Most audiologists know that humans hear from about 20 Hz to 20 kHz and as we age our frequency range might go down somewhat, according to some sources, to about 12-15 kHz.  It is, however, no fun to know the same things as your colleagues.  For your next audiological trivia encounter consider a challenge of,  “What species has hearing up to 300 kHz?”   The audience or colleagues will be in amazement and not believe that anything or anybody hears at that high of a frequency.  While our favorite audiology trivia game will not be returning to our annual American Academy of Audiology Convention anytime soon, knowing the best audiology facts can win those other trivia contests! 

Dolfins are thought to have 10 times the sensitivity of humans and also hear at a very high frequency hearing range at about 160 kHz (extra trivia to dazzle friends) that is used for communication and echolocation.  They have very small ears behind the eyes so many people don’t give their hearing much of a thought. They can hear both in the water and on the surface of it.   For many years, Bats were thought to have the highest frequency hearing at 217 kHz (more dazzling trivia).  Of course, Bats also use their high frequency hearing for echolocation. By sending out high frequency call and analyzing echoes that come back, bats and the dolfins can essentially “see” the whole picture of the world around them.  Scientists have long thought that bats judge the size of a nearby object based on the strength of this echo, but a new study shows that echo intensity alone does not paint the whole picture.   Castro (2011) suggests that what is really important to the bats, is an echo parameter called sonar aperture — the spread of angles from which echoes impinge on the bats’ ears, with a larger spread indicating a larger object.  Now you might win the contest by knowing about  about bat hearing and how the use echolocation as well as the limits of their hearing but you would be a tough contestant by knowing that the Greater Wax Moth hears up to 300 kHz.  While the workings of the echolocation of bats with their high frequency sensitivity is interesting, their frequency range capability perils in the face of the Greater Wax Moth.

Here’s the Deal…….

Research in Glasgow, Scotland, UK supports the notion that these moths hear at an incredible high frequency.  Dr. James Windmill of the University of Strathclydethe’s University’s Centre for Ultrasonic Engineering, has identified the extraordinary sensory characteristics of the moth, paving the way for developments in air-couple ultrasound.  Windmill said, “We are extremely surprised to find that the moth is capable of hearing sound frequencies at this level and we hope to use the findings to better understand air-coupled ultrasound.”  He further said, “It’s not entirely clear how the moths have developed to be able to hear at such a high frequency, but it is possible that they have had to improve the communication between each other to avoid capture from their natural predator, the bat, which use similar sounds.”  Prior to the Windmill team’s research others had tested the hearing of the greater wax moth but gave up as the frequency range approached 100 kHz. The use of a vibrometer to measure the vibrations of the ear in response to sound waves as well as the electrical signals in the auditory nerve, then watched as the sound got more n more high frequency with the response finally vanishing at 300 kHz.

Do we Really Care?

So, this is nice, but why do we care about the Greater Wax Moth having a frequency range for hearing range up to 300 kHz?  The use of ultrasound in air is extremely difficult and as high frequency signals are significantly quickly weakened in the air. Other animals such as bats are known to use ultrasound to communicate and now it is clear that moths are capable of even more advanced use of sound.  The research findings will allow the Dr. Windmill and his colleagues to further develop their understanding of ultrasound and how to transmit and receive ultrasonic pulses travelling in air.  With frequency sensitivity that is unparalleled in the animal kingdom, this moth is ready for any echolocation call adaptations made by the bat in the on-going bat–moth evolutionary war.

Dr Windmill’s multi-disciplinary research team is now working to apply the biological study of this, and other insect ears to the design of micro-scale acoustic systems. It is hoped that by studying the unprecedented capabilities of the moth’s ear, the team can produce new technological innovations, such as miniature microphones.  Click here or on the Moth for a video of the Greater Wax Moth story.

 

 

References:

Castro, J. (2011).  New picture of bats acoustic sense emerges. Live Science.  Retrieved January 17, 2017. 

Moir, H., Jackson, J., & Windmill, J. (2011). Extremely high frequency sensitivity in a ‘simple’ ear. Biology Letters, 2013; 9 (4).  Retrieved January 17, 2017.

Video:

GeoBeats news (2013).  Moths can hear ultrasonic sound.  YouTube.com.  Retrieved January 17, 2017.

 

 

 

 

 

 

 

 

Last week we discussed a bit about marijuana legalization and its general effects.  For the effects of marijuana on  hearing, however, the jury is still out.

Probably due to the drug classification, there has been minimal study of marijuana and its effects on hearing, as well as on some other body functions.  The data available in 2017 are largely anecdotal and much of the hard research is yet to be funded and conducted. 

The National Institute on Drug Abuse (NIDA) (2015) indicates that a probable cause of the lack of research also stems from the Food and Drug Administration (FDA) requiring carefully conducted studies (known as clinical trials) in hundreds to thousands of human subjects to determine the benefits and risks of a possible medication. So far, researchers have not conducted enough large-scale clinical trials that demonstrate that the benefits of the marijuana plant (as opposed to its cannabinoid ingredients) outweigh its risks in patients it is meant to treat.

