Presaccadic Brain Potentials in Conditions of Covert Attention Orienting

Twelve healthy subjects underwent investigation of averaged (electroencephalogram) EEG potentials during preparation for motor activity and in the latent period (LP) of visually evoked saccades by presentation of stimuli using Posner's (1980) design of “cost-benefit.” It has been shown that covert spatial attention orientation leads to an increase in amplitude and decrease in latency of presaccadic initiation potential peaks within the saccadic latent period (LP) (P-100, N –50). Processes of covert orientation of attention during the interstimulus interval period of anticipation of the target stimulus correlate with the increase of slow negativity of fronto-parietal-temporal localization. Spatial-temporal changes of presaccadic potentials are evidence of the fact that orientation of attention during motor preparation and saccadic initiation is reflected in intensification of fronto-parietal networks of saccadic control and attention, activating the fronto-medio-thalamic and thalamo-parietal modulating systems.

Difference Between Visually and Electrically Evoked Gaze Saccades Disclosed by Altering the Head Moment of Inertia

Differences between gaze shifts evoked by collicular electrical stimulation and those triggered by the presentation of a visual stimulus were studied in head-free cats by increasing the head moment of inertia. This maneuver modified the dynamics of these two types of gaze shifts by slowing down head movements. Such an increase in the head moment of inertia did not affect the metrics of visually evoked gaze saccades because their duration was precisely adjusted to compensate for these changes in movement dynamics. In contrast, the duration of electrically evoked gaze shifts remained constant irrespective of the head moment of inertia, and therefore their amplitude was significantly reduced. These results suggest that visually and electrically evoked gaze saccades are controlled by different mechanisms. Whereas the accuracy of visually evoked saccades is likely to be assured by on-line feedback information, the absence of duration adjustment in electrically evoked gaze shifts suggests that feedback information necessary to maintain their metrics is not accessible or is corrupted during collicular stimulation. This is of great importance when these two types of movements are compared to infer the role of the superior colliculus in the control of orienting gaze shifts.