The Effects of Human Visual Sensory Stimuli on N1b Amplitude: An EEG Study

Sensory tetanisation to induce long-term-potentiation-like plasticity: A review and reassessment of the approach

There is great interest in developing non-invasive approaches for studying cortical plasticity in humans. High-frequency presentation of auditory and visual stimuli, or sensory tetanisation, can induce long-term-potentiation-like (LTP-like) changes in cortical activity. However, contrasting effects across studies suggest that sensory tetanisation may be unreliable. We review these contrasting effects, conduct our own study of auditory and visual tetanisation, and perform meta-analyses to determine the average effect of sensory tetanisation 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 tetanisation to 1 and 4 kHz tone bursts and following a slow-presentation control. We also measured visual-evoked amplitude changes following tetanisation to horizontal and vertical sign gradients. Auditory and visual response amplitudes decreased following tetanisation, 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 tetanised stimuli. Importantly, slow presentation of auditory tone bursts produced response amplitude changes approximating those observed following tetanisation in younger adults. Meta-analyses of visual and auditory tetanisation studies found that the overall effect of sensory tetanisation was not significant across studies or study sites. The results suggest that sensory tetanisation may not produce reliable changes in cortical responses and more work is needed to determine the validity of sensory tetanisation as a method for inducing human cortical plasticity in vivo.

Biliverdin regulates NR2E3 and zebrafish retinal photoreceptor development

NR2E3 is an orphan nuclear receptor whose loss-of-function causes abnormal retinal photoreceptor development and degeneration. However, despite that many nuclear receptors are regulated by binding of small molecule ligands, biological small molecule ligands regulating NR2E3 have not been identified. Identification of an endogenous NR2E3 ligand might reveal a previously unrecognized component contributing to retinal development and maintenance. Here we report that biliverdin, a conserved green pigment from heme catabolism, regulates NR2E3 and is necessary for zebrafish retinal photoreceptor development. Biliverdin from retinal extracts specifically bound to NR2E3’s ligand-binding domain and induced NR2E3-dependent reporter gene expression. Inhibition of biliverdin synthesis decreased photoreceptor cell populations in zebrafish larvae, and this phenotype was alleviated by exogenously supplied biliverdin. Thus, biliverdin is an endogenous small molecule ligand for NR2E3 and a component necessary for the proper development of photoreceptor cells. This result suggests a possible role of heme metabolism in the regulation of retinal photoreceptor cell development.

The association of self-reported physical activity on human sensory long-term potentiation

Exercise has been shown to enhance synaptic plasticity, therefore, potentially affecting memory. While the mechanism(s) responsible for this relationship have been explored in animal models, current research suggests that exercise may possess the ability to induce synaptic long-term potentiation (LTP). Most of the LTP mechanistic work has been conducted in animal models using invasive procedures. For that reason, the purpose of the present experiment was to investigate whether self-reported exercise is related to human sensory LTP-like responses. Nineteen participants (M_AGE = 24 years; 52.6% male) completed the study. Long-term potentiation-like responses were measured by incorporating a non-invasive method that assess the change in potentiation of the N1b component produced from the visual stimulus paradigm presented bilaterally in the visual field. Results demonstrated that those with higher levels of moderate-to-vigorous physical activity (MVPA) had a greater N1b change from baseline to the early time period assessment, r = −0.43, p = 0.06. Our findings provide some suggestive evidence of an association between self-reported MVPA and LTP-like responses. Additional work is needed to support that the potentiation of the human sensory N1b component in the observed study is due to the exercise-induced synaptic changes similar to that detailed in prior animal research.