Memory-reliant Post-error Slowing Is Associated with Successful Learning and Fronto-occipital Activity

Negative feedback after an action in a cognitive task can lead to devaluing that action on future trials as well as to more cautious responding when encountering that same choice again. These phenomena have been explored in the past by reinforcement learning theories and cognitive control accounts, respectively. Yet, how cognitive control interacts with value updating to give rise to adequate adaptations under uncertainty is less clear. In this fMRI study, we investigated cognitive control-based behavioral adjustments during a probabilistic reinforcement learning task and studied their influence on performance in a later test phase in which the learned value of items is tested. We provide support for the idea that functionally relevant and memory-reliant behavioral adjustments in the form of post-error slowing during reinforcement learning are associated with test performance. Adjusting response speed after negative feedback was correlated with BOLD activity in right inferior frontal gyrus and bilateral middle occipital cortex during the event of receiving the feedback. Bilateral middle occipital cortex activity overlapped partly with activity reflecting feedback deviance from expectations as measured by unsigned prediction error. These results suggest that cognitive control and feature processing cortical regions interact to implement feedback-congruent adaptations beneficial to learning

Exploring memory impairment and post-traumatic amnesia following traumatic brain injury

Memory disturbances are among the most common and significant consequences of traumatic brain injury (TBI). The severity of these deficits can vary widely across the trajectory of recovery from TBI and can be highly heterogenous across individuals. In the acute stages memory disturbance can occur in the form of post-traumatic amnesia (PTA), but deficits are also present into the chronic stages of recovery. I present four studies that aim to understand the characteristics and underlying mechanisms of memory impairment following TBI. I investigated the cognitive profile of acute TBI patients with and without PTA. I found PTA patients show a transient deficit in working memory binding. I then assessed electrophysiological abnormalities to test the hypothesis that the binding deficit is underpinned by pathological low frequency slow-wave activity. PTA patients showed a significantly higher delta to alpha power ratio that correlated with binding impairment. To understand how this disruption to cortical communication impacts upon large-scale networks I performed a dynamic functional connectivity analysis on the resting state fMRI of acute TBI patients. I found four independent brain states that showed striking anti-correlation between core cognitive control networks. Patients in a more profound period of PTA spent more time in fewer states than those with less cognitive impairment. These findings suggest that PTA is likely underpinned by disruption to communication required for integration of features in working memory. Finally, I examined enduring memory failures in chronic TBI patients and found that patients with episodic memory impairment showed differential activation of key networks required for memory and attention. Memory impairment related to the white matter integrity directly underpinning the task-derived encoding networks. These findings suggest that in chronic TBI memory impairment may be associated with failed control of attentional resources.Open Acces

The Sustained Influence of an Error on Future Decision-Making

Post-error slowing (PES) is consistently observed in decision-making tasks after negative feedback. Yet, findings are inconclusive as to whether PES supports performance accuracy. We addressed the role of PES by employing drift diffusion modeling which enabled us to investigate latent processes of reaction times and accuracy on a large-scale dataset (>5,800 participants) of a visual search experiment with emotional face stimuli. In our experiment, post-error trials were characterized by both adaptive and non-adaptive decision processes. An adaptive increase in participants' response threshold was sustained over several trials post-error. Contrarily, an initial decrease in evidence accumulation rate, followed by an increase on the subsequent trials, indicates a momentary distraction of task-relevant attention and resulted in an initial accuracy drop. Higher values of decision threshold and evidence accumulation on the post-error trial were associated with higher accuracy on subsequent trials which further gives credence to these parameters' role in post-error adaptation. Finally, the evidence accumulation rate post-error decreased when the error trial presented angry faces, a finding suggesting that the post-error decision can be influenced by the error context. In conclusion, we demonstrate that error-related response adaptations are multi-component processes that change dynamically over several trials post-error

