Electroencephalography Measurements in Awake Marmosets Listening to Conspecific Vocalizations

Summary

To study the evolution of language, comparing brain mechanisms in humans with those in nonhuman primates is important. We developed a method to noninvasively measure the electroencephalography (EEG) of awake animals. It allows us to directly compare EEG data between humans and animals for the long term without harming them.

Abstract

Vocal communication plays a crucial role in the social interactions of primates, particularly in survival and social organization. Humans have developed a unique and advanced vocal communication strategy in the form of language. To study the evolution of human language, it is necessary to investigate the neural mechanisms underlying vocal processing in humans, as well as to understand how brain mechanisms have evolved by comparing them with those in nonhuman primates. Herein, we developed a method to noninvasively measure the electroencephalography (EEG) of awake nonhuman primates. This recording method allows for long-term studies without harming the animals, and, importantly, allows us to directly compare nonhuman primate EEG data with human data, providing insights into the evolution of human language. In the current study, we used the scalp EEG recording method to investigate brain activity in response to species-specific vocalizations in marmosets. This study provides novel insights by using scalp EEG to capture widespread neural representations in marmosets during vocal perception, filling gaps in existing knowledge.

Introduction

Primates use species-specific vocalizations to convey biologically important information, such as the caller's emotional state or intention to maintain social bonds, the presence of predators, or other dangerous situations. Investigation of the neural mechanisms underlying the perception of vocalization in vocal-rich nonhuman primates may provide us with critical clues to better understand the evolutionary origins of human language.

Common marmosets are small primates native to South America. In recent years, marmosets have been increasingly used as model animals, alongside macaque monkeys, because of their high reproductivity, ease of ....

Protocol

All experiments were approved by the Animal Experimentation Committee of EHUB (No.2022-003, 2023-104) and conducted in accordance with the Guide for Care and Use of Laboratory Primates published by EHUB. Nine common marmosets (Callithrix jacchus, six males and three females, 2-12 years old, weighing 330-490 g) were used for the experiment. Four of the nine marmosets were housed in pairs or families, while five were housed individually. Marmosets in the colony typically remain in family housing until two years of.......

Discussion

Points to note about anesthesia
Both ketamine and xylazine administration have been attempted, and while these are analgesic and therefore suitable for long painful tasks, marmosets tend to experience decreases in blood oxygen levels without oxygen inhalation⁴⁴. In short, alfaxalon is probably best suited for painless tasks such as shaving or mask making. In addition, for shaving-, which takes only 10-15 min, inhalation anesthesia would be the most suitable. Isoflurane was n.......

Materials

Name	Company	Catalog Number	Comments
Alfaxalone	Meiji Animal Health	Alfaxan
Amplifier	Brain Products	BrainAmp
Atropine	Fuso Pharmaceutical Industries	Atropine Sulfate Injection
Audio editor	Adobe	Adobe Audition
Data processing software	MathWorks	MATLAB	version R2023a
Data processing toolbox	University of California-SanDiego	EEGLAB
Data processing toolbox	University of California-Davis	ERPLAB
Electric shaver	Panasonic	ER803PPA
Electrode	Unique Medical	UL-3010	AgCl coated (custom)
Electrode gel	Neurospec AG	V16 SuperVisc
Electrode input box	Brain Products	EIB64-DUO	64ch
Glue	3M	Scotch 7005S
Hair removering cream	Kracie	epilat for sensitive skin
Isoflurane	Bussan Animal Health	ds isoflurane
Liquid gum	San-ei Yakuhin Boeki	Arabic Call SS	Gum arabic+water
Liquid nutrition	Nestlé Health Science Company	Isocal 1.0 Junior	Polymeric formula
Maropitant	Zoetis	Cerenia injectable solution
Monitor Camera	Intel	RealSense LiDAR Camera L515
Monkey pellets	Oriental Yeast	SPS
Primate chair	Natsume Seisakusho	Order made
Pulse oximeters	Covident	Nellcor	PM10N
Skin prepping pasta	Mammendorfer Institut für Physik und Medizin	NeuPrep
Slicon tube	AsONE	Φ4 x 7mm
Speaker	Fostex	PM0.3
Synchronization device	Brain Vision	StimTrak
Thermoplastic mask	CIVCO	MTAPU Type Uniframe Thermoplastic Mask 2.4mm