The Neurodynamic Organization of Modality-Dependent Hallucinations

Abstract

The pathophysiology of hallucinations remains mysterious. This research aims to specifically explore the interaction between hallucinations and spontaneous resting-state activity. We used multimodal magnetic resonance imaging during hallucinations occurrence in 20 drug-free adolescents with a "brief psychotic disorder." They were furthermore compared with 20 matched controls at rest or during exteroceptive stimuli. Anatomical and functional symptom-mapping demonstrated reduced cortical thickness and increased blood oxygen level-dependent signal in modality-dependent association sensory cortices during auditory, visual, and multisensory hallucinations. On the contrary, primary-sensory-cortex recruitment was not systematic and was shown to be associated with increased vividness of the hallucinatory experiences. Spatiotemporal activity patterns in the default-mode network (DMN) during hallucinations and symptom-free periods in patients were compared with patterns measured in healthy individuals. A disengagement of the DMN was concomitant to hallucinations, as for exogenous stimulations in healthy participants. Specifically, spatial and temporal instabilities of the DMN correlated with the severity of hallucinations but persisted during symptom-free periods. These results suggest that hallucinatory experiences emerge from a spontaneous DMN withdrawal, providing a convincing model for hallucinations beyond the auditory modality.

Imagine that: elevated sensory strength of mental imagery in individuals with Parkinson's disease and visual hallucinations

“…In addition, both disorders have displayed impairments in cognitive flexibility [39,40]. Furthermore, default mode network over-activity [41] and dissociation with cognitive control regions [42] have also been reported in patients with schizophrenia. Intriguingly, hallucinations in disorders classically associated with primary retinal impairment, such as Charles Bonnet Syndrome, are also associated with visual attentional impairments [32,33], suggesting a common neural mechanism for hallucinations across all disorders [2,43].…”

Resting-State Functional Connectivity of the Nucleus Accumbens in Auditory and Visual Hallucinations in Schizophrenia

“…48 Interestingly, the intrinsic instability of the DMN during complex hallucinations was described recently. 23,49 Moreover, a bilateral volume reduction of the anterior insula was evidenced in patients with positive symptoms. 50 The observed increase in the FC strength between the NAcc and the SN in VAH patients compared with AH patients suggests that the more these structures are connected, the more patients will exhibit aberrant salience.…”

“…Indeed, such mesolimbic hyperconnectivity appears to be linked with the number of hallucinatory modalities involved. Considering the physiological interactions between insula and the DMN, an impairment of the SN, anchored in the anterior insula, may be at the root of the spontaneous disengagement of this resting-state network, 49 and the subsequent overactivation of modality-dependent association cortices during hallucinations, which in turn might lead to the misinterpretation of erroneous percepts as hallucinations.…”

What Is the Link Between Hallucinations, Dreams, and Hypnagogic–Hypnopompic Experiences?

“…Similarly, connectivity of DMN with other networks may be unstable or weakly connected, but nonetheless functionally active. 85 In support, some level of top-down integration is necessary in hallucinations to account for appraisals and beliefs (row 7) and daytime dysfunctions (row 9); • During hallucinations, the planum temporale is activated and correlated with the experience of a sensory signal originating in external space (row 8, table 1). 86 This activation may assist in amplifying signals to acquire external qualities, and is absent during sleep.…”