The Ganzfeld experiment. Author: Daryl J. Date: June From: The Journal of Parapsychology Vol. Publisher: Parapsychology Press. Document Type: Article. Length: 3, words. Translate Article. Set Interface Language. Decrease font size. If you want to find out what your brain will conjure up, you can try to produce the ganzfeld effect on your own. Keep in mind that the experience is subjective. Hallucinations are sensations that appear real but are created by your mind.
They can affect all of your senses. Learn about the types, causes, and…. If you think you're seeing, smelling, hearing, tasting, or feeling things when you're half asleep, you may be experiencing hypnagogic hallucinations.
Learn about tactile hallucinations, including symptoms and causes. Psychosis is a serious mental disorder characterized by thinking and emotions that indicate the person experiencing them has lost contact with reality. An introvert is often thought of as a quiet, reserved, and thoughtful individual. Experts say the COVID pandemic added to the stresses of job insecurity and food shortages already felt by People of Color and young adults. You've heard the term countless times, but what does having a type A personality actually mean?
We'll go over common traits, how they compare to type…. Psychologists and psychiatrists have a lot in common, but they also have some key differences. Health Conditions Discover Plan Connect. Mental Health. What is the Ganzfeld Effect? Medically reviewed by Seunggu Han, M.
How the ganzfeld effect works. Practical uses of the ganzfeld effect. How to create the ganzfeld effect. Potential side effects of ganzfeld hallucinations. Read this next. Medically reviewed by Timothy J. Legg, Ph. To further investigate the temporal development of functional connectivity during the MMGF scan, we divided the min scan into five 5-min windows and calculated the correlation coefficients for each window.
To further explore whether different thalamic subregions showed different connectivity profiles, we used the thalamus parcellation provided in the AAL3 atlas It should be noted that this was performed as a post-hoc explorative analysis, without statistical assessment, with the purpose of displaying which thalamic nuclei and what cortical regions showed the strongest decoupling.
We used the data-driven eigenvector centrality mapping approach to characterize whole-brain functional connectivity without prior assumptions. For each individual resting-state scan, the eigenvector centrality map has been generated within the grey matter mask by using fastECM For our statistical analysis we compared the eigenvector centrality maps during MMGF exposure to the averaged pre and post scans.
The retrospective assessment of the induced ASC phenomena using questionnaires demonstrated that the MMGF-induced state during the fMRI resting-state measurement was in line with previous reports about its phenomenology The ASC analysis scheme revealed Anxiety: 2. Motion did not significantly differ between pre, MMGF, and post scans as assessed by 1 mean frame-wise displacement FD; pre: 0.
In this explorative depiction, decreases in coupling of the thalamus to sensory regions were predominantly apparent Fig. During pre and post scans the left and right thalamus exhibited stable temporal correlations of BOLD time series to V1 and A1. During the MMGF-exposure, however, this coupling was progressively reduced.
Time-resolved resting-state analysis of thalamo-cortical interactions. A progressive decrease in correlation between the thalamus and V1 as well as the thalamus and A1 across the MMGF exposure reflects a cortical decoupling from sensory thalamic inputs. To explore the connectivity profiles of different thalamic subregions, we used the thalamus parcellation of the AAL3 atlas.
No Ganzfeld-induced thalamo-cortical correlation increases above 0. This exploratory analysis indicates that thalamic decoupling is strongest for ventral lateral, and mediodorsal thalamic nuclei to pre- and postcentral regions, the cuneus, as well as visual processing-related regions e. Furthermore, the pulvinary-visual pathway showed decreased correlation values. Lateral and medial geniculate, as well as intralamiar nucleus and reuniens, showed little modulation.
Functional connectivity decreases for thalamic subregions. Correlation decreases between thalamic subregions are displayed in an exploratory analysis. We used eigenvector centrality mapping, a data-driven analysis tool without prior assumptions , to test for further changes in resting-state network properties throughout the whole brain. We compared eigenvector centrality maps during MMGF to averaged pre and post scans. The assumption-free eigenvector centrality mapping revealed increased centrality of the left inferior parietal lobulus and the precuneus both core regions of the DMN network during MMGF when contrasted to averaged pre and post scans.
In the present study, we explored the induction of an ASC with a non-pharmacological method, namely the multimodal Ganzfeld MMGF , which consists of high intensity exposure to unstructured auditory and visual stimulation. In contrast to the effects observed for serotonergic psychedelics, our resting-state functional connectivity analysis revealed that the most dominant effects were found as a reduced coupling between the thalamus and cortical areas, mainly early sensory regions.
