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P4-9 The effect of mastication on human cognitive processing: A study using event-related potentials
S122 connected to serotonergic system. The mismatch negativity (MMN) and P300 components of event-related potential (ERPs) were used. MMN is now already used as a clinical tool, therefore, revealing its genetic underpinnings is very important. Methods: 54 male participants took part in the research. EEG was recorded using 256-channel EGI system. Optimal oddball paradigm was used. Aggressiveness score was assessed by Buss-Durkee Hostility Inventory. Results: The averaged Hostility scores were higher for the carriers of LLgenotype. The increased MMN component of ERP, which responsible for the automatic change detection, and decreased P3a component, related to involuntary attention and cognitive control were found in LL-carries. Conclusions: It might be considered as a sign that SS-carries process the information with more cognitive resources. Probably they perceive the stimulus as more complicated, which lead to activation the additional resources of frontal cortex. It might be also suggested that the carries of SS-genotype tend to deeper processing of the incoming information. Probably, it is this more serious analysis of external information, which underlies the rejection of impulsive aggressive actions. P4-6 Is the mismatch negativity a symmetrical measure of change? Mathematico-philosophical and experimental investigations I.L. Freire1 , C.J. Tierra-Criollo2 , H.C. Yehia1 CEFALA, Center for Research on Speech, Acoustics, Language and Music, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil, 2 NEPEB, Nucleus for Study and Research in Biomedical Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil 1
Objective: The presentation of a rigorous methodology for examining the effects of deviance direction on the MMN and the application of this methodology to the special case of MMN to pitch differences. Methods: Standard and deviant stimuli are presented in experimental blocks according to the oddball paradigm. The magnitude of change and the probability of deviant are always the same, but deviance direction varies. Side-effects of physical stimuli on the MMN waveform are eliminated by comparing event-related potentials (ERPs) obtained from the same physical stimulus presented in roles of standard and deviant. Depending on the symmetry properties of the metric function chosen for the domain of physical stimuli, two or three blocks in the oddball paradigm are needed to compute two MMN’s to changes of same magnitude and opposite direction. Stimuli were three-harmonic tones of 196.0 and 466.2 Hz. The metric function is the absolute difference between the fundamental frequencies measured in Hertz. ERPs were recorded on seven subjects. Effects of deviance direction on peak latency and amplitude were measured by Cohen’s d, from various subsamples of ERPs, each of which determined a peak latency and amplitude. Results: The MMN computed from ERPs to the higher tone presented higher amplitude and higher latency than the MMN computed from ERPs to the lower tone. Conclusion: The question of whether the MMN is a symmetrical measure of change is ill-defined in the absence of a choice of metric function for the space of physical stimuli. In particular, the MMN behaves as an asymmetric measure of change under the metric function hereby chosen for the domain of physical stimuli, namely, the absolute difference, in Hertz, between fundamentals of three-harmonic tones. P4-7 Mismatch negativity in Williams syndrome: a window for understanding auditory oversensitivity O. Zarchi1,2,4 , L. Saporta1,2 , J. Attias4,5 , C. Avni1 , D. Gothelf1,3 The Behavioral Neurogenetics Center, Schneider Children’s Medical Center of Israel, Petah Tiqwa, Israel, 2 The Interdisciplinary Ph.D. Program in Neuroscience, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel, 3 Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel, 4 The Institute for Clinical Neurophysiology and Audiology, Schneider Children’s Medical Center of Israel, Petah Tiqwa, Israel, 5 Department of Communication Disorders, Haifa University, Haifa, Israel 1
Objective: To identify central auditory processing abnormalities in Williams syndrome (WS). Methods: Mismatch Negativity (MMN) ERPs were recorded from 12 subjects with WS (mean age ±SD = 17.2±7.5, 5 miles), 13 subjects with idiopathic developmental disability (DD; 20.0±6.2, 6 miles) and
