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349 Correlations between event-related alpha oscillations and P300
Abstracts
/International
Journal
The EEG was recorded from F3, F4, C3, C4, P3 and P4 against linked-mastoids. Additionally, the heart rate variability was recorded for load indication. Both, linear and non-linear measures were computed for 6 subsequent EEG-epochs of each single trial. Analyses of variance were conducted on each of the measures using the factors type of task(3) x block (4) x epoch (6). For all tasks, the frontal theta-power was increased, being higher for dual tasks than for both single tasks. The mean difference between the single tasks reached statistical significance only in the middle time range of the trials. The non-linear measures were negatively correlated with the theta-power. Heart rate variability, which indicated an increased load under the dual task condition, also corresponded with the EEG-measures. In this study none of the EEG-measures discriminated between physical load and cognitive load. However, frontal theta, which comes along with a significant loss of dimensional complexity, seems to represent a more general correlate of focused-attention related processes.
348 TIME-LOCKED “GAMMA BAND” ACTIVITY IN RESPONSE TO SIMULTANEOUSLY RECORDED ONSET VEP AND VISUAL P300 F. Bandini’, C. Ogliastro’, L. Mazella’, E. Guidi2, D. Gesino’, L. Narici3, W.G. Sannita’s4 ‘Center for Neuroactive Drugs, Department of Motor Sciences ‘Department of Neurological Sciences, University of Genoa, Via De Toni 5, Genoa 16132, Italy 3Department of Physics, University of “Tor Vergata” Rome, Italy 4Department of Psychiatry, SUNY, Stony Brook, NY, USA Transient contrast stimulation (counterphase modulation) evokes middle frequency (- 20-40 Hz) oscillatory activity in human visual cortex (“gamma band” activity), which reportedly reflects cognitive processes. The present study is aimed at verifying whether pattern onset/offset stimulation evokes oscillatory responses time-locked to stimulus, as pattern reversal stimulation does. In addition the simultaneous recordings of primary (VEP) and event-related (ERP) visual evoked potentials allowed us to study the eventual functional correlation and time dynamics of the oscillatory activity evoked by pattern onset stimulation and visuocognitive processes. Concurrent VEP and P300 responses with adequate morphology, latencies and amplitudes were obtained from 10 volunteers at proper scalp locations using sinusoidally modulated gratings with vertical (frequent stimulus: 80%) or oblique orientation (rare stimulus: 20%). Root mean squares (RMS) values were calculated from averaged and band-filtered (17-46 Hz) target and non-target responses. Significantly increased phase-locked oscillatory activity was observed at occipital locations in concomitance with the time window of the PlOO peak of the onset
of Psychophysiology
30 (1998)
135
95-271
VEP (80 - 140 ms) and, at central locations, at the end of the time window of the P300 (280 - 440 ms), as for a suppression of the oscillatory activity during visuocognitive processing. We conclude that the induced “gamma band” activity seems to reflect both primary sensory events and cognitive processes in the visual system with possible independent neural networks and is suggested to serve as a link between brain regions activated by simultaneous external events.
