Speaker
Description
Auditory evoked responses, recorded using electroencephalography or magnetoencephalography (MEG), are commonly used to study cognitive processes related to hearing in humans. These responses have also been recorded in other species but mostly by using invasive techniques. Here, for the first time, we present non-invasive measurements of these responses in unanesthetized domestic cats (Felis catus) using optically pumped magnetometers (OPMs). Our aim is to study the feline-equivalents of the human N100, mismatch negativity and P300 responses to bridge the gap between previous invasive animal and non-invasive human studies. N100 is an automatic response to novel sounds, mismatch negativity a response to deviant tones, and P300 an attention-related response indicating updates of the short-term memory.
We measured eight cats using an array of eight dual-axis OPMs (QZFM Gen-2, QuSpin Inc., Louisville, CO, USA) placed in a custom 3D-printed helmet that conforms to the average shape of a cat’s head. We presented the cats a series of tone beeps according to a variation of the local–global paradigm. Each trial comprised a sequence of five 50-ms tones: the first four tones were always the same and the last one was either the same or different in frequency with respect to the preceding ones. Trials were presented in blocks where in 75% of the trials the 5th tone was different and in 25% the same as the preceding four tones. In a block, we used 1-kHz tones as the common sound and 50-kHz ultrasound tones as the deviant ones.
During measurements, the cat was seated with its owner and was free to move its head, while the owner was holding the sensor helmet on the cat’s head. The experiment was performed in a three-layer magnetically shielded room.
A putative N100-response equivalent was succesfully measured on average 65 ms after the sound onset. Some evidence for mismatch negativity was observed as a larger-amplitude N100 after deviant tones. Convincing evidence for P300 was not observed. We showed that neurophysiological experiments can be performed non-invasively and without restraining the animals using OPM-based MEG.
