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Biomedical subjects

G Anogianakis

Publications and source records attributed to G Anogianakis.

11 recordsLinked to original sources
PubMed1992

On AR modelling for MEG spectral estimation, data compression and classification.

The use of the autoregressive (AR) model for magnetoencephalogram (MEG) processing is examined and compared to other methods. Spectral estimation, classification and data compression of MEG signals are studied. In application to spectral estimation the AR model is compared to the classical modified periodogram method. Also, AR modelling appears to perform very successfully when used for the classification of normal and epileptic MEG signals. Finally, the 17:1 to 23:1 data compression achieved by AR modelling, along with the above-mentioned advantages, render it suitable for storage applications. For comparison, the method of feature selection via orthogonal expansion is used as a tool to achieve data reduction. It is seen that while effective, this is less drastic than the compression of data volume achieved by AR modelling.

Brain Mapping↗
PubMed1989

Long-term effects of the administration of the convulsive substance DL-methionine-DL-sulfoximine to the rabbit.

Methionine sulfoximine (MSO) is a centrally acting neurotoxin which inhibits the glutamate metabolism enzymes and has convulsive properties. Administration of a small dose of MSO to rabbits, either intravenously or intracerebroventricularly, except for the already known convulsive effects, may also be responsible for hind leg myopathy (rigid paralysis with histological findings resembling myositis) which sets in by the 4th day after MSO administration.

Animals↗
PubMed1989

Evaluation of epileptic patients by means of magnetoencephalography.

Studies of the magnetoencephalogram (MEG) in epileptic patients suffering from focal epilepsies showed that activities in the MEG appear which are detectable in the scalp-recorded electroencephalogram. A novel technique was developed (Anninos et al., 1987) characterized by mapping the scalp distribution of the amplitude of the spectral components (or specific bands) of the MEG and which was termed "ISO-Spectral-Amplitude (ISO-SA) mapping." The most important findings in the 19 patients we studied from these maps were that in the frequency domain 2-7 HZ the major concentrated activity were projected on the scalp of the epileptic focus. Thus with the above noninvasive method we believe that it is possible to determine the localization of epileptiform foci via a method which will be a very useful tool for clinicians.

Electroencephalography↗
PubMed1989

The influence of piracetam on digoxin up-take by different rabbit tissues in vitro.

The action of increasing piracetam concentration on the digoxin up-take by various rabbit tissues was investigated in vitro. 125J-digoxin was used and radioactivity was counted in a gamma scintillation counter. Piracetam 100 micrograms/ml has a small increasing action on digoxin up-take by parenchymatous rabbit tissues. This action may be due to the beneficial effect of the substance on tissue microcirculation and cell metabolism. This action is equilibrated or reversed by piracetam 200 micrograms/ml and 400 micrograms/ml. It is suggested that piracetam displays digoxin from its binding-sites but these concentrations are above those ones used for clinical purposes.

Animals↗
PubMed1988

Tonotopic organization of the human auditory cortex revealed by transient auditory evoked magnetic fields.

The tonotopic organization of the human auditory cortex has been investigated by systematic measurements of magnetic fields evoked by tone-bursts with carrier frequencies of 250, 500, 1000, 2000 and 4000 Hz. The measured field distribution changes with both time elapsed since stimulus onset and frequency of the stimulus. Nevertheless, the field distribution has always the same overall features and can be approximated by that of an equivalent current dipole located in a semi-infinite volume. This model can be described in terms of 5 parameter values: 3 orthogonal coordinates specifying the dipole location, and amplitude and angle of the dipole moment. The amplitude of the dipole moment is maximal at about 100 msec ('component 100m') and 160 msec ('component 160m') after stimulus onset. The depth estimated for the generator site of the 100m component shows a logarithmic dependence on test frequency whereas no similar behaviour could be observed for the 160m component. Anatomical studies performed in cadaver heads suggest that the equivalent current dipoles of both the 100m and the 160m component are located in the transverse temporal gyri.

Adult↗
PubMed1988

Localization of epileptiform foci by means of MEG measurements.

Systematic studies of the magnetoencephalogram (MEG) in normal and pathological subjects (mainly with focal epilepsies) showed that the MEG may evidence significant brain activities even if they are not identifiable in the electroencephalogram (EEG). They also showed that the MEG has a considerably higher spatial resolution than the EEG. A two-dimensional mapping technique was used to get such a representation of the data that would enable the investigator to draw his conclusions mainly from inspecting the plots. The technique is characterized by an isospectral synchronized power (iso-SSP) mapping of the scalp distribution of specified frequency bands of the MEG power spectrum. In this way the precise projection on the scalp of an epileptiform focus can be determined without applying a strong eliciting stimulus or relying on the analysis of the simultaneously recorded EEG. Our results compare very favourably with the clinical picture of our pathological subjects.

Brain↗
PubMed1987

A neural net model for the release of prolactin during pseudopregnancy in the rat.

A theoretical probabilistic neural net model is proposed here based on the interaction between two subsystems, the connections of which are made up by means of chemical markers. The activity of such a system at t = n tau is exclusively dependent on the firing record of the system at t = (n-1) tau, on the level of spontaneous activity and on an external inhibitory influence which we have found that may play an important role in the prolactin release level during pseudopregnancy in rats. We explore some of the implications of this model on the possible role of the hippocampus in the phenomenon.

Animals↗
PubMed1987

Involvement of the caudate nucleus in the modulation of the brain somatosensory evoked potentials.

The participation of the caudate nucleus in the modulation of the cortical somatosensory evoked potentials was investigated in male rabbits. The power spectra of the somatosensory evoked potential recorded from the scalp in the intact animal was compared with that recorded after kainic acid lesion of specific regions of the caudate nucleus (i.e., anterior and or posterior portions of the head of the nucleus) and the "destructive" interference patterns which appeared were investigated. It was found that the caudate's head modulates the waveform at the end of the early phase of the cortical somatosensory evoked potentials, i.e., the period from 20.8 ms to 29.4 ms. These results suggest that the caudate nucleus is part of the sensory pathways belonging to the nonspecific projection system and participates in the integrating processes of the somatosensory information.

Animals↗
PubMed1987

Biomagnetic measurements using squids.

Systematic studies of the magnetoencephalogram (MEG) in normal and pathological subjects (mainly with focal epilepsies) showed that the MEG may evidence significant brain activities even if they are not present in the electroencephalogram (EEG). They also showed that the MEG has a considerably higher spatial resolution than the EEG. A novel mapping technique was introduced to get such a representation of the data that would enable the investigator to draw his conclusions mainly from inspecting the plots. This technique is characterized by an isospectral amplitude (iso-SA) mapping of the scalp distribution of specified spectral components or frequency bands of the MEG power spectrum. With the above method we were able to localize an epileptiform focus using a noninvasive technique without applying an eliciting stimulus. Furthermore using SQUID measurements we were able to describe the behavior of the MEG when the brains of different subjects were subjected to low frequency sinusoidal binaural stimuli. Under these conditions it has been shown that the MEG tends to organize around discrete frequencies that depend on the interference pattern (beat) between the two inputs.

Acoustic Stimulation↗