Does the resting brain reveal who is more vulnerable to hallucination‑like experiences?

At times, the brain seems to slip into an autopilot mode, especially when we are at rest, eyes closed, and apparently “doing nothing.” In reality, even during this apparent stillness, the brain engages in a continuous dance of fast, fluctuating electrical states. These subtle dynamics can reveal a great deal about a characteristic present across the population: the propensity to experience hallucination‑like events, which varies widely from person to person.

A new study led by Sonja Kotz and colleagues investigated how four distinct dimensions of this proneness, multisensory experiences, auditory daydreaming, vivid thoughts and inner speech, and personified experiences (the sense that a mental content comes from “someone”), are expressed in resting‑state alpha rhythms measured with EEG. Rather than focusing solely on brainwave amplitude, the team used an advanced computational approach (a Hidden semi‑Markov Model) capable of identifying transient, recurrent patterns of activity and tracking how the brain transitions between these states over just three minutes of rest.

The results showed a clear association: the higher a person’s proneness to hallucination‑like experiences (across all dimensions), the more frequently the brain switched between states, suggesting a more volatile mental landscape characterised by rapid shifts between internally and externally oriented focus.

However, for some participants, these changes were not only more frequent but also displayed specific temporal patterns. In particular, individuals with higher scores in the “personified experiences” dimension showed systematic changes over time in how they visited two brain states with nearly opposite topographies. One of these states, marked by stronger activity in parietal and frontal regions, appears to reflect increased focus on internal experience; the other, with a distinct temporal profile, may relate to control mechanisms that help differentiate what originates internally from what originates externally. When these states show diverging temporal patterns, this may reflect instability in source‑monitoring processes—the ability to distinguish the origin of one’s mental contents. Such instability has been linked in previous research to externalising bias, the tendency to attribute internally generated thoughts, sensations, or images to an external source. This bias is well documented in both clinical and non‑clinical populations and may help explain why some individuals tend to experience more vivid or intrusive mental events without this necessarily indicating pathology.

Overall, the study demonstrates that there is no single “type” of hallucination proneness. Instead, each dimension displays distinct patterns in resting‑state brain dynamics, suggesting that different vulnerability profiles have unique neural signatures. By revealing these patterns, the research deepens our understanding of how the brain manages, or sometimes struggles to manage, the boundary between internal and external experience. And it suggests that even in healthy brains, that boundary is more dynamic, fragile, and fascinating than we often assume. This study was published in the scientific journal Behavioural Brain Research, in the article Differentiating hallucination proneness dimensions through alpha resting state dynamics, as a part of research project 102/22 - Identifying altered resting state connectivity dynamics as predictors of auditory verbal hallucinations (AVH), supported by the Bial Foundation.

ABSTRACT

Hallucination-like experiences (HLEs) are untriggered sensory perceptions linked to externalizing bias - the misattribution of self-generated sensory experiences to an external source. The vulnerability to HLEs, i.e., hallucination proneness (HP), is typically assessed by the Launay-Slade Hallucination Scale (LSHS). A newly proposed LSHS factor analysis revealed four distinct HP dimensions: Multisensory HLEs, Auditory daydreaming, Vivid thoughts and inner speech, and Personified HLEs. The current study assesses whether these HP dimensions map onto distinct patterns of resting state brain dynamics in the alpha frequency band due to its modulatory role in attention and perception. We used a Hidden semi-Markov Model to segment continuous RS alpha activity into nine recurrent brain states and extracted the total number of transitions (TT) and the number of visits per state (SV). We assessed how the HP dimensions relate to these metrics, calculated across the entire 3-minute recording and within shorter sliding windows to capture finer temporal changes. All HP dimensions and increased RS time correlated with increased TT. Increased Personified HLEs scores linked to different time-dependent changes of SV in two states (SV to state 5 decreased over time, while visits to state 9 increased), highlighting distinct alpha dynamics in high- and low-hallucination prone individuals. Increased TT could indicate frequent attentional switches between internal and external states. Different SV patterns related to higher Personified HLEs scores suggest unstable source monitoring, potentially inducing an externalizing bias. These findings provide novel predictors of HP dimensions, revealing distinct neural profiles associated with different vulnerability profiles.