While there seems to be mostly anecdotal indications on the benefits or detriment of marijuana on hearing, there appear to be some logical indications as well as some seminal research that the drug might have some benefit for tinnitus.

 

New Thoughts of the Origin of Tinnitus

 

Until recently, not much was known about the cause or source of tinnitus. New thoughts on tinnitus from various researchers funded by the Veterans Administration (VA), National Institutes of Health (NIH) as well as private organizations such as the American Tinnitus Association (ATA), suggest that tinnitus is not necessarily an auditory or ear malady but a brain issue.

Prevailing older theories generally assume tinnitus is duee to inner ear malfunction of one type or another (e.g., mis-shapened or dstroyed hair cells;  lack of blood supply to the ear; etc). Yet, audiologists and otolaryngologists have known for some time that even when the auditory nerve is cut, the tinnitus from the “disconnected” ear can persist, often even worse than before.  

Dr. Thanos Tzounopoulos, Chair of Auditory Physiology within the Department of Otolaryngology at the University of Pittsburgh, was among the first researchers to suggest that the locus of tinnitus was in the brain and not the brain. His research suggests that tinnitus is likely caused by misfiring neurons in the auditory center of the brain, and may be caused by an imbalance between inhibitors and stimulus within the auditory sensation.

In other words, the brain is mistakenly responding to sound, where no sound exists, creating the tinnitus effect. These studies, begun in 2009, were further refined in 2011 and have become an ongoing investigation.

 

What does that have to do with marijuana use?

 

Naturally generated cannabinoids in the body are one of the inhibitors within the auditory center.   In 2011, Dr. Tzounopoulos and his team published research that demonstrated exaggerated activity in the brains of mice with tinnitus. They also made breakthroughs in the understanding of the endocannabinoid system, which was found to control aspects of brain plasticity. It is this activity that reacts to marijuana as these cannabinoids are present in the marijuana.

Dr. Tzounopoulos compares tinnitus to chronic pain and addiction, which also seem to involve plasticity in the brain and are treated with medical marijuana. While this does not shed light on the precise mechanism by which medical marijuana provides relief for tinnitus, it does show the components of the mechanism. 

Another recent theory of tinnitus is that it is a form of sensory epilepsy, sometimes arising from neuronal hyperactivity in the brainstem cochlear nucleus. The exact relation of tinnitus and seizure is not known but a few established facts can assist in the understanding how tinnitus and seizures might be connected. Of course, tinnitus is an auditory abnormality wherein a person hears ringing or buzzing sounds in the ear or head regions in the absence of any actual external sounds. Seizures are characterized by repeated movements of the body or body parts, sometimes violently. The intensity of both tinnitus as well as seizures can differ and present symptoms in varying degrees of intensity.  Both the conditions of tinnitus and seizures occur because of an irregularity of the electrical activities in the brain. This irregularity is usually caused by a nervous system disorder or a pathological condition in the neck and head regions. There are other causes as well that can contribute to the occurrence of both these conditions. Since the causes vary widely in both disorders sometimes the exact reason for tinnitus and seizure is difficult to pin point. At the same time, since most of the causal factors usually rise from similar root causes in many instances, it is possible that tinnitus and seizures can indicate a common origin – though they need not always coincide.  Increasing evidence suggests that cannabinoid drugs can also have antiepileptic effects.  And since the origins of both tinnitus and seizures are thought to be similar, then the possibility that cannabinoids could be beneficial holds some promise.

Of course, medicinal cannabis has been prescribed to help people cope with some of the conditions that can cause tinnitus. In those cases, it’s easy to see how marijuana might help. Even among those people whose tinnitus doesn’t respond to marijuana, it may help alleviate some of the stress, anxiety, and insomnia that plague tinnitus sufferers. 

One thing many people forget is that a marijuana prescription isn’t like a regular pharmaceutical prescription–it is essentially permission for an individual to experiment with medical-grade cannabis and determine if it helps their symptoms. Some tinnitus sufferers may find that it does, while others may find that it worsens them.   While there is no recommendation for the use of marijuana for tinnitus or hearing loss cited in the literature, it is extremely likely that new research studies will be conducted now that marijuana is legal in 7 states with more to come in the future.

 

References:

Eye and Ear of Pittsburgh (2017). Tinnitus and auditory science.  Retrieved January 9, 2017.

Marijuana Doctors (2013). Medical marijuana and tinnitus.  Retrieved January 9, 2017.

Middleton JW, Kiritani T, Pedersen C, Turner J, Gordon M, Shepherd G, Tzounopoulos T. (2011). Mice with behavioral evidence of tinnitus exhibit dorsal cochlear nucleus hyperactivity due to decreased GABAergic inhibition. Proc Natl Acad Sci U S A 108(18). Retrieved January 10, 2017.

MedicalMarijuanablog.com (2016). Marijuana a solution to tinnitus.  Retrieved January 9, 2017.

National institute on Drug Abuse (2015). Is marijuana medicine?  Drug Facts.  Retrieved January 10, 2017.

Tuneouttinnitus.org (2017). A neurological tinnitus study.  Retrieved January 9, 2017.