According to the synaptic tag and capture (STC) theory, dopamine is a crucial neuromodulator for novelty-enhanced memory. This study investigated whether tyrosine, a dopamine precursor, modulates...Show moreAccording to the synaptic tag and capture (STC) theory, dopamine is a crucial neuromodulator for novelty-enhanced memory. This study investigated whether tyrosine, a dopamine precursor, modulates the effect of novelty on memory in humans. Therefore, we expected novelty to increase memory performance, as previous studies showed. Also, we expected tyrosine to increase memory performance. In addition, based on the STC theory, we expected tyrosine to indirectly increase memory performance in the novelty condition. Participants drank orange juice with L-tyrosine or cellulose (placebo) and experienced either novel or familiar environments. An EEG was used to assess the neural mechanism of memory encoding. Memory performance was assessed with recall and recognition tests of word lists. Based on multiple repeated measures ANOVAs we did not find a novelty-enhancing memory effect, a tyrosine-enhancing memory effect or an interaction effect. Unrelatedly, we found evidence for the Ebbinghaus forgetting curve, with recall and recognition significantly decreasing after 24 hours. In addition, we did not find the experienced immersion of the virtual environment to be affecting memory performance. However, the immersion effect decreased after the first session with a virtual environment. Moreover, the EEG indicated higher theta wave activity at the Fz electrode compared to Pz and Cz, with no novelty or tyrosine effect on the neural mechanisms of memory encoding. Future research should explore other pharmacological manipulations, ensure balanced models and apply other brain imaging techniques, like fMRI or DTI.Show less
Depression is mental disorder characterized by impaired overall functioning as well as diminished cognitive performance. Its cause is associated with an imbalance of neurotransmitter functioning in...Show moreDepression is mental disorder characterized by impaired overall functioning as well as diminished cognitive performance. Its cause is associated with an imbalance of neurotransmitter functioning in affected individuals. Recent studies have demonstrated the ability of L-tyrosine, a natural amino-acid and precursor of the neurotransmitter dopamine, to increase dopamine levels within the brain and subsequently benefit different cognitive functions. Additionally, another field of research has repeatedly shown that exposure to novel stimuli can enhance memory performance in both animals and humans. In our study we investigated whether the intake of tyrosine (administered in a double-blind, betweensubjects design) enhances recall and recognition performance following the exposure to an either novel or familiar virtual reality environment (within-subjects design) in healthy participants. We expected tyrosine and the novelty exposure to result in improved cognitive performance. Furthermore, we hypothesized tyrosine to even out the assumed negative impact of increasing severity of depressive symptoms on the recall and recognition scores. Our sample consisted of 30 individuals aged 18 to 30. The study involved a total of five sessions including three laboratory and two online sessions. The first session included the familiarization to the VR environment as well as the assessment of current depressive symptoms with the patient health questionnaire. The other two laboratory sessions entailed the treatment administration, VR environment exploration as well as immediate memory assessments, while the online sessions consisted of delayed memory assessments. To examine the effects of treatment, novelty, and depressive symptoms on memory performance, our data was analysed with repeated measures analyses of variance. Contrary to our expectations we did not find significant effects of novelty or the tyrosine supplement on recall or recognition scores. While heightened symptoms of depression negatively impacted the cognitive performance in our sample, tyrosine did not have a mitigating effect on the different severity of symptoms. Future research is advised to explore methodological adjustments by making use of more immersive VR methods, alternative dosages of tyrosine, and include clinical samples to better understand these factors' potential impact on memory.Show less
