Eye movement artifact may account for putative frontal feedback-related potentials in nonhuman primates

Cross-frequency phase synchrony around the saccade period as a correlate of perceiver's internal state

In active vision, eye-movements depend on perceivers' internal state. We investigated peri-fixation brain activity for internal state-specific tagging. Human participants performed a task, in which a visual object was presented for identification in lateral visual field, to which they moved their eyes as soon as possible from a central fixation point. Next, a phrase appeared in the same location; the phrase could either be an easy or hard question about the object, answered by pressing one of two alternative response buttons, or it could be an instruction to simply press one of these two buttons. Depending on whether these messages were blocked or randomly mixed, one of two different internal states was induced: either the task was known in advance or it wasn't. Eye movements and electroencephalogram (EEG) were recorded simultaneously during task performance. Using eye-event-time-locked averaging and independent component analysis, saccade- and fixation-related components were identified. Coss-frequency phase-synchrony was observed between the alpha/beta1 ranges of fixation-related and beta2/gamma1 ranges of saccade-related activity 50 ms prior to fixation onset in the mixed-phrase condition only. We interpreted this result as evidence for internal state-specific tagging.

Event-related potentials elicited by errors during the stop-signal task. I. Macaque monkeys

The error-related negativity (ERN) and positivity (Pe) are components of event-related potential (ERP) waveforms recorded from humans and are thought to reflect performance monitoring. Error-related signals have also been found in single-neuron responses and local-field potentials recorded in supplementary eye field and anterior cingulate cortex of macaque monkeys. However, the homology of these neural signals across species remains controversial. Here, we show that monkeys exhibit ERN and Pe components when they commit errors during a saccadic stop-signal task. The voltage distributions and current densities of these components were similar to those found in humans performing the same task. Subsequent analyses show that neither stimulus- nor response-related artifacts accounted for the error-ERPs. This demonstration of macaque homologues of the ERN and Pe forms a keystone in the bridge linking human and nonhuman primate studies on the neural basis of performance monitoring.

Performance monitoring local field potentials in the medial frontal cortex of primates: supplementary eye field

We describe intracranial local field potentials (LFPs) recorded in the supplementary eye field (SEF) of macaque monkeys performing a saccade countermanding task. The most prominent feature at 90% of the sites was a negative-going polarization evoked by a contralateral visual target. At roughly 50% of sites a negative-going polarization was observed preceding saccades, but in stop signal trials this polarization was not modulated in a manner sufficient to control saccade initiation. When saccades were canceled in stop signal trials, LFP modulation increased with the inferred magnitude of response conflict derived from the coactivation of gaze-shifting and gaze-holding neurons. At 30% of sites, a pronounced negative-going polarization occurred after errors. This negative polarity did not appear in unrewarded correct trials. Variations of response time with trial history were not related to any features of the LFP. The results provide new evidence that error-related and conflict-related but not feedback-related signals are conveyed by the LFP in the macaque SEF and are important for identifying the generator of the error-related negativity.