- Email: [email protected]
Event related potentials II
S50
GUIDED POSTER SESSIONS
I,s-o4.o l
Event related potentials II
Stimulus-dependent processing of matching and non-matching items: familiar faces versus abstract patterns. E.V. Mnatsakanian ~ , P. Krn6nen", I.M. Tarkka". "Brain Research and Rehabilitation Center Neuron and Department of Neurology and Neuroscience, Kuopio University Hospital Kuopio, Finland. Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia. Pairs of matching/non-matching items (words, pictures, faces) elicit differential brain responses. Electrical scalp-recorded components with peak latencies around 350-400 ms are still debated. Our purpose was to differentiate electrical brain activity related to thejudgemant on familiar face or abstract pattern identity. Nineteen healthy right-handed subjects participated in the study. The stimuli were physieaUy identical, grayscale photographs of faces with superimposed dotted meaningless patterns, and the choice of item to compare depended on the cue. Subjects had to judge whether they had seen the same person (or pattern) in a pair, and press a corresponding button. EEG was recorded with 128-channel net with Cz reference. Analysis was made for the 600 ms from the onset of the second stimulus in the pair, for correct performance only. The waveforms had distinct components around 130-150 ms, 180-200 ms, 260-280 ms, 380-400 ms and 500 ms. Although the match/ non-match effect was spotted in almost all components (<0.05, two-tailed), the largest dissimilarities were seen after 300 ms. For faces, large and widespread differences were in 300-520 ms, in both anterior regions (largest for prefrontal areas, more for the left hemisphere), and in the left posterior regions. For patterns the differences were located anteriorly, around 320-400 ms. Non-matching faces elicited a distinct component with peak latency at 400 ms. This was not seen in matching faces. Unlike face comparisons, both matching/non-matching patterns elicited this component, although of smaller magnitude. The stimulus-invariant match/non-match effect was present only for prefrontal sites (with left preponderance) in the range of 320-540 ms. Thus, the component with peak latency at 400 ms is modulated by several variables including match/non-match effect and the type of stimulus.
Auditory event-related potentials during diminished arousal levels. H.Yppfiril~i.S.Westeren-Punnonen, T.Musialowiez, M.Hynynen, J.Karhu and J.Partanen. Kuopio University Hospital Kuopio, Finland. In order to study inlbrmation processing during deep sedation, event-related potentials (ERPs) were recorded from 25 patients scheduled tbr an elective cardiopulmonary bypass operation with propofol/alfentanil/isofturane/ pancuronium anaesthesia. Postoperative sedation was maintained with propofol to keep the sedation level between Ramsay Score 4 (asleep, brisk response to commands) and 6 (not responding to any commands) until patients were hemodynamically stable. ERPs were recorded with passive oddball paradigm from electrode locations Fz, Cz, C3 and C4 one day before the operation (baseline), immediately after the operation and after the patient had opened his eyes for the first time. During deep sedation (Ramsay Score 6) ERP waves were observed in 20/25 patients but in 5/25 patients ERPs could not be identified. In 9 patients only N I00 component was visible and in 11 patients two components, N 100 and"P375", were clearly recognisable. N 100 and "P375" were larger for the deviant stimuli than for standard stimuli. "P375" components were further studied according to preceding standard tones. "P375" did not show any habituation or change in amplitude or latency depending on the number of preceding standard tones. The latency of N 100
component was significantly increased and the amplitude decreased compared to the baseline recording. Patients in deep sedation were divided into three groups according to the appearance of ERP waveforms. No differences in background EEG between the groups were noticed in any quantitative parameter. In light sedation (Ramsay Score 4) ERP waves were observed in all patients. The latency and amplitude values were recovered closer to the baseline values, but the difference was still significant. The results suggest that auditory information processing continues during sedation up to a certain level of cognition. The appearance o f different components during deep sedation might reflect different stages in awakening which cannot be determined by EEG and Ramsay Score.
