Electrophysiology of Laminar Cortical Activity in the Common Marmoset

Custom-built micro-drives enable the sub-millimeter targeting of cortical recording sites with linear silicon arrays.

The marmoset monkey provides an ideal model for examining laminar cortical circuits due to its smooth cortical surface, which facilitates recordings with linear arrays. The marmoset has recently grown in popularity due to its similar neural functional organization to other primates and its technical advantages for recording and imaging. However, neurophysiology in this model poses some unique challenges due to the small size and lack of gyri as anatomical landmarks. Using custom-built micro-drives, researchers can manipulate linear array placement to sub-millimeter precision and reliably record at the same retinotopically targeted location across recording days. This protocol describes the step-by-step construction of the micro-drive positioning system and the neurophysiological recording technique with silicon linear electrode arrays. With precise control of electrode placement across recording sessions, researchers can easily traverse the cortex to identify areas of interest based on their retinotopic organization and the tuning properties of the recorded neurons. Further, using this laminar array electrode system, it is possible to apply a current source density analysis (CSD) to determine the recording depth of individual neurons. This protocol also demonstrates examples of laminar recordings, including spike waveforms isolated in Kilosort, which span multiple channels on the arrays.

The common marmoset (Callithrix jacchus) has quickly grown in popularity as a model to study brain function in recent years. This growing popularity is due to the accessibility of the marmoset's smooth cortex, the similarities in neural functional organization with humans and other primates, and the small size and fast breeding rate¹. As this model organism has grown in popularity, there has been rapid development in the neurophysiological techniques suited for use in the marmoset brain. Electrophysiology methods are widely used in neuroscience to study the activity of single neurons in the cortex of both rodents and primates, resu....

The experimental procedures followed the National Institutes of Health Guide for the Care and Use of Laboratory Animals. The protocols for the experimental and behavioral procedures were approved by the University of Rochester Institutional Animal Care and Use Committee.

1. Construction of the micro-drive containing the electrode for recording (Figure 1)

NOTE: Custom-built X-Y stages holding multi-channel linear silicon a.......

This protocol describes how to build an X-Y electrode stage (Figure 1) that allows for the sub-millimeter targeting of sites and maintains reliable positioning across separate recording sessions. The reliability of the X-Y positioning is illustrated in Figure 6, which demonstrates that two recording sessions conducted a week apart showed a 70.8% overlap in their mean RF locations (Figure 6A). Furthermore, minor adjustments to the mi.......

Several methods (e.g., chronic, semi-chronic, acute) are currently available for performing neurophysiology experiments in non-human primates. The common marmoset poses unique challenges for neurophysiology experiments due to its small size and lack of gyri as anatomical landmarks. This requires researchers to use neurophysiological landmarks such as the retinotopy and tuning properties of areas of interest to identify the recording targets. Therefore, when initially mapping out a cortical area, daily adjustments to the .......

This work was supported by the National Institutes of Health (NIH) grant R01 EY030998 (J.F.M., A.B., and S.C.). This method is based on methods developed in Coop et al. (under review, 2022; https://www.biorxiv.org/content/10.1101/2022.10.11.511827v2.abstract). We would like to thank Dina Graf and members of the Mitchell lab for help with the marmoset care and handling.