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Correlation between PET and ERP measurements in an auditory selective attention task
ABSTRACTS
Correlation between PET and ERP m e a s u r e m e n t s in an auditory selective attention task J.Ph. L a c h a u x * , N. Tzourio ~ F. El Massioui*, B. M a z o y e r ~ and B. Renault*
*Unitd de Psychophysiologie Cognitive (LENA-CNRS URA 654), Universitd Paris 6, H@ital de La SalpktriOre 75651 Paris Cedex 13 FRANCE ~ d'Imagerie Neurofonctionnelle, Service Hospitalier Frdddric JoIiot, DRIPP, CEA, 91401 Orsay Cedex & Universitd Paris 7 Denis Diderot Introduction In an auditory selective attention protocol, simultaneous PET and EEG measurements were done to test the relations between brain's metabolic and neuroelectrical activities. A previous analysis of the PET data (reported in a companion abstract (i)) showed that during either right or left selective attention, activation of the anterior cingulate gyrus and supplementary motor area ipsilateral to the attentive side were observed, together with a bilateral activation of the superior temporal gyms. In order to specify electrical counterparts of those activities, we tested their correlations with (a) the amplitude of the ERP's N100 component and (b) two lateralization indices for this peak. Methods In this study (see (1) for a complementary report), we limited our analysis to the results obtained during the auditory selective attention task (a classic dichotic listening of rare (20%) high (1790 Hz) and frequent low (750 Hz) tones, all lasting for 150 ms, and randomly but evenly delivered to the right or the left ear with interstimulus intervals ranging from 400 to 800 ms). The targets were the right deviant tones for 6 subjects (right attention) and the left ones for 8 other subjects (left attention). Five EEG electrodes (T4, Fd located halfway between Fz and T4, Cz, Fg symetric of Fd, T3) were recorded during PET measurements: Since our purpose was to compare PET and ERP data, we extracted the ERP's N100 component elicited by all of the stimuli, without any distinction. In a first step, we analyzed the Spearman rank correlations across subjects between PET (attention minus rest) activations and the amplitudes recorded on the different electrodes. In a second step, two topographical indices were defined in order to evaluate the lateralization of the frontal and temporo-central components of the N100. The first one, LF, was calculated as (A(Fd)-A(Fg))/(A(Fd)+A(Fg)) and the second one, LT, as (B(T4)B(T3))/(B(T4)+B(Cz)+B(T3)), where A(x) and B(x) denotes the mean amplitude recorded at x over a 50 ms or a 20ms window centered on the N100 peak, respectively. The correlations between these indices and PET activations were then computed. Results Only one significant correlation was found as regards the N100 amplitude: in the left attention condition, the value recorded on T4 was significantly correlated with the metabolic activity of the right superior temporal gyrus (Spearman, Ro=.63, p<0.03). The study of the N100 topography brought more information: first, a significant shift of LT was observed between left and right attention (t-test p<0.05) and second, this indice appeared to be reliably correlated with the PET activation of the superior temporal gyrus contralateral to the attentive side: (Spearman, Ro=-.74, p<0.05 during right attention, Ro---.68, p<0.02 during left attention and Ro=-.58, p<0.01, for both conditions together). As for LF, it was significantly correlated with the right anterior cingulum activation in the right attention condition (Spearman, Ro=.74, p<0.05); in the left attention condition, the correlation with the left anterior cingulum tends to be significant (Spearman, Ro=.48, p--0.095). No other significant correlation was found with the lateralization indices. Conclusions The results are consistent with the assumption of a correlation between EEG and PET but suggest that changes in PET activations may affect more directly the topography of the ERP components than their amplitudes. Moreover, the computation of lateralization indices seems to be a fruitful way to look for the electric effects of metabolic variations: the correlations found following this approach support an involvement of the superior temporal gyrus and the anterior cingulum in the genesis of the N100 elicited during attentive listening. Further simultaneous recordings are now required for new advances toward the fusion of EEG and PET in order to support recent suggestions that PET could provide contraints on the solutions of the EEG-MEG bioelectric inverse problem. 1. Tzourio, N., E1Massioui, F., Renault, B., Mazoyer, B.
