OBJECTIVE

Functional MRI (fMRI) was measured in responses to stimulations of different frequencies to investigate dominant hemisphere and tonotopic organization in primary and secondary auditory cortex.

METHODS

25 healthy subjects with normal hearing were examined using tones of 0.5, 2 or 4 kHz that were amplitude modulated (AM) sinusoidally at 8 Hz. The AM signals were presented at 96 dB SPL Event-related design was combined with a sparse clustered volume acquisitioning paradigm for data collection in the attempt to reduce the influence of acoustic scanner noise. SPM2 software was used for offline data analyzing.

RESULTS

Data from 9 subjects were discarded due to a large head movement during recording. In the rest of 16 subjects, activation was found mainly in the primary auditory cortex. In most of these cases, the activation area and intensity by BOLD were find to be decreased with increasing signal frequency. In a great portion of cases (6 left and 7 right hemispheres), a lateral-medial preference for low-to-high frequency response shift was clearly demonstrated in the primary auditory cortex. However, this was not clear in all other cases. No significant rule could be found in secondary auditory cortex activation.

CONCLUSION

The responses to AM signals showed a clear lateralization to left cerebral hemisphere. The activated area and response intensity decreased with increasing frequency of stimulation. The activation is related to the signal frequency with high frequency AM activating more medially.