Posters 25 subjects with velocardiofacial syndrome (VCFS; 22.3±10.4, 11 miles). MMN responses to changes in frequency, intensity, duration, location, and to a silent gap occasionally inserted in the middle of a tone were evaluated using a novel paradigm of N¨ aa ¨t¨ anen et al. (2004). Results: In comparison to the DD and VCFS groups the WS group displayed enhanced MMN amplitudes for frequency deviation, significant over frontal and central electrodes. In addition, reduced MMN amplitudes in response to intensity deviation were found in the WS compared to the DD and VCFS groups, significant in electrodes over all scalp regions. Conclusions: The preliminary MMN results support a unique auditory processing pattern in WS. Results are in line with the oversensitivity to sounds (hyperacusis) and the special musical abilities including ‘perfect pitch’, which are among the most salient features of the syndrome. Relations between auditory processing abnormalities and candidate genes from the WS minimal deleted region are discussed. P4-8 The effects of cholesterol and CYP46 polymorphism on cognitive event-related potentials C.-L. Lai1,2 , C.-Y. Hsu1,2 , H.-Y. Hsieh1 , C.-K. Liu1,2 Department of Neurology, Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan, 2 Department of Neurology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
1
Objective: For the rapidly aging population and the consequent increase in dementia patients, to identify the putative factors and preventive strategies of cognitive impairment has become a major clinical and public issue. The aims of the present study are to investigate the influence of cholesterol and CYP46 genotypes on cognitive event-related potentials (ERPs) and to determine whether there is an interactive effect between cholesterol level and CYP46 genotypes to ERPs. Methods: Using the Cognitive Abilities Screening Instrument (CASI), 145 mental healthy middle-aged and older adults were recruited. All participants were assessed for lipid profile, CYP46 polymorphism, and auditory P300 even-related potentials. Results: When the participants were stratified according to the levels of total cholesterol and high-density lipoprotein cholesterol (HDL-C), there was no difference in age, educational level, CASI scores, measures of P300, and the percentage of CYP46 polymorphism. In contrast, the subjects with high low-density lipoprotein cholesterol (LDL-C) level exhibited significant low amplitude at Pz lead and prolonged latency at Cz lead than those with normal LDL-C level after adjusted by age and sex, although the CASI scores and percentage of CYP46 polymorphism showed no difference between the two groups. The ages, educational level, CASI scores, components of cholesterol levels, and measures of P300 are compared according to the CYP46 polymorphism, revealing similar values for most items. There is no interaction between LDL-C level and CYP46 genotypes on cognitive ERPs. Conclusions: Our findings imply that LDL-C level is an independent predictor of low amplitude and long latency of P300. There is no association between CYP46 genotypes and P300 ERPs in normal elderly subjects. A combined effect of the cholesterol level and CYP 46 genotypes in cognitive ERPs was not present in this study. P4-9 The effect of mastication on human cognitive processing:A study using event-related potentials K. Sakamoto1,2 , H. Nakata2,3 , R. Kakigi2 1 Advanced Research Institute for the Sciences and Humanities (ARISH), Nihon University, Tokyo, Japan, 2 Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan, 3 Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan Objective: The purpose of the present study was to clarify the effect of mastication on cognitive processing using reaction time (RT) and eventrelated potentials (ERPs). Methods: The two experiments consisted of two conditions, Mastication (chewing gum) and Control (relaxing without chewing gum) in Experiment 1, and Jaw Movement (opening and closing the jaw) and Finger Tapping (tapping the right index finger) in Experiment 2. The subjects performed four sessions of an auditory oddball paradigm. RT and ERPs were recorded in these four sessions, Pre (before chewing), and Post 1, Post 2 and Post 3 (after chewing). Results: In Mastication for RT and the peak latencies of P300 and N100, the values were significantly longer in Pre than in Post 2 or Post 3.
