G. B. Liu

Meditation alters perceptual rivalry in Tibetan Buddhist monks

Neuroscientific studies of the mind are likely to benefit from the insights and skills of Tibetan Buddhist monks who have practiced the historic tradition of meditative training over many years — a point made recently at a forum between a selection of Buddhist leaders and distinguished scientists. Perceptual rivalries, such as binocular rivalry and motion induced blindness, are being used to study the neural mechanisms underlying consciousness and attention, as they involve fluctuations in conscious awareness despite unchanging external stimulation. Tapping into the ability of Tibetan Buddhist monks to control the flow of items being attended to and accessing consciousness, we found that meditation alters the inherent fluctuations in conscious state associated with perceptual rivalry.

Interhemispheric switching mediates perceptual rivalry

BACKGROUND Binocular rivalry refers to the alternating perceptual states that occur when the images seen by the two eyes are too different to be fused into a single percept. Logothetis and colleagues have challenged suggestions that this phenomenon occurs early in the visual pathway. They have shown that, in alert monkeys, neurons in the primary visual cortex continue to respond to their preferred stimulus despite the monkey reporting its absence. Moreover, they found that neural activity higher in the visual pathway is highly correlated with the monkeys reported percept. These and other findings suggest that the neural substrate of binocular rivalry must involve high levels, perhaps the same levels involved in reversible figure alternations. RESULTS We present evidence that activation or disruption of a single hemisphere in human subjects affects the perceptual alternations of binocular rivalry. Unilateral caloric vestibular stimulation changed the ratio of time spent in each competing perceptual state. Transcranial magnetic stimulation applied to one hemisphere disrupted normal perceptual alternations when the stimulation was timed to occur at one phase of the perceptual switch, but not at the other. Furthermore, activation of a single hemisphere by caloric stimulation affected the perceptual alternations of a reversible figure, the Necker cube. CONCLUSIONS Our findings suggest that interhemispheric switching mediates perceptual rivalry. Thus, competition for awareness in both binocular rivalry and reversible figures occurs between, rather than within, each hemisphere. This interhemispheric switch hypothesis has implications for understanding the neural mechanisms of conscious experience and also has clinical relevance as the rate of both types of perceptual rivalry is slow in bipolar disorder (manic depression).

Genetic contribution to individual variation in binocular rivalry rate

Binocular rivalry occurs when conflicting images are presented in corresponding locations of the two eyes. Perception alternates between the images at a rate that is relatively stable within individuals but that varies widely between individuals. The determinants of this variation are unknown. In addition, slow binocular rivalry has been demonstrated in bipolar disorder, a psychiatric condition with high heritability. The present study therefore examined whether there is a genetic contribution to individual variation in binocular rivalry rate. We employed the twin method and studied both monozygotic (MZ) twins (n = 128 pairs) who are genetically identical, and dizygotic (DZ) twins (n = 220 pairs) who share roughly half their genes. MZ and DZ twin correlations for binocular rivalry rate were 0.51 and 0.19, respectively. The best-fitting genetic model showed 52% of the variance in binocular rivalry rate was accounted for by additive genetic factors. In contrast, nonshared environmental influences accounted for 18% of the variance, with the remainder attributed to measurement error. This study therefore demonstrates a substantial genetic contribution to individual variation in binocular rivalry rate. The results support the vigorous pursuit of genetic and molecular studies of binocular rivalry and further characterization of slow binocular rivalry as an endophenotype for bipolar disorder.

Orientation mosaic in barn owl’s visual Wulst revealed by optical imaging: comparison with cat and monkey striate and extra-striate areas

Using the technique of intrinsic signal optical imaging, orientation preference maps were obtained from the Wulst of the barn owl in the area that represents central vision, and from the visual cortices (V1 and V2) of cat and marmoset monkey. Iso-orientation domains in barn owls visual Wulst were patch-like structures with an inter-patch distance of approximately 0.9 mm, arranged in a pinwheel-like manner around singularity points. The size of the iso-orientation domains in barn owl was larger than those found in area V1, but comparable to those found in area V2, of cat and monkey. Superficial layers of the owl visual Wulst may be equivalent to extra-striate visual areas of primates and carnivores, as already suggested by electrophysiologists discussing the much increased radial dimensions of the Wulst compared with neocortex in mammals.

