[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: There are hallucinations and there are hallucinations

Dear list

If you can stand one more comment on the hallucinations questions:

I agree with this posting that imagery and hallucination are two distinct (though possibly related) phenomena, and are certainly not equivalent. Since the question of neuroimaging was raised, anyone interested could consult my papers with Halpern where we have looked at musical imagery and document activation of auditory cortices (J Cog Neurosci, 1996, 8, 29-46; and Cerebral Cortex, 1999, 9, 697-704). A good recent paper using PET scanning on the topic of auditory hallucinations is by Tim Griffiths (Brain 2000 123: 2065-2076).

I disagree, though, that there is any difference with the visual system. One can draw very close analogies between visual imagery ("in one's head") and visual hallucinations. Neuroimaging studies by people like Kosslyn and others are relevant in this respect.

One other point to remember: hallucinations can indeed arise as a consequence of some peripheral input, such as noise, and/or as a result of peripheral deafferentation (reminiscent of "phantom limb" phenomena). However, it should also be recalled that hallucinations can also result from central (cortical) activity. I once saw a patient with a small infarct in the right Heschl's gyrus whose only complaint was loud music coming from his left side of space. And of course, there are the classic descriptions of Penfield in which music, voices, and other less-organized sound hallucinations (or "experiential phenomena"  as he called them) can be elicited upon direct electrical stimulation of the superior temporal neocortex.



At 08:22 08/08/02 -0700, you wrote:

There are two separate phenomena being discussed here.  One is the auditory
sensation of a sound being 'out there in the world', which was the original
problem mentioned.  The other is what Pierre and some others have been
talking about, which is the sound occurring in one's head, but it is not
taken as a real sensation.  These are quite different and should be treated
as such.  I would suspect the fMRI of the first type of 'hallucination'
would show acitivity in the auditory cortex.  In contrast, visual
halluciations are only perceived as being 'in the world.'  Perhaps this
says something basic about the distinct nature of the two modalities.

Please use new e-mail address from now on:


Robert J. Zatorre, Ph.D.
Montreal Neurological Institute
3801 University St.
Montreal, QC Canada H3A 2B4
phone: 1-514-398-8903
fax: 1-514-398-1338
web site: www.zlab.mcgill.ca