Infrasonic Stimuli
Infrasonic stimuli as a means to cause physical, cognitive, or behavioral disruption has been studied and debated across scientific, military and intelligence circles since the mid-20th century.
What are infrasonic stimuli?
Infrasonic stimuli are air-pressure waves that occur in frequencies below that of the audible range in reference to a particular organism. (In reference to humans, any frequency below 20 Hz is generally referred to as “infrasonic”.)
What have infrasonic stimuli been proposed to do to organisms?
Nausea: The initial description of a biobehavioral effect from infrasonic waves comes from an experience the French scientist Vladimir Gavreau and his colleagues experienced in their robotics production laboratory in 1957. Open widows high in the ceiling of his concrete building were allowing infrasonic harmonics to enter the building from a poorly installed ventilator motor. People working in the lab reported feeling periodic nausea. Once they realized the source of this employee health problem ceased when the windows were closed, they inspected the motor. They found it was not emitting chemical discharge, but it was vibrating at an infrasonic frequency. This serendipitous finding began the study of infrasound as an external, sensory stimulus that could cause physical difficulties in people exposed for prolonged periods of time. See http://www.borderlands.com/newstuff/research/gavreaus.htm for a more in-depth description of their research efforts in developing infrasonic weapons.
Healing and Relaxation: The Chinese have studied infrasonic waveforms emitted from Qi-Gong Masters has a physical mechanism for healing and well-being. Nowadays, hand-held massaging devices which vibrate at infrasonic frequencies are marketed as deep-penetrating relaxation device.
Hypertension: Danielsson and Landstrom reported that moderate to high intensity infrasonic stimuli caused increased diastolic blood pressure over 30 minutes (Acta Med Scand. 1985;217(5):531-5.)
Why are there vast differences in the proposed effects of infrasound?
Frequency specificity: The proposed effects of these stimuli are thought to be through resonating particular tissue at specific frequencies. For instance, the nausea described by Gavreau could have been due to physical vibrations in organs in the abdomen or possibly though stimulating the fluid in the semicircular canals or otoliths in the inner ear (signaling disequilibrium).
Intensity parameters: The level of intensity is an important factor in any psychophysical effect. The actions of infrasound on neurobehavioral reactivity are no different. Inasmuch as particular frequencies are necessary to cause effects, the intensity of the stimuli has to exceed a threshold level for resonating a specific tissue group. The intensity factor is related to the power of the wave to reach that tissue group through the barriers of other tissue (such as the multi-layers of the dermis, muscle, etc.).
Duration: The length of exposure is important, in that, many studies have shown changes in behavior when the infrasonic stimuli are presented over many minutes (e.g. Petounis, Spyrakis & Varonos, Physiol. Behav, 18, 153-155, 1977; Yamamura & Kishi, Eur J Appl Physiol, 45, 81-86, 1980)
Interactions: The interaction of the 3 above listed physical variables can equate into a number of permutations once the available ranges for each variable are considered. An understanding of the target tissue, the physical characteristics of the intervening tissue and the attenuating properties of that tissue.
Our Research Testing Infrasonic Stimuli on Animals:
Test Chamber: Our laboratory biomedical engineering staff constructed a testing chamber (a Norlake refrigeration box) to house the speaker and the animal testing area.
Speaker Apparatus: John Domen (ARDEC, Picatinny Arsenel) constructed a speaker system based on a Helmholtz resonator parameters (see fig. 2). A large-coned speaker, an 18" Electro-Voice EVX-180B speaker driver, produced the low frequencies. It incorporated a Heatwick design to direct heat away from the voice coil, increasing power handling and long-term reliability. A high output 700-Watt audio amplifier (1800 Series V, Bose) was used to enhance the signal power. The device had a power bandwidth of 5Hz to 40kHz and a frequency response of 20 Hz to 20kHz. Tuning forks or ports were used to control the resonate frequency. This box was made of .75 inch plywood and had two tuned ports to amplify infra-sound frequencies between 7 Hz and 14 Hz. Eight tuning devices (ports) were constructed of 6-in diameter PVC tubing, cut to a specific length thereby enhancing each of the frequencies of interest by providing room for resonation of that particular wavelength. These lengths were calculated using the Helmholtz equation
where L=length of tube, A=cross-sectional area of tube, V=volume of tube, S=speed of sound in air, and f=frequency of interest.
Stimulus Control and Signal Recording: They also designed and constructed a computer control system for stimulus amplification and delivery to the speaker and physiological detection, amplification, and A/D conversion of ECG and EEG signals from the animals.
Past Results from our Laboratory:
Singly applied pure infrasonic waves at one of 6 frequencies (9-14 Hz) at 103 dB (30 s duration) did not cause any acute effects on heart rate in male rats.
Homecage wheel running activity (which generally occurs during the dark phase - opposite of the testing time in the light phase in male rats) was reduced following the 2 initial test sessions (when the acute heart rate responses were measured), however, this could have been due to timing of the testing - not the stimuli per se.
Pure infrasonic waves (9-14Hz) with intensities reaching 113dB (30 s duration) do not cause noticeable effects on rat behavior (open field activity) or gross brain activity (EEG).
Using a 4-speaker-driven system (Crown amplifier and Turbosound cabinet speakers), we presented frequency waves of 25, 80, or 178 dB (at 110, 125, and 120 dB, respectively). These are frequencies that are both infrasonic to rats and proximate resonance frequencies for the rat's head, abdomen, and lungs.
Rats exposed to 25 Hz showed lower startle responses.
Rats exposed to either 80 Hz alone or a frequency modulation between 25 and 80 Hz fell off the rotor rod significantly quicker than those not exposed to any stimuli.