Electrophysiological correlates of interference control in the Eriksen task

This thesis examined conflict monitoring in the Eriksen task in which participants must respond to a centrally positioned target arrow and ignore simultaneously presented distractors that flank the target. Distractors were either associated with a response congruent to the target, in conflict with the target, or, in a neutral condition, not associated with a response, instead producing only perceptual interference. This thesis extended on previous Eriksen research by systematically investigating the effect of varying the level of response conflict and task difficulty on stimulus processing in six studies and clarifying the functional role of ERP components elicited in the Eriksen task. Specifically, this was achieved by (a) varying the number of flanking distractors and, (b) the level of response conflict by using different permutations of incongruent distractors, (c) reducing target stimulus perceptibility through degradation, (d) utilising both valid and invalid information to increase response preparation and make conflict monitoring more difficult, and (e) providing feedback in a speeded version of the task. In all six studies, two N2 components were clearly delineated – the first of which was increased to stimuli requiring enhanced feature detection processes (N2a), while the second N2 component (N2b) was consistently observed to increase following the detection of response conflict. The P3 component, rarely considered in the Eriksen paradigm, was reduced at parietal sites and increased in latency as the discriminability of the target amongst the distractors became more difficult. The results suggest that the P3 component may reflect stimulus evaluation processes and equivocation related to the ease of target identification and concurrent response selection processes imperative for accurate task performance. This thesis also utilised digital filtering to clarify time-domain ERP results in terms of the relative contributions of activity in the alpha, theta and delta frequency ranges. Event-related theta oscillations contributed significantly to the morphology of the two N2 components reflecting allocation of focused attentional resources following the detection of perceptual (theta N2a) or response conflict (theta N2b). Activity in both theta and delta frequency ranges was robustly observed to contribute to the P3 component. An increased theta response at frontal sites was observed along with increases in task difficulty likely indexing the activation of anterior attentional resources. The results also suggest that the parietal delta P3 component reflects a refined form of equivocation, sensitive to the perceptibility of the target, and concomitant with the relative ease of accurate response selection. This thesis has clarified successful conflict monitoring and task performance in the Eriksen task, and the relationship with stimulus-locked ERP components in the time and frequency domains. The results suggest that the second frontally maximal N2 component reflects successful conflict monitoring, while the P3 component most probably reflects equivocation arising from difficult target identification and accurate response selection, rather than response conflict per se

Familial analysis of MMN in cannabis users: A case study

Abstract presented at the 23rd Australasian Society for Psychophysiology Conference, 20-22 Nov 2013, Wollongong, Australi

An investigation of mismatch negativity in current and ex-cannabis users using a feature controlled method

Abstract presented at the 23rd Australasian Society for Psychophysiology Conference, 20-22 Nov 2013, Wollongong, Australi

Electrophysiological correlates of the brain-derived neurotrophic factor (BDNF) Val66Met polymorphism

The brain-derived neurotrophic factor (BDNF) protein is essential for neuronal development. Val66Met (rs6265) is a functional polymorphism at codon 66 of the BDNF gene that affects neuroplasticity and has been associated with cognition, brain structure and function. The aim of this study was to clarify the relationship between BDNF Val66Met polymorphism and neuronal oscillatory activity, using the electroencephalogram (EEG), in a normative cohort. Neurotypical (N = 92) young adults were genotyped for the BDNF Val66Met polymorphism and had eyes open resting-state EEG recorded for four minutes. Focal increases in right fronto-parietal delta, and decreases in alpha-1 and right hemispheric alpha-2 amplitudes were observed for the Met/Met genotype group compared to Val/Val and Val/Met groups. Stronger frontal topographies were demonstrated for beta-1 and beta-2 in the Val/Met group versus the Val/Val group. Findings highlight BDNF Val66Met genotypic differences in EEG spectral amplitudes, with increased cortical excitability implications for Met allele carriers

Attention-induced deactivations in very low frequency EEG oscillations: differential localisation according to ADHD symptom status

