Cues to body-related distortions and hallucinations? Spontaneous sensations correlate with EEG oscillatory activity recorded at rest in the somatosensory cortices

Complex Bodily Hallucinatory Experiences Scale (CBHES): Development, structure and psychometric properties

OBJECTIVES

Complex bodily hallucinations are not rare in psychiatric, neurological and toxicological conditions and may also be reported even in the total absence of any medical condition. Despite this, they are usually not clinically assessed independently from (and in comparison to) hallucinations in other modalities. The objective of this study was to develop a short scale assessing complex bodily hallucinations.

METHODS

Based on previous research and clinical reports, we present a new short scale for the assessment of four themes of such hallucinations, i.e., delusional parasitosis, the feeling of presence, autoscopic phenomena, and body distortions. The scale was completed by 623 participants from the general population.

RESULTS

Complex bodily hallucinations are frequent, with 96.6% of the sample reporting at least one. A Confirmatory Factor Analysis showed that the data best fit a hierarchical model in which the four independent themes are linked to a higher-order factor that we tentatively identifed as bodily self-consciousness. Each one of the four themes was reported in isolation in less than 5% of the sample, but combinations of themes were more frequent. The scale has good internal consistency, a good 3-month test-retest reliability, and good convergent validity. Furthermore, the scale has a good balance between specificity and sensitivity when the 90th percentile of the total score is used as a classification criterion.

CONCLUSION

The short scale developed has good psychometric properties and can be used both in clinical and research settings.

EEG resting state alpha dynamics predict an individual's vulnerability to auditory hallucinations

Task-free brain activity exhibits spontaneous fluctuations between functional states, characterized by synchronized activation patterns in distributed resting-state (RS) brain networks. The temporal dynamics of the networks' electrophysiological signatures reflect individual variations in brain activity and connectivity linked to mental states and cognitive functions and can predict or monitor vulnerability to develop psychiatric or neurological disorders. In particular, RS alpha fluctuations modulate perceptual sensitivity, attentional shifts, and cognitive control, and could therefore reflect a neural correlate of increased vulnerability to sensory distortions, including the proneness to hallucinatory experiences. We recorded 5 min of RS EEG from 33 non-clinical individuals varying in hallucination proneness (HP) to investigate links between task-free alpha dynamics and vulnerability to hallucinations. To this end, we used a dynamic brain state allocation method to identify five recurrent alpha states together with their spatiotemporal dynamics and most active brain areas through source reconstruction. The dynamical features of a state marked by activation in somatosensory, auditory, and posterior default-mode network areas predicted auditory and auditory-verbal HP, but not general HP, such that individuals with higher vulnerability to auditory hallucinations spent more time in this state. The temporal dynamics of spontaneous alpha activity might reflect individual differences in attention to internally generated sensory events and altered auditory perceptual sensitivity. Altered RS alpha dynamics could therefore instantiate a neural marker of increased vulnerability to auditory hallucinations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-024-10093-1.

Stimulus awareness is associated with secondary somatosensory cortex activation in an inattentional numbness paradigm

While inattentional blindness and deafness studies have revealed neural correlates of consciousness (NCC) without the confound of task relevance in the visual and auditory modality, comparable studies for the somatosensory modality are lacking. Here, we investigated NCC using functional magnetic resonance imaging (fMRI) in an inattentional numbness paradigm. Participants (N = 44) received weak electrical stimulation on the left hand while solving a demanding visual task. Half of the participants were informed that task-irrelevant weak tactile stimuli above the detection threshold would be applied during the experiment, while the other half expected stimuli below the detection threshold. Unexpected awareness assessments after the experiment revealed that altogether 10 participants did not consciously perceive the somatosensory stimuli during the visual task. Awareness was not significantly modulated by prior information. The fMRI data show that awareness of stimuli led to increased activation in the contralateral secondary somatosensory cortex. We found no significant effects of stimulus awareness in the primary somatosensory cortex or frontoparietal areas. Thus, our results support the hypothesis that somatosensory stimulus awareness is mainly based on activation in higher areas of the somatosensory cortex and does not require strong activation in extended anterior or posterior networks, which is usually seen when perceived stimuli are task-relevant.