Does the Brain Have an Emotion Module?
This post is part three of a short series on social psychology, made up of thought papers I wrote for the Affective Science (PSY5430) course at the University of Toronto, Department of Psychology.
This week’s post focuses on the physiological aspect of emotions, mainly the investigation into the neurological configuration of the brain which deals with affect, appropriately called Affective Neuroscience.
Our original understanding of a living organism’s body, especially primates, is the physical configuration of various body parts, and the obvious functions they perform. The heart is clearly made for pumping blood throughout our system. The human legs are meant to keep us upright and give us the ability to move about. The eye’s most obvious function is to convert light into signals our brain can interpret. This organ-function view of the body has been applied to the brain as well, which is the locationst view [Lindquist et al., 2012]. With the advancement in tools, we discovered that the brain is not simply a set of modules, but a network of neurones. The obvious question, then, is whether the brain could be understood as both individual “parts”, analogous to a leg or an eye, as well as a network of connections. This is the argument of whether a brain is modular, a network, or both, which is the constructionist view [Lindquist et al., 2012].
If we consider the constructionist view of the brain, an internal modularity can still exist in both the physiological and functional forms. Functional in the sense that a group of neurones not necessarily spatially close, work together to perform a task. The formation of modules and hubs has been observed in artificial neural networks when various real-life constraints are placed on the communication between nodes [Pan and Sinha, 2007]. This research has found that modules are formed naturally when a cost is placed on the spatial distance (based on edge-counting) between nodes. This is a realistic view of a physical organ which must balance energy consumption and effectiveness.
Consider the amygdala, a physical hub, connecting various external stimuli to parts of the brain. The amygdala is closely related to fear, meaning fear should be correlated with those senses [Janig, 2003]. Its function has to do with quick responses and interpretations, so it makes sense that the amygdala takes the architectural shape of a tightly connected and efficient hub. In contrast to physical hubs, network hubs in the human brain exist to a serve different type of function [van den Heuvel and Sporns, 2013]. They allow for high levels of functional diversity and functional synchronization between cortical regions. Interpreting emotions is a complicated task and its processing has been observed to be divided between a number of regions with multitude of complex connections. For example, the recognition of emotion from facial expressions and prosody are split between the right and left temporal lobes [Berridge, 2003]. Such hubs form early on in brain development. For example the connection between the medial posterior cingulate, frontal and insular regions are already present in the postnatal infant and child brain [van den Heuvel and Sporns, 2013]. Due to the sheer numbers of neurones in the brain and their complex interconnectedness, it may be impractical, if even possible, to try and identify the functions of individual neurones. Instead, its more feasible to identify sub-networks of neurones which function together to achieve a task. It would also be more practical to identify which hubs of neurones largely function as incoming or outgoing points, the so-called sink or source hubs [van den Heuvel and Sporns, 2013]. It may make sense to call a group of neurones a module, based on their spatial proximity, but it should not be viewed as the only architecture the brain has utilized.
[Berridge, 2003] Berridge, K. C. (2003). Comparing the emotional brains of humans and other animals. In Handbook of affective sciences, chapter 3. Oxford University Press, New York, New York, USA.
[Janig, 2003] Janig, W. (2003). The Automatic Nervous System and Its Coordination by the Brain.
[Lindquist et al., 2012] Lindquist, K. a., Wager, T. D., Kober, H., Bliss-Moreau, E., and Barrett, L. F. (2012). The brain basis of emotion: a meta-analytic review. The Behavioral and brain sciences, 35(3):121–43.
[Pan and Sinha, 2007] Pan, R. and Sinha, S. (2007). Modular networks emerge from multiconstraint optimization. Physical Review E, 76(4):045103.
[van den Heuvel and Sporns, 2013] van den Heuvel, M. P. and Sporns, O. (2013). Network hubs in the human brain. Trends in cognitive sciences, 17(12):683–96.