- Email: [email protected]
A syntactic approach to the analysis of the spontaneous EEG
$235 D P P I . I I S P E C T R A L EVALUATION OF T H E ' M I C R O S T A T E S ' O F T H E EEG. H. Ozakl, Y. Nagase, A. Katada and H. Suzuki
(Mito, Japan) ' Micro-states' of the EEG were studied in relation to the spatial characteristics of the alpha rhythm in normal adults subjects. EEGs were recorded from 16 electrodes arranged on both hemispheres against the linked ears as a common reference. By using FFT, s i n / c o s functions and power spectra of EEG were calculated in each succesive 2 second epoch. An alpha component was often observed dominantly at the occipital and neighbouring regions. But its spatial distribution altered frequently and dominant occurrences of the alpha component were observed most frequently at certain regions (O1, Oz, 0 2 and Pz). Various kinds of' micro-states' of the EEG were differentiated by the evaluation of spatial characteristics. Such an alteration of the spatial characteristics was also confirmed in the results of the vector display which was developed to evaluate the field structure of the frequency component without being biased by the reference electrode selection (Lehm a n n & Ozaki). An individual EEG is mainly characterized by the preferred patterns of spatial distribution. The alteration of the topographical characteristics of the alpha rhythm on the scalp might suggest a changing of the ' micro-states' in the brain's functioning.
DPPI.12 INTERHEMISPHERIC P R O P A G A T I O N OF LIMBIC SEIZURES: A C O H E R E N C E / P H A S E ANALYSIS. J P. Lieb and C.E. Skomer
(Los Angeles, CA, USA) C o h e r e n c e / p h a s e analysis was performed on depth ictal EEG records in 5 patients with medically refractory, complex, partial seizures. Seizures in all 5 patients were reliably initiated, in a unilateral fashion, from the amygdalo-hippocampal region. For each ictal EEG episode, 2 - 3 epochs, ranging from 5 to 9 sec in duration, were chosen for analysis. The epochs were taken from periods immediately following the electrical onset of the episode and immediately following the invasion of seizure activity into the contra-lateral amygdalo-hippocampal region. Left/right pairs of recording sites were compared in order to determine whether significant coherences over a range of frequencies developed in conjunction with a non-zero slope linear phase spectrum during interhemispheric propagation. In 3 patients, statistically significant coherences between left and right mesial temporal lobe sites were absent. In 2 patients significant coherences evolved and were accompanied by a non-zero slope linear phase spectrum. Their interhemispheric lag times ranged between 5 and 50 msec.
These results indicate that in patients with amygdalo-hippocampal seizure foci, interhemispheric propagation routes vary. A multi-synaptic pathway involving the corpus callosum is possible in those patients who failed to demonstrate significant interhemispheric coherences. More direct pathways,involving the anterior and hippocampal commissures may have been used in those patients with significant interhemispheric coherences.
DPPI.13 A S Y N T A C T I C A P P R O A C H T O T H E ANALYSIS O F T H E S P O N T A N E O U S EEG. V.A, Pollak
(Saskatoon, Canada) For syntactic analysis, the general EEG signal is regarded as a message written in an unknown language. It is assumed that a list of elementary components, the 'Alphabet', had previously been established. Interpretation of a specific message requires knowledge of its 'syntax', the set of rules which governs the structure of the language. For the 'letters' of the alphabet the syntax is determined using simplified statistical methods borrowed from mathematical linguistics. The anal3sis involves the following principal steps: the analysed realization of the EEG is first transformed into a sequence of "letters'. About half of these letters are defined by their spectral posltion, the other half by their time domain wave shape (singular waves). The first order syntax if found by specifying the distribution of certain attributes of the letters, mainly amplitude and duration: for singular waves duration is replaced by the number of repetitions in an unbroken string. For the time being, the attribute statistics are defined by their mean and standard deviation only. The measured attribute parameters are displayed in the form of a matrix (table) which contains most of the relevant information of the analysed signal. The tables (one for each channel) proved to be stable with time unless the state of the subject changes.
DATA P R O C E S S I N G EPs A N D ERPs. DPP2.01 ADAPTIVE S E G M E N T A T I O N OF EVENT-RELATED P O T E N T I A L M A P SERIES I N T O C O M P O N E N T S D E F I N E D BY M A P C O N F I G U R A T I O N . D. Lehmann, D. Brandeis, A. Horst, G.C. Jin, I. Pal and W.
