Corrigendum: Psychedelic replications in virtual reality and their potential as a therapeutic instrument: an open-label feasibility study

[This corrects the article DOI: 10.3389/fpsyt.2023.1088896.].

Psychedelic replications in virtual reality and their potential as a therapeutic instrument: an open-label feasibility study

Background

Recent research has shown promising results for the therapeutic benefits of psychedelics. One popular view claims that these benefits are mediated by the subjective experiences induced by these substances. Based on this, we designed a virtual reality experience, Psyrreal, that mimics the phenomenological components of psychedelic experiences.

Aims

We aimed to investigate the therapeutic efficacy of Psyrreal and psychedelic VR experiences in treating depressive symptoms as well as explore the effect of Psyrreal on subjective factors which have been suggested to mediate the therapeutic benefits of psychedelics.

Methods

In this open-label feasibility study, thirteen participants with mild-to-moderate depression underwent a 2-day therapeutic intervention implementing Psyrreal. Depressive symptoms were evaluated by the Emotional State Questionnaire (EST-Q2) at the start of the intervention and 2 weeks after. A thematic analysis of semi-structured interviews after Psyrreal was also conducted as an additional assessment of the method.

Results

A 2-day intervention implementing Psyrreal led to significant decreases in depressive symptoms at the 2-week follow-up (n = 10, p = 0.007, Hedges' g = 1.046) measured by the Emotional State Questionnaire (EST-Q2). The analysis of semi-structured interviews suggests that Psyrreal could lead to insight and alterations in the sense of self in some people.

Conclusion

This work proposes a novel method using virtual reality to augment the treatment of psychological disorders as well as to precisely investigate the mediating subjective factors of the therapeutic effects of psychedelic substances. Our preliminary results suggest that VR experiences combined with psychological support show potential in treating depressive symptoms and further research into similar methods is warranted.

Guidelines for immersive virtual reality in psychological research

Virtual reality (VR) holds immense promise as a research tool to deliver results that are generalizable to the real world. However, the methodology used in different VR studies varies substantially. While many of these approaches claim to use 'immersive VR', the different hardware and software choices lead to issues regarding reliability and validity of psychological VR research. Questions arise about quantifying presence, the optimal level of graphical realism, the problem of being in dual realities and reproducibility of VR research. We discuss how VR research paradigms could be evaluated and offer a list of practical recommendations to have common guidelines for psychological VR research.

Waving goodbye to contrast: self-generated hand movements attenuate visual sensitivity

It is well known that the human brain continuously predicts the sensory consequences of its own body movements, which typically results in sensory attenuation. Yet, the extent and exact mechanisms underlying sensory attenuation are still debated. To explore this issue, we asked participants to decide which of two visual stimuli was of higher contrast in a virtual reality situation where one of the stimuli could appear behind the participants’ invisible moving hand or not. Over two experiments, we measured the effects of such “virtual occlusion” on first-order sensitivity and on metacognitive monitoring. Our findings show that self-generated hand movements reduced the apparent contrast of the stimulus. This result can be explained by the active inference theory. Moreover, sensory attenuation seemed to affect only first-order sensitivity and not (second-order) metacognitive judgments of confidence.

VREX: an open-source toolbox for creating 3D virtual reality experiments

Background

We present VREX, a free open-source Unity toolbox for virtual reality research in the fields of experimental psychology and neuroscience.

Results

Different study protocols about perception, attention, cognition and memory can be constructed using the toolbox. VREX provides a procedural generation of (interconnected) rooms that can be automatically furnished with a click of a button. VREX includes a menu system for creating and storing experiments with different stages. Researchers can combine different rooms and environments to perform end-to-end experiments including different testing situations and data collection. For fine-tuned control VREX also comes with an editor where all the objects in the virtual room can be manually placed and adjusted in the 3D world.

Conclusions

VREX simplifies the generation and setup of complicated VR scenes and experiments for researchers. VREX can be downloaded and easily installed from vrex.mozello.com

Electronic supplementary material

The online version of this article (doi:10.1186/s40359-017-0173-4) contains supplementary material, which is available to authorized users.

Attention is withdrawn from the area of the visual field where the own hand is currently moving

Self-generated movement leads to the attenuation of predicted sensory consequences of the movement. This mechanism ensures that attention is generally not drawn to sensory signals caused by own movement. Such attenuation has been observed across the animal kingdom and in different sensory modalities. In this study we used novel virtual reality (VR) devices to test the hypothesis that the human brain attenuates visual sensation in the area of the visual field where the subject's hand is currently moving. We conducted three VR experiments where we monitored hand position during movement while the participants performed a visual search task. In the first two experiments we measured response time for salient moving targets and observed that reaction time (RT) is slower for targets that are behind the (invisible) hand. This result provides the first evidence that the visual motion signals generated by the subject's own hand movement are suppressed. In the third experiment we observed that RT is also slower for colored targets behind the hand. Our findings provide support for the active inference account of sensory attenuation, which posits that attenuation occurs because attention is withdrawn from the sensory consequences of own movement. Furthermore, we demonstrate how modern VR tools could open up new exciting avenues of research for studying the interplay of action and perception.

