Hearing the sound of silence: a magnetoencephalographic study

We visualized the brain activity for retrieval imagery of a sound using dual 37-channel magnetometers in seven right-handed healthy subjects. A soundless video image of a hammer striking an anvil was presented on a screen. Significantly larger evoked magnetic fields were recorded, dominantly in the right hemisphere, in six subjects when they imagined the sound than when they did not. The initial peak of the response was 151.0 +/- 26.5 ms (mean +/- s.d.) after the blow. Equivalent current dipoles (ECDs) for the responses recorded from the right hemisphere were located around the inferior frontal sulcus in three subjects and in the insular region in three subjects, but reliable ECDs were not estimated from the left hemisphere. The results suggested that the initial activity for sound retrieval imagery appeared around the inferior frontal and insular areas, dominantly in the right hemisphere.