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The BOLD response and the gamma oscillations respond differently than evoked potentials: an interleaved EEG-fMRI study.

Foucher JR, Otzenberger H, Gounot D - BMC Neurosci (2003)

Bottom Line: Both Targets and Novels triggered a P300, of larger amplitude in the Novel condition.EEG event-related oscillations in the gamma band (32-38 Hz) reacted in a way similar to the BOLD response.Those results provide further arguments for a closer relationship between fast oscillations and the BOLD signal, than between evoked potentials and the BOLD signal.

View Article: PubMed Central - HTML - PubMed

Affiliation: Clinique Psychiatrique-INSERM U405, Hôpitaux Universitaires-BP 406-67091 Strasbourg Cedex-France. jf@evc.net

ABSTRACT

Background: The integration of EEG and fMRI is attractive because of their complementary precision regarding time and space. But the relationship between the indirect hemodynamic fMRI signal and the more direct EEG signal is uncertain. Event-related EEG responses can be analyzed in two different ways, reflecting two different kinds of brain activity: evoked, i.e. phase-locked to the stimulus, such as evoked potentials, or induced, i.e. non phase-locked to the stimulus such as event-related oscillations. In order to determine which kind of EEG activity was more closely related with fMRI, EEG and fMRI signals were acquired together, while subjects were presented with two kinds of rare events intermingled with frequent distractors. Target events had to be signaled by pressing a button and Novel events had to be ignored.

Results: Both Targets and Novels triggered a P300, of larger amplitude in the Novel condition. On the opposite, the fMRI BOLD response was stronger in the Target condition. EEG event-related oscillations in the gamma band (32-38 Hz) reacted in a way similar to the BOLD response.

Conclusions: The reasons for such opposite differential reactivity between oscillations / fMRI on the one hand, and evoked potentials on the other, are discussed in the paper. Those results provide further arguments for a closer relationship between fast oscillations and the BOLD signal, than between evoked potentials and the BOLD signal.

Show MeSH
Event-related oscillations for all the electrodes. The upper part presents the event-related oscillations (EROs) time-frequency chart for Targets on the left (X-mark), and rare distractors (Novels) on the right ("no-smoking" symbol). It is shown for the 24- to 44-Hz band, and between -320 to 600 ms, summing up all 9 electrodes for all the subjects. The color scale represents the relative amount of power in standard deviation (reference period from -320 to 0 ms). This illustrates that the 32- to 38-Hz EROs in response to Targets are quite low in response to Novels. It thus does not come as a surprise that the statistical comparison of Target-related vs. Novel-related power for all electrodes is significant (lower time-frequency chart). Cold colors code for a trend towards greater power in the Novel condition, whereas hot colors represent greater power level in the Target condition. The scale represents the cumulative p distribution stated in percent. Regions above the .05 and .01 threshold are contoured in black. The numbers 1, 5, 95 and 99 represent the cumulative p value in percent, respectively equivalent to.01, .05 for Novels and .05, .01 for Targets. The solid and dotted black lines correspond to the response time and standard deviation, respectively. The result table provides the statistics for the time interval from 200 to 500 ms, and from 24 to 44 Hz, using a threshold p ≤ 0.01. Volume and time-frequency cluster p values are given corrected for multiple comparisons. Note that the ensemble statistics represent the probability to have the given amount of time-frequency points above the threshold (12 over 165 time-frequency points), and not the number of clusters as in EPs or fMRI. At the same threshold, there were no significantly larger power emissions in the Novel than in the Target condition (not even at the .05 threshold).
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Figure 3: Event-related oscillations for all the electrodes. The upper part presents the event-related oscillations (EROs) time-frequency chart for Targets on the left (X-mark), and rare distractors (Novels) on the right ("no-smoking" symbol). It is shown for the 24- to 44-Hz band, and between -320 to 600 ms, summing up all 9 electrodes for all the subjects. The color scale represents the relative amount of power in standard deviation (reference period from -320 to 0 ms). This illustrates that the 32- to 38-Hz EROs in response to Targets are quite low in response to Novels. It thus does not come as a surprise that the statistical comparison of Target-related vs. Novel-related power for all electrodes is significant (lower time-frequency chart). Cold colors code for a trend towards greater power in the Novel condition, whereas hot colors represent greater power level in the Target condition. The scale represents the cumulative p distribution stated in percent. Regions above the .05 and .01 threshold are contoured in black. The numbers 1, 5, 95 and 99 represent the cumulative p value in percent, respectively equivalent to.01, .05 for Novels and .05, .01 for Targets. The solid and dotted black lines correspond to the response time and standard deviation, respectively. The result table provides the statistics for the time interval from 200 to 500 ms, and from 24 to 44 Hz, using a threshold p ≤ 0.01. Volume and time-frequency cluster p values are given corrected for multiple comparisons. Note that the ensemble statistics represent the probability to have the given amount of time-frequency points above the threshold (12 over 165 time-frequency points), and not the number of clusters as in EPs or fMRI. At the same threshold, there were no significantly larger power emissions in the Novel than in the Target condition (not even at the .05 threshold).

