On the Keyhole Hypothesis: High Mutual Information between Ear and Scalp EEG

Kaare B. Mikkelsen, Preben Kidmose, Lars Kai Hansen

Research output: Contribution to journalJournal articleResearchpeer-review

511 Downloads (Pure)


We propose and test the keyhole hypothesis that measurements from low dimensional EEG, such as ear-EEG reflect a broadly distributed set of neural processes. We formulate the keyhole hypothesis in information theoretical terms. The experimental investigation is based on legacy data consisting of 10 subjects exposed to a battery of stimuli, including alpha-attenuation, auditory onset, and mismatch-negativity responses and a new medium-long EEG experiment involving data acquisition during 13 h. Linear models were estimated to lower bound the scalp-to-ear capacity, i.e., predicting ear-EEG data from simultaneously recorded scalp EEG. A cross-validation procedure was employed to ensure unbiased estimates. We present several pieces of evidence in support of the keyhole hypothesis: There is a high mutual information between data acquired at scalp electrodes and through the ear-EEG "keyhole," furthermore we show that the view represented as a linear mapping is stable across both time and mental states. Specifically, we find that ear-EEG data can be predicted reliably from scalp EEG. We also address the reverse view, and demonstrate that large portions of the scalp EEG can be predicted from ear-EEG, with the highest predictability achieved in the temporal regions and when using ear-EEG electrodes with a common reference electrode.
Original languageEnglish
Article number341
JournalFrontiers in Human Neuroscience
Number of pages9
Publication statusPublished - 2017


  • EEG
  • Ear-EEG
  • Mobility
  • Mutual information
  • Prediction


Dive into the research topics of 'On the Keyhole Hypothesis: High Mutual Information between Ear and Scalp EEG'. Together they form a unique fingerprint.

Cite this