4,077 research outputs found
Human midcingulate cortex encodes distributed representations of task progress: FMRI and Computational Archives
No full textClay B. Holroyd, José J. F. Ribas-Fernandes, Danesh Shahnazian, Massimo Silvetti, and Tom Verguts. (2018).
Proceedings of the National Academy of Sciences of the United States of America
Exploring personality: the impact of impulsivity on decision making and reward processing
No full textImpulsivity is a common and multifaceted personality trait that is characterized by the presence of heightened reward sensitivity, novelty seeking, lack of premeditation, and behavioural and emotional inhibition deficits (Leshem, 2016a). These behaviours are often associated with substance abuse, gambling disorders, obesity, abnormal time perception, and other psychological and neurological conditions (Bari & Robbins, 2013; Berlin & Rolls, 2004). Reward processing deficits have also been well documented, with many researchers finding an association between impulsivity and the inclination towards smaller, immediate, rewards over larger, delayed rewards (Petry, 2001). Additionally, a larger reward positivity amplitude – an event-related potential component associated with rewards and expectancy – was found for the immediate rewards, relative to delayed rewards in high impulsivity individuals (Cherniawsky & Holroyd, 2013; B. Schmidt, Holroyd, Debener, & Hewig, 2017). The purpose of this thesis was to replicate and extend previous findings, by having participants complete two tasks: delayed gratification and time estimation. In the time estimation task, participants estimated the length of one second. The first task, a replication, assesses subject’s preference for immediate rewards; moreover, the second task extended previous research and functioned as an additional way of assessing reward processing and examined participant’s ability to estimate time. Abnormal time perception in impulsive individuals is thought to contribute to atypical delay gratification behaviour (Wittmann & Paulus, 2008). Electroencephalography (EEG) was recorded from participants during both tasks. Based on previous research on impulsivity (Cherniawsky & Holroyd, 2013; Coull, Cheng, & Meck, 2011; Holroyd & Krigolson, 2007; B. Schmidt et al., 2017), I predicted that impulsivity would affect performance on the time estimation task (which is novel in its use with impulsivity and EEG), and response times and reward positivity amplitudes on both tasks. Counter to my hypothesis, I found that response times and task performance were not affected by impulsivity levels. I also observed that the reward positivity was mediated by impulsivity in the delayed gratification task, but not in the time estimation tasks, suggesting that the tasks activate different neural pathways for reward processing. My results indicate that impulsivity can influence the amplitude of the reward positivity, but that different neural pathways are associated with distinct tasks. Further investigation into quantifiable measures of impulsivity and their effect on various reward processing tasks needs to be conducted. Graduate2020-04-2
Neural mechanisms of cognitive control and reward learning in children with Attention Deficit Hyperactivity Disorder
No full textA substantial amount of behavioural, genetic, and neurophysiological data suggest that Attention Deficit Hyperactivity Disorder (ADHD) is influenced by an underlying abnormality in the midbrain dopamine system. A previous study found that children with ADHD are unusually sensitive to the salience of rewards, mediated in part by the dopamine system (Holroyd, Baker, Kerns & Mueller, 2008). The current study aimed to replicate and expand upon the previous finding using event-related potentials (ERP) recorded from typically developing children and children with ADHD as they navigated a “virtual T-Maze” in two conditions differing on reward saliency. Children also completed a behavioural task designed to measure decision making and sensitivity to reward and punishment. Both groups of children responded to the behavioural task in a way that is indicative of increased sensitivity to reward. Unlike the previous study, the salience of reward as reflected in the ERP did not have an effect on either children with ADHD or typically developing children. However, both groups displayed a larger error-related negativity (ERN) in the condition presented second
Mineral acquisition from clay by Budongo Forest chimpanzees
No full textDate of Acceptance: 06/07/2015Chimpanzees of the Sonso community, Budongo Forest, Uganda were observed eating clay and drinking clay-water from waterholes. We show that clay, clay-rich water, and clay obtained with leaf sponges, provide a range of minerals in different concentrations. The presence of aluminium in the clay consumed indicates that it takes the form of kaolinite. We discuss the contribution of clay geophagy to the mineral intake of the Sonso chimpanzees and show that clay eaten using leaf sponges is particularly rich in minerals. We show that termite mound soil, also regularly consumed, is rich in minerals. We discuss the frequency of clay and termite soil geophagy in the context of the disappearance from Budongo Forest of a formerly rich source of minerals, the decaying pith of Raphia farinifera palms.Peer reviewe
Event-related potential correlates of catecholinergic neuromodulators norepinephrine and dopamine
No full textAdaptive decision making depends on multiple processes, including fast and efficient processing of stimulus events for effective responding and slow trial-to-trial learning of action values for optimization of the selection process. I applied the event-related brain potential (ERP) technique to investigate the involvement of two neuromodulatory systems in learning and decision making: The locus coeruleus-norepinephrine (LC-NE) system and the mesencephalic dopamine system (DA system). I present evidence that the "oddball" N2, a negative deflection in the ERP elicited by task-relevant events that begins approximately 200 ms after onset of the eliciting stimulus and that is sensitive to low-probability events, is a manifestation of cortex-wide noradrenergic modulation recruited to facilitate the processing of unexpected stimuli. Further, Holroyd and Coles (2002) proposed that the impact of DA reinforcement learning signals on the anterior cingulate cortex (ACC) produces a component of the ERP called the feedback-related negativity (FRN). I present electroencephalographic evidence that both the DA system and the LC-NE system act in concert when learning from rewards that vary in expectedness, but that the DA system is relatively more exercised when subjects are highly engaged/challenged by learning tasks, whereas the impact of the LC-NE system is attenuated by this manipulation.Graduat
Guide to the nature and methods of analysis of the clay fraction of tephras from the South Auckland region, New Zealand.