Components of aging

Age-related cognitive decline has been linked to a reduction in attentional resources that are assumed to result from alterations in the aging brain. A core ability that is subject to age-related decline is visual attention, which enables individuals to select the most important information for conscious processing and action. However, visual attention is considered a conglomerate of various functions and the specific components underlying age differences in performance remain little understood. The present PhD project aimed at dissociating age effects on several (sub-) components that concur in visual attention tasks within a neurocognitive approach. Established and theoretically grounded psychological paradigms that allow separating various attentional components were combined with event-related potentials (ERPs), which provide a temporally fine-graded dissociation of cognitive processes involved in a task. 1st Project The first project was designed to determine the origin(s) of age-related decline in visual search, a key paradigm of attention research. To pursue this goal on a micro-level, response time measures in a compound-search task, in which the target-defining feature of a pop-out target (color/shape) was dissociated from the response-defining feature (orientation), were coupled with lateralized ERPs. Several ERP components tracked the timing of processing stages involved in this task, these being (1) allocation of attention to the target, marked by the posterior-contralateral negativity (PCN), (2) target analyses in vSTM, marked by the sustained posterior-contralateral negativity (SPCN), (3) response selection, marked by the stimulus-locked lateralized readiness potential (LRP) and (4) response execution, marked by the response-locked LRP. Slowed response times (RT) in older participants were associated with age differences in all analyzed ERPs, indicating that behavioural slowing accrues across multiple stages within the information processing stream. Furthermore, v behavioral data and ERPs were analyzed with respect to age and carry-over effects from one trial to the next. The intertrial analyses revealed relatively automatic processes – such as dimension weighting facilitating the early stage of visual selection, and response weighting facilitating the late stage of response execution – to be preserved in older age. By contrast, more controlled processes – such as the flexible stimulus-response (S-R) (re-) mapping across trials on the intermediate stages of response selection - were particularly affected by aging. This indicates that besides general slowing, specific age decrements in executively controlled processes contribute to age-related decline in visual search. 2nd Project The second project explored neural markers of individual and age differences in attention parameters formally integrated in Bundesen’s computational Theory of Visual Attention (TVA). According to the model, two parameters of general visual attention capacity, perceptual processing speed C and visual short-term memory (vSTM) storage capacity K are defined and can be modeled mathematically independently for a particular individual. More recently, the neural interpretation of the model (NTVA) suggested that the two functions (at least partly) rely on distinct brain mechanisms. To test this assumption in an empirical approach, individual TVA-based estimates were derived in a standard TVA whole report task, and ERPs of the same participants were recorded in an adapted EEG-compatible version of the task. In the first study of the second project, we explored neurophysiological markers of interindividual differences in the two functions in younger participants. The results revealed distinct ERP correlates to be related to the parameters: Individuals with higher compared to lower processing speed C had significantly smaller posterior N1 amplitudes, suggesting that the rate of object categorization is associated with the efficiency of early visual processing. Individuals with higher compared to lower storage capacity showed stronger contralateral delay activity (CDA) over visual areas, indicating that the limit of vi vSTM relies on topographically-organized sustained activation within the visual system. These results can be regarded as direct neuroscientific evidence for central assumptions of the theoretical framework. In the second study of the second project, the same approach was pursued to investigate whether and how TVA attentional capacity parameters and their neural markers change with aging. First, the same ERP correlates of processing speed and storage capacity indexing individual differences in younger participants (i.e., the posterior N1 marked differences in processing speed C and the CDA marked differences in storage capacity K, respectively) were found to be valid also in the older group. In addition to this, two further components marked performance differences in the parameters exclusively within the older group: Older participants with lower processing speed showed smaller anterior N1 amplitudes relative to faster older and all younger participants, suggesting a selective loss of resources supporting early control of attentional guidance. Older participants with higher storage capacity exhibited a stronger right-central positivity than older participants with lower storage capacity and all younger participants. This pattern is indicative of compensatory recruitment of additional neural resources in high-functioning older individuals, presumably related to enhanced executive control fostering sustained activation of vSTM representations. Again, these findings strongly support the NTVA framework, proposing distinct neural mechanisms underlying processing speed and storage capacity. Furthermore, they show that distinct mechanisms of attentional control determine the two functions in older age

Visual Puzzles, Figure Weights, and Cancellation: Some Preliminary Hypotheses on the Functional and Neural Substrates of These Three New WAIS-IV Subtests

