Brain’s Fear Center Is Equipped With A Built-In Suffocation Sensor

The portion of our brains that is responsible for registering fear and even panic has a built-in chemical sensor that is triggered by a primordial terror – suffocation. A report in the November 25th issue of the journal Cell, a Cell Press publication, shows in studies of mice that the rise in acid levels in the brain upon breathing carbon dioxide triggers acid-sensing channels that evoke fear behavior.

In addition to the insight into the normal fear response, the discovery may help to explain and perhaps even correct what goes wrong in those who suffer from panic attacks, the researchers say. (It’s been known for almost a century that carbon dioxide inhalation can trigger panic attacks, and that patients with panic disorder are particularly susceptible.)

“The amygdala has been thought of as part of the fear circuitry of the brain,” said John Wemmie of the University of Iowa, Iowa City. “Now we see it isn’t just part of a circuit, it is also a sensor.”

“It’s interesting that evolution positioned an acid sensor right in this central circuit,” added Michael Welsh, also of the University of Iowa. “Detecting an elevated carbon dioxide is critical for survival. When you are suffocating, this circuit triggers mechanisms for escape or relief of the problem.”

The circuit in question resides in the amygdala, a structure that stimulates the sympathetic nervous system for fight-or-flight and links to other brain regions involved in the response to threat. The amygdala is known from earlier studies to play a role in both innate and learned fears.

In previous studies, Wemmie’s and Welsh’s team discovered that the acid-sensing ion channel-1a (ASIC1a) is particularly abundant in the amygdala and other fear circuit structures, where it is required for normal responses in tests of fear behavior. As the name suggests, ASICs are sensitive to pH and become activated when pH levels fall. Read more