After anesthetizing the marmoset, monitor the vitals with a pulse oximeter. If necessary, administer an oxygen air mixture. Maintain the room temperature above 27 degrees Celsius, and wrap a warming cloth around the body of the marmoset to prevent hypothermia.
Using an electric shaver, shave the head. Apply hair removal cream for sensitive skin. After five minutes, wipe off the cream with wet gauze.
Drill four screw holes into the protruding back portion of the mask to align with the vertical length of the chair. Next place the anesthetized marmoset on the primate chair. Secure the animal on the chair using neck and waist plates.
Place the thermoplastic mask plate in hot water to soften it to fit the head of the marmoset. Remove the mask plate from the water and allow it to cool before placing it on the subject's head. After hardening, remove the mask from the marmoset head.
Cut out the top of the head and ear parts of the mask to expose the area for the electrode setting. Habituate the marmoset to the chair under awake conditions and reward it for approximately 30 minutes. Connect a 64 channel electrode input box to the amplifier.
Arrange the speaker near the amplifier and control the sound level at 65 to 75 decibels to deliver auditory stimuli. Place the camera in front of the subject to monitor their condition during the EEG recording. Then arrange the primate chair in front of the camera.
Attach a transfer cage to a small window of the home cage and allow the marmoset to move to the transfer cage. Cover the carrying cage with a cloth and transfer it to the experimental room. Hold the mart using protective gloves and place it on the primate chair.
Put the previously prepared mask on the mart's head. Pass the screws attached to the chair through the hole in the mask and fix it using thumb screws. Use the nasion, inion, and ear lobes as anatomical landmarks to determine the location of the electrodes according to the international 10:20 method.
Measure the distance between the nasion and inion in the midline with a tape. Define the location of Cz in the middle of the distance. Position the other electrodes with 20%of the inion/nasion length as the electrode spacing.
Mark the electrode positions on the scalp using an oil-based dermatograph. Rub the marked area with a thin cotton swab dipped in alcohol to remove dirt and sebum from the scalp. Using a tube cutter, cut a piece of silicon tubing into a length of approximately seven to nine millimeters.
Apply adhesive to the edges of the cut tube and adhere it to the scalp. Using a syringe with a non-pointed needle, fill the inside of the tube with EEG gel. Connect the reference electrode to PZ and the ground electrodes to F4 or F3.Insert electrodes into the tube and connect the electrode cable to the input box.
Launch the EEG recording application. Adjust the parameters to ensure all electrodes are below five kilo-Ohms and measure the electrode impedance. During head immobilization and between task sessions, administer one to three milliliters of liquid reward using a syringe.
Specify the file to be saved on the EEG recording software and press the start recording button. Immediately run the script for stimulus presentation. When the stimulus presentation script execution is completed, press the stop button to end all recordings.
Then remove the electrodes and head mask from the marmoset. Capture the animal and place it back in the carrying cage. Record simple and compound calls from marmoset that are not used in subsequent EEG recordings.
Extract three species-specific simple and compound calls from the recorded files. Next, create white noise using a function in the programming software and use that as a stimulus. To follow this, use three auditory files of marmoset calls in the experiment.
Control the task using a custom script. In each sound stimulus file, the right channel contains the marmoset call or noise data, and the left channel contains the trigger signal for the onset of the stimulus. Send the trigger signal to the EEG system via a synchronization device and record it as event time.
The auditory evoked potential was prominent in the noise condition reflecting the clear onset of the stimuli. The time frequency analysis showed that event related spectral power increased at a lower frequency immediately after stimulus onset. The CZ region showed a decrease in gamma range power lasting for one second post stimulus onset in younger subjects.
The initial transient responses in the FZ region revealed significant main effects of stimulus, type, and age with no significant interaction. Sustained responses in CZ showed a significant effect of stimulus type, but no effect of age or interaction.
