Omissions of Auditory Stimuli May Activate Frontal Cortex.
We measured, with a 7 channel SQUID gradiometer, cerebral magnetic responses, time-locked to unpredictable and infrequent stimulus omissions (10% of stimuli) in an otherwise regular sequence of short tones, repeated once every 510 ms. In 10 out of 12 subjects broad responses with multiple peaks and with wide interindividual variability were detected. Attention clearly increased the observed signals. The magnetic field patterns evoked by stimulus omissions could be explained by single current dipoles, whose locations agree with activation of the posterolateral frontal cortex.
Joutsiniemi
S.-L.
SL
Low Temperature Laboratory, Helsinki University of Technology, SF-02150 Espoo, Finland.
Hari
R.
R