Background: the default-mode network (DMN) is characterised by coherent very low frequency (VLF) brain oscillations. The cognitive significance of this VLF profile remains unclear, partly because of the temporally constrained nature of the blood oxygen-level dependent (BOLD) signal. Previously we have identified a VLF EEG network of scalp locations that shares many features of the DMN. Here we explore the intracranial sources of VLF EEG and examine their overlap with the DMN in adults with high and low ADHD ratings.Methodology/Principal Findings: DC-EEG was recorded using an equidistant 66 channel electrode montage in 25 adult participants with high- and 25 participants with low-ratings of ADHD symptoms during a rest condition and an attention demanding Eriksen task. VLF EEG power was calculated in the VLF band (0.02 to 0.2 Hz) for the rest and task condition and compared for high and low ADHD participants. sLORETA was used to identify brain sources associated with the attention-induced deactivation of VLF EEG power, and to examine these sources in relation to ADHD symptoms. There was significant deactivation of VLF EEG power between the rest and task condition for the whole sample. Using s-LORETA the sources of this deactivation were localised to medial prefrontal regions, posterior cingulate cortex/precuneus and temporal regions. However, deactivation sources were different for high and low ADHD groups: In the low ADHD group attention-induced VLF EEG deactivation was most significant in medial prefrontal regions while for the high ADHD group this deactivation was predominantly localised to the temporal lobes.Conclusions/Significance: attention-induced VLF EEG deactivations have intracranial sources that appear to overlap with those of the DMN. Furthermore, these seem to be related to ADHD symptom status, with high ADHD adults failing to significantly deactivate medial prefrontal regions while at the same time showing significant attenuation of VLF EEG power in temporal lobe

Second-Hand Exposure of Staff Administering Vaporised Cannabinoid Products to Patients in a Hospital Setting

Background In many health settings, administration of medicinal cannabis poses significant implementation barriers including drug storage and safety for administering staff and surrounding patients. Different modes of administration also provide different yet potentially significant issues. One route that has become of clinical interest owing to the rapid onset of action and patient control of the inhaled amount (via breath timing and depth) is that of vaporisation of cannabinoid products. Although requiring a registered therapeutic device for administration, this is a relatively safe method of intrapulmonary administration that may be particularly useful for patients with difficulty swallowing, and for those in whom higher concentrations of cannabinoids are needed quickly. A particular concern expressed to researchers undertaking clinical trials in the hospital is that other patients, nurses, and clinical or research staff may be exposed to second-hand vapours in the course of administering vaporised products to patients. Objective The objective of this study was to take samples from two research staff involved in administering vaporised D9-tetrahydrocannabinol to participants in a clinical trial, to examine and quantitate cannabinoid presence. Methods Blood samples from two research staff were taken during the exposure period for three participants (cannabis users) over the course of approximately 2.5 h and analysed using tandem mass spectrometry. Results Blood samples taken over a vaporised period revealed exposure below the limit of detection for D9-tetrahydrocannabinol and two metabolites, using tandem mass spectrometry analytical methods. Conclusions These results are reassuring for hospital and clinical trial practices with staff administering vaporised cannabinoid products, and helpful to ethics committees wishing to quantify risk

Acute and chronic effects of cannabinoids on human cognition-a systematic review

Cannabis use has been associated with impaired cognition during acute intoxication as well as in the unintoxicated state in long-term users. However, the evidence has been mixed and contested, and no systematic reviews of the literature on neuropsychological task-based measures of cognition have been conducted in an attempt to synthesize the findings. We systematically review the empirical research published in the past decade (from January 2004 to February 2015) on acute and chronic effects of cannabis and cannabinoids and on persistence or recovery after abstinence. We summarize the findings into the major categories of the cognitive domains investigated, considering sample characteristics and associations with various cannabis use parameters. Verbal learning and memory and attention are most consistently impaired by acute and chronic exposure to cannabis. Psychomotor function is most affected during acute intoxication, with some evidence for persistence in chronic users and after cessation of use. Impaired verbal memory, attention, and some executive functions may persist after prolonged abstinence, but persistence or recovery across all cognitive domains remains underresearched. Associations between poorer performance and a range of cannabis use parameters, including a younger age of onset, are frequently reported. Little further evidence has emerged for the development of tolerance to the acutely impairing effects of cannabis. Evidence for potential protection from harmful effects by cannabidiol continues to increase but is not definitive. In light of increasing trends toward legalization of cannabis, the knowledge gained from this body of research needs to be incorporated into strategies to minimize harm