Topographical EEG Recordings of Visual Evoked Potentials in Mice using Multichannel Thin-film Electrodes

Published: June 23, 2022

doi:

Rüdiger Land, Sarah Christine Sentis², Andrej Kral

¹Institute for Audioneurotechnology, Department of Experimental Otology,Hannover Medical School, ²Institute for Endocrinology and Diabetes, Center of Brain, Behavior and Metabolism,University of Lübeck

Summary

The present protocol describes a simple procedure to acquire and analyze the topography of epicranial visual evoked potentials with 32-multichannel thin-film electrodes in the mouse.

Abstract

Visual evoked potentials (VEP) allow the characterization of visual function in preclinical mouse models. Various methods exist to measure VEPs in mice, from non-invasive EEG, subcutaneous single-electrodes, and ECoG to fully invasive intracortical multichannel visual cortex recordings. It can be useful to acquire a global, topographical EEG-level characterization of visual responses previous to local intracortical microelectrode measurements in acute experimental settings. For example, one use case is to assess global cross-modal changes in VEP topography in deafness models before studying its effects on a local intracortical level. Multichannel epicranial EEG is a robust method to acquire such an overview measure of cortical visual activity. Multichannel epicranial EEG provides comparable results through a standardized, consistent approach to, for example, identify cross-modal, pathological, or age-related changes in cortical visual function. The current study presents a method to obtain the topographical distribution of flash-evoked VEPs with a 32-channel thin-film EEG electrode array in anesthetized mice. Combined with analysis in the time and frequency domain, this approach allows fast characterization and screening of the topography and basic visual properties of mouse cortical visual function, which can be combined with various acute experimental settings.

Introduction

Mice are a preclinical model of degenerative processes of vision and ophthalmological diseases¹^,²^,³^,⁴. Visual evoked potentials (VEPs) are commonly used to measure cortical visual function and, for example, to assess visual degeneration in pathological models⁵^,⁶. The VEP latency, conduction time, amplitude, multifocal characteristics, or spatial acuity of cortical visual evoked potentials provide diagnostic information on the functional integrity of the visual system⁷^,⁸^,⁹.

In mice, cortical visual evoked potentials can be measured across various spatial scales with methods of different complexity from non-invasive EEG, subdermal needle electrodes, and skull-implanted screws, to fully invasive intracranial approaches with epicortical ECoG, to intracortical electrode recordings¹⁰^,¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷. These methods have different strengths and weaknesses. For example, a low number of electrodes only provides limited information on cortical VEP distribution, whereas subcutaneous needle electrodes often fail to ensure consistent recording locations. Moreover, implanted screws or fully invasive methods require damaging, penetrating, or removing of the skull and often provide only local information.

In acute experiments, a first global overview of cortical visual function is often desired, which is eventually followed by further experimental steps and compared to local intracortical recordings. For example, one potential use case is utilized first to investigate the EEG-level effects of visual cross-modal reorganization of deafness or hearing loss on VEP topography and cortical visual activity¹⁸^,¹⁹ before studying the impacts on a local intracortical level.

Multichannel EEG recordings with thin-film multi-electrode arrays can provide a systematized VEP topography from the mouse skull²⁰^,²¹^,²²^,²³^,²⁴. Such epicranial recordings can have advantages over ECoG recordings by leaving the integrity of the skull intact and avoiding direct manipulation of the cortical surface. In addition, thin-film multi-electrodes provide a standardized electrode configuration, allowing the comparison of visual evoked spatio-temporal brain activity between experiments similar to a standardized EEG system in humans²⁵. A standardized framework also facilitates using common EEG analysis toolboxes (e.g., Fieldtrip, Chronux, EEGLAB, and ERPLAB) to analyze mouse EEG in the time and frequency domain or in terms of connectivity²⁶^,²⁷^,²⁸^,²⁹^,³⁰^,³¹.

The present protocol describes a procedure for topographical VEP recordings in mice using a 32-channel thin-film electrode. This can be used as part of acute experiments followed by additional experimental steps, such as intracortical microelectrode recordings from specific brain areas. It is demonstrated here how to reliably record epicranial flash evoked VEPs with 32-channel thin-film electrodes from the mouse. In addition, exemplary analysis of topographical VEP recordings in the time and frequency domain is presented.

