Intentional inhibition of actions in humans

A crucial component of human behavioural flexibility is the capacity to inhibit actions at the last moment before action execution. This behavioural inhibition is often not an immediate reaction to external stimuli, but rather an endogenous ‘free’ decision. Knowledge about such ‘intentional inhibition’ is currently limited, with most research focused on stimulus-driven inhibition. This thesis will examine intentional inhibition, using several different experimental approaches. The behavioural experiments reported in the initial chapters found that intentional inhibition directly alters sensory processing during decision-making. In addition, there were unique effects of prior event sequences on subsequent decisions to either act or inhibit. Brain imaging methods using EEG and fMRI showed distinct neural mechanisms associated with intentional inhibition, which did not apply to rule-based inhibition. Work with Tourette syndrome patients indicated that the intentional inhibition of involuntary motor tics affects brain activity associated with voluntary actions. Furthermore, attentional manipulation strategies were shown to be highly effective in reducing tics, which may open up alternative behavioural treatment approaches for tic disorders. This thesis concludes by demonstrating that intentional inhibition is a bona fide cognitive function worth studying. It also develops a cognitive model in which behavioural inhibition varies along a continuum from ‘instructed inhibition’ to ‘intentional inhibition’. This model may be useful as a guide for future work

Spatial primes produce dissociated inhibitory effects on saccadic latencies and trajectories.

In masked priming, a briefly presented prime can facilitate or inhibit responses to a subsequent target. In most instances, targets with an associated response that is congruent with the prime direction speed up reaction times to the target (a positive compatibility effect; PCE). However, under certain circumstances, slower responses for compatible primes are obtained (a negative compatibility effect; NCE). NCEs can be found when a long pre-target delay is used. During the delay, inhibition is assumed to take place, and therefore an effect on saccade trajectories may also be expected. In a previous study, we found the effects of inhibition on response times and trajectories to be dissociated, but this experiment varied the timing of several aspects of the stimulus sequence and it is therefore unclear what caused the dissociation. In the present study, we varied only one aspect of the timing, but replicated the dissociation. By varying just the pre-target delay, we found a PCE for a short delay, and an NCE for a long delay, but saccade trajectories deviated away from prime directions in both conditions. This suggests dissociated inhibitory effects of primes on response times and saccade trajectories

Source Memory: A Review

Memory records include different kinds of information representing from whom, how, where and when those records were obtained. Source monitoring is an attribution process of memories to their origins. This monitoring is also required for discriminating a specific memory record among other memory traces. Investigating in which situations individuals are more prone to source misattributions and in which situations they are more resistant to these source errors may help us understand this mechanism, with which the origin of knowledge is monitored. According to source monitoring theory, false memories are considered as a failure in this monitoring mechanism (Johnson, Hashtroudi and Lindsay 3; Lindsay 325). Thus, source memory studies are crucial from both theoretical and a practical point of view. In the introduction part of the review, the source memory literature is reviewed in detail and the factors affecting the source monitoring process are mentioned. In the second and the third part of the review, the relation between memory for item and its source and the methods used in source memory research are presented, respectively

Veto and Vacillation: A Neural Precursor of the Decision to Withhold Action.

The capacity to inhibit a planned action gives human behavior its characteristic flexibility. How this mechanism operates and what factors influence a decision to act or not act remain relatively unexplored. We used EEG readiness potentials (RPs) to examine preparatory activity before each action of an ongoing sequence, in which one action was occasionally omitted. We compared RPs between sequences in which omissions were instructed by a rule (e.g., "omit every fourth action") and sequences in which the participant themselves freely decided which action to omit. RP amplitude was reduced for actions that immediately preceded a voluntary omission but not a rule-based omission. We also used the regular temporal pattern of the action sequences to explore brain processes linked to omitting an action by time-locking EEG averages to the inferred time when an action would have occurred had it not been omitted. When omissions were instructed by a rule, there was a negative-going trend in the EEG, recalling the rising ramp of an RP. No such component was found for voluntary omissions. The results are consistent with a model in which spontaneously fluctuating activity in motor areas of the brain could bias "free" decisions to act or not

The Effects of Survival Context on False Memories

Research on human memory has shown some encoding procedures to be better than others. Recent studies in the literature proposed that survival context might provide the best encoding conditions identied in human memory research. The aim of the current study is to investigate the effects of survival context on suggestibility to post-event misinformation. Participants read a neutral story and rated certain target words in the story with regard to their relevance to a survival or a moving scenario; or their pleasantness. Next, participants either read the same story a second time or they read another version containing post-event misinformation. A between-subject design was used in Experiment 1 and participants' memory for correct and false information was tested with a recall (Experiment 1A) or a recognition (Experiment 1B) test. In Experiment 2 a within-subjects design was used and participants' memory for correct and false information was tested with a recall (Experiment 2A) or recognition (Experiment 2B) test. In total 198 students (Experiment 1A=54, Experiment 1B=48, Experiment 2A=48, Experiment 2B=48) participated in the study. Results showed that words rated within a context, regardless of the specic context, were more resilient to post-event misinformation than words that were not rated. However, there were no differences between the survival, moving or pleasantness contexts with regard to correct or false recall or recognition. Overall, survival advantage was not observed for neither correct nor false memory. Results did not demonstrate a consistent survival advantage for decreasing the post-event misinformation effect

Face perception enhances insula and motor network reactivity in Tourette syndrome

Tourette syndrome is a neurodevelopmental disorder, characterised by motor and phonic tics. Tics are typically experienced as avolitional, compulsive, and associated with premonitory urges. They are exacerbated by stress and can be triggered by external stimuli, including social cues like the actions and facial expressions of others. Importantly, emotional social stimuli, with angry facial stimuli potentially the most potent social threat cue, also trigger behavioural reactions in healthy individuals, suggesting that such mechanisms may be particularly sensitive in people with Tourette syndrome. Twenty-one participants with Tourette syndrome and 21 healthy controls underwent functional magnetic resonance imaging while viewing faces wearing either neutral or angry expressions to quantify group differences in neural activity associated with processing social information. Simultaneous video recordings of participants during neuroimaging enabled us to model confounding effects of tics on task-related responses to the processing of faces. In both Tourette syndrome and control participants, face stimuli evoked enhanced activation within canonical face perception regions, including the occipital face area and fusiform face area. However, the Tourette syndrome group showed additional responses within the anterior insula to both neutral and angry faces. Functional connectivity during face viewing was then examined in a series of psychophysiological interactions. In Tourette syndrome participants, the insula showed functional connectivity with a set of cortical regions previously implicated in tic generation: the pre-supplementary motor area, premotor cortex, primary motor cortex, and the putamen. Furthermore, insula functional connectivity with the globus pallidus and thalamus varied in proportion to tic severity, while supplementary motor area connectivity varied in proportion to premonitory sensations, with insula connectivity to these regions increasing to a greater extent in patients with worse symptom severity. In addition, the occipital face area showed increased functional connectivity in Tourette syndrome participants with posterior cortical regions, including primary somatosensory cortex, and occipital face area connectivity with primary somatosensory and primary motor cortices varied in proportion to tic severity. There were no significant psychophysiological interactions in controls. These findings highlight a potential mechanism in Tourette syndrome through which heightened representation within insular cortex of embodied affective social information may impact the reactivity of subcortical motor pathways, supporting programmed motor actions that are causally implicated in tic generation. Medicinal and psychological therapies that focus on reducing insular hyper-reactivity to social stimuli may have potential benefit for tic reduction in people with Tourette syndrome