349 CORRELATIONS ALPHA OSCILLATIONS
BETWEEN AND P300
EVENT-RELATED
V. Kolev* and J. Yordanova Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 23, 1113 Sofia, Bulgaria Both the endogenous P300 component of the event-related brain potentials (ERPs) and event-related alpha (7-14 Hz) oscillations have been associated with attention and memory processes. Because of their similar sensitivity to experimental variables, P300 and event-related alpha oscillations may reflect identical cognitive processes. This implies that P300 should correlate with alpha components generated during stimulus processing, but the relationships between P300 parameters and event-related alpha activity have not been described systematically. The present study examined the association between P300 and alpha responses produced by auditory oddball stimuli. ERPs to randomized rare targets (800 Hz tones, p = .25) and frequent nontargets (1200 Hz, p = .75) were recorded at Fz, Cz, and Pz in 17 healthy adults. Targets had to be responded by button pressing. P300 latency and amplitude were measured. Event-related power increase (ERS) or decrease (ERD) of alpha activity was quantified by means of the Hilbert transform. This method allowed to measure not only the amount but also the precise time localization of maximal alpha power changes after stimulation. Event-related variations of slow (7-10 Hz) and fast (lo-14 Hz) alpha activity were analyzed. For both alpha sub-ranges, auditory oddball stimuli produced an initial central-frontal ERS peaking at 150-200 ms followed by a parietal ERD peaking between 400 and 1000 ms for different leads and stimulus types. P300 latency was correlated across subjects with the peak latencies and P300 amplitude was correlated with the peak magnitudes of slow and fast alpha ERS and ERD. The following new findings were obtained: (1) At frontal and central locations, P300 amplitude was positively correlated with the peak magnitude of fast alpha ERS, and P300 latency was positively correlated with the peak latency of fast alpha ERS. Slow alpha ERS was not associated with P300. (2) P300 amplitude did not correlate with slow or fast alpha ERD magnitude. In contrast, P300 latency was correlated negatively with the peak latency of slow alpha ERD and positively with the peak latency of fast alpha ERD. These results indicate that: (1) Both the enhanced and suppressed event-related
136
Abstracts
/International
Journal
alpha oscillations are closely associated with P300, which emphasizes the functional role of EEG alpha activity in cognitive processes; (2) The associations are specific for the slow and fast alpha activity, which provides further evidence for the functional dissociation between the two sub-ranges within the alpha band; (3) As no correlations were obtained between ERS and ERD latencies, P300 may be regarded as a functional event occurring during the transition of the event-related alpha activity from synchronized to desynchronized state.
350 PHASE-LOCKED FAST CREASES DURING P300
ALPHA
ACTIVITY
IN-
J. Yordanova* and V. Kolev Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 23, 1113 Sofia, Bulgaria The endogenous P300 component of the event-related brain potentials (ERPs) has been associated with cognitive process@ such as memory updating and attention allocation. By quantifying event-related changes in the electroencephalographic (EEG) activity, it has been demonstrated that EEG oscillations in the alpha (7-14 Hz) band manifest a similar sensitivity to conditions engaging attention and memory processes. This similarity in functional responsiveness suggests that event-related alpha activity and P300 may ret&t the same cognitive processes. If this is the case, it may be expected that when P300 emerges as an objective and time-localized marker of specific cognitive processing, alpha EEG activity within the same time period would also vary with task demands. The present study evaluated the effects of auditory oddball task processing on event-related alpha oscillations.generated in the P300 latency range. The task series used to elicit the classical P300 consisted of randomly distributed rare (800 Hz, p = .2) and frequent (1200 Hz, p = 8) tones. The rare tones were targets and required a mental count. ERPs were recorded at Fz, Cz, and Pz sites in nine subjects. Analyses of variance (stimulus x electrode) were performed for P300 amplitude and for the following parameters of alpha activity within P300 latency range (250-600 ms): power of phase-locked oscillations, power of non-phase-locked oscillations, and stability of phase-locking of alpha responses. Slow (7-10 Hz) and fast (lo-14 Hz) alpha oscillations were analyzed separately. Major results demonstrated that both the phase-locked and non-phase-locked alpha oscillations during P300 development were functionally relevant to the oddball task processing: (1) At frontal and central locations, targets produced significantly larger and better synchronized phase-locked lo-14 Hz oscillations than nontargets did. As P300 showed a parietal maximum, the frontally distributed synchronized and enhanced fast alpha oscillations appear to reflect a specific process or state that is functionally linked to the major processes eliciting P300. (21 At the parietal site, targets led to a significantly greater reduction of non-phase-locked 7-10 Hz activity relative
of Psychophysiology
30 (1998)
95-271
to nontargets. The suppression of non-phase-locked and the increase of phase-locked alpha oscillations during P300 development suggest that P300-related cognitive processes tend to be accompanied by ordered and synchronized alpha states.
