The human cortex responds to an interoceptive challenge

Functional neuroimaging with positron emission tomography (PET) and functional MRI permits identification of neurophysiological correlates of distinctly human psychological functions such as language, conscious experience, and philosophical thought. In the enthusiasm to attribute regional brain activity in humans to high-order functions, low-level accounts may be underemphasized. It is widely appreciated that brainstem and hypothalamic nuclei have a critical role in regulating neuroendocrine cycles and controlling homeostatic autonomic reflexes and vegetative processes (1). However, psychologists frequently ascribe autoregulatory control only to subcortical “reptilian” (2) regions, whereas cortical areas emote, evaluate, and reason. In recent years, Damasio (3, 4) has reemphasized the dependence of higher-order functions on bodily states of arousal. In a recent issue of PNAS, the work of Teves et al. (5) represents an important reminder that cortical and thalamic activity is modulated directly by perturbations in peripheral homeostasis that evoke autonomic arousal. The authors undertook a PET study to examine changes in regional brain activity (reflected in regional cerebral blood flow) during states of low blood glucose (hypoglycemia). Hypoglycemia evoked sympathetic and parasympathetic autonomic arousal, apparent in a range of physiological and neuroendocrine measures. States of hypoglycemia and autonomic arousal were associated with enhanced activity in rostral anterior cingulate (ACC), orbitofrontal cortex, thalamus, and brainstem. One interpretation is that these activity increases reflect generation and control of autonomic responses to the low-level physiological challenge of hypoglycemia (5).