Consciousness and how it got to be that way

Saturday, May 15, 2010

Ultrasound, Neuronal Excitability, and Hallucinations

A few years ago it was announced that a U.S. patent had been filed by Thomas Dawson on behalf of Sony for direct neural input of sensory information. There are a few: the most recent related patent by the same inventor here, but the one that I believe attracted media attention is here).

The patents describe a method of stimulating multi-modality sensory experience through the use of sound energy. The basic idea is that neuronal excitability can be increased with ultrasound (review here) although to date it seems that all the work has been either with CNS neurons in culture, or PNS neurons, rather than CNS neurons inside a spine or skull. Obviously if these patents represent functioning technology the implications are profound. For that reason I scrutinized 6,536,440 for evidence that the concept had in fact been reduced to practice, which (naively I'm told) I had thought was still a requirement for the issue of a patent. There's precious little in the document to suggest anyone is ready to build a transducer capable of producing any sensory experience in subjects, let alone a coherent one.

Of course ultrasound is already used in medical imaging all the time, in a similar range to that reported in the review (optimal transcranial transmission of ultrasound at 7 x 10^5 Hz, but in vitro studies showed neuronal excitability changes at higher frequencies around 2-7 x 10^6 Hz. Medical imaging ultrasounds use frequencies up to 10^7 Hz, but the intensity range is 1-10 W/cm^2, and the imaging device is rarely applied to the skull (useless for imaging, because bone blocks commercial ultrasound). That said, I'm unaware of anecdotal reports of patients hallucinating by any modality during ultrasound imaging, a very common outpatient procedure, and quick search of Pubmed reveals no such cases among the first 30 articles.

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