Methods for chair restraint and training of the common marmoset on oculomotor tasks

Abstract

The oculomotor system is the most thoroughly understood sensorimotor system in the brain, due in large part to electrophysiological studies carried out in macaque monkeys trained to perform oculomotor tasks. A disadvantage of the macaque model is that many cortical oculomotor areas of interest lie within sulci, making high-density array and laminar recordings impractical. Many techniques of molecular biology developed in rodents, such as optogenetic manipulation of neuronal subtypes, are also limited in this species. The common marmoset ( Callithrix jacchus) possesses a smooth cortex, allowing easy access to frontoparietal oculomotor areas, and may bridge the gap between systems neuroscience in macaques and molecular techniques. Techniques for restraint, training, and neural recording in these animals have been well developed in auditory neuroscience. Those for oculomotor neuroscience, however, remain at a relatively early stage. In this article we provide details of a custom-designed restraint chair for marmosets, a combination head restraint/recording chamber allowing access to cortical oculomotor areas and providing stability suitable for eye movement and neural recordings, as well as a training protocol for oculomotor tasks. We additionally report the results of a psychophysical study in marmosets trained to perform a saccade task using these methods, showing that, as in rhesus and humans, marmosets exhibit a "gap effect," a decrease in reaction time when the fixation stimulus is removed before the onset of a visual saccade target. These results are the first evidence of this effect in marmosets and support the common marmoset model for neurophysiological investigations of oculomotor control. NEW & NOTEWORTHY The ability to carry out neuronal recordings in behaving primates has provided a wealth of information regarding the neural circuits underlying the control of eye movements. Such studies require restraint of the animal within a primate chair, head fixation, methods of acclimating the animals to this restraint, and the use of operant conditioning methods for training on oculomotor tasks. In contrast to the macaque model, relatively few studies have reported in detail methods for use in the common marmoset. In this report we detail custom-designed equipment and methods by which we have used to successfully train head-restrained marmosets to perform basic oculomotor tasks.

Face selective patches in marmoset frontal cortex

“…The purpose of the chamber was to fix the head and thereby prevent animal motion during MRI acquisition. For the chamber implantation procedure 18 , 27 , several coats of adhesive resin (All-bond Universal, Bisco, Schaumburg, Illinois, USA) were applied using a microbrush, air dried, and cured with an ultraviolet dental curing light (King Dental). Then, a two-component dental cement (C & B Cement, Bisco, Schaumburg, Illinois, USA) was applied to the skull and to the bottom of the chamber, which was then lowered onto the skull via a stereotactic manipulator to ensure correct location and orientation.…”

“…5 for representative stimuli). For the directed and averted-gaze videos, five marmosets were filmed while they sat non head-fixed in a marmoset chair 27 ; 12 s clips were created using custom video-editing software (iMovie, Apple Incorporated, California, USA). Scrambled versions of the videos were created by random rotation of the phase information using a custom program (Matlab, The Mathworks, Matick, MA)—the same random rotation matrix was used for each frame to preserve motion components.…”

“…Eye positions were digitally recorded at 1 kHz via video tracking of the left pupil (EyeLink 1000, SR Research, Ottawa, ON, Canada). Animals were head restrained in a custom chair 27 mounted to a table in a sound attenuating chamber (Crist Instruments Co., Hagerstown, MD, USA). A spout was placed at the monkey’s mouth to deliver reward (acacia gum) via an infusion pump (Model NE-510, New Era Pump Systems, Inc., Farmingdale, New York, USA).…”

Ketamine disrupts gaze patterns during face viewing in the common marmoset

“…Prior to these experiments, all 4 marmosets underwent an aseptic surgical procedure to implant a combination recording chamber/head restraint, the purpose of which was to stabilize the head during eye tracking experiments. The chamber implantation procedure is described in detail in Johnston et al (2018). Subsequently, each animal was acclimated to restraint in a custom designed primate chair (Johnston et al, 2018;Schaeffer et al, 2019).…”

“…The chamber implantation procedure is described in detail in Johnston et al (2018). Subsequently, each animal was acclimated to restraint in a custom designed primate chair (Johnston et al, 2018;Schaeffer et al, 2019).…”