r norman <rsnorman_ at _comcast.net> wrote in message news:<o9bqdvg2nh04bt9gl53fjslqsndo4mpgjl at 4ax.com>...
> A lot of the tinnitus speculation assumes it is a peripheral
> phenomenon. That is, there really is a sound to be heard or else that
> the hair cells (or auditory nerve neurons) are generating it. What if
> it were a central process? I was told that my situation was most
> likely caused by the ABSENCE of auditory nerve activity -- the central
> auditory centers "didn't like" the absence of normal stimulation and
> took things into their own hands. That is, the frequency range of the
> ringing was higher than my upper limit of hearing. Over the years as
> the my high frequency cutoff dropped lower and lower, so did the
> tinnitus tone.
I accept the possibility of centrally generated tinnitus, but feel
there are a lot of arguments against it.
1. Research in that area, eg Salvi & Lockwood, which suggests that
'tinnitus is central' invariably looks at tinnitus *perception* rather
than generation. eg lymbic or colliculus involvement. This is imo a
shortcoming in interpretation by the researchers... I'm not aware of
any research properly suggesting central generation.
2. Beyond the retina and the cochlea, the sensory components become
structually very similar. If a centrally generated auditory signal was
common (esp in healthy people), one would expect a centrally generated
visual signal to be common. Pain too.
3. As in argument '2' , it is common to have louder tinnitus in one
ear than the other. It is common to have it in a specific frequency
range, and similar frequency ranges are found in groups of people.
Beyond the assymetrical cochlea, there isn't a great physical
difference between the high frequency pathway and the low frequency
pathway. If tinnitus was central, one might expect a totally arbitrary
distribution of frequency.
4. Tinnitus can be caused by physical injury to the ear.
I think there is often a blurring of the concept of tinnitus
generation, and tinnitus perception.
Counter arguments to mine are:
1. Profoundly (??) deaf people have tinnitus to the same extent as
hearing people. So it must in some cases be central.
2. Phantom limb pain is, by definition not in the severed limb, so it
must be central. Similar phenomenon.
In conclusion, there are 4 arguments above supporting my case , and
only two opposing it, therefore I must be right ;-)