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Biomedical subjects

G L Romani

Publications and source records attributed to G L Romani.

At least 19 recordsLinked to original sources
PubMed1996

Changes in movement-related brain activity during transient deafferentation: a neuromagnetic study.

Neuromagnetic fields from the left cerebral hemisphere of three healthy, right-handed subjects were investigated preceding and during voluntary index finger movements performed every 8-15 s under two different experimental conditions: before (stage A) and during (stage B) anesthetic block of median and radial nerves at the wrist. The anesthesia caused blocking of cutaneous receptors and some of the proprioreceptors from a wide hand area, including the entire index finger. However, the index finger movements were not impaired because the muscles participating in the task were not anesthetized. The magnetic signals of the brain sources corresponding to the main components of the movement-related neuromagnetic fields (motor field, MF and movement-evoked field I, MEFI) were mapped and localized using a moving dipole model. In the three investigated subjects the MF and MEFI dipole sources were stronger (30% on average) during stage B than during stage A. No significant changes in spatial coordinates of the estimated dipole locations between stages A and B were observed. This was true for both MF and MEFI. The results show that the MEFI reflects not only proprioceptive input from the periphery but cutaneous inputs as well. In this way the results support the view that cutaneous inputs play a specific role in the cortical control of movement.

Action Potentials↗
PubMed1996

Neuromagnetic localization of the late component of the contingent negative variation.

The contingent negative variation (CNV) in a warned choice reaction time task was studied in 24 healthy subjects by use of magnetoencephalography (MEG). Special interest was focused on the late component of the CNV, CNVL. Source localization of the magnetically recorded CNVL, mCNVL was performed on 13 subjects, selected on the basis of the strength and stationarity of the electrically recorded CNV, eCNVL. To achieve whole head mapping, up to 500 epochs from different scalp positions were recorded, including a pretrial learning period of 40 epochs. The neuromagnetic signals studied in this experimental protocol are thus related to neurological processes that are present after an initial learning period has occurred. In 11 subjects, a goodness of fit between 88% and 95% was achieved using a two-dipole model with one equivalent source localized close to the precentral cortex contralateral to the side of movement, at mean a depth of 30 mm. Estimates of ipsilateral equivalent sources were less consistent across subjects. In 9 subjects the estimated ipsilateral sources were located symmetrically to the contralateral source. The results of this study suggest that the dominant source of the mCNVL is located near the bottom of the sulcus precentralis at the anterior bank of the gyrus precentralis, close to the sulcus frontalis superior. This supports previous findings that the CNVL is closely related to the readiness potential, and that the major cortical activity is symmetrically located in the left and right premotor areas.

Adult↗
PubMed1996

Topography and sources of electromagnetic cerebral responses to electrical and air-puff stimulation of the hand.

SEPs and SEFs after air-puff stimulation of index and little fingers have been studied and compared to the responses following electrical stimulation of the same digits and of the median nerve at the wrist in 5 subjects. The differences in morphology of the evoked signals are described and the generator characteristics are analysed for SEFs by means of a moving dipole model inside a homogeneous sphere. In our measurements the magnetic fields following electrical finger stimulation show a 30 msec component, which was absent following air-puff stimulation. This could not be seen in the electric field activity. The generators of the first component of SEFs after air-puff finger stimulation proved to be deeper (8 mm on average across all subjects and for both fingers) than in the case of electrically evoked SEFs. A similar behaviour was also observed for the second component of SEFs for the 2 stimulus modalities.

Adult↗
PubMed1996

A SQUID based AC susceptometer for the investigation of large samples.

We developed a SQUID based susceptometer with a large available magnetized volume for the investigation of large objects. The magnetizing field is generated by a pair of Helmoltz coils. To achieve a high signal-to-noise ratio, the susceptometer is operated in a lock-in mode with an AC magnetizing field. A negative feedback control allows the rejection of the applied field with a relative residual of 1 x 10(-7). The apparatus was tested with substances of known magnetic susceptibility. The overall sensitivity, stated in terms of the magnetic moment, is better than 7 x 10(-11) A m2 for small samples.

Humans↗
PubMed1995

Neuromagnetic fields of the brain evoked by voluntary movement and electrical stimulation of the index finger.

Neuromagnetic fields from the left cerebral hemisphere of five healthy, right-handed subjects were investigated under two different experimental conditions: (1) electrical stimulation of the right index finger (task somatosensory evoked fields, task SEF's), and (2) voluntary movement of the same finger referred to as movement-related fields, (MRFs). The two conditions were, performed in random order every 5-8 s. In addition, the task SEF's were compared to control SEF's recorded at the beginning of the experiment in order to find the optimal dewar position for localizing the central sulcus. The magnetic signals of the sources corresponding to the main components of the somatosensory evoked fields (early ones at 24 ms and at 34 ms, and late ones after 50 ms) and movement-related fields (motor field, MF and movement-evoked field I-MEF I) were mapped and localized by means of a moving dipole model. In four out of five subjects the MEF I dipoles were found to be located deeper than the early task SEF dipoles. In addition, all of the task SEF's components were found to exhibit larger amplitudes than the control SEF's components. The results are discussed in respect to the ability to selectively analyze contributions of mainly proprioceptive (area 3a) and cutaneous (area 3b) areas in the primary somatosensory cortex using magnetoencephalography. An additional finding of the study was that all of the task SEF's components were found to exhibit larger amplitudes than the control SEF's components.

