Saccade related layer specific local field potential activity in macaque V1 during free viewing

Meyes R, Ito J, Yamane Y, Tamura H, Fujita I, Gruen S

​11th Goettingen meeting of the German Neuroscience Society (Goettingen), JuSER Report

No: FZJ-2015-02184

2015/3/18-21

Abstract: Primates perform frequent saccadic eye movements (SEMs) to sample visual information from the environment. These SEMs are accompanied in the primary visual cortex (V1) by local field potential (LFP) modulations that precede the arrival of the visual input [Ito et al. (2011) Cereb Cortex 21:2482-97].In the present study we aim to elucidate how the SEM related LFP modulations depend on the properties of visual input during saccades. For this purpose, we presented stationary, full-field grating stimuli to an awake macaque monkey, who freely explored the stimuli with voluntary saccadic eye movements. Eye movements were recorded with a scleral eye coil and the LFP from V1 with a 24-channel linear electrode array. We identified SEM related LFP modulations by averaging the LFP signal aligned to the onsets of saccades and subsequent fixations, and reconstructed the corresponding current source density (CSD) signal (Figure a and b) from the LFP via the inverse CSD method [Pettersen et al. (2006) J Neurosci Meth 154:116–33]. For a comparison we also computed the average LFP and CSD signal aligned to the onset of the stimulus images preceded by fixation on a central fixation spot (Figure c).The monkey preferred to perform saccades in the direction parallel to the stripes of the stimulus image. Those parallel saccades (PSs) had a larger median amplitude, velocity and duration than orthogonal saccades (OSs) and intermediate saccades. We found that the SEM related LFP modulation was stronger for OSs than for PSs. The CSD signal showed a current sink in the granular layer, that was observed for the saccade-onset and fixation-onset triggered averages but notfor the image-onset triggered averages, confirming that this sink reflected SEM related activity(Figure a and b, red frames vs. c, red frame). The OSs evoked stronger current sinks than the PSs. We observed a positive correlation between the amplitude of saccades and the magnitude of the evoked current sink. The increase of the CSD signal for larger saccades saturated more quickly for OSs than for PSs (Figure d vs. e). This SEM related current sink probably reflects an inhibitory process because it was accompanied by a concurrent decrease in high-gamma band (~160 Hz)power, which has been shown to be strongly positively correlated to the firing rates of local neurons[Ray et al. (2008) J Neurosci 28:11526-36].In summary, saccades causing larger changes in the retinal image, such as those with larger amplitude and/or in directions more orthogonal to the stripes of the stimulus images, evoked stronger CSD modulations. This seems to suggest mere excitation of V1 by the retinal changes caused by saccades, but a comparison with the concurrent high-gamma power modulation rather suggests that the CSD modulation reflects an inhibitory process. A possible implication of these observations would be that the CSD signal might reflect an active suppression mechanism that matches the amount of inhibition to the strength of the visual input during saccades.