351 CHARACTERIZATION OF THE DYNAMICS OF CHILDHOOD ABSENCE SEIZURES WITH METHODS OF NONLINEAR SYSTEM ANALYSIS U. Moeller*, M. Feucht, H. Witte and M. Friedrich Institute of Medical Statistics, Computer Sciences and Documentation, Friedrich Schiller University, Jahnstrasse 1, 07740 Jena, Germany Models by means of which one can generate time series in correlation to EEG target signals may help to understand dynamic phenomena underlying the EEG. Since in several studies nonlinearities were found in EEGs of epileptic seizures it is self-evident to use nonlinear (or dynamic) modeling approaches for related attempts. The relevance of a model can be tested comparing characteristics of the nonlinear dynamics obtained for both the EEG and the signal of the model. We present a new nonlinear approach according to this scheme for the analysis of nearly periodic EEG signals [l]. It is demonstrated with scalp EEGs of 14 unprovoked typical (3 c/s) absence seizures of 5 unmedicated patients with childhood absence epilepsy. These data were strictly classified at the Department for Seizure Disorders at the Vienna University Clinic of Neuropsychiatry for Children and Adolescents and further selected according to method-based acceptance criteria A (nonlinear) self-exciting threshold autoregressive (SETAR) model, a surrogate data technique, and a simulation of pure spike-and-wave (SW) signals provided models and 5 types of SW test signals to be compared with the target EEG by means of autocorrelation, correlation dimension, averaged pointwise dimension and largest Lyapunov exponents. The SETAR model exhibited stationary SW dynamics, visually very similar to the EEG target signal, and with clear nonlinear structure. According to the results, the EEG episodes investigated represent low-dimensional dynamics and were possibly recorded during nonstationary periods. The methods used did not provide arguments that justify the assumption of deterministic chaos. From the results one may conclude that two global oscillatory modes are present for the SETAR model, and three modes are active during the EEG recording periods.
352 WORKING MEMORY INDUCES EEG ENCE CHANGES IN NORMAL SUBJECTS
COHER-
Albert0 Yorio*, Irene Brauer, Claudia Marro and Enrique T Segura Instituto de Biologia y Medicina Experimental (CONICET), Vuelta de Obligado 2490, 1428 Argentina
/International
Journal
The EEG was recorded from F3, F4, C3, C4, P3 and P4 against linked-mastoids. Additionally, the heart rate variability was recorded for load indication. Both, linear and non-linear measures were computed for 6 subsequent EEG-epochs of each single trial. Analyses of variance were conducted on each of the measures using the factors type of task(3) x block (4) x epoch (6). For all tasks, the frontal theta-power was increased, being higher for dual tasks than for both single tasks. The mean difference between the single tasks reached statistical significance only in the middle time range of the trials. The non-linear measures were negatively correlated with the theta-power. Heart rate variability, which indicated an increased load under the dual task condition, also corresponded with the EEG-measures. In this study none of the EEG-measures discriminated between physical load and cognitive load. However, frontal theta, which comes along with a significant loss of dimensional complexity, seems to represent a more general correlate of focused-attention related processes.
348 TIME-LOCKED “GAMMA BAND” ACTIVITY IN RESPONSE TO SIMULTANEOUSLY RECORDED ONSET VEP AND VISUAL P300 F. Bandini’, C. Ogliastro’, L. Mazella’, E. Guidi2, D. Gesino’, L. Narici3, W.G. Sannita’s4 ‘Center for Neuroactive Drugs, Department of Motor Sciences ‘Department of Neurological Sciences, University of Genoa, Via De Toni 5, Genoa 16132, Italy 3Department of Physics, University of “Tor Vergata” Rome, Italy 4Department of Psychiatry, SUNY, Stony Brook, NY, USA Transient contrast stimulation (counterphase modulation) evokes middle frequency (- 20-40 Hz) oscillatory activity in human visual cortex (“gamma band” activity), which reportedly reflects cognitive processes. The present study is aimed at verifying whether pattern onset/offset stimulation evokes oscillatory responses time-locked to stimulus, as pattern reversal stimulation does. In addition the simultaneous recordings of primary (VEP) and event-related (ERP) visual evoked potentials allowed us to study the eventual functional correlation and time dynamics of the oscillatory activity evoked by pattern onset stimulation and visuocognitive processes. Concurrent VEP and P300 responses with adequate morphology, latencies and amplitudes were obtained from 10 volunteers at proper scalp locations using sinusoidally modulated gratings with vertical (frequent stimulus: 80%) or oblique orientation (rare stimulus: 20%). Root mean squares (RMS) values were calculated from averaged and band-filtered (17-46 Hz) target and non-target responses. Significantly increased phase-locked oscillatory activity was observed at occipital locations in concomitance with the time window of the PlOO peak of the onset
of Psychophysiology
30 (1998)
135
95-271
VEP (80 - 140 ms) and, at central locations, at the end of the time window of the P300 (280 - 440 ms), as for a suppression of the oscillatory activity during visuocognitive processing. We conclude that the induced “gamma band” activity seems to reflect both primary sensory events and cognitive processes in the visual system with possible independent neural networks and is suggested to serve as a link between brain regions activated by simultaneous external events.
