Effects of stimulus presentation rate on the activity of primary somatosensory cortex: a functional magnetic resonance imaging study in humans

Abstract

To investigate the effect of stimulus presentation rate on the activity of primary somatosensory cortex, we performed echo-planar functional magnetic resonance imaging using a 1.5-tesla magnetic resonance system. Eight right-handed normal volunteers underwent functional magnetic resonance imaging during somatosensory stimulation with a 0.2 ms electrical square wave to the left index finger at 1, 4, 8, 16, and 32 Hz at constant intensity. Activated areas were located mainly around ‘the hand area’ of the right postcentral gyrus. Between 4 and 16 Hz, almost all subjects showed significant activation, but at 1 Hz and 32 Hz, five of eight subjects showed no activation. The average number of activated pixels in this area between 4 and 16 Hz were significantly greater than those at 1 Hz and 32 Hz, and the average percent signal increase had its activation peak at 8 Hz. Our results suggest that the existence of the optimal stimulation rate range may be a common phenomenon to a variety of sensory modalities. The electrical somatosensory stimulation rates from 4 Hz to 16 Hz are advisable to investigate the activation of the primary somatosensory cortex in human subjects.