Abstract
Source monitoring, or the ability to recall the origin of information, is a crucial aspect of remembering past experience. One facet of this, reality monitoring, refers to the ability to distinguish between internally generated and externally generated information, biases in which have previously been associated with auditory verbal hallucinations in schizophrenia. Neuroimaging evidence suggests that medial prefrontal and superior temporal (STG) regions may play a role in reality monitoring for auditory verbal information, with evidence from a previous neurostimulation experiment also suggesting that modulation of excitability in STG may affect reality monitoring task performance. Here, two experiments are reported that used transcranial direct current stimulation (tDCS) to modulate excitability in medial prefrontal and superior temporal cortex, to further investigate the role of these brain regions in reality monitoring. In the first experiment (N = 36), tDCS was applied during the encoding stage of the task, while in the second experiment, in a separate sample (N = 36), it was applied during the test stage. There was no effect of tDCS compared to a sham condition in either experiment, with Bayesian analysis providing evidence for the null hypothesis in both cases. This suggests that tDCS applied to superior temporal or medial prefrontal regions may not affect reality monitoring performance, and has implications for theoretical models that link reality monitoring to the therapeutic effect of tDCS on auditory verbal hallucinations.
Highlights
The ability to recall the origin, or ‘source’, of information is a crucial aspect of remembering past experiences, and has been termed ‘source monitoring’ (Johnson et al, 1993)
This is consistent with neuroimaging evidence suggesting that primary and secondary auditory cortical regions are active during the experience of auditory verbal hallucinations (AVH) (Jardri et al, 2011)
After the task was described, the transcranial direct current stimulation (tDCS) electrodes were placed on the participants scalp, before the stimulation commenced, participants listened to a brief sound clip, consisting of the male voice used in the source memory task reading a short extract from a book (60 s)
Summary
The ability to recall the origin, or ‘source’, of information is a crucial aspect of remembering past experiences, and has been termed ‘source monitoring’ (Johnson et al, 1993). One possibility highlighted by the source monitoring framework is that individuals who hallucinate generate excessively vivid mental imagery (Aleman et al, 2003), which is more likely to become misattributed This is consistent with neuroimaging evidence for superior temporal gyrus (STG) activation in both vivid verbal imagery and during AVH (Jardri et al, 2011; Zvyagintsev et al, 2013). Sugimori et al investigated the link between reality monitoring, cortical activation, and the tendency of the participants to experience auditory hallucinations (assessed using a self-report measure), finding that activity in the STG (encompassing primary and secondary auditory cortex) when participants externally misattributed a word they had imagined as ‘heard’ was significantly correlated with the tendency to experience auditory hallucinations This is consistent with neuroimaging evidence suggesting that primary and secondary auditory cortical regions are active during the experience of auditory verbal hallucinations (AVH) (Jardri et al, 2011). We conducted further analysis of data from both experiments together, regarding task performance, imagery vividness, and self-reported hallucination-proneness
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