349 CORRELATIONS ALPHA OSCILLATIONS
BETWEEN AND P300
EVENT-RELATED
V. Kolev* and J. Yordanova Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 23, 1113 Sofia, Bulgaria Both the endogenous P300 component of the event-related brain potentials (ERPs) and event-related alpha (7-14 Hz) oscillations have been associated with attention and memory processes. Because of their similar sensitivity to experimental variables, P300 and event-related alpha oscillations may reflect identical cognitive processes. This implies that P300 should correlate with alpha components generated during stimulus processing, but the relationships between P300 parameters and event-related alpha activity have not been described systematically. The present study examined the association between P300 and alpha responses produced by auditory oddball stimuli. ERPs to randomized rare targets (800 Hz tones, p = .25) and frequent nontargets (1200 Hz, p = .75) were recorded at Fz, Cz, and Pz in 17 healthy adults. Targets had to be responded by button pressing. P300 latency and amplitude were measured. Event-related power increase (ERS) or decrease (ERD) of alpha activity was quantified by means of the Hilbert transform. This method allowed to measure not only the amount but also the precise time localization of maximal alpha power changes after stimulation. Event-related variations of slow (7-10 Hz) and fast (lo-14 Hz) alpha activity were analyzed. For both alpha sub-ranges, auditory oddball stimuli produced an initial central-frontal ERS peaking at 150-200 ms followed by a parietal ERD peaking between 400 and 1000 ms for different leads and stimulus types. P300 latency was correlated across subjects with the peak latencies and P300 amplitude was correlated with the peak magnitudes of slow and fast alpha ERS and ERD. The following new findings were obtained: (1) At frontal and central locations, P300 amplitude was positively correlated with the peak magnitude of fast alpha ERS, and P300 latency was positively correlated with the peak latency of fast alpha ERS. Slow alpha ERS was not associated with P300. (2) P300 amplitude did not correlate with slow or fast alpha ERD magnitude. In contrast, P300 latency was correlated negatively with the peak latency of slow alpha ERD and positively with the peak latency of fast alpha ERD. These results indicate that: (1) Both the enhanced and suppressed event-related
136
Abstracts
/International
Journal
alpha oscillations are closely associated with P300, which emphasizes the functional role of EEG alpha activity in cognitive processes; (2) The associations are specific for the slow and fast alpha activity, which provides further evidence for the functional dissociation between the two sub-ranges within the alpha band; (3) As no correlations were obtained between ERS and ERD latencies, P300 may be regarded as a functional event occurring during the transition of the event-related alpha activity from synchronized to desynchronized state.
