It would appear that our genetic legacy also features some very intriguing left-overs, which are not necessarily of use to us today. One such feature is the fact that the human brain triggers a primordial type of fear when exposed to increased amounts of carbon dioxide (CO2), which makes us fear suffocation in the most “thorough” way possible. The cortex seems to have what scientists have termed a built-in sensor against high CO2 concentrations, which circumvents other alert mechanisms.

The new study could have significant implications for the people that suffer from panic attacks very often. The condition, which severely affects their lives – even if it's not lethal –, may come from mechanisms such as the recently discovered one, which malfunctions in some individuals. The work may also be able to finally explain why people drawing deep breaths can calm down when suffering from such anxiety attacks, LiveScience reports. The investigation was conducted on unsuspecting mice.

In the research, scientists from the University of Iowa focused on a region of the brain known as the amygdala, which had been proven in past studies to play a major role in mediating innate and learned fear. The acid-sensing ion channel-1a (ASIC1a) was also a target of the scientific effort. This is a chemical that has been found in high concentrations in the amygdala, and in other fear-sensing neural circuits inside the brain. The researchers corroborated the data they had on this chemical with the knowledge that rising levels of carbon inside the body could force the brain to alarm itself on the dangers of suffocation.

CO2 does not interfere with the body's functions directly. Rather, it reacts with water to form carbonic acid, the same substance that is found in carbonated soft drinks. The team hypothesized that it was this increased acidity that was responsible for generating the suffocation sensation. It argued that carbonic acid interacting with the ASIC1a might have provided the foundation for this mechanism. “The amygdala has been thought of as part of the fear circuitry of the brain. Now we see it isn't just part of a circuit, it is also a sensor,” UI physician John Wemmie, who worked on the new study, says.

“Detecting an elevated carbon dioxide is critical for survival. When you are suffocating, this circuit triggers mechanisms for escape or relief of the problem,” UI researcher Michael Welsh concludes. Details of the team's work appear in the November 25 issue of the scientific journal Cell.