29th International Congress of Clinical Neurophysiology By contrast, in Control, Jaw Movement, and Finger Tapping, they were almost identical among sessions or significantly shorter in Pre than in Post 2 or Post 3. Conclusions: Mastication influences cognitive processing time as reflected by RT and the latency of ERP waveforms. Significance: This is the first study investigating the effect of mastication on the central nervous system using event-related potentials. P4-10 Computer games training may affect normative values of some event related potentials in children J.I.S. Farina1 , T. Schaefer1 , V.K. Lopes1 , S. Moojen1 , F. Loureiro1 , A. Schilikman1 1 Cognitive Neurology Group, Department of Neurology and Neurosurgery, Moinhos de Vento Hospital, Porto Alegre, Brazil Objective: Reaction times became faster as the subject is better trained in certain tasks. The aim of this paper was to find out if central processing speed as measured by event evoked responses latencies would reflect these changes. Methods: Event related evoked potentials (auditory odd-ball paradigm) were recorded in 22 normal children from a third grade class after completing tests and teacher interview showing good educational achievement (average or better) and no behavior or neurological problems. Latencies of the N100, P200 and P300 components were analyzed as well as the time devoted to computer games in a week trough Spearman correlation test. The amplitudes of the components were analyzed through Pearson correlation test. Results: A strong positive correlation was found for the latencies of N100 (r = 0.91, p = 0.001) and P200 (r = 0.88, p = 0.001) and the number of hours of computer games activities in this group. A strong negative correlation was found for P200 amplitudes. Discussion: These preliminary results point out to the need to reviewing some normative values of the event related responses in children taking account the time they regularly spend in computer games. The correlations found in this paper show the possible important role of the primary processing speed itself underling the reaction time modifications in these tasks. P4-11 Effects of odor on event-related potential (P300) and pleasantness H. Akimoto1 , T. Sugiura1 , I. Takahashi2 , H. Hirata1 , Y. Okita2 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan, 2 Graduate School of Electronic Science and Technology, Hamamatsu, Shizuoka University, Japan
1
Objective: Smell is considered to be the most primitive sense and the region of rhinencephalon (smell-brain) is right next door to the limbic system, the regions of human brain that control the most basic functions for life. Because of this proximity, many scientists are convinced that certain pleasant odors are able to stimulate the brain in a manner that instigates brain response. However, there are controversial findings on the effects of odor stimuli on the cognitive task performance in the form of P300 activity. The present study examines the effects of odors on both P300 amplitude and its peak latency while conducting simple auditory oddball tasks. Methods: The subjects were 6 male university students, between 22 and 24 years of age. The standard stimulus was a 1,000 Hz tone (P = 0.85 0.75) and the target stimulus was a 2,000 Hz tone (P = 0.15 0.25). Both tones were presented for 100 ms. While pleasant odor (5% geraniol) or unpleasant odor (hexa-1,5-diyne in pentane) were presented at 5 cm under their noses, subjects were instructed to count the number of the target tones. Results: Results showed that P300 amplitudes for unpleasant odor were lower in 4 subjects than that for pleasant odor while P300 latencies were shorter in 5 subjects for unpleasant odor than for pleasant odor. Conclusions: These findings indicate that odor has an influence on emotion and the unpleasant odor used in this study might increase the vigilance level.
