FIGURE 2.

Schematic diagram illustrating the stage-by-stage workflow for obtaining energy source. Active behavior and autonomic function in each stage are listed in the second row, while possible external and internal sensory inputs including stressors that occur in each stage are shown in the third and fourth rows. At the external stage, the brain shows active waking state (fifth row) and attends to the orthonasal/exteroceptive odor information and other exteroceptive sensory information (blue boxes). At the oral and swallowing stages, the brain shows active waking state attending to the retronasal/interoceptive odor information and other interoceptive sensory information (orange boxes). At the gastrointestinal and blood-circulation stages, the brain shows quiet and relaxed state with reduced attention to the exteroceptive and interoceptive sensory inputs (Brown et al., 2012). At any stage, retronasal detection of aversive odors indicating metabolic abnormality may alert the animal and induce the stress responses (Bollen and Beikler, 2012; Poniewierka et al., 2022).