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Biomedical subjects

C Salustri

Publications and source records attributed to C Salustri.

9 recordsLinked to original sources
PubMed2000

Conscious and preconscious adaptation to rhythmic auditory stimuli: a magnetoencephalographic study of human brain responses.

This study was triggered by the experimental evidence that subjects required to tap in synchrony with a heard rhythm spontaneously time their tapping to variations in rhythm frequency even when these variations are so small that they are not consciously detectable. We performed a series of magnetoencephalographic (MEG) measurements, aimed at investigating whether the response of the auditory cortex discriminates randomly administered series of brief tones differing from each other only by their interstimulus intervals (ISI). Moreover, by combining psychophysical measurements, conscious and preconscious adjustments of tapping to rhythm variations were compared with brain cortical responses. The ISIs were varied by 2% or 20% from a "central" value of 500 ms. Subjects always consciously detected the 20% ISI changes and easily adjusted their tapping accordingly, whereas they never consciously detected the 2% ISI changes, even though they always correctly adjusted their tapping to them. Analysis of the auditory evoked fields (AEFs) showed that the intensity of the M100 component decreased with decreasing ISI both for 20% and 2% variations in a statistically significant manner, despite the fact that the 2% variation was not consciously perceived. The M100 behavior indicated that connections between auditory and motor cortexes may exist that are able to use the information on rhythm variations in the stimuli even when these are not consciously identified by the subject. The ability of the auditory cortex to discriminate different time characteristics of the incoming rhythmic stimuli is discussed in this paper in relation to the theories regarding the physiology of time perception and discrimination.

Acoustic Stimulation↗
PubMed1999

Simple but reliable solutions for spiral MRI gradient design.

The efficiency of gradient design in MRI is limited by the simple fact that the gradient coil current and slew rate cannot exceed hardware threshold values. In spiral MRI, which requires gradients to be very rapidly switched between positive and negative values, minimization of the acquisition time is achieved by maintaining the current and slew rate as high as possible during the entire measurement. Since the current and slew rate compete against each other, an efficient gradient design consists of two parts in which current and slew rate are pushed alternatively to their limits. Values for these types of gradients can be obtained by solving numerically the equation of motion for the spiral trajectory. This paper shows that simple but reasonable mathematical approximations deliver reliable analytical solutions. Images obtained using these analytical solutions do not show evident distortions when compared with images obtained with numerical solutions.

Algorithms↗
PubMed1993

Word meaningfulness and event-related potentials during phrase processing.

Evoked Potentials (EP) were recorded to visual presentation of words in phrases. Three EP components, P250, N400, P560, and their dependence on the role that each word plays in the phrase were studied. Subjects were requested to perform a congruity/incongruity task after the presentation of short phrases of two-types that differed in the position of meaningful keywords. We show how these keywords contribute substantially to N400 and possibly to P560 but do not reliably affect P250.

Adolescent↗
PubMed1989

A simple method for 3-dimensional localization of epileptic activity recorded by simultaneous EEG and MEG.

A simple method is presented to average target patterns in the magnetoencephalographic trace of epileptic activity by finding markers in an EEG channel. This method proves to be useful even in cases of low magnetic signal-to-noise ratio. After simultaneously recording electric and magnetic activity the user chooses in the electric trace a template of interest and determines within the same trace all the time points at which the EEG pattern is highly correlated with the chosen template. The magnetic trace portions recorded at those times are averaged together, extracting in this way the magnetic signal from the noise. The MEG results are applied to localize in the brain the active sources that contribute to the recorded signals.

Electroencephalography↗
PubMed1987

Study of focal epilepsy by multichannel neuromagnetic measurements.

A systematic investigation of several cases of focal epilepsy has been performed in an unshielded environment using a 4-channel neuromagnetic sensor. The localizations provided by the magnetic measurements have been compared with clinical evidence and confirmed by X-ray findings, and in one case also by intracranial surgery. The results show the importance of simultaneous detection of magnetic fields at different sites of the scalp in order to get a dynamic view of the epileptic activity and to detect multifocal activity unsuspected on the basis of the EEG investigation.

Brain Mapping↗
PubMed1987

Novel data analysis for synchronised spontaneous neuromagnetic activity.

A novel approach to neuromagnetic data analysis is presented. This technique is aimed at studying synchronised spontaneous activity (SSA) and has been used to resolve two different signals from one single evoked response, providing evidence for two possibly distinct sources. The data presented are consistent with a model that permits the generators of spontaneous activity to be synchronised by sensory stimuli.

Brain↗
PubMed1987

Neuromagnetic evidence of synchronized spontaneous activity in the brain following repetitive sensory stimulation.

Neuromagnetic measurements in the visual and somatosensory modalities reveal that, following repetitive stimulation, the brain persists in emitting synchronized after-discharges in the form of oscillations with highly specific spectral composition. In the visual modality, this rhythmic activity is centered at the frequency of the resting alpha rhythm and it is most readily induced by stimulation of the same frequency. This suggests that the phenomenon is due to synchronization of the generators responsible for the natural rhythms by the steady-state stimulation and that these generators behave as resonant oscillators. The phenomenon could then be referred to as Synchronized Spontaneous Activity (SSA). The discovery of this phenomenon has important implications for modelling the dynamics of normal evoked and spontaneous cerebral activity as well as for the understanding of pathological conditions such as photically induced epilepsies.

Adult↗
PubMed1987

Neuromagnetic characterization of the cortical response to median nerve stimulation in the steady state paradigm.

Magnetic methods for localizing evoked neural activity in the human brain have been used to search for evidence of a functional organization in primary somatosensory cortex. We have found that in response to median nerve stimulation the deduced source for the evoked component with a latency of 45 ms lies at a depth in the central sulcus that depends on stimulus repetition rate, whereas the sources of the 20 ms and 24 ms components lie at a fixed depth. Moreover we have identified this 45 ms component with the dominant sinusoidal feature characteristic of steady state response.

Brain Mapping↗