addition, participation of heterotopic cortex in physiological activities could be demonstrated in the man.

Model-based diagnosis of brain disorders: a prototype framework

This paper describes a prototype framework, named NEUROLAB, dedicated to research and diagnosis in the area of brain disorders. The diagnostic task uses a blending of factual knowledge, formal knowledge, and experiential knowledge. The prototypes first target clinical application is partial seizures in epilepsy. Diagnosis is carried out using qualitative electroencephalographic descriptions, clinical attack pattern descriptions, and pre- and post-ictal observations. From this information, the system builds explanations in the form of candidate epileptogenic foci and trajectories of the seizure spread. Hypothesis-testing and discrimination is based on minimal set coverage, and consistency-checking is performed using the general background knowledge. Upon completion, NEUROLAB will provide specific physiological knowledge for solving the so-called inverse problems in electroencephalography (EEG) and magnetoencephalography (MEG).

Phosphocreatine and pH Recovery Without Restoration of Mechanical Function During Prolonged Activity of Rat Gastrocnemius Muscle: an in Vivo 31P NMR Study

Metabolic impairment in skeletal muscle was suggested to be involved in the development of local mechanical fatigue but until now results have dealt with short activity periods whereas little data on exhaustive and prolonged exercises are available. Stimulations of rat leg muscle lasting 45 min were induced by tetanic trains delivered via sciatic nerve at five different rhythms. Energy metabolism of the stimulated gastrocnemius muscle was followed by 31P NMR spectroscopy using surface coil while mechanical function was recorded. Our data showed a decrease in the force level to very low values a few minutes after exercise onset. This mechanical impairment only induced a transient metabolic failure followed by rapid restoration of high phosphocreatine (PCr) values and intracellular pH, without mechanical recovery. In addition, at the end of exercise, the PCr content was proportional to the fatigue level. As these experiments could not have impaired neuromuscular junction, the data would indicate that fatigue was maintained by a mechanism which does not appear to depend directly on muscle cell energy stores.