Substantial animal research has found novelty-related enhanced memory persistence, a mechanism hypothesized to be mediated by dopamine. Despite this, comprehensive human research on the neural...Show moreSubstantial animal research has found novelty-related enhanced memory persistence, a mechanism hypothesized to be mediated by dopamine. Despite this, comprehensive human research on the neural mechanisms underlying this effect is scarce. Therefore, the aim of this paper was to assess the influence of dopamine manipulation on novelty learning. We examined the effects of dopamine manipulation through L-tyrosine administration, the precursor of dopamine. Moreover, we aimed to explore the impact of individual differences in dopamine levels. Previous research has proposed that depression, particularly the memory impairments present in this population, is underlined by dopamine deficiency. Therefore, we examined the differences in novelty-related memory enhancement based on participants' severity of depressive symptoms. For the experiment, 29 participants were randomly assigned to the tyrosine or placebo condition prior to the exploration of a novel or familiar virtual reality environment. Afterward, they completed a word recall and recognition test, both immediately after and following a 24-hour delay, to test their short and long-term memory retention. The results indicate no significant effects of novelty and tyrosine on memory performance. However, significant group differences in memory performance based on depression scores were found, demonstrating that participants with higher depression scores perform worse at free recall tasks than those with lower depression scores. Crucially, this finding was not influenced by the tyrosine or novelty conditions. Potential limitations in the operationalization of the tasks, dopamine manipulation, and measurement, as well as the characteristics of the sample, may explain the non-significant findings. Future research could address this through replication studies into the novelty learning effect that take into account the role of these variables. Positive findings could provide opportunities for maximization of memory retention through environmental manipulations, as well as evidence for using dopaminergic compounds to treat memory impairments in clinical populations. Overall, this study promotes societally relevant new research areas that could alter the understanding of novelty-related memory enhancement.Show less
Research master thesis | Psychology (research) (MSc)
open access
Human decision-making in the context of value-based learning considerably deviates from the premise to always maximise short-term reward. This sort of behavioural variability has been attributed to...Show moreHuman decision-making in the context of value-based learning considerably deviates from the premise to always maximise short-term reward. This sort of behavioural variability has been attributed to exploration during the choice process and has been linked to the locus coeruleusnoradrenaline (LC-NA) system. A recent computational account implementing a “noisy” reinforcement learning (RL) model provides evidence that computational imprecision during the learning process contributes to behavioural variability in decision-making as well. In the present study, the role of the LC-NA system in modulating learning imprecision has been investigated, using a multi-modal approach including the newly developed noisy RL model, a double-blind pharmacological manipulation, and EEG. The responses of thirty participants in a decision-making task were investigated during two experimental sessions in which either atomoxetine, a NA reuptake inhibitor, or placebo was administered, and the model fit of the noisy RL model was tested against the classical RL model without learning imprecision parameter. Contrary to our expectations, we did not find evidence for a modulatory role of the LC-NA system of learning imprecision. However, in line with our expectations, increased NA levels did not impact exploratory behaviour either. Crucially, the noisy RL model outperformed the classical RL model assuming exact learning and learning imprecision led to a significant number of non-maximising decisions contributing to behaviour variability. Moreover, the exploratory EEG analyses on potential underlying mechanisms of learning imprecision suggest learning noise to emerge broadly during feedback processing, rather than within a certain time window. The current study provides further evidence for the importance of computational imprecision during value-based learning.Show less
Decision making is a necessary skill people use every day. We, as humans, learn from our previous decisions and use this new-learned information as a basis for our future decisions. This way we aim...Show moreDecision making is a necessary skill people use every day. We, as humans, learn from our previous decisions and use this new-learned information as a basis for our future decisions. This way we aim to maximize the value of the outcome of our decisions. However, sometimes we seem to make decisions that are non-greedy and will result in a lower outcome. This behaviour could be explained by noise during the learning of these value-based stimuli. One neurotransmitter that is involved in the modulation of learning noise is norepinephrine, and can be manipulated using tVNS. Using a learning noise model, the data obtained during this study shows that previous findings by Findling et al. can be replicated, suggesting that many non-greedy decisions can be explained by learning noise. Further results showed no significant effect of our tVNS manipulation, taking into question the effectiveness of the tVNS method, as well as tonic and phasic manipulation. Further research is needed into the specific neurotransmitter pathways related to value-based decision making in order to create a better understanding of our decision making process.Show less
