LTP-like plasticity in the visual system and in the motor system appear related in young and healthy subjects

Abstract

LTP-like plasticity measured by visual evoked potentials (VEP) can be induced in the intact human brain by presenting checkerboard reversals. Also associated with LTP-like plasticity, around two third of participants respond to transcranial magnetic stimulation (TMS) with a paired-associate stimulation (PAS) protocol with a potentiation of their motor evoked potentials. LTP-like processes are also required for verbal and motor learning tasks. We compared effect sizes, responder rates and intercorrelations as well as the potential influence of attention between these four assessments in a group of 37 young and healthy volunteers. We observed a potentiation effect of the N75 and P100 VEP component which positively correlated with plasticity induced by PAS. Subjects with a better subjective alertness were more likely to show PAS and VEP potentiation. No correlation was found between the other assessments. Effect sizes and responder rates of VEP potentiation were higher compared to PAS. Our results indicate a high variability of LTP-like effects and no evidence for a system-specific nature. As a consequence, studies wishing to assess individual levels of LTP-like plasticity should employ a combination of multiple assessments.

A review of plasticity induced by auditory and visual tetanic stimulation in humans

“…However, the widely varying results between research groups suggest that potentiation effects may not be as robust as suggested by the evidence from the early sensory tetanization studies. Intersubject variability in LTP‐like effects after sensory tetanization has only recently been examined in the published literature (Klöppel et al., ; Lahr et al., ). Understanding these differences will be vital if the paradigm is to be used as a clinical tool.…”

“…EEG is the result of widespread brain activity and is prone to noise and the ‘inverse problem’ of trying to establish the locus of scalp voltage from outputs that could result from various combinations of sources (Cohen, ). While cellular LTP effects tend to be consistent, variability has been shown in sensory‐induced LTP‐like effects (Klöppel et al., ; Lahr et al., ). Contrary with the findings of Clapp, Zaehle, et al.…”

“…Paired‐associative stimulation (PAS), where potentiation of motor‐evoked potentials is induced by pairing peripheral nerve stimulation with TMS, is another widely used technique for examining LTP‐like effects (Müller‐Dahlhaus, Orekhov, Liu, & Ziemann, ; Stefan, Kunesch, Cohen, Benecke, & Classen, ). In a recent study, visually induced LTP‐like effects were compared with PAS effects in the same participants (Klöppel et al., ). The majority showed visually induced potentiation effects, but almost a quarter of participants did not.…”

“…Whether the LTP‐like plasticity induced by the two techniques shares underlying mechanisms is unclear but the results from Klöppel et al. () indicate that both are prone to individual differences and are not as consistent as cellular LTP effects.…”

Tuning noninvasive brain stimulation with MRI to cope with intersubject variability

“…Second, this homogenization would lend immediate assistance to the effective application of such treatments in clinical cases. Naturally, not all covariates are as simple to supervise and to control for as the participants' attention to the task [54], their serotonin levels [55,56 & ], or the presence of low doses of ethanol [57,58], which were all shown to affect the elicitation of plasticity processes. In fact, identified genotypic markers for the expected effect of stimulation protocols, like the Val66Met polymorphism [40 & ], can only be registered and not regulated.…”