In a small animal like a zebrafish, it is possible to look at a movie of its brain activity in real time, and get a fairly clear picture of what the animals is looking at. For the human, we have no such convenient tool as whole brain calcium imaging, but the experimentalist has one thing going for them over the zebrafish — they can simply ask the subject about what they are experiencing.
The Japanese researchers began with early-stage dream sleep reports from their three subjects and used a lexical database called WordNet to extract common key words that appeared in the descriptions. They then scanned the subjects while they were viewing images selected from another database called ImageNet, which had been matched to the keywords. They could then compare the results of these image set scans, with previous sleep scans used to generate the verbally reported keywords.
The full glamour of trying to decode true REM stage dreams is just not experimentally practical — it usually takes a few hours just to reach REM from normal sleep. Lying still inside an MRI tube until you start dreaming – several times a day for 10 days — would be too difficult. For the present study, the researchers could guess pretty accurately when the subjects first drifted off to sleep by watching simultaneously recorded EEG signals, and promptly roused them for reports of what they were imagining upon entering Neverland. Typically subjects could get pretty groggy in less than ten minutes, and could reliably report their visual imagery when awakened.
While the experimental protocols and scale of computational resource applied here are impressive, a few red flags typically appear in these kinds of studies. MRI scans do not directly access neural activity per se; it is a signal derived from blood flow changes only peripherally linked to activity, and on a much slower timescale than actual neural spiking (or even synapses firing).
( via extremetech.com )