Cortical sources of event-related potentials in the prosaccade and antisaccade task

Abstract

The cortical sources of event-related potentials (ERP) were examined in a prosaccade and antisaccade task in college-age participants. The task included a cue that indicated the spatial location of the target, a cue that indicated the type of eye movement, or no cue. A principal component analysis and equivalent current dipole analysis showed that a peripheral spatial cue resulted in extrastriate activity localized in Brodmann's area 19 whereas a central cue results in activity in areas 19 or 37. This extrastriate activity reflects an enhanced response to the target when attention was directed to that location. The presaccadic ERP activity primarily consisted of a contralateral positive potential and ipsilateral negative potential, localized in Brodmann's areas 8, 10, and 11. The temporal proximity of this cortical activity and its relation to movement cueing suggests it reflects eye movement planning processes.

Figure 1

Topographical scalp potential maps for the grand average ERP in the pretarget period and immediately preceding the saccade, collapsed across conditions. The pretarget map is plotted as the average for 200-ms intervals from 1 s until target onset. The presaccade map is plotted as 32-ms averages from 182 ms preceding the saccade through 40 ms following saccade onset. For all topographical maps, the stimulus-locked segments are positioned so that the target appeared on the left side and the response-locked segments are positioned so that the eye movement went toward the left side.

Figure 2

Grand average ERP for representative electrodes. The frontal-central electrodes contain data from the pretarget period and represent the negative pretarget potential (CNV). The parietal-occipital electrodes contain data from the presaccade period and represent the spike potential. The approximate location of the 10–20 midline electrodes are shown.

Figure 3

Topographical scalp potential maps for the average of the PC clusters (collapsed across conditions). The top two panels show clusters that were nearly identical in the stimulus-locked and response-locked EEG segments. The bottom panels show clusters that were unique in these periods. The eigenvector weights of the PC are plotted.

Figure 4

The activations of the PCs with the negative potential found in the frontal-central scalp electrodes and the positive potential found in the parietal leads. The PCs were from the 1,200-ms stimulus-locked EEG segments, and the activations came from 25-ms segments.

Figure 5

The activations in the posttarget period of the PCs with the occipital activity contralateral to the target location and the positive parietal activity following target onset.

Figure 6

Topographical scalp potential maps for the projections in the posttarget interval, separately for the four cueing procedures. The peripheral cue procedure resulted in an “early P1,” the spatial cue procedure resulted in a “late P1,” and all four procedures had significant parietal activity.

Figure 7

The activations in the presaccadic period of the PCs with frontal-occipital activity, activity ipsilateral to the eye movement, and activity contralateral to the eye movement. The arrow points to an apparent ERP component occurring about 75 ms prior to saccade onset primarily in the movement cue procedure. Immediately preceding saccade onset, there was a large activation of all three PCs probably corresponding to the spike potential seen in the grand average ERP (Figures 1 and 2).

Figure 8

Topographical scalp potential maps for the projections in the presaccadic interval, separately for the movement cue procedure and the other procedures. The positive presaccadic activity occurring about 75 ms before saccade onset corresponds to the ERP component found in the activations (Figure 7). The spike potential occurs in the last two panels, but was maximal in the grand average ERP about 8 to 12 ms prior to saccade onset (Figure 2).

Figure 9

Equivalent current dipole locations for the pretarget PC clusters. Each location on the MRI recording represents a PC from one individual. The three MRIs on the left came from the negative frontal-central activity and the two on the right from the positive parietal activity. More information about the locations may be found in Table 2.

Figure 10

Equivalent current dipole locations for the presaccadic PC clusters. Each location on the MRI recording represents a PC from one individual. The MRI on the left came from the PC with the frontal-occipital activity, the next two came from the PC with activity in the frontal scalp region ipsilateral to the saccade, and the two on the right from the PC with activity in the frontal scalp region contralateral to the saccade. More information about the locations may be found in Table 3.