Effects of a small dose of Triazolam on cognitive function and resting EEG. IF'.L~ngeri, A. Polo, *R. Camisasca, *L. Squassante, *L. Ziviani, *S. Milleri,
Verona University, Verona,Ital): *Glaxo WellcomeS. p. A., Medicine Reseamh Center, Verona,Italy. We conducted a randomised, double-blind, placebo-controlled study with nine young healthy male volunteers, 18-35 years, fight handed, three period cross-over: one with triazolam (TRZ) 0.125 rag, two at different periods with a placebo (PL). Resting electroencephalogram (EEG) and event-related potential (ERP) under oddball paradigm were recorded before drug administration and 2, 4, and 8 hours afterward; blood samples for determination of TRZ plasma levels were taken pre-dose and 0.5, 1, 2, 4, 6, 7 and 8 hours after each dose. We analyzed absolute and relative power data and mean frequencies of alpha and beta-activity, latency and amplitude of P300 wave in Cz and Pz. After TRZ the EEG revealed a significant decrease of alpha (8-12Hz) absolute power in Cz at 2 and 4 h (Cz: 26%, p 0.05; 27%, p 0.014), in Pz (32% p 0.022 at 4 h) and of alpha relative power in Cz at 2 h (TRZ-PL 0.06, p 0.02) with a significant increase of beta-activity (more than 12 Hz) mean frequency at 4 h in Cz (23% p 0.025). We found no significant changes about P300 (mean latency increased at 2 h and mean amplitude decreased at 4 h). TRZ caused a significant modification of EEG parameters without alteration of ERP under auditory simple task. The EEG data showed a variation of alpha band (2- 4 h) more than beta band (4 h) within the pharmacokinetic parameter of a time to maximum observed serum concentrations ( T ) of I hour (min-max 0.5-2).
Effect of a uniform unpatterned visual field on the alpha wave. A.M. Maher, ED. Swift, L. Kirkup, D. Martin. Univers'iO"of Technology.
Sydney, Sydney. NSW, Australia. The work of Lehtonen and Lehtinen [Electroenceph. Clin. Neurophysiol., 1972, 32(2), pp 139-147] has led to general acceptance of the view that the behaviour of the electroencepbalographic alpha wave, under conditions of eyes open in a uniform visual field, resembles the alpha wave when eyes are closed. The work reported here investigated the effect on the alpha wave of a uniform, unpatterned visual field. A large, custom built, integrating sphere was used to provide a uniform illuminance of 30 lux to the entire visual field, in addition to a complete lack of visual detail. 17 volunteers participated (mean age 26 yrs) and 16 of these subjects exhibited an increase in the alpha wave amplitude when the visual field was uniform and unpatterned. The average increase in amplitude with eyes open in this field was 38%, relative
Event related potentials H
to eyes open in a patterned field and a furtl3er 35% increase in amplitude following eye closure was measured. A Repeated Measures ANOVA analysis showed that there is a statistically significant difference (p<0.01) in the mean amplitude of the alpha wave, between the situations of eyes open in a patterned field, relative to eyes open in an unpattemed, uniform field. The difference in means, as indicated by the Repeated Measures ANOVA, is however, of much greater statistical significance (p
Intracerebral recordings of ERD/ERS and P3 in visual oddball paradigm. D. Sochurkova ~,M. Br'~dzddI, P. Jurak-, I. Rektor I. Departement of Neurology, Masaryk University, Saint-Anne Hospital. Brno, Czech Republic; - Laboratory of NMR electronics, Institute of Scientific Instruments, Academy of Sciences, Brno, Czech Republic. Event-related potentials (ERP) reflect phase-locked responses to event. On the other hand, an event-related desynchronization/synchronization (ERD/ERS) reflects non-phased locked changes of the rhythmical background activity. The aim of our study was to investigate concurrent occurrence of E RPs and ERD/ ERS intracerebrally in subjects performing visual oddball task. Six patients with an average age of 31.6 years, all with medically intractable epilepsy, participated in the study. Depth electrodes were inserted to localise the seizure origin prior to surgical treamaent. EEG activity from mesiotemporal limbic structures (amygdala, hippocampus and parahippocampal gyrus) was analysed using two methods: 1. Averaging procedure to obtain ERPs. The sites with the occurrence of P3 generator were chosen for further analysis. 2. Complex demodulation in frequency bands ~, o~1, cx2., 13 and ~/to obtain ERD/ERS. Prior to the quantification the averaged ERPs were subtracted from each trial. ERD/ERS to target and non-target stimuli were evaluated. We observed two changes in oscillatory activities after the target stimuli: ERS in theta frequency band preceding the P3 potential and ERD in lower and in upper alfa frequency bands. No apparent ERD/ERS changes were found in gamma frequency band in our data. in response to the non-target stimuli, only subtle non-significant power changes were fuund. The cognitive processing of visual information is accompanied by several eleetrophysiological phenomena. Beside the phase-locked ERPs, changes of the oscillatory activity were detected in intracerebral recordings.
