research highlights

NEUROSCIENCE Dream stream decoded

Machine learning and imaging show what gators, who transcribed the accounts and decoders had to be personalized. “A decoder the dreaming sees. then matched terms to a lexical database. built for one person does not generalize to Dreaming shows how busy the brain Using these terms, the team mined image another person,” says Kamitani. stays during . A research team in Japan databases to compile visuals that approxi- To recognize patterns in the data, the has now found a way to infer dreams from mated the dreams. They measured brain researchers applied a brain activity. “Dreaming is a fascinating activity when awake study participants algorithm, which they trained on the fMRI phenomenon because it often accompanies looked at these image compilations. data from awake subjects looking at the visual experience, but there is no physical fMRI reveals activity image compilations. This approach linked sensory input,” says Yukiyasu Kamitani through changes in blood flow and oxy- neural activity and dream content. from ATR Computational genation, but the naked eye cannot discern Kamitani now plans to expand his dream Laboratories, who led the work. “When differences in activity between dreaming research to look at basic visual features such a person is dreaming about an object or and brains processing visual sum- as color and shape. “It may also be possible scene, the brain activity is similar to that maries of dreams. “That’s why we need pat- to decode contents related to action and caused by actually seeing the same object tern recognition by machine learning,” says emotion.” In these experiments, participants or s c e n e .” Kamitani. The scientists created a compu- must fall asleep in an MRI scanner, which is The scientists recruited people to their tational approach to compare and contrast not so hard, says Kamitani. Stage fright gives sleep lab and used functional magnetic the changes in grayscale pixel intensity in way to boredom, and it becomes difficult to resonance (fMRI) imaging to decode the fMRI images. stay awake. dreams indirectly. Sleeping test subjects The team developed mathematical for- Vivien Marx were repeatedly wakened when vital signs mulas called decoders to read out dream RESEARCH PAPERS revealed they were dreaming. The test sub- content from fMRI data. Detailed activity Horikawa, T. et al. Neural decoding of visual imagery jects recounted their dreams to the investi- patterns are specific to individuals, so the during sleep. Science 340, 639–642 (2013). © 2013 Nature America, Inc. All rights reserved. America, Inc. © 2013 Nature npg

462 | VOL.10 NO.6 | JUNE 2013 | nature methods