The Neuroscience of Visual Hallucinations

Each year, some two million people in the United Kingdom experience visual hallucinations. Infrequent, fleeting visual hallucinations, often around sleep, are a usual feature of life. In contrast, consistent, frequent, persistent hallucinations during waking are strongly associated with clinical disorders; in particular delirium, eye disease, psychosis, and dementia. Research interest in these disorders has driven a rapid expansion in investigatory techniques, new evidence, and explanatory models. In parallel, a move to generative models of normal visual function has resolved the theoretical tension between veridical and hallucinatory perceptions. From initial fragmented areas of investigation, the field has become increasingly coherent over the last decade. Controversies and gaps remain, but for the first time the shapes of possible unifying models are becoming clear, along with the techniques for testing these. This book provides a comprehensive survey of the neuroscience of visual hallucinations and the clinical techniques for testing these. It brings together the very latest evidence from cognitive neuropsychology, neuroimaging, neuropathology, and neuropharmacology, placing this within current models of visual perception. Leading researchers from a range of clinical and basic science areas describe visual hallucinations in their historical and scientific context, combining introductory information with up-to-date discoveries. They discuss results from the main investigatory techniques applied in a range of clinical disorders. The final section outlines future research directions investigating the potential for new understandings of veridical and hallucinatory perceptions, and for treatments of problematic hallucinations. Fully comprehensive, this is an essential reference for clinicians in the fields of the psychology and psychiatry of hallucinations, as well as for researchers in departments, research institutes and libraries. It has strong foundations in neuroscience, cognitive science, optometry, psychiatry, psychology, clinical medicine, and philosophy. With its lucid explanation and many illustrations, it is a clear resource for educators and advanced undergraduate and graduate students.

Visual Hallucinations in Eye Disease and Lewy Body Disease

Objective: Visual hallucinations (VH) most commonly occur in eye disease (ED), Parkinson’s disease (PD), and Lewy body dementia (LBD). The phenomenology of VH is likely to carry important information about the brain areas within the visual system generating them. Methods: Data from five controlled cross-sectional VH studies (164 controls, 135 ED, 156 PD, 79 (PDD 48 + DLB 31) LBD) were combined and analysed. The prevalence, phenomenology, frequency, duration, and contents of VH were compared across diseases and gender. Results: Simple VH were most common in ED patients (ED 65% vs. LBD 22% vs. PD 9%, Chi-square [χ2] test: χ2=31.43, df=2, p<0.001), whilst complex VH were more common in LBD (LBD 76% vs. ED 38%, vs PD 28%, Chi-square test: χ2=96.80, df=2, p<0.001). The phenomenology of complex VH was different across diseases and gender. ED patients reported more “flowers” (ED 21% vs. LBD 6% vs. PD 0%, Chi-square test: χ2=10.04, df=2, p=0.005) and “body parts” (ED 40% vs. LBD 17% vs. PD 13%, Chi-square test: χ2=11.14, df=2, p=0.004); in contrast LBD patients reported “people” (LBD 85% vs. ED 67% vs. PD 63%, Chi-square test: χ2=6.20, df=2, p=0.045) and “animals/insects” (LBD 50% vs. PD 42% vs. ED 21%, Chi-square test: χ2=9.76, df=2, p=0.008). Males reported more “machines” (13 % vs. 2%, Chi-square test: χ2=6.94, df=1, p=0.008), whilst females reported more “family members/children” (48% vs. 29%, Chi-square test: χ2=5.10, df=1, p=0.024). Conclusions: The phenomenology of VH is likely related to disease specific dysfunctions within the visual system and to past, personal experiences.

15 Years of Microstate Research in Schizophrenia - Where Are We? A Meta-Analysis

Schizophrenia patients show abnormalities in a broad range of task demands. Therefore, an explanation common to all these abnormalities has to be sought independently of any particular task, ideally in the brain dynamics before a task takes place or during resting state. For the neurobiological investigation of such baseline states, EEG microstate analysis is particularly well suited, because it identifies subsecond global states of stable connectivity patterns directly related to the recruitment of different types of information processing modes (e.g., integration of top-down and bottom-up information). Meanwhile, there is an accumulation of evidence that particular microstate networks are selectively affected in schizophrenia. To obtain an overall estimate of the effect size of these microstate abnormalities, we present a systematic meta-analysis over all studies available to date relating EEG microstates to schizophrenia. Results showed medium size effects for two classes of microstates, namely, a class labeled C that was found to be more frequent in schizophrenia and a class labeled D that was found to be shortened. These abnormalities may correspond to core symptoms of schizophrenia, e.g., insufficient reality testing and self-monitoring as during auditory verbal hallucinations. As interventional studies have shown that these microstate features may be systematically affected using antipsychotic drugs or neurofeedback interventions, these findings may help introducing novel diagnostic and treatment options.

Visual-auditory differences in duration discrimination of intervals in the subsecond and second range

A common finding in time psychophysics is that temporal acuity is much better for auditory than for visual stimuli. The present study aimed to examine modality-specific differences in duration discrimination within the conceptual framework of the Distinct Timing Hypothesis. This theoretical account proposes that durations in the lower milliseconds range are processed automatically while longer durations are processed by a cognitive mechanism. A sample of 46 participants performed two auditory and visual duration discrimination tasks with extremely brief (50-ms standard duration) and longer (1000-ms standard duration) intervals. Better discrimination performance for auditory compared to visual intervals could be established for extremely brief and longer intervals. However, when performance on duration discrimination of longer intervals in the 1-s range was controlled for modality-specific input from the sensory-automatic timing mechanism, the visual-auditory difference disappeared completely as indicated by virtually identical Weber fractions for both sensory modalities. These findings support the idea of a sensory-automatic mechanism underlying the observed visual-auditory differences in duration discrimination of extremely brief intervals in the millisecond range and longer intervals in the 1-s range. Our data are consistent with the notion of a gradual transition from a purely modality-specific, sensory-automatic to a more cognitive, amodal timing mechanism. Within this transition zone, both mechanisms appear to operate simultaneously but the influence of the sensory-automatic timing mechanism is expected to continuously decrease with increasing interval duration.

Disturbances of agency and ownership in schizophrenia: An auditory verbal event related potentials study

A ‘sense of self’ is essentially the ability to distinguish between self-generated and external stimuli. It consists of at least two very basic senses: a sense of agency and a sense of ownership. Disturbances seem to provide a basic deficit in many psychiatric diseases. The aim of our study was to manipulate those qualities separately in 28 patients with schizophrenia (14 auditory hallucinators and 14 non-hallucinators) and 28 healthy controls (HC) and to investigate the effects on the topographies and the power of the event-related potential (ERP). We performed a 76-channel EEG while the participants performed the task as in our previous paper. We computed ERPs and difference maps for the conditions and compared the amount of agency and ownership between the HC and the patients. Furthermore, we compared the global field power and the topographies of these effects. Our data showed effects of agency and ownership in the healthy controls and the hallucinator group and to a lesser degree in the non-hallucinator group. We found a reduction of the N100 during the presence of agency, and a bilateral temporal negativity related to the presence of ownership. For the agency effects, we found significant differences between HC and the patients. Contrary to the expectations, our findings were more pronounced in non-hallucinators, suggesting a more profoundly disturbed sense of agency compared to hallucinators. A contemporary increase of global field power in both patient groups indicates a compensatory recruitment of other mechanisms not normally associated with the processing of agency and ownership.