Mentions: EROs also presented a statistical difference between the Target and Novel conditions, but in an opposite manner. Figure 2 shows the statistical comparison map between Targets (red) and Novels (blue). Targets evoked a greater increase in power than Novels between 200 and 500 ms in the 32-Hz band in F7, Cz, C3, C4 and Pz, and in the 34-Hz band in Fz and F8. Figure 3 (top) shows the time frequency chart for all the electrodes, for Targets (right) and Novels (left), with color-coded standard deviation relative to the reference distribution (-320 to 0 ms). There was a greater difference between the Target and Novel conditions in the 200 to 500 ms interval for the 32- to 38-Hz band. This was confirmed by the statistical map used to compare the two conditions (fig. 3 lower part), with two significant time-frequency clusters between 200 and 500 ms at 32 Hz (p = 0.002) and 38 Hz (p = 0.001) and a global significance of p < 0.0005. There was no significant time-frequency point for the reverse statistics (Novels > Targets). Subject-by-subject conjunction analysis produced the same results, with a multi-subject conjunction probability of p = 0.0014 on electrode Cz at 38 Hz and 320 ms (see table 2 for subject by subject results). It could be argued that EROs were found to be larger in the Target condition, relative to the Novel condition, owing to the limited frequency range explored, so that we performed further analysis in the 25- to 200-Hz range, every 5 Hz. Between 100 and 400 ms, and considering an uncorrected p ≤ 0.01 for report, Novels failed to present larger EROs than Targets, whereas the latter presented larger EROs at 35, 95, 110 and 140 Hz (additional material available on request).


The BOLD response and the gamma oscillations respond differently than evoked potentials: an interleaved EEG-fMRI study.

Foucher JR, Otzenberger H, Gounot D - BMC Neurosci (2003)

Event-related oscillations for all the electrodes. The upper part presents the event-related oscillations (EROs) time-frequency chart for Targets on the left (X-mark), and rare distractors (Novels) on the right ("no-smoking" symbol). It is shown for the 24- to 44-Hz band, and between -320 to 600 ms, summing up all 9 electrodes for all the subjects. The color scale represents the relative amount of power in standard deviation (reference period from -320 to 0 ms). This illustrates that the 32- to 38-Hz EROs in response to Targets are quite low in response to Novels. It thus does not come as a surprise that the statistical comparison of Target-related vs. Novel-related power for all electrodes is significant (lower time-frequency chart). Cold colors code for a trend towards greater power in the Novel condition, whereas hot colors represent greater power level in the Target condition. The scale represents the cumulative p distribution stated in percent. Regions above the .05 and .01 threshold are contoured in black. The numbers 1, 5, 95 and 99 represent the cumulative p value in percent, respectively equivalent to.01, .05 for Novels and .05, .01 for Targets. The solid and dotted black lines correspond to the response time and standard deviation, respectively. The result table provides the statistics for the time interval from 200 to 500 ms, and from 24 to 44 Hz, using a threshold p ≤ 0.01. Volume and time-frequency cluster p values are given corrected for multiple comparisons. Note that the ensemble statistics represent the probability to have the given amount of time-frequency points above the threshold (12 over 165 time-frequency points), and not the number of clusters as in EPs or fMRI. At the same threshold, there were no significantly larger power emissions in the Novel than in the Target condition (not even at the .05 threshold).
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Related In: Results  -  Collection

