fNIRS suggests increased effort during executive access in ecstasy polydrug users

Abstract

Background: Ecstasy use is associated with cognitive impairment, believed to result from damage to 5-HT axons. Neuroimaging techniques to investigate executive dysfunction in ecstasy users provide a more sensitive measure of cognitive impairment than behavioural indicators. The present study assessed executive access to semantic memory in ecstasy polydrug users and nonusers. Methods: Twenty ecstasy polydrug users and 20 non-user controls completed an oral variant of the Chicago Word Fluency Test (CWFT), whilst the haemodynamic response to the task was measured using functional Near Infrared Spectroscopy (fNIRS). Results: There were no between group differences in many background measures including measures of sleep and mood state (anxiety, arousal, hedonic tone). No behavioural differences were observed on the CWFT. However there were significant differences in oxy-Hb level change at several voxels relating to the left DLPFC and right medial PFC during the CWFT, indicating increased cognitive effort in ecstasy users relative to controls. Regression analyses showed that frequency of ecstasy use, total lifetime dose and amount used in the last 30 days were significant predictors of oxy-Hb increase at several voxels after controlling for alcohol and cannabis use indices. Conclusion: The results suggest that ecstasy users show increased activation in the PFC as a compensatory mechanism, to achieve equivalent performance to non-users. These findings are in agreement with much of the literature in the area which suggests that ecstasy may be a selective serotonin neurotoxin in humans.

Updating of working memory in ecstasy polydrug users: Findings from fNIRS

“…Indices of ecstasy use were significantly associated with all changes in cortical haemodynamics, frequency of use with RPFC oxygenation change and LPFC and RPFC deoxygenation change, lifetime dose with RPFC deoxygenation change, and recent use with all significant haemodynamic changes. This is in line with recent studies from our own lab where recency of use was a significant predictor of oxy-Hb change during an inhibition task (Roberts & Montgomery, 2015a) and a semantic access task (Roberts & Montgomery, 2015b).…”

Preparation for mental effort recruits Dorsolateral Prefrontal Cortex: an fNIRS investigation

“…Previous fNIRS studies have investigated DLPFC contribution to several processes cognitive, such as word-encoding in a memory task (Ferreri et al, 2014), inhibitory control in drug users (Roberts & Montgomery, 2015), dual motor and cognitive task-performance (Mandrick et al, 2013). Relevant to the current results, two studies targeted hemodynamic responses in DLPFC in effortful tasks, specifically testing the effect of varying mental load in a working memory task (Molteni et al, 2012), and comparing laboratory measures of load (executive function task) with real-life effort (operating a flight-simulator Causse et al, 2017).…”

Meta-analysis of executive functioning in ecstasy/polydrug users

“…Decreased pre-synaptic SERT and increased post-synaptic 5-HT 2A receptor availability are consistent with serotonin axon damage. Moreover, functional neuroimaging studies have observed ecstasy-related adjustments to cerebral blood flow in frontal areas, with functional near-infrared spectroscopy (Roberts & Montgomery, 2015 a ) and fMRI (Moeller et al 2004 ; Jager et al 2008 ; Roberts & Garavan, 2010 ). It is noteworthy that all of the functional imaging studies mentioned observe increased neuronal activity to achieve similar behavioural performance to controls.…”

“…Several neuroimaging studies have concluded that ecstasy-related neuronal adaptations may occur neurophysiologically before they manifest functionally. Roberts & Montgomery ( 2015 a ) suggested that ecstasy users display increased blood flow to areas of the PFC during a verbal fluency task, despite no differences in task performance. This suggests that ecstasy users work harder to achieve similar performance to controls, and that functional differences may be apparent with increased workload.…”