Distinct molecular phenotypes in murine cardiac muscle development, growth, and hypertrophy

The onset of cardiac hypertrophy is associated with characteristic changes in myocardial gene expression that are thought to recapitulate a developmental gene program. We report here the first gene expression profile of the murine myocardium, using a rapid method of quantitative expression analysis based on real-time analytical RT-PCR. This assay was used to measure expression levels of 29 genes in (1) late stage development as represented by day 1 neonatal ventricles, (2) normal cardiac growth in 3 and 18 month old mice, and (3) cardiac hypertrophy following pressure overload by aortic constriction. For males and females normal growth is not associated with differential expression although there is elevated expression of skeletal and smooth muscle actin mRNA's in males compared to females. Using normal adult ventricles as a reference, there are many qualitative and quantitative differences between the day 1 neonatal myocardium and experimental cardiac hypertrophy. These data suggest that the response to POL involves a subset of re-expressed developmental genes together with altered expression of genes not necessarily associated with cardiac development.

Synthesis and properties of cross-linked DNA duplexes

A method has been devised to synthesize DNA duplexes with covalently connected strands. The structure of cross-linked duplexes was confirmed by a reaction with the restriction endonuclease AluI. The thermal stability of the resulting compounds was investigated.

Protein sorting by high-performance liquid chromatography. I. Biomimetic interaction chromatography of recombinant human deoxyribonuclease I on polyionic stationary phases

Chromatographic separations can be tailored to exploit specific interactions between a stationary phase ligand and a protein structural feature of interest. Variations in this feature then form the basis for sorting a mixture of closely related proteins into defined subpopulations. This report describes the sorting of variants of recombinant human deoxyribonuclease I (rhDNase) that differ in the occurrence of deamidation at a single residue. rhDNase, an enzyme that non-specifically hydrolyzes DNA, is glycosylated and exhibits considerable charge heterogeneity owing to the sialylation and phosphorylation of its N-linked oligosaccharides. This heterogeneity obscures the relatively subtle differences between deamidated and intact rhDNase, preventing separation on this basis in conventional ion-exchange HPLC. Published structural information on bovine DNase reveals that the analogous labile asparagine residue is involved in DNA binding, so stationary phases containing polyanionic ligands mimicking nucleic acids were employed to separate the deamidation variants of rhDNase. Electrostatically immobilized DNA, a "tentacle" cation exchanger (TCX) and immobilized heparin columns all resolved the deamidated and intact forms of rhDNase when operated at pH 4.5. The ligands of the TCX and heparin columns are sufficiently long, flexible and polyanionic to interact with rhDNase in a manner similar to DNA and to sort rhDNase variants on the basis of the charge difference of a single residue involved in that interaction. A non-hydrolyzable double-stranded oligonucleotide analogue of DNA was also synthesized and immobilized to an HPLC support. This column, operated at pH 6, where rhDNase is active, resolved the two isomeric products of deamidation of rhDNase, i.e., variants of the enzyme containing either aspartate or isoaspartate in lieu of asparagine at the deamidation site in rhDNase. This is the first reported separation of intact variants of a glycoprotein differing on the basis of these isomeric products of deamidation through the common cyclic imide mechanism.

Codon replacement in the PGK1 gene of Saccharomyces cerevisiae: experimental approach to study the role of biased codon usage in gene expression

The coding sequences of genes in the yeast Saccharomyces cerevisiae show a preference for 25 of the 61 possible coding triplets. The degree of this biased codon usage in each gene is positively correlated to its expression level. Highly expressed genes use these 25 major codons almost exclusively. As an experimental approach to studying biased codon usage and its possible role in modulating gene expression, systematic codon replacements were carried out in the highly expressed PGK1 gene. The expression of phosphoglycerate kinase (PGK) was studied both on a high-copy-number plasmid and as a single copy gene integrated into the chromosome. Replacing an increasing number (up to 39% of all codons) of major codons with synonymous minor ones at the 5' end of the coding sequence caused a dramatic decline of the expression level. The PGK protein levels dropped 10-fold. The steady-state mRNA levels also declined, but to a lesser extent (threefold). Our data indicate that this reduction in mRNA levels was due to destabilization caused by impaired translation elongation at the minor codons. By preventing translation of the PGK mRNAs by the introduction of a stop codon 3' and adjacent to the start codon, the steady-state mRNA levels decreased dramatically. We conclude that efficient mRNA translation is required for maintaining mRNA stability in S. cerevisiae. These findings have important implications for the study of the expression of heterologous genes in yeast cells.

Production of native, correctly folded bovine pancreatic trypsin inhibitor by Escherichia coli

A gene for bovine pancreatic trypsin inhibitor (BPTI) was fused to the coding sequence for the Escherichia coli alkaline phosphatase signal peptide and expressed in E. coli under the control of the alkaline phosphatase promoter. When induced in phosphate-depleted medium such cells produced a trypsin inhibitor that was indistinguishable from native, properly folded BPTI. In particular, the BPTI produced by E. coli had three disulfide bonds that appeared to be identical to those found in native BPTI, as assayed by sensitivity to iodoacetate, dithiothreitol, and urea. This expression/secretion system will make possible the production of variant BPTI molecules, thus allowing the perturbing effects of amino acid substitutions on BPTI folding, structure, and function to be assessed.