This thalamo-cortical decoupling was found to progressively develop over time, as revealed by a time resolved connectivity analysis.
Additionally, we assessed changes in global brain network properties by applying eigenvector centrality EC mapping. We found increased EC within core regions of the default mode network, which could relate to the inward-directed phenomenological nature of the MMGF-induced state.
Thalamic dysfunction is well known to play an important role for the emergence of different psychopathologic symptoms, particularly with regards to perceptual distortions. Dysfunctional thalamic filtering is reflected by reduced pre-pulse inhibition in schizophrenic patients, which is also used as a measure to validate animal models of schizophrenic symptoms 35 , Schizophrenic patients also report an uncontrolled instream of information from the senses, which is experienced as overwhelming 21 , Previous pharmacological studies indicate that ASC symptoms could also be driven by reduced sensory filtering of the thalamus, reflected by increased thalamo-cortical coupling The suggestion that ASC effects directly relate to thalamo-cortical interactions indicates that the thalamus could be affected in the MMGF-induced state as well.
Antithetical to schizophrenia and the findings in psychedelic-induced states, we observed a reduction in thalamo-cortical coupling during MMGF exposure. We carefully controlled for potential confounding effects of motion by demonstrating that participants did not move more during the MMGF condition than during the pre and post measurements, which could otherwise substantially affect the validity of the presented findings.
Relative selectivity of connectivity changes exists between the thalamus and regions that are known to be anatomically connected with the thalamus, i.
We further performed a time-resolved analysis to show that the thalamo-cortical effects demonstrate a plausible development together with the progressing depth of the MMGF induced state. Finding thalamo-cortical decoupling is interesting, as on the one hand the eyes and ears are exposed to input with high signal intensity, namely bright light and loud white noise, which should lead to strong signals from the sensory organs to the brain. On the other hand, these sensory signals did not contain structure, such as differences in brightness or color, edges or shapes, or systematic pitch or loudness variations.
This lack of structure is highly unnatural and causes a distortion of normal signal processing to a degree that pseudo- hallucinations can occur Whether participants in the current experiment had such experiences is, however, uncertain as we only assessed ASC experiences with a retrospective questionnaire.
Hallucinations during MMGF exposure are typically short-lasting events with relatively clear on- and offset In contrast, the applied Altered States of Consciousness Rating scale asked for overall changes from an average, normal state. We found the ratings on hallucination-related scales e. The change in experience that was rated highest was reduced vigilance. Taken together, this suggests that the MMGF-induced state creates a regime of sensory processing in which hallucinatory events are more likely to occur.
To directly relate their occurrence with fMRI data, however, a precise tracking of such events in time would be necessary, which remains a task for future research. Interestingly, in contrast to ASCs induced by psychedelic substances, our data do not show increased, unfiltered signal propagation to the cortex.
One previous study explored the ASC described as shamanic trance by measuring changes in resting-state connectivity in brains of shamans who entered a trance state inside the fMRI scanner, guided by rhythmic drumming sound Similar to our data, they also found a reduction of connectivity from the thalamus to sensory regions, despite the substantial amount of sensory input.
Taken together, the reduced thalamo-cortical interaction is not a result of reduced sensory input but can be observed in situations of highly monotonous and unstructured sensory stimulation. Another situation where changes of thalamo-cortical interaction are well document is sleep In particular, reduced thalamo-cortical interaction is found as a feature of early sleep states N1 in resting-state fMRI 38 , 39 and intracranial electrophysiological recordings The MMGF-induced state is often phenomenologically described as a hypnagogic state; i.
Indeed, it has been reported that this phenomenological description matches with the finding that the EEG power spectrum of the MMGF state lays in between wakefulness and early sleep states A direct comparison of the MMGF data with existing sleep data 39 , 42 would be informative for identifying resting-state signatures that distinguish the MMGF state from early sleep states. The applied measure of functional connectivity for fMRI resting-state time series reflects the correlation of BOLD signal between the thalamus and cortical regions.
Thereby, it cannot be directly inferred that the thalamus has less influence on the cortex; cortico-thalamic feedback signals could instead be reduced, or both.
The main challenge in investigating thalamo-cortical interactions with resting-state functional connectivity is the small size of subthalamic nuclei in combination with the relatively low spatial resolution of full-brain resting-state fMRI scans e. To the best of our knowledge, until now, no comparison data is available, where fine grained thalamic parcellation were applied in studies where ASCs were investigated.
