EEG Recordings of Dogs in Sleep: Control and Trazodone Conditions

Description

Methods (English)

Population study

Twelve young, healthy domestic dogs (mean age 64.4 ± months), representing a mix of breeds and sexes, participated in this study (mean weight 20.08 ± 9.1 kg). All animals underwent three stages carried out on different days: acclimatization, recording with trazodone, and recording without trazodone. A summary of the information for each participant is presented in the table below.

All procedures were approved by the Institutional Animal Care and Use Committee at North Carolina State University (NCSU; protocol number 21-303). The dogs were client-owned and were serving as age control in an ongoing longitudinal study on neuro-aging at the NCSU College of Veterinary Medicine, as described in previous publications (Fefer, 2022; Panek, 2020; Panek, 2020b). Before participation, informed consent was obtained from all dog owners, who reviewed and signed consent forms.

Table. Information on the population of dogs used in the study

Polysomnographic studies

The dogs underwent polysomnographic recordings, during which electroencephalogram (EEG), electrooculogram (EOG), electromyogram (EMG), and electrocardiogram (ECG) signals were simultaneously collected, following a slightly modified version of the protocol described by Reicher (2020).

Four active EEG electrodes were placed: F3 and F4 (left and right frontal, respectively), Fz (midline frontal), and Cz (vertex). This electrode placement was designed to capture activity in the frontal and parietal cortices. The EEG electrodes were referenced to an Oz electrode located over the external occipital protuberance.

Bipolar EOG signals were recorded with electrodes placed on the left and right zygomatic arches, near the lateral canthus of each eye. EMG signals were recorded bipolarly from two electrodes placed on the dorsal neck muscles bilaterally. Additionally, ECG signals were captured with an electrode positioned over the fifth intercostal space, referenced to the Cz electrode.

All recordings were conducted using gold-coated electrodes (Genuine Grass 10 mm Gold Cup, Natus Medical Inc.), which were secured with SAC2 electrode cream (Cadwell Laboratories) after preparing the skin with a preparation solution and Signa Spray electrode solution (Parker Laboratories). A ground electrode was positioned over the left temporal muscles. The polysomnographic recordings were managed using Cadwell Easy II software (Cadwell Laboratories). Before each recording session, electrode impedance was verified to ensure it remained below 20 kΩ, and a sampling rate of 400 Hz was maintained throughout the study.

Recordings were conducted in a quiet, dimly lit room with white noise generated from a laptop, and the temperature was maintained at 20 °C. Owners brought their dogs for polysomnography on three separate days: an adaptation day, intended to minimize the “first-night effect” (Reicher, 2020), and two different recording days (with and without trazodone). For added comfort, owners were encouraged to bring familiar bedding items, such as their dogs’ own beds or blankets.

On the adaptation day, a 30-minute recording session was conducted to allow the dogs to acclimate to the room and the recording setup. Subsequently, two additional sessions were performed on different days to record data under two conditions: without medication and with trazodone. The order of these conditions (with or without trazodone) was counterbalanced. The drug dose used was 5 mg/kg orally, which is the dose used as a sedative in dogs (Gilbert, 2016).

Following the adaptation session, the initial condition (with or without the drug) was randomly assigned, and during the third visit, the opposite condition was implemented. The interval between the adaptation and recording days was kept under two weeks. During the testing day, a 2-hour polysomnography session was conducted, beginning between 12:30 PM and 1:30 PM to align with the dogs’ natural nap times. If any dog displayed signs of anxiety or removed its electrodes, the session was paused.