Learning by trial and error is a very fundamental type of learning. In cognitive sciences, this concept is called reinforcement learning and is widely used for research, since it allows comparably...Show moreLearning by trial and error is a very fundamental type of learning. In cognitive sciences, this concept is called reinforcement learning and is widely used for research, since it allows comparably easy operationalisation. In order to translate this into computable data, models of reinforcement learning such as the Rescorla-Wagner learning rule are used. These models usually neglect disturbance in learning, which is called computational noise and reduces the precision of neural computations during the learning process. Recent research has looked further into exactly this parameter of learning and found that it indeed plays a big part and should not be neglected (Drugowitsch, Wyart, Devauchelle & Koechlin, 2016). Besides replicating a study by Findling and colleagues (2019), this study specifically looks into the role of noradrenaline in the reinforcement learning process and learning noise. Noradrenaline excretion was triggered by transcutaneous vagus nerve stimulation, while a two-armed bandit task was used as learning task. We did not find significant effects of this neurotransmitter on the learning process, however, successfully replicated the research of Findling et al. (2019). These results imply that computational noise during the learning process is still a crucial factor in reinforcement learning and should therefore be further investigated. Noradrenaline might not impact the amount of learning noise to the expected extent.Show less
Research master thesis | Psychology (research) (MSc)
closed access
Our current understanding of the neural signals entailing motor preparation is heavily based on tightly controlled laboratory experiments, which studies movement under prohibitively narrow...Show moreOur current understanding of the neural signals entailing motor preparation is heavily based on tightly controlled laboratory experiments, which studies movement under prohibitively narrow constraints. Despite a large body of literature on motor related cortical potentials (MRCPs), neural motor preparation in real life situations in still poorly understood: Insights from experimental studies often explore movement in low-dynamics contexts, meaning that most aspects of the movement are controlled by the experimental design rather than the participant. However, real life movements are more dynamic and display higher degrees of freedom, such as movement frequency, amplitude, speed, or spontaneity. In this study we address the temporal dynamics of touchscreen taps during unconstrained smartphone use and how they affect premotor EEG potentials. We used hierarchical linear modelling in order to determine how simple dynamics in inter-movement intervals can affect MRCPs. We found movement-preceding spatial and temporal clusters of EEG activity that are significantly affected by intervals to adjacent smartphone touches. Our results indicate that shorter intervals to previous touches result are related to a smaller amplitude of the readiness potential (RP) component, while shorter intervals to following touches are related to increased RP amplitude.Show less
Interoception i.e. the perception of our internal bodily functions has been found to relate to the perception of our physical appearance, as well as our perception of other people’s emotions. As...Show moreInteroception i.e. the perception of our internal bodily functions has been found to relate to the perception of our physical appearance, as well as our perception of other people’s emotions. As interoception was also shown to play an important role in several mental health conditions (e.g., Autism Spectrum Disorder and depression), exploring these relationships in clinical population is crucial for improving people’s interoceptive ability, perception of emotions of others as well as body image. Therefore, one objective of this study was to thoroughly explore how interoceptive accuracy and interoceptive awareness relate to accuracy in emotion recognition as well as the level of perceived emotional intensity. Another objective was to examine the association between interoceptive awareness and body appreciation. A sample of 99 participants completed a facial emotion recognition task measuring accuracy and intensity ratings of five facial expressions – anger, fear, happiness, sadness, or a neutral expression. Additionally, self-reported measures were used to assess the participants’ interoception and body appreciation. As expected, we found a positive relationship between interoceptive awareness and perceived emotional intensity. However, we could not find a significant positive relationship between the other explored variables. One use of a potential link between interoception and emotion recognition as well as body appreciation could be to assist treatment of clinical conditions. Therefore, we suggest further exploration of this link.Show less