In this study, five consecutive patients with focal strokes and/or cortical excisions were examined with the Wechsler Adult Intelligence Scale and Wechsler Memory Scale—Fourth Editions along with a comprehensive battery of other neuropsychological tasks. All five of the lesions were large and typically involved frontal, temporal, and/or parietal lobes and were lateralized to one hemisphere. The clinical case method was used to determine the cognitive neuropsychological correlates of mental rotation (Visual Puzzles), Piagetian balance beam (Figure Weights), and visual search (Cancellation) tasks. The pattern of results on Visual Puzzles and Figure Weights suggested that both subtests involve predominately right frontoparietal networks involved in visual working memory. It appeared that Visual Puzzles could also critically rely on the integrity of the left temporoparietal junction. The left temporoparietal junction could be involved in temporal ordering and integration of local elements into a nonverbal gestalt. In contrast, the Figure Weights task appears to critically involve the right temporoparietal junction involved in numerical magnitude estimation. Cancellation was sensitive to left frontotemporal lesions and not right posterior parietal lesions typical of other visual search tasks. In addition, the Cancellation subtest was sensitive to verbal search strategies and perhaps object-based attention demands, thereby constituting a unique task in comparison with previous visual search tasks

The Impact Of Color on Response Inhibition

Response inhibition is an important cognitive function that affects decision-making and action selection. Impairments in it occur in neurodegenerative diseases therefore, ways to support response inhibition are important for quality of life. One possibility is the use of color, as color has been shown to modulate inhibitory processes. The overall objective of this work was to determine the prefrontal networks underlying response inhibition that can be modulated through an automatic attentional process such as color. A series of three studies were performed whereby young adults performed a stop-signal task (SST) or a Go/No-go task (GNGT) with colored stimuli. In our first study, the SST, a reactive response inhibition task, was performed to determine whether the effect of color on response inhibition was due to color opponency, attentional color hierarchy, or visual associations. We found that while red stop signals produced faster response inhibition compared to green, blue and yellow stop signals did not differ from each other. This pattern of results was not consistent with color opponency or the attentional color hierarchy of red > green > yellow > blue. Therefore, red facilitating and green impairing response inhibition suggested that response inhibition was modulated by visual color associations where red means stop and green means go. In our second study, we tested if the color modulations between red and green extended beyond countermanding to more general inhibitory control by using a proactive response inhibition task, the GNGT. Indeed, participants were more successful on red in comparison to green No-go trials. Based on these results, a modified accumulator model and putative neural circuitry of color modulation response inhibition was proposed. In our third study, event-related potentials (ERPs) were recorded while participants performed a GNGT to test the putative underlying neural network. While the P300 was not modulated by color, we observed reduced N200 amplitudes and earlier N200 latencies over the prefrontal areas proposed in study 2 in response to red No-go stimuli over green, yellow, and blue. The increased accuracy was argued to be an advantage conferred by learned and evolutionary associations to the colour red. The decreased N200 amplitudes suggested reduced conflict on No-go trials with red No-go stimuli compared to other colours. These findings bring us a step closer to mapping out the differential colour modulated neural circuitry involved in response inhibition and such research will help pave the way for efficient decision-making and staving off cognitive decline

The Impact Of Color on Response Inhibition

Response inhibition is an important cognitive function that affects decision-making and action selection. Impairments in it occur in neurodegenerative diseases therefore, ways to support response inhibition are important for quality of life. One possibility is the use of color, as color has been shown to modulate inhibitory processes. The overall objective of this work was to determine the prefrontal networks underlying response inhibition that can be modulated through an automatic attentional process such as color. A series of three studies were performed whereby young adults performed a stop-signal task (SST) or a Go/No-go task (GNGT) with colored stimuli. In our first study, the SST, a reactive response inhibition task, was performed to determine whether the effect of color on response inhibition was due to color opponency, attentional color hierarchy, or visual associations. We found that while red stop signals produced faster response inhibition compared to green, blue and yellow stop signals did not differ from each other. This pattern of results was not consistent with color opponency or the attentional color hierarchy of red > green > yellow > blue. Therefore, red facilitating and green impairing response inhibition suggested that response inhibition was modulated by visual color associations where red means stop and green means go. In our second study, we tested if the color modulations between red and green extended beyond countermanding to more general inhibitory control by using a proactive response inhibition task, the GNGT. Indeed, participants were more successful on red in comparison to green No-go trials. Based on these results, a modified accumulator model and putative neural circuitry of color modulation response inhibition was proposed. In our third study, event-related potentials (ERPs) were recorded while participants performed a GNGT to test the putative underlying neural network. While the P300 was not modulated by color, we observed reduced N200 amplitudes and earlier N200 latencies over the prefrontal areas proposed in study 2 in response to red No-go stimuli over green, yellow, and blue. The increased accuracy was argued to be an advantage conferred by learned and evolutionary associations to the colour red. The decreased N200 amplitudes suggested reduced conflict on No-go trials with red No-go stimuli compared to other colours. These findings bring us a step closer to mapping out the differential colour modulated neural circuitry involved in response inhibition and such research will help pave the way for efficient decision-making and staving off cognitive decline