Adult↗
PubMed1995

Detection and counting of specific cell populations by means of magnetic markers linked to monoclonal antibodies.

We report on experiments aimed at the assessment of a new method for cell marking. This method combines superparamagnetic particles, commonly used for cell separation, linked to monoclonal antibodies, and biomagnetic instrumentation featuring an extremely high magnetic field sensitivity. The final goal of the method is to locate and estimate specific cell populations in the human body. In this experiment, quantitative features of the method are evaluated in vitro with lymphocytes and carcinoma cells. Comparison between estimation and direct counting of cells is quite satisfactory and motivates further development of the technique.

Antibodies, Monoclonal↗
PubMed1994

Short-term brain 'plasticity' in humans: transient finger representation changes in sensory cortex somatotopy following ischemic anesthesia.

Transient rearrangements of finger representation in primary somatosensory cortex induced by an anesthetic block of the sensory information from adjacent fingers have been shown invasively in animals. Such a phenomenon has been now replicated in seven healthy human volunteers. Somatosensory Evoked Fields (SEFs) have been recorded during separate electrical stimulation of the 1st, 3rd, or 5th finger. Recordings were obtained in control conditions (stage A), following complete ischemic anesthesia of the 4 non-stimulated fingers (stage B), and after regaining sensation (stage C). SEFs were recorded using a 28-channel DC-SQUID magnetometer; a single position of the sensor was enough to identify the source of N20m, P30m and following components using the Equivalent Current Dipole (ECD) model. The amount of afferent input during stages A through C was monitored with surface electrodes placed on the nerve at wrist and elbow. No variation of the nerve compound potential was observed during stages A through C. In stage A, the localizing algorithm was able to discriminate the individual finger representation in accordance with the somatotopic organisation of the sensory homunculus. It was observed that the ECDs responsible for the cortical responses from the unanesthetized finger were significantly changing following a relatively brief period of sensory deprivation from the adjacent fingers. Such changes of the ECDs with respect to the control conditions were characterized by an increase in strength and deepening for the middle finger, and by a shift on the coronal plane for the thumb and the little finger (medial for the former, lateral for the latter). Such changes became progressively evident in stage B, but were persisting in stage C.

Action Potentials↗
PubMed1994

Analysis of interhemispheric asymmetries of somatosensory evoked magnetic fields to right and left median nerve stimulation.

This paper represents the first neuromagnetic systematic investigation of the asymmetries between the sources activated in the right and left hemispheres after electric median nerve stimulation. We focused our attention on the location and strength of the equivalent sources activated in the primary somatosensory cortex contralateral to the stimulated nerve in the 50 msec post-stimulus epoch. The spatial coordinates of the equivalent sources did not differ statistically significantly in the two hemispheres. Minor individual asymmetries are shown to be related to the interhemispheric differences in the position of the central sulcus as revealed by MRI investigation. The equivalent sources were significantly stronger in the left hemisphere. When comparing the location of the generators across individuals, we show that interhemispheric differences fluctuate less than absolute values. A quantitative evaluation of these findings is also given. Based on these results, a normative data set has been established, to be used as a baseline in following up changes of interhemispheric asymmetries due to hemispheric lesions and subsequent cortical reorganization.

Adult↗
PubMed1994

Magnetocardiography and exercise testing.

Twenty healthy male subjects (age range, 15-25 years; median, 21 years) underwent magnetocardiography during physical exercise. Significant ST-segment displacements of the magnetic signal were found during exercise at a heart rate of 120 beats/min compared to the magnetic signal at rest (P < .001). Since no significant ST-segment changes were found in the electrocardiogram recorded simultaneously with the magnetocardiogram, it is concluded that the magnetocardiogram shows junctional ST-T segment changes earlier than the electrocardiogram.

Adolescent↗
PubMed1993

[The use of magnetic tracers in hemodynamics. A proposed model study].

Velocity of blood flow is critical in specific clinical situations. Available non invasive blood velocimeters gives only qualitative informations; quantitative estimates can be obtained invasively. We investigated the possibility of estimating the velocity of fluids using magnetic tracer. A model for the laminar blood flow inside a vessel was developed. A biomagnetometer was used to measure the fluid tracer velocity. The experimental setup was designed to mimic blood flow. A PVC tube simulated the vessel. The tube was connected to a bottle of normal saline. The tracer injection took place 25 cm distal to the saline bottle. The system was calibrated to a constant flow velocity of about 1 cm/s. A paramagnetic fluid (Magnevist, Schering, Berlin) was adopted as a tracer. In each session an amount of 2 cm3 was injected into the tube within 5 seconds. The recording equipment consisted of a second order gradiometer (baseline 7 cm, pick-up coil diameter 1.5 cm) coupled to a rfSQUID magnetometer. The recording bandwidth was dc-3 Hz, the sampling rate 32 Hz with 12 bit digitalization. The biomagnetic system was positioned immediately above the tube 55 cm away from the injection site. The total recording time for each session was 240 seconds. The injection of the tracer took place 60 seconds after the beginning of the data acquisition. Five measuring sessions in the earth magnetic field were performed at first and showed a low signal-to-noise ratio.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Flow Velocity↗
PubMed1991

Neuromagnetic somatosensory homunculus: a non-invasive approach in humans.

