Hunger and thirst are induced by deficiencies in nutrient and water, respectively, and elicit clear adaptive motivations and behaviors. Internal sensing is a key modulator of behavior. In addition, a key characteristic of traditional sensory epithelia such as the olfactory system and retina in many vertebrate species is that neurogenesis continues into adulthood, and neurogenesis is also prominent in adult hippocampus, principally underlying the dentate gyrus (DG) (reviewed in. It is of note that the 'rostral migratory stream' in neonatal mice directly connects the HPC and the chemosensing olfactory system, consistent with a common developmental origin. Ī role for the HPC in internal sensing is consistent with evolutionary theory that the HPC (and olfactory system) arose from a chemosensory epithelium, but with the closing of the brain ventricles during evolution the hippocampus retained the capacity to sense the internal milieu of the body. Similar observations have been made in rodents with selective HPC lesions. was unable to sense internal states such as hunger. The HPC (and adjoining amygdala) is a prominent contender–in addition to his profound learning and memory deficits following HPC surgery to alleviate severe recurrent epilepsy, the famous patient H.M. Previous studies have implicated cortical regions, limbic brain, and thalamus, as well as the hypothalamus and brainstem regions, among others, in interoception. However, the central function of the HPC in both memory and neuropsychological disorders may be consistent with an underlying role in internal sensing (interoception).
Implications for anxiety and depression are discussed.Ĭurrent thinking predominantly attributes to the hippocampus (HPC) a pivotal role in learning and memory, in spatial navigation, and in anxiety, stress, and depression. These findings suggest that the hippocampus acts as an integrator of body status, extending its role in context-dependent memory encoding from 'where' and 'when' to 'how I feel'. Further, we report that ligands of DG receptors predominantly inhibit both synaptic potentiation and neurogenesis, whereas CA receptor ligands conversely promote both synaptic potentiation and neurogenesis. Selective expression of endocrine receptors in the HPC argues that interoception remains a core feature of hippocampal function. (ii) Surprisingly, the distribution of endocrine receptor expression within mouse HPC was found to be highly structured: receptors signaling 'challenge' are segregated in dentate gyrus (DG), whereas those signaling 'sufficiency' are principally found in cornu ammonis (CA) regions. Key findings are (i) the proportions and levels of endocrine receptor expression in the HPC are significantly higher than in all other comparable brain regions. We studied the expression patterns in mouse brain of 250 endocrine receptors that respond to blood-borne ligands. Deficits in sensing of internal body status ('interoception') in patients with HPC lesions argue that internal sensing may be conserved in higher vertebrates. Implicated in learning and memory, spatial navigation, and neuropsychological disorders, evolutionary theory suggests that the HPC evolved from a primeval chemosensory epithelium. The primeval function of the mammalian hippocampus (HPC) remains uncertain.