science forum beginner
Joined: 25 Oct 2005
|Posted: Wed Jun 21, 2006 4:37 pm Post subject:
40hz spike in EEG
I was told that sound at 40hz of a few cycles in length produces a
spike on an EEG. My question is, what causes the neurons in the primary
auditory cortex to disregard that signal as noise, and not cause a
spike that we can hear?
Also, what's the effect of more cycles of this sound being played
through the speakers?
"The auditory cortex exhibits some strange behavior pertaining to the
gamma wave frequency. When subjects are exposed to three or four cycles
of a 40 hertz click, an abnormal spike appears in the EEG data, which
is not present for other stimuli. The spike in neuronal activity
correlating to this frequency is not restrained to the tonotopic
organization of the auditory cortex. It has been theorized that this is
a "resonant frequency" of certain areas of the brain, and appears
to affect the visual cortex as well (10)."
What causes people to get songs stuck in their heads?
"Hallucinations have been shown to produce oscillations which are
parallel (although not exactly the same as) the gamma frequency range.
Sperling showed in his 2004 study that auditory hallucinations produce
band wavelengths in the range of 12.5-30 Hz. The bands occurred in the
left auditory cortex of a schizophrenic and were controlled against 13
controls (1 . This aligns with the studies of people remembering a
song in their minds; they do not perceive any sound, but experience the
melody, rhythm and overall experience of sound." - also from the
primary auditory cortex article.