Event related potentials in children with AIDS. M.J. SemariA,L. Czornyj,A.M. Soprano, N. Fejerman,C. Medina. Garrahan Hospital, Buenos Aires, Argentina. Though HIV Associated Encepahalopathy (HAE) is the most common CNS complication of AIDS in children. There are no reports about Event Related Potentials (ERP) in this condition, as far as we know. We assessed ERP abnormalities in children with AIDS, correlating those results with the neurological, neuropsychological and neuroimaging findings. We studied 19 children with AIDS (I I girls, aged between 4 and 10 yrs). Fifteen of them had diagnosis of mild HAE. All patients underwent complete neurological history and examination, as well as Brain CT Scan and/or MRI. Neuropsychological assessment included IQ measurement (NEMI or WISC tests) and gmpho-motor skills (GMS) (Bender Test). ERP were obtained through a go auditory odd-ball paradigm consisting of a pseudo-randomized merge of rare tones (2 KHz, probability 20%) and frequent tones (1 kHz) delivered through earphones with an inter-stimuli interval of 2 sees. Signals were recorded from Cz and referred to bi-mastoid electrodes. Low and high filters were 0.15 and 30 Hz respectively; the analysis time was 1000 ms, and 30 responses to the rare stimulus were averaged. P300 latencies were normalized as SD of the mean expected value for each patient age. Patients in whom P300 was absent or who had latencies beyond the mean control value showed a significantly lower IQ (92.5 + 12.1; n=8) than those with shorter P300 latencies ( 102.2 + ! 1.8; n- 11) (p<0.05). Six patients had absolute abnormalities of P300 (absent in 2 and delayed beyond 2.5 SD over the mean control value in the other 4) and presented a lower IQ and GMS than the
$51
remainder. Five o f these patients had diagnosis o f HAE; half o f them presenting pyramidal signs. While only 4 out o f the 13 patients with normal P300 had abnormal neuroimaging studies, 5 out o f 6 with abnormal P300 potentials showed either brain atrophy or demyielinating lesions. Finally, patients with abnormal P300 were significantly older (mean age 8 + 1.2 yrs) than those with normal results (mean age 6 + 1.7 yrs) (p<0.02). Our results suggest that P300 has a moderate sensibility to detect cognitive impairment in children with mild HAE. Nevertheless, this test identifies those with lower IQ and GMS, as well as those with more frequent abnormal neuroimaging studies and with longer disease duration.
