Chronic, Multi-Site Recordings Supported by Two Low-Cost, Stationary Probe Designs Optimized to Capture Either Single Unit or Local Field Potential Activity in Behaving Rats

Abstract

Rodent models of cognitive behavior have greatly contributed to our understanding of human neuropsychiatric disorders. However, to elucidate the neurobiological underpinnings of such disorders or impairments, animal models are more useful when paired with methods for measuring brain function in awake, behaving animals. Standard tools used for systems-neuroscience level investigations are not optimized for large-scale and high-throughput behavioral battery testing due to various factors including cost, time, poor longevity, and selective targeting limited to measuring only a few brain regions at a time. Here we describe two different “user-friendly” methods for building extracellular electrophysiological probes that can be used to measure either single units or local field potentials in rats performing cognitive tasks. Both probe designs leverage several readily available, yet affordable, commercial products to facilitate ease of production and offer maximum flexibility in terms of brain-target locations that can be scalable (32–64 channels) based on experimental needs. Our approach allows neural activity to be recorded simultaneously with behavior and compared between micro (single unit) and more macro (local field potentials) levels of brain activity in order to gain a better understanding of how local brain regions and their connected networks support cognitive functions in rats. We believe our novel probe designs make collecting electrophysiology data easier and will begin to fill the gap in knowledge between basic and clinical research.

Cortico-striatal beta-oscillations as a marker of learned reward value

“…A local anesthetic, Lidocaine (max .2cc), was injected under the skin at the incision site while the animal was anesthetized but before surgery initiation. The fabrication and implantation procedures of our custom fixed field potential and single-unit probes are described in detail (Francoeur et al, 2021).…”

“…Neural data was cleaned and referenced off-line using Wave_Clus v.2.5., a Matlab-based spike-sorting program (Quiroga et al, 2004). Signals were processed as two polytrode (16-electrode) groups with median referencing applied to each channel (see Francoeur et al, 2021). A threshold of spike detection was set at 5 times standard deviation of voltage potential for each channel.…”

“…To record single-units we used a 32-channel stationary array with microwires arranged in a brush-like formation (see Francoeur et al, 2021). Initial preparation of the animal and location of ground screws was identical to the LFP probe surgical procedures described above.…”

“…We carried out standard pre-processing and time frequency (TF) analyses using custom MATLAB scripts and functions from EEGLAB (Fakhraei et al, 2021b(Fakhraei et al, , 2021aFrancoeur et al, 2021). 1) Data epoching: We first extracted time-points for events of interest during each task.…”

From End to End: Gaining, Sorting, and Employing High-Density Neural Single Unit Recordings

“…Grading up from tetrodes, polytrodes, typically insulated metal wires (Francoeur et al, 2021 ) or micro-assembled silicon probes, have increased exponentially the number of neurons in a single observation (Neto et al, 2016 ). With a channel count ranging from 8 to 64, each one set 25–200 μm apart and arranged in 1–3 columns, U-/V- or S-probes are reliable tools for study on different cortical layers (Wang et al, 2021 ).…”