Protocol

All animals were handled and housed according to German (TierSchG, BGBl. I S. 1206, 1313) and European Union (ETS 123; Directive 2010/63/EU) guidelines for animal research. The animal experiments were approved by German state authorities (Lower Saxony State Office for Consumer Protection and Food Safety, LAVES) and were monitored by the university animal welfare officer. A 3-month-old male C57BL/6J mouse was used for the present study. 1. Animal details Perform the…

Representative Results

Recording visual evoked potentials with multichannel EEG allows the assessment of the topography of VEP amplitudes, latencies, or frequency components in mice. Figure 2A shows an example of a flash evoked VEP topography recorded with an epicranial 32-channel EEG from a 3-month-old male C57BL/6J mouse. The strongest visual evoked activity occurs in the occipital region above the visual cortex. Figure 2B shows the voltage distribution o…

Discussion

This article describes a method for recording epi-cranial multichannel EEG with thin-film electrodes and how to acquire a consistent topographical representation of visual evoked potentials in the mouse. Here, we exemplarily showed binocular flash stimulation, but this approach can also be applied with other types of visual stimuli (i.e., monocular, spatial gratings, focal visual field) using, for example, a larger display.

A critical step in the protocol is the positioning of the electro…

Divulgazioni

The authors have nothing to disclose.

Acknowledgements

This work was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft, Cluster of Excellence 2177 "Hearing4all", Project number 390895286).

Materials

Bepanthen 5% Dexpantheol	Bayer		Ophtamic gel
Cheetah software 5.11	Neuralnyx	Version 5.11	Recording software for neurophysiologcal signals
Digital Lynx SX	Neuralynx	Digital Lynx 16SX	Recording system
ECG differential amplifier	Otoconsult	WDA2 V1.0
Electric shaver	Aesculap	GT420
Electrode Holder	TSE Systems	430005-HE
Examination light	Heine	HL 5000	Cold light source lamp
Heating Pad + Temperature Control system	CWE	TC-1000 Mouse
Histoacryl 0.5 mL	B.Braun		Tissue adhesive
Infrared heat lamp	Sanitas	SIL 06
Ketamine 10%	WDT		Ketaminhydrochlorid
LED stroboscope	Monarch	Nova Strobe PBL	Visual stimulation
Matlab 2021a	The Mathworks	2021a	Stimulus control and analysis
Moria Vessel Clamp	Fine Science Tools	18320-11
Mouse EEG electrode	NeuroNexus	H32 (Reticular)	32-channel EEG electrode. Thickness: 20 μm; length: 8.6 mm; width 6.8 mm. Platinum sites: 500 μm diameter
Mouse Frame	custom made		Information available on request
Multifunction I/O device	National Instruments	PCIe-6353 with BNC 2090A	Analog stimulus generation, output, and trigger
NaCl 0.9%	B.Braun		Isotonic, sterile, nonpyrogenic
Neuralynx HS36	Neuralynx	HS-36	Headstage
Neuronexus probe connector	Neuralynx	ADPT-HS36-N2T-32A	Electrode connector
Oscilloscope	Tektronix	TDS 2014B
Progent Intensive Cleaner	Menicon		Protein remover and disinfecting solution for rigid gas permeable lenses
Recording PC	HP	HP Z800	Recording PC
Rimadyl (Carprofen)	Zoetis		Carprofen
Silicon Oil M 1000	Carl Roth	4045.1
Silver wire	Science Products	AG-8W	Diameter 203 µm; ECG and reference electrode
Sound proof chamber	IAC acoustics
Stereotactic Micromanipulator	TSE Systems	430005-M/P	For EEG electrode placement
Stimulation PC	Dell	Dell Precision T5810	Stimulation PC
Surgical microscope	Zeiss	Op-Mi Focus
Surgical tape	3M	1527-0	1.25 cm x 9.1 m
Thilo-Tears 3 mg/g	Alcon Pharma GmbH		Ophtamic gel
Vaselin Lichtenstein	Winthrop		White vaselin ointment
Xylazin 2%	Bernburg		Xylazinehydrochlorid
Xylocaine Spray (10 mg/puff)	Aspen		Lidocaine

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