N400 effect during different sleep stages. V. L6nez Hernhndez, L. Carmenate Mili~in, A. Alvarez Amador. Cuban
Neuroscience Center, Cuba. The main purpose of this work was to establish whether semantic processing continues or not during different sleep stages. Polygraphic recordings were obtained on two consecutive nights from 10 healthy adult subjects (five females, five males) during wakefulness, before and after sleep (A) and during II, Ill-IV and REM sleep stages (B). Pairs of words (category-exemplar) were delivered binaurally through earphones. The exemplars belonged to the associated category in fit'cy percent of the trials. In none of the previous conditions were the subjects asked to give any type of answer. A week later, recording during wakefulness (C), subjects were asked to pay attention to the lists and press a key in response to unrelated pairs of words. ERP were obtained averaging EEG segments of 1048 ms. Wakefulness recordings showed a significant N400 effect, although the onset latency was prolonged in condition C compared to A. Results were similar on both nights studied. A significant N400 effect was found on REM and Ill-IV sleep stages. During stage I! the effect did not reach the statistical significance level. Recordings obtained the morning after the night of the study showed a significant decrease of N400 amplitude. It was concluded that there is some kind of semantic processing during sleep. These results support the hypotheses that semantic processing is a lexical processing without awareness and N400 is a reflection of an automatic process.
Relations between the target and non target response of the 1'300 event related potentials in cognitive deterioration. F. Ferrando. A.M. Garcia, D.S. Adamec, F. Oddo, J.O. Prost. Section of Neurophysiology - Unit of Neurology, Bernardino Rivadavia General Hospital, Buenos Aires, Argentina. In P 300 event-related potentials, obtained by odd-ball paradigm, a response to a target tone and another to a non target tone were measured. In nonrml subjects these responses differ in their latencies and amplitudes. A P 300 event-related potential was measured in 312 subjects to determine differences in the latencies o f the precocious components of both responses: those from normal patients and those from patients with cognitive deterioration. The subjects studied (all older than 5 I), were divided into two groups: patients with cognitive deterioration and healthy volunteers. A potential was developed by tonal stimulation, with count task of the target stimulus. The response was chosen from the Cz-M 1derivation of the system 10-20. The latencies and amplitudes of N I, P2 and N2 waves and N I -P2 and P2-N2 times were quantified, in both responses: target and non-target. The variables were analyzed by a two way ANOVA. Differences were not observed in the N 1 and P2 waves latency, neither in the amplitude of any of the waves, nor in N I-P2 time. The difference in N2 wave latency (p <0.001 ) and in P2-N2 time (p <0.001 ) for the interaction of the deterioration variables and response type (target/ non target), was highly significant. These discoveries suggest that the relationship between the response to the target stimulus and the non target stimulus would be helpful in the diagnosis of cognitive deterioration.
S52
Event related potentials I J
Influence of the count task and passive discrimination in the long latency auditory responses. R. Linares, A.M. Garcia, D.S. Adamec, G. Prada, J.O. Prost. Section of Neurophysiology - Unit o f Neurology. Bernardino Rivadavia General Hospital, Buenos Aires, Argentina. The long-latency evoked responses evaluate neuropsychological factors such as attention, anxiety level and processing speed. The characteristics of the obtained response are conditioned by the task undertaken by the subject. We studied 30 healthy voluntaries, with an average age of 43.8 + 10.3 years, to evaluate the influence of attention and discrimination of those potentials. We instigated successively: 1- a long latency evoked potential (PEALL). 2- a PEALL with a task: the patient had to count all the tones, with the objective of fixing his attention (PEALL-C). 3- an event-related potential (P300), obtained by an odd-ball paradigm, in which we analyzed the response to non-target tone, or frequent tone (FT). The stimulus characteristics were constant for the different situations: we used a burst tone of 30 ms duration, with 75 dB intensity, and a frequency of presentation of one stimulus every two seconds. Significant differences were obtained among the N2 latencies, and among the N1 ,P2 and N2 amplitudes. N2 latency was minor in FT response. N I amplitude was different between PEALL-C and FT. P2 amplitude was greater in PEALL-C responses. N2 amplitude was different in the three situations. We concluded that the discrimination process provoked a N2 wave with minor latency, while the amplitude was greater when the patient attended to the stimulus and less when the process was interfered with by a discrimination task.
