Cortical activation patterns in functional magnetic resonance images following monaural pure tone stimulation

To investigate cross-projection of pure tone stimulation, optimal stimulation level and cross-talk effect, we examined the auditory processing of monaural pure-tone stimuli using functional magnetic resonance imaging (fMRI). We examined fMRI responses to monaural pure tones (1 kHz, 95 or 115 dB SPL) in 11 subjects with normal hearing and 4 patients with with profound unilateral deafness. Group analysis showed bilateral cortical activation in primary auditory and auditory association regions at 115 dB SPL. The activation was strong and mostly contralateral. At 95 dB SPl, only 2 of 11 subjects showed weak cortical activation. No activated area in the auditory cortex was observed in subjects with profound unilateral deafness in response to monaural stimulation of the deaf ear. The results supported the cross-projection of pure tone stimulation. Pure tone with 115 dB SPL was needed to obtain intense and stable activation without cross-talk using conventional boxcar model.