This week’s BEACON Researchers at Work blog post is by University of Texas at Austin graduate student Sean Maguire.
The Networked Brain
The brain has long been viewed as being composed of isolated regions controlling specific functions. Modern neuroscience has revealed that the brain is in fact a highly distributed and interconnected system. The brain can be viewed as a network of networks that span different spatial and temporal scales: from molecular networks within a single neuron, to synaptic connections between neurons, to local and regional circuitry, to long range interregional circuits and finally to social (brain to brain) networks (See Figure 1). The really interesting thing is that each level can affect the levels below it, as well as the levels above it. For example, the activity of a single neuron is affected by its gene expression, and its activity can then affect the other neurons that it synapses with. Likewise the neuron is part of a circuit and is receiving signals from other neurons that can modulate its gene expression. The Hofmann lab at The University of Texas does integrative studies across every level of the system shown in Figure 1. My research has focused specifically on the top two levels: social networks and interregional brain circuits, and how those two levels may interact.
Figure 1: The brain can be viewed as a network of networks. Depicted from top to bottom: Social (brain to brain) Networks, interregional brain networks, local and regional synaptic circuits and finally intercellular molecular networks.
Social networks affect health and behavior
Social connections are extremely important for human health and behavior. Using large observational studies of human social networks, researchers have shown that serious health problems like obesity and depression correlate with the disease status of each individual’s friends. One interpretation of these data is that if your friends are, for example, obese you are more likely to become obese in the future. The direct effect that people can have on their friends has been shown using experiments in large online social networks. In one experiment (which many of us may have unknowingly participated in) researchers displayed a banner to every user that logged into Facebook during the 2010 congressional election. Some users received a social message showing that their friends had voted along with information about how to vote. The control group received a non-social message with just the information on how to vote. The results showed that users that received the social message were much more likely to vote themselves. In fact, the researchers estimate that the “Facebook effect” accounted for about 340,000 extra votes!
How do social interactions affect physiology and behavior?
These effects must occur via individuals affecting the physiology and behavior of their social partners; however, the mechanisms of these effects are still unclear. In order to study these mechanisms, my collaborators and I are using the African cichlid fish, Astatotilapia burtoni, a model system in social neuroscience. A. burtoni live in social groups and display different phenotypes depending on where they are in the dominance hierarchy. Dominant (DOM) males are brightly colored, aggressive and territorial while subordinate (SUB) males are dull and spend their time schooling with females. These phenotypes are entirely determined by social interactions and SUBs can start transitioning to DOMs within minutes given an opportunity.
It may seem like a far-fetched proposition to study fish in order to learn about how social interactions affect brain and behavior more generally; however, the neural circuitry controlling social behavior (the Social Decision Making Network) has a deep evolutionary history that is conserved over at least 350 million years of vertebrate evolution. The Hofmann lab has recently synthesized evidence from 88 species across all vertebrate lineages to infer the ancestry and conservation of this brain network.
Social networks in A. burtoni
Figure 2: A. burtoni can be either dominant or subordinate and can transition back and forth between these phenotypes.
We have reconstructed the social networks of replicate groups of A. burtoni and have found that social network position predicts many aspects of individual behavior and physiology. For example, one of the most important predictors of testosterone levels in males is not social status alone but community membership. In some communities DOM and SUB males have nearly equal testosterone levels while in others DOMs have much higher levels. This can be explained by the stability of the social networks in the community. In stable social networks DOM males have higher levels and in unstable communities DOMs and SUBs have similar levels.
How does social network position affect the brain?
Behavior is ultimately determined, not by the activity of any one region of the Social Decision Making Network, but rather by the patterns of activity across these nodes. My hypothesis is that social network position affects this neural patterning thereby modulating behavioral decision making. I predict that DOM males higher in the social hierarchy will have a different pattern of activity across these nodes compared to SUBs and that this will directly correlate with their behavior.
My current experiments aim to test this by giving SUB males and opportunity to transition to DOM status and observing their neural patterning (using gene expression markers that correlate to neural activity) at different stages of their transition.
Keep your friends close…
Ultimately my research is part of a growing body of evidence showing that the social environment has very important effects on individual behavior, physiology and gene expression. I think that it is important to be mindful of ones own social environment and to try and curate friendships that are engaging and positive, which has been shown to correlate with overall life satisfaction as well as success in things like adopting healthy lifestyle changes.
For more about Sean’s work, you can contact him at smmaguire at gmail dot com.
