After just reading the Allen et al., article I think we need to be conservative in our conclusions that the use of hearing aids improves cognitive function. The authors themselves state:
“Hearing aids do not improve cognitive function or reduce behavioural or psychiatric symptoms.”
The PTA of this group was ~60 dB, this is clearly more than a mild hearing loss. Certainly this article and others like it have shown hearing aids can improve communication function, in the presence of hearing loss, and hence reduce the negative effects of hearing loss in a variety of psychosocial realms for many different populations. Tying this improvement to changes in neurophysiology, however, may difficult and not really necessary as we see immediate improvements in speech understanding when the speech goes from inaudible to audible.
Please note that I am talking about cases of mild-moderate hearing loss. The situation is vastly different for individuals with severe to profound loss. In these cases conversational speech is often inaudible and the use of a cochlear implant can drastically change the input that the auditory system is receiving. In these types of situations bringing in neural plasticity seems, at least intuitively, to make more sense. For individuals with mild to moderate losses, however, (which is where this thread started) much of (low frequency) conversational speech is audible without a hearing aid. Adding the aid will help with soft sounds and improve some but not all high frequency audibility. Acclimatization studies with these types of patients have shown only minimal (or no) long term improvement in speech understanding, suggesting changes in neural networks due to plasticity is minimal.
Allen, N.H.; et.al.: The effects of improving hearing in dementia. Age Aging 2003;32: 189-193
This article is the most recent. Dementia patients were fit with one hearing aid (should have been two.) After 24 weeks of wearing the aids, 30% showed no further cognitive decline and 40% showed cognitive improvement. Those who wore their aids for 8 hours or more per day were seen by caregivers to have significantly improved compared to those who wore them less.
You can put in a search for an article that is on my updated list that states even mild hearing losses can cause verbal memory problems. This may be due to a weakening of synaptic density and other neurophysiological changes to those neurons that respond to sound in the hippocampus and other regions implicated in working memory.
On Monday, if you would like, I wrote an article that I'm attempting to get publish that describes the effect of Alzheimer's disease on the auditory system. Let me know if you would like a copy of this article in the format that I have it right now. It will probably need to be edited, but there has been interest in a shortened version of the article. It is referenced.
Please let me know.
>From: "Ward Drennan" <email@example.com>
>To: "Barbara Reynolds" <firstname.lastname@example.org>
>Subject: Re: Affordable hearing aids extant?
>Date: Sat, 27 Mar 2004 23:38:57 -0500 (EST)
>I've found you comments quite interesting and I think there's a lot of
>good ideas in them. It's apparent that you've done lots of reading. I
>ceratinly could learn much more about these topics. I wrote some
>questions, comments and citations requests within your writing (see
>attached document). These requests should be quite specific--- I'm trying
>to point to the main or most significant points that should be addressed
>(by someone at least). If this information is true and is to be widely
>disseminated and accepted, we would need to be in some tractable form
>accessable to scientists and clinicians i.e. a few well-written and
>thorough reviews or research studies to verify the accuracy of the
>statements. I'm not sure for example what research has been established
>and what reserach still needs to be done.
>If some of your statements can be or have been shown to be true, then by
>golly it should be public knowledge. "Wear hearing aids or you'll lose
>your mind" sounds like a pretty good motivation, but then how much do we
>(the research and clinical community) really know about that?
>I have done a number of medline searches, but just haven't yet been able
>to find much on hearing loss and cogntnitive degeneration independent of
> > I'll try to run a filter on my database for the references. They'll be
> > without the titles, but the author and the reference. I'll try to limit
> > it to the last five years. Another way would be to search on
> > www.pubmed.com anything you might be interested in. I search journals
> > from Journal of Neuroscience to Nature Neuroscience, NeuroReport,
> > Perceptual and Motor Skills, Dementia and Geriatric Cogntivie Disorders,
> > Age and Ageing, Neurotoxopharmacology, Neuroscience Nursing, PNAS, etc.
> > This accumulation has been over 6 1/2 years. Every 6 months I go to the
> > libraries at McGill (not that I'm in Canada) and the Montreal Neurological
> > Institute. I usually come back with anywhere between 250 to 350 journal
> > articles that either directly test the auditory system, or use the
> > auditory system to test a disease state such as Alzheimer's or
> > Parkinson's, Dyslexia or emotional prosody deficits, stroke, etc. As!
> > an audiologist, if it uses the auditory system to test a disease state,
> > it's still a test of the auditory system as well. And since my patients
> > are at risk for some of these conditions (including alcoholism, drug
> > abuse, nutritional deficiencies, etc), I should know if it will affect
> > their perception and recovery through the use of hearing aids.
> > By using this information, 1) you'll definitely become a better clinician
> > and 2) your patients will try harder to become more compliant with the use
> > of hearing aids because they trust that you know what you're doing and 3)
> > by considering all these conditions (diabetes, MS, etc) you'll be able to
> > counsel the patients more effectively on the benefits and limitations of
> > amplifications.
> > I was at a conference of a manufacturer several years ago and one of the
> > representatives actually said "If you fix the hearing aid, you'll fix the
> > hearing loss". I about had a cow. You cannot fix Alzheimer's or stroke
> > damage through a new digital algorithm. No matter what we do, we are
> > still sending information through an impaired system that may or may not
> > recover significantly depending on how severe the loss is and how we
> > counsel the patients.
> > I will try to see what I can do though in regards to references. I have a
> > list I used for my Alzheimer's presentation in Vancouver that I can send
> > an attachment when I get back to work.
> > Barb
> > email@example.com_auditory@HOTMAIL.COM Check out MSN PC Safety &
> > Security to help ensure your PC is protected and safe.
>Ward R. Drennan, Ph. D.
>Kresge Hearing Research Institute
>Ann Arbor, MI 48109
><< CommentsandcitationrequestonBRswriting.doc >>