No full textThe manual outlines some of the more common laboratory procedures available for qualitatively and quantitatively analysing the composition of the tephric clays, many of which are difficult to determine because of their short range order or 'amorphous' nature. Techniques described and assessed in terms of their rapidity and quantitativeness include XRD, IR, DTA, TEM and SEM, sodium fluoride reactivity, chemical dissolution analyses, and surface area measurements. No one technique alone produces a definitive clay fraction analysis of tephric deposits. -from Author
Feedback Related Negativity: Reward Prediction Error or Salience Prediction Error?
No full textThe reward positivity is a component of the human event-related brain potential (ERP) elicited by feedback stimuli in trial-and-error learning and guessing tasks. A prominent theory holds that the reward positivity reflects a reward prediction error that is differentially sensitive to the valence of the outcomes, namely, larger for unexpected positive events relative to unexpected negative events (Holroyd & Coles, 2002). Although the theory has found substantial empirical support, most of these studies have utilized either monetary or performance feedback to test the hypothesis. However, in apparent contradiction to the theory, a recent study found that unexpected physical punishments (a shock to the finger) also elicit the reward positivity (Talmi, Atkinson, & El-Deredy, 2013). Accordingly, these investigators argued that this ERP component reflects a salience prediction error rather than a reward prediction error. To investigate this finding further, I adapted the task paradigm by Talmi and colleagues to a more standard guessing task often used to investigate the reward positivity. Participants navigated a virtual T-maze and received feedback on each trial under two conditions. In a reward condition the feedback indicated that they would either receive a monetary reward or not for their performance on that trial. In a punishment condition the feedback indicated that they would receive a small shock or not at the end of the trial. I found that the feedback stimuli elicited a typical reward positivity in the reward condition and an apparently delayed reward positivity in the punishment condition. Importantly, this signal was more positive to the stimuli that predicted the omission of a possible punishment relative to stimuli that predicted a forthcoming punishment, which is inconsistent with the salience [email protected]
Exploring individual differences in task switching : persistence and other personality traits related to anterior cingulate cortex function
No full textAnterior cingulate cortex (ACC) is involved in cognitive control and decision-making but its precise function is still highly debated. Based on evidence from lesion, neurophysiological, and neuroimaging studies, we have recently proposed a critical role for ACC in motivating extended behaviors according to learned task values (Holroyd and Yeung, 2012). Computational simulations based on this theory suggest a hierarchical mechanism in which a caudal division of ACC selects and applies control over task execution, and a rostral division of ACC facilitates switches between tasks according to a higher task strategy (Holroyd and McClure, 2015). This theoretical framework suggests that ACC may contribute to personality traits related to persistence and reward sensitivity (Holroyd and Umemoto, 2016). To explore this possibility, we carried out a voluntary task switching experiment in which on each trial participants freely chose one of two tasks to perform, under the condition that they try to select the tasks "at random" and equally often. The participants also completed several questionnaires that assessed personality trait related to persistence, apathy, anhedonia, and rumination, in addition to the Big 5 personality inventory. Among other findings, we observed greater compliance with task instructions by persistent individuals, as manifested by a greater facility with switching between tasks, which is suggestive of increased engagement of rostral ACC
The Impact of Deliberative Strategy Dissociates ERP Components Related to Conflict Processing vs. Reinforcement Learning
No full textWe applied the event-related brain potential (ERP) technique to investigate the involvement of two neuromodulatory systems in learning and decision making: The locus coeruleus-norepinephrine (LC-NE) system and the mesencephalic dopamine system (DA system). We have previously presented evidence that the N2, a negative deflection in the ERP elicited by task-relevant events that begins approximately 200 ms after onset of the eliciting stimulus and that is sensitive to low-probability events, is a manifestation of cortex-wide noradrenergic modulation recruited to facilitate the processing of unexpected stimuli (Warren, Tanaka, & Holroyd, in press). Further, Holroyd and Coles (2002) proposed that the impact of DA reinforcement learning signals on the anterior cingulate cortex (ACC) produces a component of the ERP called the feedback-related negativity (FRN). The N2 and the FRN share a similar time range, a similar topography, and similar antecedent conditions. We varied factors related to the degree of cognitive deliberation across a series of experiments to dissociate these two ERP components. Across four experiments we varied the demand for a deliberative strategy, from passively watching feedback, to more complex/challenging decision tasks. Consistent with our predictions, the FRN was largest in the experiment involving active learning and smallest in the experiment involving passive learning whereas the N2 exhibited the opposite effect. Within each experiment, when subjects attended to color, the N2 was maximal at frontal-central sites, and when they attended to sex it was maximal over lateral-occipital areas, whereas the topology of the FRN was frontal-central in both task conditions. We conclude that both the DA system and the LC-NE system act in concert when learning from rewards that vary in expectedness, but that the DA system is relatively more exercised when subjects are relatively more engaged by the learning task
Collective effects on the settling of clay flocs
No full textIn this work a high-magnification digital video camera in combination with a settling column is used to study in a first part the influence of the amount of flocs transferred into the settling column on their settling velocity. In a second part, the setup was used to study the properties of flocs prepared at different clay concentrations but at same flocculant to clay ratio (2.5mgg−1). Illite clay was used and flocculated in a 1 L jar with an anionic polyacrylamide (flocculant). Results show that the average settling velocity of flocs is a function of the amount of transferred flocs. It was also found that floc size and settling velocity depend on clay concentration. This is attributed to the fast aggregation happening in the jar when flocculant and clay are mixed: at higher clay concentrations, larger flocs are created in the first minutes of the experiment, with low densities that prevent them from settling to the bottom of the jar.Environmental Fluid MechanicsRivers, Ports, Waterways and Dredging Engineerin
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