S123 P4-12 Influence of parameters of the Sternberg memory task (the set size and probe item affiliation) on cognitive event-related potentials M. Krbot1 , A.B. Sefer1 , V. Isgum2 , M. Cifrek3 University of Zagreb, Zagreb, Croatia, 2 University Hospital Zagreb, Department of Neurology, Zagreb, Croatia, 3 Faculty of Electrical Engineering and Computing, Department of Electronic Systems and Information Processing, Zagreb, Croatia 1
The main field of interest of this study is cerebral dynamics that occur as a result of memorizing and retrieving information from working memory. A modified Stenberg memory task with auditory stimuli was performed. We recorded cognitive event-related potentials evoked by the memory task. Participants were healthy adults with no cognitive or auditory impairments. During the Sternberg experiment, sets of two or four digits were presented to subjects. Three seconds after the last item in the set, the target digit (probe) was presented. By pressing appropriate buttons participants had to indicate whether the probe did (positive probe) or did not (negative probe) belong to the presented set. According to results the reaction time increases with the increase of the memory set size. The activity in the period in which participants rehearse the previously presented set is stronger expressed for the set consisted of two digits. For the set of two digits the major positive wave (MPW) appears earlier and its amplitude is greater than for the set of four digits. The amplitude of the MPW is greater for the positive probe than for the negative probe, and the latency of the MPW evoked by the negative probe is greater than for the positive probe. Obtained results are in accordance with the presently accepted theory, and also offer interesting features for further research. P4-13 Event-related potentials to target and distractor: localization of the P300 cortical sources by swLORETA P. Bocquillon1,2,3 , J.-L. Bourriez2,3 , E. Palmero-Soler4 , N. Betrouni1,5 , E. Houdayer2,3 , P. Derambure1,2,3 , K. Dujardin1,2,6 1 Universite Lille Nord de France, UDSL, France, 2 Lab. Neurosciences Fonctionnelles et Pathologies, CNRS, FRE 3291, France, 3 Clinical Neurophysiology Department, Lille University Medical Center, France, 4 eemagine Medical Imaging Solutions GmbH, Germany, 5 INSERM U703 Unit, France, 6 Neurology and Movement Disorders Department, Lille University Medical Center, France Objective: Cognitive event-related potentials (ERPs), especially P300, have been used for long to explore attention processes. Their cortical generators are still controversial. The aim of this study is to identify the cortical areas involved in the generation of the P300 wave components. Methods: 15 healthy controls underwent a high density EEG recording (128 channels) during a three stimulus visual oddball paradigm, allowing to identify distractor and target-elicited P300 components. Repeatedmeasures analyses of variances (ANOVAs) were performed on the latency and amplitude data. The P300 individual sources were localized with the swLORETA method and comparison analyses were performed using SPM5 (one sample and paired T-tests). Results: ANOVAs on latency and amplitude data confirm known P300 features. Common sources for both P300 components were observed in a large fronto-parietal network, including the frontal eye field and dorsal parietal cortex, also known as the dorsal fronto-parietal network (p < 0.0005). In addition, more inferior parietal areas, prefrontal and cingulated cortices, corresponding to the ventral frontoparietal network, were involved in the generation of target-elicited P300 (p < 0.005). Conclusions: These results suggest that genesis of P300 elicited by both distractor and target stimuli involves a common dorsal frontoparietal network, while target detection also requires a specific ventral network. These data agree with results of previous studies using different methods. They help to improve our knowledge of the anatomical networks underlying attention processes.
Objective: The presentation of a rigorous methodology for examining the effects of deviance direction on the MMN and the application of this methodology to the special case of MMN to pitch differences. Methods: Standard and deviant stimuli are presented in experimental blocks according to the oddball paradigm. The magnitude of change and the probability of deviant are always the same, but deviance direction varies. Side-effects of physical stimuli on the MMN waveform are eliminated by comparing event-related potentials (ERPs) obtained from the same physical stimulus presented in roles of standard and deviant. Depending on the symmetry properties of the metric function chosen for the domain of physical stimuli, two or three blocks in the oddball paradigm are needed to compute two MMN’s to changes of same magnitude and opposite direction. Stimuli were three-harmonic tones of 196.0 and 466.2 Hz. The metric function is the absolute difference between the fundamental frequencies measured in Hertz. ERPs were recorded on seven subjects. Effects of deviance direction on peak latency and amplitude were measured by Cohen’s d, from various subsamples of ERPs, each of which determined a peak latency and amplitude. Results: The MMN computed from ERPs to the higher tone presented higher amplitude and higher latency than the MMN computed from ERPs to the lower tone. Conclusion: The question of whether the MMN is a symmetrical measure of change is ill-defined in the absence of a choice of metric function for the space of physical stimuli. In particular, the MMN behaves as