Final answer:
The amygdala, a part of the limbic system located in the medial temporal lobe, is larger in individuals with large social networks and is involved in processing emotional reactions, such as fear.
Step-by-step explanation:
The region of the brain involved in processing emotional reactions and that has been observed to be larger among individuals with large, complex social networks is the amygdala.
The amygdala is a group of nuclei within the medial temporal lobe that is part of the limbic lobe, a system critical for emotional responses and memory function. It is known to play a central role in emotional processing, particularly in the formation of fear-related memories.
Research has demonstrated both structural and functional differences in the amygdala related to mood and anxiety disorders, suggesting it is crucial for normal emotional regulation.
The amygdala's basolateral complex is linked with sensory areas of the brain and is important for classical conditioning and emotional valuation of memories.
In contrast, the central nucleus of the amygdala is involved in attention and regulating the activity of autonomic nervous and endocrine systems via connections to the hypothalamus and brainstem.
Individuals with larger amygdalae have been associated with larger and more complex social networks. This supports the notion that the size and functionality of the amygdala could have an influence on the complexity of social behaviors.