The relationship between neurocognitive disorders, prospective memory impairment and white matter damage in clade C HIV-positive subjects

Includes bibliographical references.AIMS: To examine the relationship between prospective memory, cognitive function and Diffusion tensor imaging (DTI)/ White matter integrity of human immunodeficiency virus (HIV) positive individuals in the Western Cape. We hypothesize that: 1. Individuals infected with HIV will exhibit significantly poorer microstructural integrity of the white matter than HIV negative individuals, as determined by in vivo diffusion tensor imaging. We expect that values of fractional anisotropy (FA) - a measure of directional water diffusion- in the frontal white matter will be significantly lower among HIV patients compared to controls 2. Lower FA measured in the frontal white matter will correlate significantly with impaired performance on tests of prospective memor

Conflict and adaptation: Identifying the markers of cognitive control in the transition from wakefulness to sleep

This thesis aims to investigate the cognitive changes that follow the transition from wakefulness to sleep. All studies presented have been driven by the hypothesis that consciousness is selectively required for some cognitive processes and not others. As such, fluctuations in alertness are hypothesised expected to produce a larger effect in those processes that are more reliant on consciousness. In chapter 2 we begin by investigating the effect of alertness on conflict monitoring. Conflict monitoring is the environmental scanning process by which the brain detects conflicting information and identifies the need for top-down behavioural control. Using a combined Go/NoGo and Go-left/Go-right paradigm, we investigated effects of alertness on reaction times and responsiveness. We revealed an interaction between the task requirement to monitor conflict (Go/NoGo) and the level of alertness. Crucially, the difference between both tasks was only observed in the later stage of drowsiness. This suggests that conflict monitoring is more susceptible to reductions in alertness. Our results from Chapter 2 also provide further evidence for the ecological validity of the Hori scale as a way to classify of the sleep onset period into functionally meaningful sub-stages. However, manual scoring of trials is an arduous process subject to interrater variability. In order to overcome these limitations, we developed an automated algorithm to classify trials into 3 alertness categories using Hori stage principles. This microstaging method was published in the journal Neuroimage (Jahannathan, Ezquerro-Nassar, et al., 2018) and is included in its published form. The method in Chapter 3 was then employed in Chapters 4 and 5, where we investigated effects of alertness and sleep deprivation in an auditory Simon task. This research was published in Journal of Neuroscience (Canales-Johnson, et al., 2020) and the manuscript is included in this thesis. Participants attended two sessions in the lab and performed an auditory Simon task, after a night of normal sleep or a night of partial sleep deprivation. We hypothesised that conflict detection processes necessary for an immediate conflict effect would be preserved under drowsiness, in line with studies showing residual processing for local, short stimuli during early sleep. Similarly, we predicted that sleep deprivation would not impair conflict detection. Furthermore, we investigated the capacity to modify behavioural control using information from the previous trial via top-down mechanisms, known as conflict adaptation. The process that mediates the conflict adaptation effect is hypothesised to require consciousness. Therefore, we hypothesised that trial-by-trial conflict adaptation would be impaired during drowsiness and sleep deprivation. In Chapter 4, we confirmed our hypothesis that the conflict detection is preserved under drowsiness, as indicated by slower reaction times for incongruent stimuli. However, we revealed an interaction between alertness, previous trial congruency and current trial congruency, suggesting a deleterious effect of drowsiness on conflict adaptation. At odds with our hypothesis, sleep deprivation was found to have a main effect on reaction times but it did not interact with any of the variables. In Chapter 5, we found an increase in theta power associated to incongruent trials, a classic neural marker of cognitive control. This effect was observed during wakefulness but not during drowsiness, suggestive of potential alternative mechanisms underlying cognitive control under reduced alertness. Overall, the findings of this thesis suggest that alertness has a different bearing depending on the cognitive process required. This has wider implications for the functional role of consciousness and suggests that sleep onset period is a useful framework to evaluate theories of consciousness