an asymmetric measure of change under the metric function hereby chosen for the domain of physical stimuli, namely, the absolute difference, in Hertz, between fundamentals of three-harmonic tones. P4-7 Mismatch negativity in Williams syndrome: a window for understanding auditory oversensitivity O. Zarchi1,2,4 , L. Saporta1,2 , J. Attias4,5 , C. Avni1 , D. Gothelf1,3 The Behavioral Neurogenetics Center, Schneider Children’s Medical Center of Israel, Petah Tiqwa, Israel, 2 The Interdisciplinary Ph.D. Program in Neuroscience, Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel, 3 Sackler School of Medicine, Tel Aviv University, Tel Aviv, Israel, 4 The Institute for Clinical Neurophysiology and Audiology, Schneider Children’s Medical Center of Israel, Petah Tiqwa, Israel, 5 Department of Communication Disorders, Haifa University, Haifa, Israel 1
Objective: To identify central auditory processing abnormalities in Williams syndrome (WS). Methods: Mismatch Negativity (MMN) ERPs were recorded from 12 subjects with WS (mean age ±SD = 17.2±7.5, 5 miles), 13 subjects with idiopathic developmental disability (DD; 20.0±6.2, 6 miles) and
Posters 25 subjects with velocardiofacial syndrome (VCFS; 22.3±10.4, 11 miles). MMN responses to changes in frequency, intensity, duration, location, and to a silent gap occasionally inserted in the middle of a tone were evaluated using a novel paradigm of N¨ aa ¨t¨ anen et al. (2004). Results: In comparison to the DD and VCFS groups the WS group displayed enhanced MMN amplitudes for frequency deviation, significant over frontal and central electrodes. In addition, reduced MMN amplitudes in response to intensity deviation were found in the WS compared to the DD and VCFS groups, significant in electrodes over all scalp regions. Conclusions: The preliminary MMN results support a unique auditory processing pattern in WS. Results are in line with the oversensitivity to sounds (hyperacusis) and the special musical abilities including ‘perfect pitch’, which are among the most salient features of the syndrome. Relations between auditory processing abnormalities and candidate genes from the WS minimal deleted region are discussed. P4-8 The effects of cholesterol and CYP46 polymorphism on cognitive event-related potentials C.-L. Lai1,2 , C.-Y. Hsu1,2 , H.-Y. Hsieh1 , C.-K. Liu1,2 Department of Neurology, Faculty of Medicine, College of Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan, 2 Department of Neurology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
1
Objective: For the rapidly aging population and the consequent increase in dementia patients, to identify the putative factors and preventive strategies of cognitive impairment has become a major clinical and public issue. The aims of the present study are to investigate the influence of cholesterol and CYP46 genotypes on cognitive event-related potentials (ERPs) and to determine whether there is an interactive effect between cholesterol level and CYP46 genotypes to ERPs. Methods: Using the Cognitive Abilities Screening Instrument (CASI), 145 mental healthy middle-aged and older adults were recruited. All participants were assessed for lipid profile, CYP46 polymorphism, and auditory P300 even-related potentials. Results: When the participants were stratified according to the levels of total cholesterol and high-density lipoprotein cholesterol (HDL-C), there was no difference in age, educational level, CASI scores, measures of P300, and the percentage of CYP46 polymorphism. In contrast, the subjects with high low-density lipoprotein cholesterol (LDL-C) level exhibited significant low amplitude at Pz lead and prolonged latency at Cz lead than those with normal LDL-C level after adjusted by age and sex, although the CASI scores and percentage of CYP46 polymorphism showed no difference between the two groups. The ages, educational level, CASI scores, components of cholesterol levels, and measures of P300 are compared according to the CYP46 polymorphism, revealing similar values for most items. There is no interaction between LDL-C level and CYP46 genotypes on cognitive ERPs. Conclusions: Our findings imply that LDL-C level is an independent predictor of low amplitude and long latency of P300. There is no association between CYP46 genotypes and P300 ERPs in normal elderly subjects. A combined effect of the cholesterol level and CYP 46 genotypes in cognitive ERPs was not present in this study. P4-9 The effect of mastication on human cognitive processing:A study using event-related potentials K. Sakamoto1,2 , H. Nakata2,3 , R. Kakigi2 1 Advanced Research Institute for the Sciences and Humanities (ARISH), Nihon University, Tokyo, Japan, 2 Department of Integrative Physiology, National Institute for Physiological Sciences, Okazaki, Japan, 3 Faculty of Sport Sciences, Waseda University, Tokorozawa, Japan Objective: The purpose of the present study was to clarify the effect of mastication on cognitive processing using reaction time (RT) and eventrelated potentials (ERPs). Methods: The two experiments consisted of two conditions, Mastication (chewing gum) and Control (relaxing without chewing gum) in Experiment 1, and Jaw Movement (opening and closing the jaw) and Finger Tapping (tapping the right index finger) in Experiment 2. The subjects performed four sessions of an auditory oddball paradigm. RT and ERPs were recorded in these four sessions, Pre (before chewing), and Post 1, Post 2 and Post 3 (after chewing). Results: In Mastication for RT and the peak latencies of P300 and N100, the values were significantly longer in Pre than in Post 2 or Post 3.
