Russ & matti,
The links I posted on pages one and three of this thread are the best articles I have found. Here's an interesting one
http://www.scuba-doc.com/LTE.htm on the cognitive problems of long-term scuba divers which is directly related to our situation. In the last few weeks I've been concentrating on the space program. Here's my e-mail to Dr. Chuck Oman at MIT (
http://www.nsbri.org/Research/Neuro.html )and his reply. They are generally now focussed on spatial thinking problems but the American astronaut now on the space station is doing more broadly based cognitive testing using a program that I will red flag with with a new thread when it is available.
Dr. Oman,
I wanted to call your attention to recent research linking compensated balance disorders resulting from vestibular damage to cognitive dysfunction and atrophy of the hippocampus. A summary of the research is here,
http://64.233.179.104/search?q=cache:VdgsHxqeJaMJ:www.jvr-web.org/Volume_15/Number_1/Feature_15-1.pdf+%22does+vestibular+damage+cause+cognitive%22&hl=enÂÂ
The cognitive disorders that are often experienced by people with vestibular nerve damage, such as myself, are similar to some of the symptoms of "Chronic space motion": fatigue, space stupids, decreased vigilance and loss of motivation. Long-time scuba divers commonly have cognitive problems identical to many vestibular nerve damage patients. In the case of scuba divers it is thought that they experience direct vestibular nerve damage from underwater pressure, but this may be an unproven assumption. In the case of astronauts the possibility exists that even without direct vestibular nerve damage, the incoherent balance data could cause physical damage to the hippocampus. I have seen no evidence indicating how long after the vestibular nerve is affected resulting damage to the hippocampus occurs. Is there evidence of changes to cognitive function before and long after prolonged weightlessness? In vestibular patients that have cognitive problems, the problems persist even after balance is well compensated and episodes of vertigo are no longer experienced.
Whether the incidence of cognitive dysfunction concurrent with weightlessness is temporary, or past a certain point is permanent, I would appreciate hearing about any strategies for ameliorating the symptoms so that I can try them, if practicable, to see if they might benefit my struggles with the "Earth stupids". Stephen Kosslyn and Jennifer Shepard at Harvard plan on having a web based version of the MiniCog software they are using available in two weeks and I plan on using it to gauge the effectiveness of any therapies that I try.
Thank you for your kind attention to this e-mail.
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Greg Stone, CPA
Greg -
Many thanks for your thoughtful and insightful note.
I had seen the Smith et al review... The question of how vestibular signals drive hippocampal centers, particularly the direction and place cells that mediate our sense of direction and where we are, is the subject of much current research. Attached is a recent paper by Taube et al which has a review of the relevant background literature you might want to skim. It discusses what happens to head direction cells in weightlessness.
One important thing to keep in mind is that (at least based on what we know so far) astronauts don't experience pathological changes in their vestibular end organs or peripheral nerves the way vestibular patients such as yourself do. The vestibular organ nerve pattern going to the brain changes, but doesn't cease. It's true that some morphologic changes have been seen in rat cerebellum and other structures (e.g. Holstein, 1998 Neurolab experiments), but in all probability these just reflect normal adaptive response to the change in the information pattern, and are probably not "pathologic" in the sense that they are not reversible. As our experiments with rats in parabolic flight (Taube et al) imply, hippocampal directional sense changes in 0-G, but we believe this is just because our CNS navigation centers are primarily adapted to 2D terrestrial navigation on a locomotion surface, and so our direction sense is optimized for 2D. As a result astronauts living in 3D environments naturally find themselves suceptible to Visual Reorientation Illusions, a cousin to the "direction vertigo" in azimuth that we sometimes experience on Earth (e.g. in the subway). We don't fully understand what happens to hippocampal function in 0-G - there has been only one experiment, and the way things are going in the space program it may be many years till it is done again. But the Knieriem et al Neurolab study on place cell responses in Neurolab rats suggests that animals initially experience something akin to visual reorientation illusions in humans but are capable of developing a veridical 3D sense of place.
In your situation, if you are looking out for CNS/limbic changes as a result of your vestibular infarct, you'd want to look for subtle but Alzheimer's like changes in your sense of direction, and ability to automatically "dead reckon" when you walk around inside buildings. Do you think you can point back in the direction of the unseen front door of the building as well as you could earlier in life ? Tests of ability to mentally rotate objects in 2D or 3D may show correlated changes - one of these is in Steve K's battery as I recall. Researchers are beginning to recognize though that mental rotation and directional abilities - though related - are not quite the same. Some navigation researchers, such as Mary Hegarty at UCSB and Maria Kozhevnikov at Rutgers are working on tests of "perspective taking ability" that may tap more directly into the spatial navigation system.ÂÂ
A relationship between vestibular loss and incidence of anxiety and depression has been noted clinically. There are several recent reviews of what is known. Search for articles by Joe Furman of Pittsburgh, who is one of the clinical experts in this area.
Hope this is of some help.
Chuck Oman
