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

Abstract

Background: 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 LTP-like changes in cortical activity. However, contrasting effects across studies suggest that sensory tetanization may be unreliable. Method: We used sensory tetanization to try to induce auditory and visual LTP-like plasticity in younger and older adults. We measured auditory-evoked amplitude changes 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. Results: Auditory and visual response amplitudes decreased following tetanization, consistent with some studies but contrasting with others finding amplitude increases (i.e. LTP-Like). 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 changes in response amplitude that were like those observed following tetanization. Comparison with Existing Methods: A meta-analysis incorporating our results with studies employing similar tetanization techniques to study cortical plasticity revealed that the overall effect size across studies and labs is not significant, suggesting sensory tetanization does not produce reliable changes in cortical responses. Conclusions: We discuss our findings with respect to other inconsistent findings across the literature concerning stimulus specificity and age effects and conclude that sensory tetanization is an unreliable method for inducing human cortical plasticity in vivo.

Stability of steady‐state visual evoked potential contrast response functions

“…Additionally, it is important to note that there is large cross‐study variability in the sensory LTP literature. Some have questioned if sensory LTP is even a valid construct (Dias et al, 2022), and the largest studies have shown modest and inconsistent effects across hundreds of participants (Valstad et al, 2020). Our finding of response stability with repeated stimulus presentation further emphasizes that sensory LTP may not be a robust phenomenon and/or may only occur under a narrow range of stimulus parameters.…”

“…Although initial demonstrations of human sensory LTP were encouraging, and at least two regimes of sensory stimulation have been shown to induce LTP‐like effects (9–10 Hz flicker stimuli, and 2 Hz contrast‐reversing stimuli; Sanders et al, 2018), recent large studies of sensory LTP have shown inconsistent and highly variable neuroplastic effects following the use of sensory LTP protocols (Valstad et al, 2020), leading some to question if sensory LTP is a valid construct (Dias et al, 2022).…”

Stability of steady-state visual evoked potential contrast response functions

“…Additionally, it is important to note along these lines that there is large variability in the sensory LTP literature. Some have questioned if sensory LTP is even a valid construct (Dias et al, 2022), and the largest studies have shown modest if any consistent effects across hundreds of participants (Valstad et al, 2020). Our finding of response stability with repeated stimulus presentation provides further support for VEP stability, but a more thorough investigation of stimulus parameters is needed to determine in what regime ssVEP stimuli do or do not generate neuroplastic effects.…”

Opposite effects of rapid auditory stimulation on tetanized and non-tetanized tone of adjacent frequency: Mismatch negativity study

“…At the same time results are rather inconsistent, probably related to different experimental designs across studies [4-6, 12, 24-27]. Moreover, the recent meta-analysis [28] revealed that the overall effect of tetanization across ERP studies is not significant. However this meta-analysis pointed to the relatively few studies on auditory tetanization that might be of importance due to potential link to speech development.…”