Sensory Tetanization to Induce LTP-Like Plasticity: A Review and Reassessment of the Approach

Abstract

Great interest has been given to developing non-invasive approaches for studying cortical plasticity in humans. High frequency presentation of auditory and visual stimuli, or sensory tetanization, can induce long-term-potentiation-like (LTP-like) changes in cortical activity. However, contrasting effects across studies suggest that sensory tetanization may be unreliable. We review these contrasting effects, conduct our own study of auditory and visual tetanization, and perform meta-analyses to determine the average effect of sensory tetanization across studies. We measured auditory-evoked amplitude changes in a group of younger (18-29 years of age) and older (55-83 years of age) adults following tetanization to 1 kHz and 4 kHz tone bursts and following a slow-presentation control. We also measured visual-evoked amplitude changes following tetanization to horizontal and vertical sign gradients. Auditory and visual response amplitudes decreased following tetanization, consistent with some studies but contrasting with others finding amplitude increases (i.e., LTP-like changes). Older adults exhibited more modest auditory-evoked amplitude decreases, but visual-evoked amplitude decreases like those of younger adults. Changes in response amplitude were not specific to tetanized stimuli. Importantly, slow presentation of auditory tone-bursts produced response amplitude changes approximating those observed following tetanization in younger adults. Meta-analyses of visual and auditory tetanization studies found that the overall effect of sensory tetanization was not significant across studies or study sites. The results suggest that sensory tetanization may not produce reliable changes in cortical responses and more work is needed to determine the validity of sensory tetanization as a method for inducing human cortical plasticity in vivo.