MRI machines are extraordinary tools for studying brains, but they aren’t often used on animals unless they are sedated. Why? Because keeping them still often proves to be quite a challenge! Fortunately though, scientists from Emory University were able to train a group of dogs to lie still long enough to successfully perform MRI scans.
The purpose of the experiments was to determine which parts of the brain were most active when the dogs responded to signals that they associated with rewards (in this case, hot dogs). The first study1 included only two dogs, but subsequent studies2,3 expanded with 11 more dogs. All were trained to both lie in the MRI machines and recognize the experimenters’ hand signals. One hand signal indicated that the dogs would receive a hot dog reward, while the other hand signal indicated that the dogs would not receive a reward at all. The scientists recorded the brain activity that occurred when each hand signal was shown to the dogs.
Because of evidence that a brain part called the ventral striatum is one of the most active areas when processing information about rewards, such as their value and predictability, it is considered a key reward center of the brain.4 The researchers chose to place their attention on this area of the dogs’ brains while analyzing the MRI scans. They put particular focus on the caudate nucleus, one of the components of the ventral striatum. The caudate not only plays a large role in reward-evaluation, but also positive emotional responses, especially those associated with pleasure and affection.5
The caudate is significantly more active to the ‘‘reward’’ hand signal compared to the ‘‘no-reward’’ hand signal. The same region of activation was observed in both dogs and is identified as the right caudate as indicated on the corresponding slice of each dog’s structural image (CD). The structural image has been uniformly scaled to match the size of the brain of the functional images. The underlay of the functional map is the mean of the non-excluded functional images. McKenzie was rotated slightly out of plane, but this was a consistent position in both functional and structural scans. The significance of the peak voxel in this cluster was p,0.01 in Callie and p,0.001 in McKenzie (colorbar indicates tvalues and maps are thresholded at p,0.05 to show full spatial extent). The time series of activation was extracted for the cluster (9 voxels in Callie, and 18 voxels in McKenzie after restricting spatial extent with p,0.01), and after adjusting for the other effects in the design matrix (including motion), the average trial response is seen to match a typical hemodynamic response function, which is significantly greater for the ‘‘reward’’ signal than the ‘‘no-reward’’ signal (error bars are +/2 1 s.e.) Bottom: statistical map of the combined model with both dogs, co-registered and overlaid on Callie’s structural scan. Activation of the caudate cluster (CD) was significant at p,0.05 after correcting for FDR over the search volume of the ventral brain from olfactory bulb to internal capsule (p,0.01 height and cluster extent.6). Averaged over both dogs, the timecourse of activation in the caudate showed a distinct response to the reward hand signal which differentiates from the no-reward signal (lower right). Scan volumes are 1610 ms apart, indicating a peak in the response 3–5 s after the onset of the reward hand signal.1
The scans showed that there was significant activation of the right caudate in all of the dogs when they were shown the hand signal indicating a treat reward. The region was less likely to be activated when they were shown the hand signal indicating no reward. The dogs reliably exhibited positive responses when they believed they were going to receive a reward. These results are very similar to those of a similar experiment done on humans.6 “The results are showing that dogs, and probably most animals, have brains and minds that are far more sophisticated than we ever gave them credit for.” – Study lead Gregory S. Berns, PhD.
The findings and success of the studies have opened the door to further exploration of the canine mind:
“Although we chose a simple instrumental conditioning task to demonstrate the feasibility of canine fMRI, a wide variety of future studies is now possible. Dogs have had a prolonged evolution with humans, and they are uniquely attuned to our behaviors. For example, one might reasonably ask to what extent the dog mentalizes the minds of humans. Dogs are intensely visual and pay attention to our facial expressions and where we look and point.
How do they represent these actions? How do dogs distinguish humans, and is it by vision or smell? Is human language processed as arbitrary sounds, or do dogs have neural structures that respond in a deeper manner to language? What is the difference between how dogs represent humans and other dogs or animals? The questions are endless.
And 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.”
The video below features footage from one of the experiments:
Because of dogs’ prolonged evolution with humans, many of the canine cognitive skills are thought to represent a selection of traits that make dogs particularly sensitive to human cues. But how does the dog mind actually work? To develop a methodology to answer this question, we trained two dogs to remain motionless for the duration required to collect quality fMRI images by using positive reinforcement without sedation or physical restraints. The task was designed to determine which brain circuits differentially respond to human hand signals denoting the presence or absence of a food reward. Head motion within trials was less than 1 mm. Consistent with prior reinforcement learning literature, we observed caudate activation in both dogs in response to the hand signal denoting reward versus no-reward.1
This article was written by Amanda Pachniewska, founder & editor of AnimalCognition.org
1- Berns GS, Brooks AM, Spivak M
Functional MRI in Awake Unrestrained Dogs
2 -Berns GS, Brooks A, Spivak M
Replicability and Heterogeneity of Awake Unrestrained Canine fMRI Responses
3 – Berns GS, Brooks A, Spivak M
Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors
Behavioral Processes: New Directions in Canine Behavior
4 – Haber SN, Gottfried JA, Editor
Neuroanatomy of Reward: A View from the Ventral Striatum. Neurobiology of Sensation and Reward.
Boca Raton (FL): CRC Press
5 – Villablanca JR
Why do we have a caudate nucleus?
Acta Neurobiol Exp (Wars).
6- Samuel M. McClure, Gregory S. Berns, P. Read Montague
Temporal Prediction Errors in a Passive Learning Task Activate Human Striatum