29th International Congress of Clinical Neurophysiology By contrast, in Control, Jaw Movement, and Finger Tapping, they were almost identical among sessions or significantly shorter in Pre than in Post 2 or Post 3. Conclusions: Mastication influences cognitive processing time as reflected by RT and the latency of ERP waveforms. Significance: This is the first study investigating the effect of mastication on the central nervous system using event-related potentials. P4-10 Computer games training may affect normative values of some event related potentials in children J.I.S. Farina1 , T. Schaefer1 , V.K. Lopes1 , S. Moojen1 , F. Loureiro1 , A. Schilikman1 1 Cognitive Neurology Group, Department of Neurology and Neurosurgery, Moinhos de Vento Hospital, Porto Alegre, Brazil Objective: Reaction times became faster as the subject is better trained in certain tasks. The aim of this paper was to find out if central processing speed as measured by event evoked responses latencies would reflect these changes. Methods: Event related evoked potentials (auditory odd-ball paradigm) were recorded in 22 normal children from a third grade class after completing tests and teacher interview showing good educational achievement (average or better) and no behavior or neurological problems. Latencies of the N100, P200 and P300 components were analyzed as well as the time devoted to computer games in a week trough Spearman correlation test. The amplitudes of the components were analyzed through Pearson correlation test. Results: A strong positive correlation was found for the latencies of N100 (r = 0.91, p = 0.001) and P200 (r = 0.88, p = 0.001) and the number of hours of computer games activities in this group. A strong negative correlation was found for P200 amplitudes. Discussion: These preliminary results point out to the need to reviewing some normative values of the event related responses in children taking account the time they regularly spend in computer games. The correlations found in this paper show the possible important role of the primary processing speed itself underling the reaction time modifications in these tasks. P4-11 Effects of odor on event-related potential (P300) and pleasantness H. Akimoto1 , T. Sugiura1 , I. Takahashi2 , H. Hirata1 , Y. Okita2 Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan, 2 Graduate School of Electronic Science and Technology, Hamamatsu, Shizuoka University, Japan
1
Objective: Smell is considered to be the most primitive sense and the region of rhinencephalon (smell-brain) is right next door to the limbic system, the regions of human brain that control the most basic functions for life. Because of this proximity, many scientists are convinced that certain pleasant odors are able to stimulate the brain in a manner that instigates brain response. However, there are controversial findings on the effects of odor stimuli on the cognitive task performance in the form of P300 activity. The present study examines the effects of odors on both P300 amplitude and its peak latency while conducting simple auditory oddball tasks. Methods: The subjects were 6 male university students, between 22 and 24 years of age. The standard stimulus was a 1,000 Hz tone (P = 0.85 0.75) and the target stimulus was a 2,000 Hz tone (P = 0.15 0.25). Both tones were presented for 100 ms. While pleasant odor (5% geraniol) or unpleasant odor (hexa-1,5-diyne in pentane) were presented at 5 cm under their noses, subjects were instructed to count the number of the target tones. Results: Results showed that P300 amplitudes for unpleasant odor were lower in 4 subjects than that for pleasant odor while P300 latencies were shorter in 5 subjects for unpleasant odor than for pleasant odor. Conclusions: These findings indicate that odor has an influence on emotion and the unpleasant odor used in this study might increase the vigilance level.