GUIDED POSTER SESSIONS
I,s-o4.o l
Event related potentials II
Stimulus-dependent processing of matching and non-matching items: familiar faces versus abstract patterns. E.V. Mnatsakanian ~ , P. Krn6nen", I.M. Tarkka". "Brain Research and Rehabilitation Center Neuron and Department of Neurology and Neuroscience, Kuopio University Hospital Kuopio, Finland. Institute of Higher Nervous Activity and Neurophysiology RAS, Moscow, Russia. Pairs of matching/non-matching items (words, pictures, faces) elicit differential brain responses. Electrical scalp-recorded components with peak latencies around 350-400 ms are still debated. Our purpose was to differentiate electrical brain activity related to thejudgemant on familiar face or abstract pattern identity. Nineteen healthy right-handed subjects participated in the study. The stimuli were physieaUy identical, grayscale photographs of faces with superimposed dotted meaningless patterns, and the choice of item to compare depended on the cue. Subjects had to judge whether they had seen the same person (or pattern) in a pair, and press a corresponding button. EEG was recorded with 128-channel net with Cz reference. Analysis was made for the 600 ms from the onset of the second stimulus in the pair, for correct performance only. The waveforms had distinct components around 130-150 ms, 180-200 ms, 260-280 ms, 380-400 ms and 500 ms. Although the match/ non-match effect was spotted in almost all components (<0.05, two-tailed), the largest dissimilarities were seen after 300 ms. For faces, large and widespread differences were in 300-520 ms, in both anterior regions (largest for prefrontal areas, more for the left hemisphere), and in the left posterior regions. For patterns the differences were located anteriorly, around 320-400 ms. Non-matching faces elicited a distinct component with peak latency at 400 ms. This was not seen in matching faces. Unlike face comparisons, both matching/non-matching patterns elicited this component, although of smaller magnitude. The stimulus-invariant match/non-match effect was present only for prefrontal sites (with left preponderance) in the range of 320-540 ms. Thus, the component with peak latency at 400 ms is modulated by several variables including match/non-match effect and the type of stimulus.
Auditory event-related potentials during diminished arousal levels. H.Yppfiril~i.S.Westeren-Punnonen, T.Musialowiez, M.Hynynen, J.Karhu and J.Partanen. Kuopio University Hospital Kuopio, Finland. In order to study inlbrmation processing during deep sedation, event-related potentials (ERPs) were recorded from 25 patients scheduled tbr an elective cardiopulmonary bypass operation with propofol/alfentanil/isofturane/ pancuronium anaesthesia. Postoperative sedation was maintained with propofol to keep the sedation level between Ramsay Score 4 (asleep, brisk response to commands) and 6 (not responding to any commands) until patients were hemodynamically stable. ERPs were recorded with passive oddball paradigm from electrode locations Fz, Cz, C3 and C4 one day before the operation (baseline), immediately after the operation and after the patient had opened his eyes for the first time. During deep sedation (Ramsay Score 6) ERP waves were observed in 20/25 patients but in 5/25 patients ERPs could not be identified. In 9 patients only N I00 component was visible and in 11 patients two components, N 100 and"P375", were clearly recognisable. N 100 and "P375" were larger for the deviant stimuli than for standard stimuli. "P375" components were further studied according to preceding standard tones. "P375" did not show any habituation or change in amplitude or latency depending on the number of preceding standard tones. The latency of N 100
component was significantly increased and the amplitude decreased compared to the baseline recording. Patients in deep sedation were divided into three groups according to the appearance of ERP waveforms. No differences in background EEG between the groups were noticed in any quantitative parameter. In light sedation (Ramsay Score 4) ERP waves were observed in all patients. The latency and amplitude values were recovered closer to the baseline values, but the difference was still significant. The results suggest that auditory information processing continues during sedation up to a certain level of cognition. The appearance o f different components during deep sedation might reflect different stages in awakening which cannot be determined by EEG and Ramsay Score.
