The neural pathway by which we feel stimuli originating inside our bodies ― such as our heartbeat ― is illuminated by studying an unusual patient with unique patterns of brain damage, according to a study published online this week in Nature Neuroscience.
Previous brain imaging studies reported that a network of brain regions were critical for sensing internal stimulus, such as heartbeat. Two such regions of interest are the insular cortex ― an area deep in the brain which plays a role in the body's homeostasis ― and the anterior cingulate cortex ― a region that regulates automatic functions, such as blood pressure and heart rate. These brain regions are also involved in emotion processing and other cognitive functions.
Sahib Khalsa and colleagues report that a patient who had suffered damage to his insular cortex and anterior cingulate cortex is surprisingly still able to sense an increase in his heartbeat, when given a drug that increased his heart rate. However, when a topical anesthetic was applied to his chest, this patient was no longer able to sense the change in his heart rate.
This study suggests that the neural structures innervating the skin are able to independently monitor self-awareness of one's own heartbeat and that moreover the insular cortex and anterior cingulate cortex are not necessary for this type of self-awareness.