SSS 2009-11-03（在线收听）

The other day my 3-year old God son and I were pillow fighting when he sat down, panting, and said with surprise, "I can feel my heart beating!" Sometimes it takes little kids to remind us just how amazing our bodies are.

Scientists believe that an area of the brain, the interior and anterior cingulate cortex, is involved in what is known as interoceptive awareness—the awareness of our own physiological sensations, like a heart beating deep within your body.

But recent research from the University of Iowa has shown that we can also use another separate pathway when we consciously experience our internal physical states.

This second pathway, they believe, runs from the skin to the somatosensory cortex, which is the part of the brain that maps the external body.

The results came from a study with a neurological patient, “Roger,” who has been studied in the lab for 15 years, after suffering brain damage from herpes simplex encephalitis. Roger has nearly complete damage to his insula and anterior cingulate cortex, but his somatosensory cortex is completely intact.

Researchers injected 11 healthy male subjects and Roger with a synthetic form of adrenaline, which made their pulses’ shoot up by 25 beats per minute.

Roger felt his heartbeat as clearly as the other subjects, although slightly delayed. Researchers suspected Roger’s brain registered his heartbeats from the surface of his chest wall and from blood vessels pulsating under his skin. To confirm this they anesthetized his skin in specific areas, and administered adrenaline again.

The healthy subjects felt their heartbeat, as before. But Roger felt nothing.

This study suggests that both brain pathways are involved in interoceptive awareness, which can cover anything from a panic attack, to the sick-feeling of rejection, to a pounding heart from an afternoon pillow fight.