Effects of a small dose of Triazolam on cognitive function and resting EEG. IF'.L~ngeri, A. Polo, *R. Camisasca, *L. Squassante, *L. Ziviani, *S. Milleri,
Verona University, Verona,Ital): *Glaxo WellcomeS. p. A., Medicine Reseamh Center, Verona,Italy. We conducted a randomised, double-blind, placebo-controlled study with nine young healthy male volunteers, 18-35 years, fight handed, three period cross-over: one with triazolam (TRZ) 0.125 rag, two at different periods with a placebo (PL). Resting electroencephalogram (EEG) and event-related potential (ERP) under oddball paradigm were recorded before drug administration and 2, 4, and 8 hours afterward; blood samples for determination of TRZ plasma levels were taken pre-dose and 0.5, 1, 2, 4, 6, 7 and 8 hours after each dose. We analyzed absolute and relative power data and mean frequencies of alpha and beta-activity, latency and amplitude of P300 wave in Cz and Pz. After TRZ the EEG revealed a significant decrease of alpha (8-12Hz) absolute power in Cz at 2 and 4 h (Cz: 26%, p 0.05; 27%, p 0.014), in Pz (32% p 0.022 at 4 h) and of alpha relative power in Cz at 2 h (TRZ-PL 0.06, p 0.02) with a significant increase of beta-activity (more than 12 Hz) mean frequency at 4 h in Cz (23% p 0.025). We found no significant changes about P300 (mean latency increased at 2 h and mean amplitude decreased at 4 h). TRZ caused a significant modification of EEG parameters without alteration of ERP under auditory simple task. The EEG data showed a variation of alpha band (2- 4 h) more than beta band (4 h) within the pharmacokinetic parameter of a time to maximum observed serum concentrations ( T ) of I hour (min-max 0.5-2).
Effect of a uniform unpatterned visual field on the alpha wave. A.M. Maher, ED. Swift, L. Kirkup, D. Martin. Univers'iO"of Technology.
Sydney, Sydney. NSW, Australia. The work of Lehtonen and Lehtinen [Electroenceph. Clin. Neurophysiol., 1972, 32(2), pp 139-147] has led to general acceptance of the view that the behaviour of the electroencepbalographic alpha wave, under conditions of eyes open in a uniform visual field, resembles the alpha wave when eyes are closed. The work reported here investigated the effect on the alpha wave of a uniform, unpatterned visual field. A large, custom built, integrating sphere was used to provide a uniform illuminance of 30 lux to the entire visual field, in addition to a complete lack of visual detail. 17 volunteers participated (mean age 26 yrs) and 16 of these subjects exhibited an increase in the alpha wave amplitude when the visual field was uniform and unpatterned. The average increase in amplitude with eyes open in this field was 38%, relative
Event related potentials H
to eyes open in a patterned field and a furtl3er 35% increase in amplitude following eye closure was measured. A Repeated Measures ANOVA analysis showed that there is a statistically significant difference (p<0.01) in the mean amplitude of the alpha wave, between the situations of eyes open in a patterned field, relative to eyes open in an unpattemed, uniform field. The difference in means, as indicated by the Repeated Measures ANOVA, is however, of much greater statistical significance (p
Intracerebral recordings of ERD/ERS and P3 in visual oddball paradigm. D. Sochurkova ~,M. Br'~dzddI, P. Jurak-, I. Rektor I. Departement of Neurology, Masaryk University, Saint-Anne Hospital. Brno, Czech Republic; - Laboratory of NMR electronics, Institute of Scientific Instruments, Academy of Sciences, Brno, Czech Republic. Event-related potentials (ERP) reflect phase-locked responses to event. On the other hand, an event-related desynchronization/synchronization (ERD/ERS) reflects non-phased locked changes of the rhythmical background activity. The aim of our study was to investigate concurrent occurrence of E RPs and ERD/ ERS intracerebrally in subjects performing visual oddball task. Six patients with an average age of 31.6 years, all with medically intractable epilepsy, participated in the study. Depth electrodes were inserted to localise the seizure origin prior to surgical treamaent. EEG activity from mesiotemporal limbic structures (amygdala, hippocampus and parahippocampal gyrus) was analysed using two methods: 1. Averaging procedure to obtain ERPs. The sites with the occurrence of P3 generator were chosen for further analysis. 2. Complex demodulation in frequency bands ~, o~1, cx2., 13 and ~/to obtain ERD/ERS. Prior to the quantification the averaged ERPs were subtracted from each trial. ERD/ERS to target and non-target stimuli were evaluated. We observed two changes in oscillatory activities after the target stimuli: ERS in theta frequency band preceding the P3 potential and ERD in lower and in upper alfa frequency bands. No apparent ERD/ERS changes were found in gamma frequency band in our data. in response to the non-target stimuli, only subtle non-significant power changes were fuund. The cognitive processing of visual information is accompanied by several eleetrophysiological phenomena. Beside the phase-locked ERPs, changes of the oscillatory activity were detected in intracerebral recordings.
