Decisions, Decisions

It doesn't take much to notice how different animals
can be... But look closer and you'll see how similar
they are too. Figure from O'Connell and Hofmann
2011 Frontiers in Neuroendocrinology paper.

Animals live in social environments that repeatedly present both challenges (like an aggressive neighbor) and opportunities (like a flirtatious neighbor). Although animals can usually respond to such challenges and opportunities in a number of different ways, there are patterns to how animals do respond. Scientists find that animals tend to make behavioral decisions that improve their chances of survival and reproduction. To do this, they evaluate the importance of what they perceive in their environment and their own internal physiology and then respond in ways that are appropriate to the social context.

Vertebrates (animals with spinal columns, such as mammals, birds, fish, reptiles and amphibians) have amazingly similar brain anatomy and physiology to control these behavioral decision-making processes. All five of these vertebrate groups have a social behavior network (a set of brain areas that are known to be sensitive to steroid hormones and to regulate social behavior) and a mesolimbic reward system (a brain system that uses dopamine to regulate motivation, among other things). When a vertebrate is faced with a social decision, these two brain systems work together as an integrated brain network called the social decision-making network.

Drawing of a rodent brain from the side showing brain areas in the mesolimbic reward system in blue and the social behavior network in yellow. Brain areas that are part of both systems are in green. Figure from O'Connell and Hofmann 2011 Frontiers in Neuroendocrinology paper.

Researchers Lauren O’Connell and Hans Hofmann from The University of Texas at Austin compared the neurochemistry of these brain regions across 88 vertebrate species, including mammals, birds, fish, reptiles and amphibians. In each of these brain areas for each species, they looked for the presence or absence of molecules involved in the chemical signaling of important behavior modulators (dopamine, estrogen, androgen, progesterone, vasopressin/vasotocin and oxytocin).

The researchers found that despite the diversity in the animals and their ecologies, their social decision-making networks were remarkably similar. One of the most striking similarities was that receptors for all of these behavior modulators were found in the same brain areas for almost all of the animals studied. This suggests that this common distribution pattern of where these receptors are in vertebrate brains is important for helping animals make decisions that improve their survival and reproduction regardless of what their social and environmental context is. This similarity may also explain, in part, why such diverse animals show similar behaviors in similar circumstances.

Drawing comparing animal brains from the front-view from front (left side ) to back (right side). Again, brain areas in the mesolimbic reward system are in blue, brain areas in the social behavior network are in yellow, and brain areas that are part of both systems are in green. Figure from O'Connell and Hofmann 2012 Science paper.

Although O’Connell and Hofmann found strong similarities across all vertebrates, that’s not to say there weren’t differences. Interestingly, the biggest differences were found between major groups of animals. For example, the fish species studied (although similar to each other) had a different distribution of dopamine-producing neurons than did all the 4-limbed animal groups (amphibians, mammals, birds, and reptiles). Additionally, birds and reptiles have more brain areas with vasotocin- and oxytocin-producing neurons compared to the other animal groups. Changes in where these neurochemicals are produced in the brain may correspond to changes in the animals’ social environments and the behaviors best adapted to such social environments.

The approach that O’Connell and Hofmann used in this study integrated decades of research on the brains, neurochemistry and behavior of nearly 100 different species, but it shows us that when we stand back and look at the bigger picture some remarkable patterns emerge. All vertebrates, from giraffes to tree frogs to iguanas likely have very similar brain systems that work in very similar ways to regulate very similar behaviors.

Want to know more? Check these out:

1. O'Connell, L., & Hofmann, H. (2012). Evolution of a Vertebrate Social Decision-Making Network Science, 336 (6085), 1154-1157 DOI: 10.1126/science.1218889

2. O'Connell, L., & Hofmann, H. (2011). The Vertebrate mesolimbic reward system and social behavior network: A comparative synthesis The Journal of Comparative Neurology, 519 (18), 3599-3639 DOI: 10.1002/cne.22735

3. O’Connell, L., & Hofmann, H. (2011). Genes, hormones, and circuits: An integrative approach to study the evolution of social behavior Frontiers in Neuroendocrinology, 32 (3), 320-335 DOI: 10.1016/j.yfrne.2010.12.004