S123 P4-12 Influence of parameters of the Sternberg memory task (the set size and probe item affiliation) on cognitive event-related potentials M. Krbot1 , A.B. Sefer1 , V. Isgum2 , M. Cifrek3 University of Zagreb, Zagreb, Croatia, 2 University Hospital Zagreb, Department of Neurology, Zagreb, Croatia, 3 Faculty of Electrical Engineering and Computing, Department of Electronic Systems and Information Processing, Zagreb, Croatia 1
The main field of interest of this study is cerebral dynamics that occur as a result of memorizing and retrieving information from working memory. A modified Stenberg memory task with auditory stimuli was performed. We recorded cognitive event-related potentials evoked by the memory task. Participants were healthy adults with no cognitive or auditory impairments. During the Sternberg experiment, sets of two or four digits were presented to subjects. Three seconds after the last item in the set, the target digit (probe) was presented. By pressing appropriate buttons participants had to indicate whether the probe did (positive probe) or did not (negative probe) belong to the presented set. According to results the reaction time increases with the increase of the memory set size. The activity in the period in which participants rehearse the previously presented set is stronger expressed for the set consisted of two digits. For the set of two digits the major positive wave (MPW) appears earlier and its amplitude is greater than for the set of four digits. The amplitude of the MPW is greater for the positive probe than for the negative probe, and the latency of the MPW evoked by the negative probe is greater than for the positive probe. Obtained results are in accordance with the presently accepted theory, and also offer interesting features for further research. P4-13 Event-related potentials to target and distractor: localization of the P300 cortical sources by swLORETA P. Bocquillon1,2,3 , J.-L. Bourriez2,3 , E. Palmero-Soler4 , N. Betrouni1,5 , E. Houdayer2,3 , P. Derambure1,2,3 , K. Dujardin1,2,6 1 Universite Lille Nord de France, UDSL, France, 2 Lab. Neurosciences Fonctionnelles et Pathologies, CNRS, FRE 3291, France, 3 Clinical Neurophysiology Department, Lille University Medical Center, France, 4 eemagine Medical Imaging Solutions GmbH, Germany, 5 INSERM U703 Unit, France, 6 Neurology and Movement Disorders Department, Lille University Medical Center, France Objective: Cognitive event-related potentials (ERPs), especially P300, have been used for long to explore attention processes. Their cortical generators are still controversial. The aim of this study is to identify the cortical areas involved in the generation of the P300 wave components. Methods: 15 healthy controls underwent a high density EEG recording (128 channels) during a three stimulus visual oddball paradigm, allowing to identify distractor and target-elicited P300 components. Repeatedmeasures analyses of variances (ANOVAs) were performed on the latency and amplitude data. The P300 individual sources were localized with the swLORETA method and comparison analyses were performed using SPM5 (one sample and paired T-tests). Results: ANOVAs on latency and amplitude data confirm known P300 features. Common sources for both P300 components were observed in a large fronto-parietal network, including the frontal eye field and dorsal parietal cortex, also known as the dorsal fronto-parietal network (p < 0.0005). In addition, more inferior parietal areas, prefrontal and cingulated cortices, corresponding to the ventral frontoparietal network, were involved in the generation of target-elicited P300 (p < 0.005). Conclusions: These results suggest that genesis of P300 elicited by both distractor and target stimuli involves a common dorsal frontoparietal network, while target detection also requires a specific ventral network. These data agree with results of previous studies using different methods. They help to improve our knowledge of the anatomical networks underlying attention processes.