Event related potentials in children with AIDS. M.J. SemariA,L. Czornyj,A.M. Soprano, N. Fejerman,C. Medina. Garrahan Hospital, Buenos Aires, Argentina. Though HIV Associated Encepahalopathy (HAE) is the most common CNS complication of AIDS in children. There are no reports about Event Related Potentials (ERP) in this condition, as far as we know. We assessed ERP abnormalities in children with AIDS, correlating those results with the neurological, neuropsychological and neuroimaging findings. We studied 19 children with AIDS (I I girls, aged between 4 and 10 yrs). Fifteen of them had diagnosis of mild HAE. All patients underwent complete neurological history and examination, as well as Brain CT Scan and/or MRI. Neuropsychological assessment included IQ measurement (NEMI or WISC tests) and gmpho-motor skills (GMS) (Bender Test). ERP were obtained through a go auditory odd-ball paradigm consisting of a pseudo-randomized merge of rare tones (2 KHz, probability 20%) and frequent tones (1 kHz) delivered through earphones with an inter-stimuli interval of 2 sees. Signals were recorded from Cz and referred to bi-mastoid electrodes. Low and high filters were 0.15 and 30 Hz respectively; the analysis time was 1000 ms, and 30 responses to the rare stimulus were averaged. P300 latencies were normalized as SD of the mean expected value for each patient age. Patients in whom P300 was absent or who had latencies beyond the mean control value showed a significantly lower IQ (92.5 + 12.1; n=8) than those with shorter P300 latencies ( 102.2 + ! 1.8; n- 11) (p<0.05). Six patients had absolute abnormalities of P300 (absent in 2 and delayed beyond 2.5 SD over the mean control value in the other 4) and presented a lower IQ and GMS than the
$51
remainder. Five o f these patients had diagnosis o f HAE; half o f them presenting pyramidal signs. While only 4 out o f the 13 patients with normal P300 had abnormal neuroimaging studies, 5 out o f 6 with abnormal P300 potentials showed either brain atrophy or demyielinating lesions. Finally, patients with abnormal P300 were significantly older (mean age 8 + 1.2 yrs) than those with normal results (mean age 6 + 1.7 yrs) (p<0.02). Our results suggest that P300 has a moderate sensibility to detect cognitive impairment in children with mild HAE. Nevertheless, this test identifies those with lower IQ and GMS, as well as those with more frequent abnormal neuroimaging studies and with longer disease duration.
