The model in figure 5.2 incorporates the bodily perception theory of emotion by virtue of the role
played by the amygdala and the insula in collecting input from internal sensors that respond to bodily
changes. These changes are the result of both sensory input conveyed via the thalamus and the
feedback relations between physiological processes such as heartbeat and respiration and brain
processes in areas such as the amygdala and the insula. People have a penchant for simple linear
causal explanations: factor A causes factor B, which causes factor C. But biological systems often
involve extensive causal interactions based on feedback, so that A and B interact to cause C, which
then has a causal influence on A. For example, your liver function and diet both increase your
cholesterol level, which then induces your liver to produce less cholesterol. Understanding how the
brain produces emotions requires appreciating the complex of reciprocal connections shown in figure
5.2, producing highly nonlinear processes because of all the feedback that occurs.