Characteristics of Spontaneous Square-Wave Jerks in the Healthy Macaque Monkey during Visual Fixation

Abstract

Saccadic intrusions (SIs), predominantly horizontal saccades that interrupt accurate fixation, include square-wave jerks (SWJs; the most common type of SI), which consist of an initial saccade away from the fixation target followed, after a short delay, by a return saccade that brings the eye back onto target. SWJs are present in most human subjects, but are prominent by their increased frequency and size in certain parkinsonian disorders and in recessive, hereditary spinocerebellar ataxias. SWJs have been also documented in monkeys with tectal and cerebellar etiologies, but no studies to date have investigated the occurrence of SWJs in healthy nonhuman primates. Here we set out to determine the characteristics of SWJs in healthy rhesus macaques (Macaca mulatta) during attempted fixation of a small visual target. Our results indicate that SWJs are common in healthy nonhuman primates. We moreover found primate SWJs to share many characteristics with human SWJs, including the relationship between the size of a saccade and its likelihood to be part of a SWJ. One main discrepancy between monkey and human SWJs was that monkey SWJs tended to be more vertical than horizontal, whereas human SWJs have a strong horizontal preference. Yet, our combined data indicate that primate and human SWJs play a similar role in fixation correction, suggesting that they share a comparable coupling mechanism at the oculomotor generation level. These findings constrain the potential brain areas and mechanisms underlying the generation of fixational saccades in human and nonhuman primates.

Microsaccade-rhythmic modulation of neural synchronization and coding within and across cortical areas V1 and V2

“…In line with earlier experimental observations in monkey V1 [ 21 , 22 , 27 , 53 , 72 , 101 ], we observed the quasiperiodic occurrence (every 200–500 ms) of MSs during normal awake visual processing. They continuously modulated visual neuronal processing and prohibited the network dynamics from reaching an equilibrium state.…”

“…Recent work has shown that MSs, in tandem with drifts, have important implications for transforming visual spatial information into temporal modulations [ 35 , 36 , 50 , 51 , 101 ]. MSs induce transient modulations that relate to lower- and high-frequency content of the visual image, whereas drifts lead to temporal modulations related mainly to higher-frequency (more local) content.…”

Reduced fixation stability induced by peripheral viewing does not contribute to crowding

“…This may have been due to an increase in the number of microsaccades made toward and away from the peripheral target stimulus, as has been reported in previous studies of covert attention ( Engbert & Kliegl, 2003 ; Laubrock et al, 2005 ; Rolfs, Engbert, & Kliegl, 2004 ). Alternatively, this result may simply reflect that fact the microsaccades tend to be horizontal ( Costela et al, 2015 ) and that a larger proportion of horizontal microsaccades may occur as fixation stability decreases.…”

Dynamic gaze-position prediction of saccadic eye movements using a Taylor series

“…Standard sterile surgical techniques, recording procedures, and animal care methods were approved by the Institutional Animal Care and Use Committee at Barrow Neurological Institute. Information about the breeding, care, and maintenance of the macaques can be found in previously reported studies that addressed different experimental questions (Costela et al, 2015 ; Costela et al, 2014 ). Prior to the eye movement recordings, cranial head-post and scleral search-coil implantation surgeries were conducted, under general anesthesia using aseptic techniques, and with full postoperative analgesia and antibiotic therapy.…”