Background: Transcutaneous auricular vagus nerve stimulation (taVNS) is a promising brain stimulation method for the treatment of pharmaco-resistant epilepsy and depression. Its clinical efficacy is thought to depend on taVNS-induced activation of the locus coeruleus. However, unlike for invasive VNS, there is little evidence for an effect of taVNS on noradrenergic activity. Objective: We attempted to replicate recently published findings by Sharon et al. (2021), showing that short bursts of taVNS transiently increased pupil size and decreased EEG alpha power, two correlates of central noradrenergic activity. Methods: Following the original study, we used a single-blind, sham-controlled, randomized cross-over design. We applied short-term (3.4 s) taVNS in healthy human volunteers (n=29), while collecting resting-state pupil-size and EEG data. To analyze the data, we used scripts provided by Sharon and colleagues. Results: Consistent with Sharon et al. (2021), pupil dilation was significantly larger during taVNS than during sham stimulation (p = .009; Bayes factor supporting the difference = 7.45). However, we failed to replicate the effect of taVNS on EEG alpha power (p = .37); the data were four times more likely under the null hypothesis (BF10 = 0.28). Conclusion: Our findings support the effectiveness of short-term taVNS in inducing transient pupil dilation, a correlate of phasic noradrenergic activity. However, we failed to replicate the recent finding by Sharon et al. (2021) that taVNS attenuates EEG alpha activity. Overall, this study highlights the need for continued research on the neural mechanisms underlying taVNS efficacy and its potential as a treatment option for pharmaco-resistant conditions. It also highlights the need for direct replications of influential taVNS studies.
Prospective memory (PM) is the ability to remember to carry out an intention in the future. PM is particularly impaired in Korsakoff syndrome (KS). We investigated the benefit of a smartwatch and smartphone compared to no aid in supporting time accuracy and PM task performance in KS. Time accuracy was improved with a smartwatch compared to the other conditions. Furthermore, the smartwatch and phone conditions were more effective than no aid in assisting memory for task content. Together these results suggest that using an external memory aid is beneficial for successful PM in KS.
Neuromodulatory nuclei that are part of the ascending arousal system (AAS) play a crucial role in regulating cortical state and optimizing task performance. Pupil diameter, under constant luminance conditions, is increasingly used as an index of activity of these AAS nuclei. Indeed, task-based functional imaging studies in humans have begun to provide evidence of stimulus-driven pupil-AAS coupling. However, whether there is such a tight pupil-AAS coupling during rest is not clear. To address this question, we examined simultaneously acquired resting-state fMRI and pupil-size data from 74 participants, focusing on six AAS nuclei: the locus coeruleus, ventral tegmental area, substantia nigra, dorsal and median raphe nuclei, and cholinergic basal forebrain. Activation in all six AAS nuclei was optimally correlated with pupil size at 0–2 s lags, suggesting that spontaneous pupil changes were almost immediately followed by corresponding BOLD-signal changes in the AAS. These results suggest that spontaneous changes in pupil size that occur during states of rest can be used as a noninvasive general index of activity in AAS nuclei. Importantly, the nature of pupil-AAS coupling during rest appears to be vastly different from the relatively slow canonical hemodynamic response function that has been used to characterize task-related pupil-AAS coupling.
Neuromodulatory nuclei that are part of the ascending arousal system (AAS) play a crucial role in regulating cortical state and optimizing task performance. Pupil diameter, under constant luminance conditions, is increasingly used as an index of activity of these AAS nuclei. Indeed, task-based functional imaging studies in humans have begun to provide evidence of stimulus-driven pupil-AAS coupling. However, whether there is such a tight pupil-AAS coupling during rest is not clear. To address this question, we examined simultaneously acquired resting-state fMRI and pupil-size data from 74 participants, focusing on six AAS nuclei: the locus coeruleus, ventral tegmental area, substantia nigra, dorsal and median raphe nuclei, and cholinergic basal forebrain. Activation in all six AAS nuclei was optimally correlated with pupil size at 0- to 2-second lags, suggesting that spontaneous pupil changes were almost immediately followed by corresponding BOLD-signal changes in the AAS. These results suggest that spontaneous changes in pupil size that occur during states of rest can be used as a noninvasive general index of activity in AAS nuclei. Importantly, the nature of pupil-AAS coupling during rest appears to be vastly different from the relatively slow canonical hemodynamic response function that has been used to characterize task-related pupil-AAS coupling.
Performance validity tests (PVTs) and Symptom validity tests (SVTs) are developed to identify people that present false or exaggerated symptoms. Although a key factor of both types of tests includes relative insensitivity to cognitive disorders, the direct effects of amnesia have been poorly studied. Therefore, a sample of 20 patients diagnosed with Korsakoff Amnesia (KA) through neuropsychological assessment and 20 healthy comparisons (HC) were administered the Test of Memory Malingering (TOMM), the Structured Inventory of Malingered Symptomatology (SIMS), and the newly developed Visual Association Test -Extended (VAT-E). Our results show that KA patients scored systematically lower on the TOMM and VAT-E, while performance on the SIMS was comparable with healthy comparisons. Some KA patients were regarded as underperformers based on the TOMM and VAT-E, suggesting limitations in applying these instruments in severe amnesia. There was a strong interdependence of PVTs in logistic regression. We conclude that the TOMM and VAT-E are not fully robust against severe memory disorders and show a serious risk of false positives. Complete neuropsychological profile analysis is needed, and PVTs should be interpreted with caution in patients with suspected amnesia.
Objective. Patients with Korsakoff's syndrome (KS) have difficulty carrying out tasks which rely on prospective memory (PM). Since remembering to carry out an action in the future is crucial for living independently, it is of primary interest to develop strategies that improve PM performance in KS patients. Design. The study employed a computer categorization task as an ongoing activity into which a PM task was embedded. We included episodic future thinking (EFT) and observational learning (Experiment 2) to boost PM. Methods. Experiment 1 evaluated the efficacy of EFT following written PM task instructions in ten KS patients. Due to floor-level PM performance in Experiment 1, Experiment 2 included an instructional video demonstrating the PM intention. In Experiment 2, twenty-six KS patients performed both conditions (EFT and no-EFT) at least 1 week apart, while twelve controls with alcohol use disorder without KS performed the no-EFT condition. In Experiment 2, the PM instructions were also shown through video (observational learning component). Mild cognitive impairment was assessed in a short test battery. Results. Experiment 1 showed overall floor performance in both conditions. Experiment 2 showed that KS patients performed PM tasks less accurately than the control group in the no-EFT condition. In Experiment 2, where the observational learning This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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