Cassette mutagenesis: an efficient method for generation of multiple mutations at defined sites

A method is described for the efficient insertion of mutagenic oligodeoxynucleotide cassettes which allow saturation of a target amino acid codon with multiple mutations. Restriction sites are introduced by oligonucleotide-directed mutagenesis procedures to flank closely the target codon in the plasmid containing the gene. The restriction sites to be introduced are chosen based on their uniqueness to the plasmid, proximity to the target codon and conservation of the final amino acid coding sequence. The flanking restriction sites in the plasmid are digested with the cognate restriction enzymes, and short synthetic duplex DNA cassettes (10-25 bp) are inserted. The mutagenic cassette is designed to restore fully the wild-type coding sequence, except over the target codon, and to eliminate one or both restriction sites. Elimination of a restriction site facilitates selection of clones containing the mutagenic oligodeoxynucleotide cassette. To make the cassettes, single-stranded oligodeoxynucleotides and their complements are synthesized in separate pools containing different codons over the target. This method has been successfully applied to generate 19 amino acid substitutions at position 222 in the subtilisin protein sequence.

In vitro deletional mutagenesis for bacterial production of the 20,000-dalton form of human pituitary growth hormone

The 20,000-dalton (20K) variant form of human growth hormone (hGH) present in extracts from pituitary glands differs from the major form of hGH (22K, 191 amino acids) by the deletion of amino acid residues 32-46. Using oligonucleotide-mediated mutagenesis, the DNA coding for these amino acids was deleted from the gene previously constructed by us (Goeddel et al., 1979) for microbial hGH production. The DNA to be deleted was looped out by the annealing of a synthetic oligodeoxyribonucleotide to the coding strand of the hGH gene contained on recombinant phage M13 mp8 DNA. Resulting heteroduplex structures were stabilized using primer-directed in vitro DNA synthesis in the presence of T4 DNA ligase. On transformation of Escherichia coli, these heteroduplex DNAs yielded phage whose genomes contained either the original or the partially deleted hGH gene, and genotypes were distinguished by in situ plaque hybridization with synthetic oligonucleotide probes. A gene with the correct deletion was used to express the short hGH variant in E. coli.

Portable Shine-Dalgarno regions: a system for a systematic study of defined alterations of nucleotide sequences within E. coli ribosome binding sites

We have developed a gene expression system in Escherichia coli that contains a portable Shine-Dalgarno region. Transcription of this system is under the direction of a hybrid promoter (tacII) derived from trp and lac-UV5 promoter sequences which is followed by a region that encodes a portable Shine-Dalgarno region (PSDR). Using a series of synthetic PSDRs, we varied the four bases that follow the Shine-Dalgarno (SD) region. We found that the presence of four A residues or four T residues in this position gives the highest translational efficiency. The presence of four C residues reduces the translation efficiency by 50% as compared with PSDRs with A or T residues. The presence of four G residues following the SD region lowers the translational efficiency by at least 75% with respect to PSDRs with A or T residues.

The tac promoter: a functional hybrid derived from the trp and lac promoters

Two hybrid promoters that are functional in Escherichia coli have been constructed. These hybrid promoters, tacI and tacII, were derived from sequences of the trp and the lac UV5 promoters. In the first hybrid promoter (tacI), the DNA upstream of position -20 with respect to the transcriptional start site was derived from the trp promoter. The DNA downstream of position -20 was derived from the lac UV5 promoter. In the second hybrid promoter (tacII), the DNA upstream of position -11 at the Hpa I site within the Pribnow box was derived from the trp promoter. The DNA downstream of position -11 is a 46-base-pair synthetic DNA fragment that specifies part of the hybrid Pribnow box and the entire lac operator. It also specifies a Shine-Dalgarno sequence flanked by two unique restriction sites (portable Shine-Dalgarno sequence). The tacI and the tacII promoters respectively direct transcription approximately 11 and 7 times more efficiently than the derepressed parental lac UV5 promoter and approximately 3 and 2 times more efficiently than the trp promoter in the absence of the trp repressor. Both hybrid promoters can be repressed by the lac repressor and both can be derepressed with isopropyl beta-D-thiogalactoside. Consequently, these hybrid promoters are useful for the controlled expression of foreign genes at high levels in E. coli. In contrast to the trp and the lac UV5 promoters, the tacI promoter has not only a consensus -35 sequence but also a consensus Pribnow box sequence. This may explain the higher efficiency of this hybrid promoter with respect to either one of the parental promoters.

Conformational stability of alternating d (CG) oligomers in high salt solution

The conformation of d (CG)n oligomers with n = 2,3 has been studied in aqueous solution in the presence of high salt concentration. A minimum n value of three is necessary to obtain a left-handed Z-helix. When d (CG)3 is flanked by three non Z-helicogenic alternating AT sequences the left-handed helix is unstable and a B-type conformation is obtained also at high salt concentration.