N400 effect during different sleep stages. V. L6nez Hernhndez, L. Carmenate Mili~in, A. Alvarez Amador. Cuban
Neuroscience Center, Cuba. The main purpose of this work was to establish whether semantic processing continues or not during different sleep stages. Polygraphic recordings were obtained on two consecutive nights from 10 healthy adult subjects (five females, five males) during wakefulness, before and after sleep (A) and during II, Ill-IV and REM sleep stages (B). Pairs of words (category-exemplar) were delivered binaurally through earphones. The exemplars belonged to the associated category in fit'cy percent of the trials. In none of the previous conditions were the subjects asked to give any type of answer. A week later, recording during wakefulness (C), subjects were asked to pay attention to the lists and press a key in response to unrelated pairs of words. ERP were obtained averaging EEG segments of 1048 ms. Wakefulness recordings showed a significant N400 effect, although the onset latency was prolonged in condition C compared to A. Results were similar on both nights studied. A significant N400 effect was found on REM and Ill-IV sleep stages. During stage I! the effect did not reach the statistical significance level. Recordings obtained the morning after the night of the study showed a significant decrease of N400 amplitude. It was concluded that there is some kind of semantic processing during sleep. These results support the hypotheses that semantic processing is a lexical processing without awareness and N400 is a reflection of an automatic process.
Relations between the target and non target response of the 1'300 event related potentials in cognitive deterioration. F. Ferrando. A.M. Garcia, D.S. Adamec, F. Oddo, J.O. Prost. Section of Neurophysiology - Unit of Neurology, Bernardino Rivadavia General Hospital, Buenos Aires, Argentina. In P 300 event-related potentials, obtained by odd-ball paradigm, a response to a target tone and another to a non target tone were measured. In nonrml subjects these responses differ in their latencies and amplitudes. A P 300 event-related potential was measured in 312 subjects to determine differences in the latencies o f the precocious components of both responses: those from normal patients and those from patients with cognitive deterioration. The subjects studied (all older than 5 I), were divided into two groups: patients with cognitive deterioration and healthy volunteers. A potential was developed by tonal stimulation, with count task of the target stimulus. The response was chosen from the Cz-M 1derivation of the system 10-20. The latencies and amplitudes of N I, P2 and N2 waves and N I -P2 and P2-N2 times were quantified, in both responses: target and non-target. The variables were analyzed by a two way ANOVA. Differences were not observed in the N 1 and P2 waves latency, neither in the amplitude of any of the waves, nor in N I-P2 time. The difference in N2 wave latency (p <0.001 ) and in P2-N2 time (p <0.001 ) for the interaction of the deterioration variables and response type (target/ non target), was highly significant. These discoveries suggest that the relationship between the response to the target stimulus and the non target stimulus would be helpful in the diagnosis of cognitive deterioration.
S52
Event related potentials I J
Influence of the count task and passive discrimination in the long latency auditory responses. R. Linares, A.M. Garcia, D.S. Adamec, G. Prada, J.O. Prost. Section of Neurophysiology - Unit o f Neurology. Bernardino Rivadavia General Hospital, Buenos Aires, Argentina. The long-latency evoked responses evaluate neuropsychological factors such as attention, anxiety level and processing speed. The characteristics of the obtained response are conditioned by the task undertaken by the subject. We studied 30 healthy voluntaries, with an average age of 43.8 + 10.3 years, to evaluate the influence of attention and discrimination of those potentials. We instigated successively: 1- a long latency evoked potential (PEALL). 2- a PEALL with a task: the patient had to count all the tones, with the objective of fixing his attention (PEALL-C). 3- an event-related potential (P300), obtained by an odd-ball paradigm, in which we analyzed the response to non-target tone, or frequent tone (FT). The stimulus characteristics were constant for the different situations: we used a burst tone of 30 ms duration, with 75 dB intensity, and a frequency of presentation of one stimulus every two seconds. Significant differences were obtained among the N2 latencies, and among the N1 ,P2 and N2 amplitudes. N2 latency was minor in FT response. N I amplitude was different between PEALL-C and FT. P2 amplitude was greater in PEALL-C responses. N2 amplitude was different in the three situations. We concluded that the discrimination process provoked a N2 wave with minor latency, while the amplitude was greater when the patient attended to the stimulus and less when the process was interfered with by a discrimination task.