Skrandies (Zurich, Switzerland) Muhichannel event-related potential data when displayed as sequences of scalp field maps show sub-epochs of varying durations during which the mapped configuration of the field is relatively stable. In order to determine the time boundaries of stable map configurations, the global dissimilarity index can be
(Mito, Japan) ' Micro-states' of the EEG were studied in relation to the spatial characteristics of the alpha rhythm in normal adults subjects. EEGs were recorded from 16 electrodes arranged on both hemispheres against the linked ears as a common reference. By using FFT, s i n / c o s functions and power spectra of EEG were calculated in each succesive 2 second epoch. An alpha component was often observed dominantly at the occipital and neighbouring regions. But its spatial distribution altered frequently and dominant occurrences of the alpha component were observed most frequently at certain regions (O1, Oz, 0 2 and Pz). Various kinds of' micro-states' of the EEG were differentiated by the evaluation of spatial characteristics. Such an alteration of the spatial characteristics was also confirmed in the results of the vector display which was developed to evaluate the field structure of the frequency component without being biased by the reference electrode selection (Lehm a n n & Ozaki). An individual EEG is mainly characterized by the preferred patterns of spatial distribution. The alteration of the topographical characteristics of the alpha rhythm on the scalp might suggest a changing of the ' micro-states' in the brain's functioning.
DPPI.12 INTERHEMISPHERIC P R O P A G A T I O N OF LIMBIC SEIZURES: A C O H E R E N C E / P H A S E ANALYSIS. J P. Lieb and C.E. Skomer
(Los Angeles, CA, USA) C o h e r e n c e / p h a s e analysis was performed on depth ictal EEG records in 5 patients with medically refractory, complex, partial seizures. Seizures in all 5 patients were reliably initiated, in a unilateral fashion, from the amygdalo-hippocampal region. For each ictal EEG episode, 2 - 3 epochs, ranging from 5 to 9 sec in duration, were chosen for analysis. The epochs were taken from periods immediately following the electrical onset of the episode and immediately following the invasion of seizure activity into the contra-lateral amygdalo-hippocampal region. Left/right pairs of recording sites were compared in order to determine whether significant coherences over a range of frequencies developed in conjunction with a non-zero slope linear phase spectrum during interhemispheric propagation. In 3 patients, statistically significant coherences between left and right mesial temporal lobe sites were absent. In 2 patients significant coherences evolved and were accompanied by a non-zero slope linear phase spectrum. Their interhemispheric lag times ranged between 5 and 50 msec.
These results indicate that in patients with amygdalo-hippocampal seizure foci, interhemispheric propagation routes vary. A multi-synaptic pathway involving the corpus callosum is possible in those patients who failed to demonstrate significant interhemispheric coherences. More direct pathways,involving the anterior and hippocampal commissures may have been used in those patients with significant interhemispheric coherences.
DPPI.13 A S Y N T A C T I C A P P R O A C H T O T H E ANALYSIS O F T H E S P O N T A N E O U S EEG. V.A, Pollak
(Saskatoon, Canada) For syntactic analysis, the general EEG signal is regarded as a message written in an unknown language. It is assumed that a list of elementary components, the 'Alphabet', had previously been established. Interpretation of a specific message requires knowledge of its 'syntax', the set of rules which governs the structure of the language. For the 'letters' of the alphabet the syntax is determined using simplified statistical methods borrowed from mathematical linguistics. The anal3sis involves the following principal steps: the analysed realization of the EEG is first transformed into a sequence of "letters'. About half of these letters are defined by their spectral posltion, the other half by their time domain wave shape (singular waves). The first order syntax if found by specifying the distribution of certain attributes of the letters, mainly amplitude and duration: for singular waves duration is replaced by the number of repetitions in an unbroken string. For the time being, the attribute statistics are defined by their mean and standard deviation only. The measured attribute parameters are displayed in the form of a matrix (table) which contains most of the relevant information of the analysed signal. The tables (one for each channel) proved to be stable with time unless the state of the subject changes.
DATA P R O C E S S I N G EPs A N D ERPs. DPP2.01 ADAPTIVE S E G M E N T A T I O N OF EVENT-RELATED P O T E N T I A L M A P SERIES I N T O C O M P O N E N T S D E F I N E D BY M A P C O N F I G U R A T I O N . D. Lehmann, D. Brandeis, A. Horst, G.C. Jin, I. Pal and W.
Skrandies (Zurich, Switzerland) Muhichannel event-related potential data when displayed as sequences of scalp field maps show sub-epochs of varying durations during which the mapped configuration of the field is relatively stable. In order to determine the time boundaries of stable map configurations, the global dissimilarity index can be