$72
This book of Abstracts.
Correlation between PET and ERP m e a s u r e m e n t s in an auditory selective attention task J.Ph. L a c h a u x * , N. Tzourio ~ F. El Massioui*, B. M a z o y e r ~ and B. Renault*
*Unitd de Psychophysiologie Cognitive (LENA-CNRS URA 654), Universitd Paris 6, H@ital de La SalpktriOre 75651 Paris Cedex 13 FRANCE ~ d'Imagerie Neurofonctionnelle, Service Hospitalier Frdddric JoIiot, DRIPP, CEA, 91401 Orsay Cedex & Universitd Paris 7 Denis Diderot Introduction In an auditory selective attention protocol, simultaneous PET and EEG measurements were done to test the relations between brain's metabolic and neuroelectrical activities. A previous analysis of the PET data (reported in a companion abstract (i)) showed that during either right or left selective attention, activation of the anterior cingulate gyrus and supplementary motor area ipsilateral to the attentive side were observed, together with a bilateral activation of the superior temporal gyms. In order to specify electrical counterparts of those activities, we tested their correlations with (a) the amplitude of the ERP's N100 component and (b) two lateralization indices for this peak. Methods In this study (see (1) for a complementary report), we limited our analysis to the results obtained during the auditory selective attention task (a classic dichotic listening of rare (20%) high (1790 Hz) and frequent low (750 Hz) tones, all lasting for 150 ms, and randomly but evenly delivered to the right or the left ear with interstimulus intervals ranging from 400 to 800 ms). The targets were the right deviant tones for 6 subjects (right attention) and the left ones for 8 other subjects (left attention). Five EEG electrodes (T4, Fd located halfway between Fz and T4, Cz, Fg symetric of Fd, T3) were recorded during PET measurements: Since our purpose was to compare PET and ERP data, we extracted the ERP's N100 component elicited by all of the stimuli, without any distinction. In a first step, we analyzed the Spearman rank correlations across subjects between PET (attention minus rest) activations and the amplitudes recorded on the different electrodes. In a second step, two topographical indices were defined in order to evaluate the lateralization of the frontal and temporo-central components of the N100. The first one, LF, was calculated as (A(Fd)-A(Fg))/(A(Fd)+A(Fg)) and the second one, LT, as (B(T4)B(T3))/(B(T4)+B(Cz)+B(T3)), where A(x) and B(x) denotes the mean amplitude recorded at x over a 50 ms or a 20ms window centered on the N100 peak, respectively. The correlations between these indices and PET activations were then computed. Results Only one significant correlation was found as regards the N100 amplitude: in the left attention condition, the value recorded on T4 was significantly correlated with the metabolic activity of the right superior temporal gyrus (Spearman, Ro=.63, p<0.03). The study of the N100 topography brought more information: first, a significant shift of LT was observed between left and right attention (t-test p<0.05) and second, this indice appeared to be reliably correlated with the PET activation of the superior temporal gyrus contralateral to the attentive side: (Spearman, Ro=-.74, p<0.05 during right attention, Ro---.68, p<0.02 during left attention and Ro=-.58, p<0.01, for both conditions together). As for LF, it was significantly correlated with the right anterior cingulum activation in the right attention condition (Spearman, Ro=.74, p<0.05); in the left attention condition, the correlation with the left anterior cingulum tends to be significant (Spearman, Ro=.48, p--0.095). No other significant correlation was found with the lateralization indices. Conclusions The results are consistent with the assumption of a correlation between EEG and PET but suggest that changes in PET activations may affect more directly the topography of the ERP components than their amplitudes. Moreover, the computation of lateralization indices seems to be a fruitful way to look for the electric effects of metabolic variations: the correlations found following this approach support an involvement of the superior temporal gyrus and the anterior cingulum in the genesis of the N100 elicited during attentive listening. Further simultaneous recordings are now required for new advances toward the fusion of EEG and PET in order to support recent suggestions that PET could provide contraints on the solutions of the EEG-MEG bioelectric inverse problem. 1. Tzourio, N., E1Massioui, F., Renault, B., Mazoyer, B.
$72
This book of Abstracts.