350 PHASE-LOCKED FAST CREASES DURING P300
ALPHA
ACTIVITY
IN-
J. Yordanova* and V. Kolev Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev str. bl. 23, 1113 Sofia, Bulgaria The endogenous P300 component of the event-related brain potentials (ERPs) has been associated with cognitive process@ such as memory updating and attention allocation. By quantifying event-related changes in the electroencephalographic (EEG) activity, it has been demonstrated that EEG oscillations in the alpha (7-14 Hz) band manifest a similar sensitivity to conditions engaging attention and memory processes. This similarity in functional responsiveness suggests that event-related alpha activity and P300 may ret&t the same cognitive processes. If this is the case, it may be expected that when P300 emerges as an objective and time-localized marker of specific cognitive processing, alpha EEG activity within the same time period would also vary with task demands. The present study evaluated the effects of auditory oddball task processing on event-related alpha oscillations.generated in the P300 latency range. The task series used to elicit the classical P300 consisted of randomly distributed rare (800 Hz, p = .2) and frequent (1200 Hz, p = 8) tones. The rare tones were targets and required a mental count. ERPs were recorded at Fz, Cz, and Pz sites in nine subjects. Analyses of variance (stimulus x electrode) were performed for P300 amplitude and for the following parameters of alpha activity within P300 latency range (250-600 ms): power of phase-locked oscillations, power of non-phase-locked oscillations, and stability of phase-locking of alpha responses. Slow (7-10 Hz) and fast (lo-14 Hz) alpha oscillations were analyzed separately. Major results demonstrated that both the phase-locked and non-phase-locked alpha oscillations during P300 development were functionally relevant to the oddball task processing: (1) At frontal and central locations, targets produced significantly larger and better synchronized phase-locked lo-14 Hz oscillations than nontargets did. As P300 showed a parietal maximum, the frontally distributed synchronized and enhanced fast alpha oscillations appear to reflect a specific process or state that is functionally linked to the major processes eliciting P300. (21 At the parietal site, targets led to a significantly greater reduction of non-phase-locked 7-10 Hz activity relative
of Psychophysiology
30 (1998)
95-271
to nontargets. The suppression of non-phase-locked and the increase of phase-locked alpha oscillations during P300 development suggest that P300-related cognitive processes tend to be accompanied by ordered and synchronized alpha states.
351 CHARACTERIZATION OF THE DYNAMICS OF CHILDHOOD ABSENCE SEIZURES WITH METHODS OF NONLINEAR SYSTEM ANALYSIS U. Moeller*, M. Feucht, H. Witte and M. Friedrich Institute of Medical Statistics, Computer Sciences and Documentation, Friedrich Schiller University, Jahnstrasse 1, 07740 Jena, Germany Models by means of which one can generate time series in correlation to EEG target signals may help to understand dynamic phenomena underlying the EEG. Since in several studies nonlinearities were found in EEGs of epileptic seizures it is self-evident to use nonlinear (or dynamic) modeling approaches for related attempts. The relevance of a model can be tested comparing characteristics of the nonlinear dynamics obtained for both the EEG and the signal of the model. We present a new nonlinear approach according to this scheme for the analysis of nearly periodic EEG signals [l]. It is demonstrated with scalp EEGs of 14 unprovoked typical (3 c/s) absence seizures of 5 unmedicated patients with childhood absence epilepsy. These data were strictly classified at the Department for Seizure Disorders at the Vienna University Clinic of Neuropsychiatry for Children and Adolescents and further selected according to method-based acceptance criteria A (nonlinear) self-exciting threshold autoregressive (SETAR) model, a surrogate data technique, and a simulation of pure spike-and-wave (SW) signals provided models and 5 types of SW test signals to be compared with the target EEG by means of autocorrelation, correlation dimension, averaged pointwise dimension and largest Lyapunov exponents. The SETAR model exhibited stationary SW dynamics, visually very similar to the EEG target signal, and with clear nonlinear structure. According to the results, the EEG episodes investigated represent low-dimensional dynamics and were possibly recorded during nonstationary periods. The methods used did not provide arguments that justify the assumption of deterministic chaos. From the results one may conclude that two global oscillatory modes are present for the SETAR model, and three modes are active during the EEG recording periods.
352 WORKING MEMORY INDUCES EEG ENCE CHANGES IN NORMAL SUBJECTS
COHER-
Albert0 Yorio*, Irene Brauer, Claudia Marro and Enrique T Segura Instituto de Biologia y Medicina Experimental (CONICET), Vuelta de Obligado 2490, 1428 Argentina