fMRI in Dogs

We can learn a lot about animal cognition by using behavioral experiments, where we rely on the actions of an animal in a particular situation to infer what processes are occurring in the animal’s brain. But what about looking more directly at what the brain is doing?

One way to do that is to record the activity of neurons in the brain using electrodes. There are a few downsides to this method, though. First, neural recordings can only show us the activity of very small areas of the brain at a time. Additionally, the animals used in these experiments have usually been raised in a lab, rather than in their natural environment, which could affect their cognitive development.

263px-MRI-Philips

MRI Machine

Another way to look at brain activity is through imaging such as functional Magnetic Resonance Imaging, or fMRI. The MRI machine uses a magnetic field to look at oxygen flow to different areas of the brain. More active brain areas need more oxygen, so by tracking the oxygen flow to the brain over time, we can determine the pattern of activity in the brain. And, unlike with neural recordings with electrodes, we can look at the activity of the entire brain at once.

 

Unfortunately, fMRI requires that the person (or animal) being scanned lie completely still inside the MRI scanner, which is a bit confining and noisy. While this isn’t a problem for anesthetized animals, it’s nearly impossible for awake animals. But recently, researchers have made incredible progress in using fMRI to study dogs.

In 2012, a group of researchers managed to train two dogs to lie still in an MRI machine long enough to have their brains scanned. They first got the dogs used to laying with their chins in a chin rest, then slowly acclimated them to the noise of the machine, ear muffs (to muffle some of the machine’s noise), and the MRI machine itself. While in the scanner, the dogs were shown two different hand signals: one was followed by a food reward (“reward”), while the other was not (“no reward”).

The researchers were interested in the response of an area of the brain called the caudate nucleus. Among other important functions including voluntary movement and learning, the caudate nucleus in involved in the reward system of the brain; previous studies have found that the caudate becomes more active when a reward is expected.

2241616932_107199f0fa_mSure enough, the researchers found that the dogs’ caudate nuclei were more active when the “reward” hand signal was given than when the “no reward” signal was given. They later replicated this study with 11 more dogs and found that the increase in activity in the caudate was comparable to that found in humans. Interestingly, some of the dogs studied were service dogs, and they had nearly significantly greater caudate activation than the non-service dogs when the “reward” hand signal was given. The researchers theorized that, due to their extensive training, the service dogs may have found the hand signal itself intrinsically more rewarding.

(Check out the Supporting Information for the first paper for an interesting video detailing the training that the dogs underwent!)

Before these studies, fMRI studies with animals required that they be restrained or anesthetized, both of which could greatly affect brain activity. Believe it or not, researchers actually ran studies investigating brain activity in response to odors…in anesthetized dogs! While the brain does respond to such stimuli even under the influence of anesthesia, it clearly does so in a different way than it would normally. (Of course researchers were aware of this, but there just wasn’t another option at the time.)

Once it had been shown that dogs could be trained to lie still in an MRI machine, some researchers decided to see just how different the brain’s response to odors is in anesthetized and awake dogs. They found that, in addition to the sensory brain areas active in anesthetized dogs, the frontal cortex was activated by odor in awake dogs. (The frontal cortex is implicated in complex cognitive functions like decision-making and planning.) The researchers suggested that the frontal cortex activity could be involved in understanding what an odor means in a particular context, and could inform how the dog behaves in response to that odor. Understanding this kind of brain activity could have major implications for how we train drug- and bomb-sniffing dogs.

443627085_4fe6f95f01_mThe first group of researchers also studied dogs’ brain activity in response to odors. They presented dogs with five different odors: a familiar dog, an unfamiliar dog, the dog itself, a familiar human, and an unfamiliar human. They found that, compared to the other four odors, there was greater activity in the caudate nucleus in response to the familiar human odor. This indicates that not only could the dogs discriminate between the different odors, but that they also associated that particular human with reward. And again, the researchers found that the response was stronger in service dogs, possibly due to their more extensive human contact during training.

Finally, another group of researchers compared the brain activity of humans and dogs as they were listening to human and dog vocalizations and natural sounds. They found that similar areas of the brain were more active when they heard the vocalizations of conspecifics (i.e. when humans heard humans and dogs heard dogs). This suggests that these brain areas may have evolved for that particular purpose more than 30 million years ago (although convergent evolution is a possibility). Additionally, some brain areas responded more strongly to more positive vocalizations (i.e. laughing versus crying). These brain areas were in similar locations in both dogs and humans, and responded to both species’ vocalizations. This suggests that dogs and humans may have comparable emotional processing of sounds.

Interestingly, part of the training of the dogs used in this study involved social learning – naïve dogs watched an experienced dog get in the MRI scanner and receive praise and treats, which motivated the naïve dogs to behave in the same way!

(Although the paper of this study isn’t freely available, the researchers did make a fascinating video summarizing their study, and NPR wrote an article about it.)

4840054871_b79aef16f2_mStudying canine cognition using fMRI is a relatively new application of the method, but the research so far looks promising. Not only will it allow us to get a direct look at what’s going on in dogs’ brains, but it could also improve the way we train service dogs and care for our best friends.

 

I’ll end with a thought-provoking quote from one of the above papers, about canine cognition research:

“…While the study of the canine mind is fascinating for its own sake, it also provides a unique mirror into the human mind. Because humans, in effect, created dogs through domestication, the canine mind reflects back to us how we see ourselves through the eyes, ears, and noses of another species.”

-Berns et al. (2012)

 

Sources Cited:

Andics, Attila, et al. “Voice-Sensitive Regions in the Dog and Human Brain Are Revealed by Comparative fMRI.” Current Biology (2014).

Berns, Gregory S., Andrew M. Brooks, and Mark Spivak. “Functional MRI in awake unrestrained dogs.” PloS one 7.5 (2012): e38027.

Berns, Gregory S., Andrew Brooks, and Mark Spivak. “Replicability and Heterogeneity of Awake Unrestrained Canine fMRI Responses.” PloS one 8.12 (2013): e81698.

Berns, Gregory S., Andrew M. Brooks, and Mark Spivak. “Scent of the Familiar: An fMRI Study of Canine Brain Responses to Familiar and Unfamiliar Human and Dog Odors.” Behavioural Processes (2014).

Jia, Hao, et al. “Functional MRI of the Olfactory System in Conscious Dogs.” PloS one 9.1 (2014): e86362.

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