The insular cortex serves as a hub cortical region that is bidirectionally connecting to an extensive cortical and subcortical brain areas and plays a crucial role in interoception, the sensation of internal states of the body, such as heartbeats, hunger, and blood pressure. However, neurophysiological mechanisms and insights supporting this hypothesis remain to be clarified. To address this issue, we performed simultaneous recordings of multiunit spike patterns and local field potential (LFP) signals from the insular cortex, an electrocardiogram signal, and a peripheral blood glucose concentration from freely moving rats. Recordings were daily obtained for seven hours. No pronounced temporal correlational changes were found between ongoing heart rate and blood glucose fluctuations. Insular cortical LFP power in some frequency bands, such as the delta and theta bands, showed apparent temporal correlational changes with ongoing heart rates when the rats were resting. At single-cell levels, a subset of insular cortical neurons increased or decreased their spike rates in response to changes in heart rates and blood glucose levels. These results highlight insular cortical neurons as a detector of temporal changes in interoceptive signals.