The somatosensory homunculus has been identified during stimulation of median (at wrist and elbow), femoral, tibial and pudendal nerves of the left hemibody via the neuromagnetic imaging technique. The somatic representations of different body districts have been localized in the somatosensory cortex, by means of an equivalent dipole localization algorhythm. Dipole locations agree with the well-known somatotopic organization obtained with invasive techniques. The proposed method is, therefore, an important investigating tool for studies on normal and diseased subjects.

Evoked Potentials, Somatosensory↗
PubMed1991

Multichannel hybrid system for neuromagnetic measurements.

This paper describes progress toward the development of a 28-multichannel system for neuromagnetic measurements. A novel 'hybrid' design consisting of 16 first-order axial gradiometers and 12 first-order planar gradiometers was chosen, which optimises the use of the available cylindrical volume of the dewar tail. This configuration maintains the symmetry of the detected pattern with respect to rotation of a biomagnetic source located under the centre of the array and features a localisation power considerably better than an array of all first-order planar gradiometers. The detecting array permits simultaneous magnetic measurements over a circular scalp region of 16 cm diameter. The magnetic sensors used are Nb/PbAuIn DC SQUIDs fabricated at the IBM. The devices incorporate resonant damping resistors shunting the inductance, resulting in smooth flux-voltage characteristics and, consequently, very low noise figures in a flux-locked loop configuration. A simple and low cost electronic system has been designed and fabricated for the DC SQUID sensors.

Equipment Design↗
PubMed1991

Localization properties of multi-sensor biomagnetic systems.

The recent development of large multi-channel biomagnetic systems, with 20-30 adjacent magnetic sensors, is marking a significant progress in the detection and interpretation of biomagnetic signals, and definitely traces a new avenue towards a proper assessment of the technique in the clinical field. Several technological problems are being solved, mainly concerning the reliability of the SQUIDs and of the superconducting assembly, as well as the criogenic dewar. Also the choice of the geometry for the gradiometers to be coupled to the SQUIDs has a fundamental importance, not only from a technological point of view, but also in that it affects the localization properties of the system. The major attractions and drawbacks of both vertical and planar configurations will be briefly reviewed and few practical suggestions to overcome some of the difficulties will be proposed.

Action Potentials↗
PubMed1990

Evoked alpha- and mu-rhythm in humans: a neuromagnetic study.

We present the results of a neuromagnetic study on the spatial structure of brain rhythms enhanced by photic and somatosensory stimulation, as measured on the occipital, rolandic and frontorolandic regions in humans. It emerges that, while it is always possible to drive the cerebral activity during sustained stimulation at any given frequency, only certain specific frequencies can produce prolonged synchronization (i.e. the oscillating activity elicited by the repetitive stimulation continues well beyond its termination). In both studied modalities we were able to localize equivalent sources for the synchronized responses; their relationship with the known evoked responses is discussed. In the visual modality the synchronization was characterized by a potentiation of the subjects' alpha-rhythm. In the somatosensory modality synchronization was reflecting two different activities: one probably related to the rolandic mu-rhythm, the second suggesting the presence of two widely separated and time correlated sources possibly driven by a unique, deep clock. Possible implications for other studies of the dominant brain rhythms, or experimental checks on specific brain models, as well as of the visual and somatosensory evoked responses are discussed.

Adult↗
PubMed1990

Advances in neuromagnetic topography and source localization.

The development of ultra-low noise instrumentation for neuromagnetic mapping has yielded significant progress in the study of brain function and pathology. New multi-channel systems, belonging to an "intermediate" generation, are already in use, or are going to become operative in the near future. These systems permit simultaneous field mapping over a relatively large area of the scalp, and allow source localization on the basis of a single trial, although they still do not permit topographic mapping over the whole scalp. Significant improvements are being made also in realistic modeling of the human head and brain, with the aim at increasing the accuracy of source localization. Finally, a few examples of recent studies on normal brain function and application of the technique in the clinical field will be illustrated.

Brain↗
PubMed1990

Neuromagnetic topography of photoconvulsive response in man.

The neuromagnetic method was applied to the study of photoconvulsive responses. The identification of specific magnetic field distributions over the scalp was achieved by; (a) a stimulation paradigm consisting of series of trains of flicker stimuli randomly presented to the epileptic patient, after eye closure, to get epileptic responses while avoiding seizures; (b) a novel procedure for data analysis, to select consistent responses. These patterns, when sufficiently stable in time and dipolar in shape, were used for source localization in the usual biomagnetic framework of the equivalent current dipole source representation. The results of this approach suggest that different specific cortical areas are repeatedly and randomly activated, involving mainly the frontal, occipital and temporal areas, often with a hemispheric prevalence.

Brain↗