Hear Ye! Directional Sound Enabled by Superfast Neurons

How can you tell where sounds come from?  The brain is quicker than the speed of sound between your ears.

There’s only about 8 inches between your ears (more, perhaps, for fatheads).  The speed of sound is finite.  The tiny time lag between the arrival at one ear compared to the other is what enables us to sense the source direction of the sound, but there’s more to it than that.  If signals did not get processed in the brain faster than the time lag, the information would not be useful.

Science Daily asks, “How Do We Locate the Spatial Position of Sounds? Mechanism Responsible for Creation of Giant Synapses Discovered.”  Sure enough, there are massive hubs or neural intersections in our brains that can process information faster than the speed of sound.  Here’s the upshot (notice the astonishment):

Humans and most mammals can determine the spatial origin of sounds with remarkable acuity. We use this ability all the time — crossing the street; locating an invisible ringing cell phone in a cluttered bedroom. To accomplish this small daily miracle, the brain has developed a circuit that’s rapid enough to detect the tiny lag that occurs between the moment the auditory information reaches one of our ears, and the moment it reaches the other. The mastermind of this circuit is the “Calyx of Held,” the largest known synapse in the brain. EPFL scientists have revealed the role that a certain protein plays in initiating the growth of these giant synapses.

Because it resembles the calyx of a flower, anatomist H. Held described it as such in 1893.  Regarding it, Wikipedia says, “This structure is specially designed for fast, efficient transportation of information from one cell to the next.”  The part of the brain that processes auditory information has a number of these structures.

According to the Science Daily article, studies at the Ecole Polytechnique Fédérale de Lausanne (EPFL) show the Calyx of Held to act “almost like peer-to-peer communication between neurons.”  These synapses have hundreds of inputs.  “The result is that information is processed extremely quickly, in a few fractions of a millisecond, instead of the slower pace of more than 10 milliseconds that occurs in most other neuronal circuits.”

EPFL scientists identified a protein named BMP that is implicated in developing the contact points for the Calyx of Held.  “The impact of this study will go well beyond increasing our understanding of the auditory system,” the article says.  “The results suggest that the BMP protein plays an important role in developing connectivity in the brain.”

Medical Xpress begins with an image of the giant synapse.

“The brain has developed” this circuit.  Funny; did you ever ask your brain to do that?  There’s another example of pulling off evolutionary magic by misdirection.

In his excellent book, The Wonder of Man (1999), Dr. Werner Gitt provided numerous amazing details about our senses.  The ear, “our highest precision sense organ,” is able to detect energy ratios of one million million to one, an “astonishing feat” that approaches auditory perfection.  Since each ear provides two sound paths, we actually get four inputs for localizing sound sources.  Considering the path lengths and the speed of sound, the brain must be able to process inputs arriving as close as 0.00003 seconds apart.  “In acoustic orientation terms this means that a sound source located only about 3° from the centre line of the head is recognized as being off-centre,” he said.  The slight difference in sound intensity between the two ears also gives us information on the distance to the sound.

Dr. Gitt’s book, though 14 years old, is highly recommended if you can find it.  It’s well illustrated and extremely interesting.  Not only does he provide a wealth of information about the senses and other body organs, he gives the glory not just to an unspecified designer, but to the Lord Jesus Christ.  [Note: None of the secular sources in this entry dared mention their idol, Charlie.]  The power of the Christian explanation for the wonders of creation is in the details that this book so beautifully presents.