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Figure 3: Event-related oscillations for all the electrodes. The upper part presents the event-related oscillations (EROs) time-frequency chart for Targets on the left (X-mark), and rare distractors (Novels) on the right ("no-smoking" symbol). It is shown for the 24- to 44-Hz band, and between -320 to 600 ms, summing up all 9 electrodes for all the subjects. The color scale represents the relative amount of power in standard deviation (reference period from -320 to 0 ms). This illustrates that the 32- to 38-Hz EROs in response to Targets are quite low in response to Novels. It thus does not come as a surprise that the statistical comparison of Target-related vs. Novel-related power for all electrodes is significant (lower time-frequency chart). Cold colors code for a trend towards greater power in the Novel condition, whereas hot colors represent greater power level in the Target condition. The scale represents the cumulative p distribution stated in percent. Regions above the .05 and .01 threshold are contoured in black. The numbers 1, 5, 95 and 99 represent the cumulative p value in percent, respectively equivalent to.01, .05 for Novels and .05, .01 for Targets. The solid and dotted black lines correspond to the response time and standard deviation, respectively. The result table provides the statistics for the time interval from 200 to 500 ms, and from 24 to 44 Hz, using a threshold p ≤ 0.01. Volume and time-frequency cluster p values are given corrected for multiple comparisons. Note that the ensemble statistics represent the probability to have the given amount of time-frequency points above the threshold (12 over 165 time-frequency points), and not the number of clusters as in EPs or fMRI. At the same threshold, there were no significantly larger power emissions in the Novel than in the Target condition (not even at the .05 threshold).
Mentions: EROs also presented a statistical difference between the Target and Novel conditions, but in an opposite manner. Figure 2 shows the statistical comparison map between Targets (red) and Novels (blue). Targets evoked a greater increase in power than Novels between 200 and 500 ms in the 32-Hz band in F7, Cz, C3, C4 and Pz, and in the 34-Hz band in Fz and F8. Figure 3 (top) shows the time frequency chart for all the electrodes, for Targets (right) and Novels (left), with color-coded standard deviation relative to the reference distribution (-320 to 0 ms). There was a greater difference between the Target and Novel conditions in the 200 to 500 ms interval for the 32- to 38-Hz band. This was confirmed by the statistical map used to compare the two conditions (fig. 3 lower part), with two significant time-frequency clusters between 200 and 500 ms at 32 Hz (p = 0.002) and 38 Hz (p = 0.001) and a global significance of p < 0.0005. There was no significant time-frequency point for the reverse statistics (Novels > Targets). Subject-by-subject conjunction analysis produced the same results, with a multi-subject conjunction probability of p = 0.0014 on electrode Cz at 38 Hz and 320 ms (see table 2 for subject by subject results). It could be argued that EROs were found to be larger in the Target condition, relative to the Novel condition, owing to the limited frequency range explored, so that we performed further analysis in the 25- to 200-Hz range, every 5 Hz. Between 100 and 400 ms, and considering an uncorrected p ≤ 0.01 for report, Novels failed to present larger EROs than Targets, whereas the latter presented larger EROs at 35, 95, 110 and 140 Hz (additional material available on request).

Bottom Line: Both Targets and Novels triggered a P300, of larger amplitude in the Novel condition.EEG event-related oscillations in the gamma band (32-38 Hz) reacted in a way similar to the BOLD response.Those results provide further arguments for a closer relationship between fast oscillations and the BOLD signal, than between evoked potentials and the BOLD signal.

View Article: PubMed Central - HTML - PubMed

Affiliation: Clinique Psychiatrique-INSERM U405, Hôpitaux Universitaires-BP 406-67091 Strasbourg Cedex-France. jf@evc.net

ABSTRACT

Background: The integration of EEG and fMRI is attractive because of their complementary precision regarding time and space. But the relationship between the indirect hemodynamic fMRI signal and the more direct EEG signal is uncertain. Event-related EEG responses can be analyzed in two different ways, reflecting two different kinds of brain activity: evoked, i.e. phase-locked to the stimulus, such as evoked potentials, or induced, i.e. non phase-locked to the stimulus such as event-related oscillations. In order to determine which kind of EEG activity was more closely related with fMRI, EEG and fMRI signals were acquired together, while subjects were presented with two kinds of rare events intermingled with frequent distractors. Target events had to be signaled by pressing a button and Novel events had to be ignored.

Results: Both Targets and Novels triggered a P300, of larger amplitude in the Novel condition. On the opposite, the fMRI BOLD response was stronger in the Target condition. EEG event-related oscillations in the gamma band (32-38 Hz) reacted in a way similar to the BOLD response.

Conclusions: The reasons for such opposite differential reactivity between oscillations / fMRI on the one hand, and evoked potentials on the other, are discussed in the paper. Those results provide further arguments for a closer relationship between fast oscillations and the BOLD signal, than between evoked potentials and the BOLD signal.

Show MeSH