The effect of reward-induced arousal on the success and precision of episodic memory retrieval.

Moment-to-moment fluctuations in arousal can have large effects on learning and memory. For example, when neutral items are predictive of a later reward, they are often remembered better than neutral items without a reward association. This reward anticipation manipulation is thought to induce a heightened state of arousal, resulting in stronger encoding. It is unclear, however, whether these arousal-induced effects on encoding are 'all-or-none', or whether encoding precision varies from trial to trial with degree of arousal. Here, we examined whether trial-to-trial variability in reward-related pupil-linked arousal might correspond to variability in participants' long-term memory encoding precision. We tested this using a location memory paradigm in which half of the to-be-encoded neutral items were linked to later monetary reward, while the other half had no reward association. After the encoding phase, we measured immediate item location memory on a continuous scale, allowing us to assess both memory success and memory precision. We found that pre-item baseline pupil size and pupil size during item encoding were not related to subsequent memory performance. In contrast, the anticipation of instrumental reward increased pupil size, and a smaller anticipatory increase in pupil size was linked to greater subsequent memory success but not memory precision.

Non-invasive vagus nerve stimulation and the motivation to work for rewards: A replication of Neuser et al. (2020, Nature Communications).

The vagus nerve is thought to be involved in the allostatic regulation of motivation and energy metabolism via gut-brain interactions. A recent study by Neuser and colleagues (2020) provided novel evidence for this process in humans, by reporting a positive effect of transcutaneous auricular vagus nerve stimulation (taVNS) on the invigoration of reward-seeking behaviors, especially for food rewards. We conducted an independent direct replication of Neuser et al. (2020), to assess the robustness of their findings. Following the original study, we used a single-blind, sham-controlled, randomized cross-over design. We applied left-sided taVNS in healthy human volunteers (n = 40), while they performed an effort allocation task in which they had to work for monetary and food rewards. The replication study was purely confirmatory in that it strictly followed the analysis plans and scripts used by Neuser et al. Although, in line with Neuser et al., we found strong effects of task variables on effort invigoration and effort maintenance, we failed to replicate their key finding: taVNS did not increase the strength of invigoration (p = .62); the data were five times more likely (BF10 = 0.19) under the null hypothesis. We also found substantial evidence against an effect of taVNS on effort maintenance (p = .50; BF10 = 0.20). Our results provide evidence against the idea that left-sided taVNS boosts the motivational drive to work for rewards. Our study also highlights the need for direct replications of influential taVNS studies.

Pupil size reflects activation of subcortical ascending arousal system nuclei during rest.

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.

Short-term transcutaneous vagus nerve stimulation increases pupil size but does not affect EEG alpha power: A replication of Sharon et al. (2021, Journal of Neuroscience).

BACKGROUND: Transcutaneous auricular vagus nerve stimulation (taVNS) has been tested as a potential treatment for pharmaco-resistant epilepsy and depression. Its clinical efficacy is thought to depend on taVNS-induced activation of the locus coeruleus and other neuromodulator systems. However, unlike for invasive VNS in rodents, 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. Human volunteers (n = 29) received short-term (3.4 s) taVNS at the maximum level below the pain threshold, while we collected 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.

Episodic future thinking together with observational learning benefits prospective memory in high-functioning Korsakoff's syndrome patients.

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 component was included, EFT improved PM performance in KS patients. This effect was driven by a sub-group of high-functioning KS patients. CONCLUSIONS: This study showed the value of an observational learning component together with EFT in improving PM performance, in relatively high-functioning KS patients. PRACTITIONER POINTS: KS patients performed the PM task less accurately than non-KS controls with alcohol use disorder, confirming PM impairment in this patient population. Controls with alcohol use disorder performed the PM task at ceiling level. Showing an instructional video demonstrating the PM intention improved PM performance and later recall of PM task instructions in KS patients. Episodic future thinking strategy improved PM performance in KS patients with relatively intact cognitive functioning.

Effects of Korsakoff Amnesia on performance and symptom validity testing.

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.

Smartwatch aids time-based prospective memory in Korsakoff syndrome: a case study.

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.