Different connectivity studies that have investigated thalamo-cortical interactions, did not reveal one-to-one mappings of thalamic subregions with cortical regions Instead, competing thalamo-cortical networks were indicated Due to these limitations, our analysis of subthalamic connectivity changes remain exploratory.
Conversely, this analysis did not display the strongest modulations for sensory thalamic subregions auditory: MGN, visual: LGN. Instead, anterior and mediodorsal connections to visual, somatosensory and motor regions showed strongest decreases together with aspects of the pulvinary-visual pathway.
An explanation for this could be that the character of the MMGF exposure comes with no reduced sensory input but a lack of structure. However, it remains a task for future research to test if these initial hints reflect more complex thalamo-cortical circuitries that drive the observed main effects, potentially via indirect pathways, including top-down cortico-thalamic mechanisms. In sum, the reduced thalamo-cortical coupling displays a hallmark characteristic of the MMGF induced connectivity state of the brain, while it remains a question for future research to identify the exact thalamo-cortical and cortico-thalamic mechanisms that contribute to specific experiences.
In addition to the hypothesis-driven analysis of thalamo-cortical coupling, we applied eigenvector centrality mapping as a data-driven method to analyze large-scale network effects. Eigenvector centrality mapping favors regions that are connected to regions that are themselves central within the whole-brain network, and thus measures the global centrality of each voxel Our analysis revealed increased centrality in core regions of the default mode network DMN , namely in the precuneus and the left inferior parietal lobules.
DMN activity is classically associated with inwards directed thoughts, mind wandering and general processes when no task is performed 45 , 46 , A centrality increase in those regions means that during MMGF exposure they are more strongly integrated within the whole-brain connectome.
Thereby, the DMN appears to take a more central role in orchestrating other brain processes 48 , Consistently, participants of a previous study had reported increased self-awareness as a characteristic feature of the MMGF induced state 13 , confirming the classical attribution of DMN with self-related processing.
Additionally, the ASC of shamanic trance has been characterized as an inward directed state and consistently was associated with increased eigenvector centrality in DMN regions Interestingly, a characteristic feature of LSD and psilocybin-induced states is the reduction of self-importance; reports extend to a full dissolution of the usually-experienced ego Taken together, our finding of increased centrality can be interpreted to reflect the dissociation from the outer world and more inward-directed processing.
This finding is plausible, since opposing effects were found for psychedelic-induced states which are characterized by ego-dissolving effects. Symptoms elicited by different drugs have been discussed as resulting from altered bottom-up and top-down signaling within hierarchical cortical processing 1. This idea has been fostered within the framework of predictive coding, where top-down signals are thought to reflect predictions about sensory events i.
Within the cortical hierarchy, predictions are compared and integrated with sensory signals, thus allowing the brain to derive meaning and perceptual interpretations in a fast and efficient way. Imbalance in the interaction of top-down and bottom-up signaling is thought to be a causal mechanism underlying psychotic hallucinations On the one hand, hallucinations can result from weak or imprecise priors Alternatively, it is speculated that reduced bottom-up signaling by sensory deprivation can also cause an imbalance leading to hallucinations 1.
The mechanisms of psychedelic-induced hallucinations were also recently discussed in the context of predictive brain processes In that model, the DMN is considered a top-level source for priors and its functional disintegration reflects a change in top-down influence.
In the case of MMGF, the perceptual deprivation reduced thalamo-cortical coupling, which can be interpreted as reduced bottom-up signaling. In contrast, the top-down propagation of internally generated predictions should be intact. While during normal perception these top-down predictions are compared with structures in the sensory input, during MMGF such integration is not possible due to the lack of structure in the sensory signals.
We believe that the maintained top-down predictions can lead to a misallocation of structures into the sensory noise, which can sometimes lead to the experience of hallucinations during MMGF conditions.
Future studies need to address the exact contribution of the DMN to the initiation of priors and top-down signals, as well as on which hierarchical level the assumed misallocation manifests. Our data do not allow to directly link the findings to the potential occurrence of hallucinations, as participants only reported their experiences in retrospect.
Future studies should therefore assess in more detail if and when participants experience hallucinations during MMGF exposure to establish direct links with neural mechanisms. Taken together, our data suggest that an imbalance of intact top-down signaling in combination with the unnatural reduction of bottom-up input could explain why participants sometimes experience hallucinations during MMGF.
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