Binocular rivalry and perceptual coherence

We thank Nikos Logothetis for drawing our attention to the work of Diaz-Caneja. This work was supported by the National Health and Medical Research Council of Australia.

The changing face of perceptual rivalry

Functional brain-imaging studies of house-face binocular rivalry and Rubins vase-faces illusion have consistently reported face perception-dependent activity in the right fusiform gyrus. Here we use Rubins illusion and report that activation of the left hemisphere by caloric vestibular stimulation increases the predominance of the faces percept in a substantial number of test subjects. While partially supporting the brain-imaging lateralization reports, our findings also challenge these studies by suggesting that neural mechanisms of Rubins illusion cannot be limited to extrastriate perception-dependent processing. In accordance with our previously proposed interhemispheric switch model, the present findings support the notion that perceptual rivalry engages high-level cortical structures that mediate unihemispheric attentional selection.

Dichoptic Viewing Methods for Binocular Rivalry Research: Prospects for Large-Scale Clinical and Genetic Studies

Binocular rivalry (BR) is an intriguing phenomenon that occurs when two different images are presented, one to each eye, resulting in alternation or rivalry between the percepts. The phenomenon has been studied for nearly 200 years, with renewed and intensive investigation over recent decades. The rate of perceptual switching has long been known to vary widely between individuals but to be relatively stable within individuals. A recent twin study demonstrated that individual variation in BR rate is under substantial genetic control, a finding that also represented the first report, using a large study, of genetic contribution for any post-retinal visual processing phenomenon. The twin study had been prompted by earlier work showing BR rate was slow in the heritable psychiatric condition, bipolar disorder (BD). Together, these studies suggested that slow BR may represent an endophenotype for BD, and heralded the advent of modern clinical and genetic studies of rivalry. This new focus has coincided with rapid advances in 3D display technology, but despite such progress, specific development of technology for rivalry research has been lacking. This review therefore compares different display methods for BR research across several factors, including viewing parameters, image quality, equipment cost, compatibility with other investigative methods, subject group, and sample size, with a focus on requirements specific to large-scale clinical and genetic studies. It is intended to be a resource for investigators new to BR research, such as clinicians and geneticists, and to stimulate the development of 3D display technology for advancing interdisciplinary studies of rivalry.

Comprehensive analysis of prokaryotic mechanosensation genes: Their characteristics in codon usage

In the present study, we examined GC nucleotide composition, relative synonymous codon usage (RSCU), effective number of codons (ENC), codon adaptation index (CAI) and gene length for 308 prokaryotic mechanosensitive ion channel (MSC) genes from six evolutionary groups: Euryarchaeota, Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Firmicutes, and Gammaproteobacteria. Results showed that: (1) a wide variation of overrepresentation of nucleotides exists in the MSC genes; (2) codon usage bias varies considerably among the MSC genes; (3) both nucleotide constraint and gene length play an important role in shaping codon usage of the bacterial MSC genes; and (4) synonymous codon usage of prokaryotic MSC genes is phylogenetically conserved. Knowledge of codon usage in prokaryotic MSC genes may benefit from the study of the MSC genes in eukaryotes in which few MSC genes have been identified and functionally analysed.

Estrogen-induced cholestasis: pathogenesis and therapeutic implications

Cholestasis syndromes characterised by impairment of bile formation and secretion arecaused by many diseases. Estrogen-induced cholestasis among the cholestasis syndromes is a very common form. Based on the molecular studies of bile formation and transportation, a significant advancement has been achieved in understanding the mechanism of the disease. Estrogen can inhibit bile acids transportation from hepatocytes into bile canaliculi by interfering with the bile salt export pump and multidrug resistance-associated transporter 2 as well. It also inhibits Na+-taurocholate cotransporting polypeptide and Na+-independent organic anion-transporting polypeptides in the basolateral membrane of hepatocytes to interfere with the uptake of bile acids. Thus, co-treatment strategy can be considered which combines nuclear receptor inducers and cAMP enhancer to increase bile acids transporters activities, and the agents to reduce serum estrogen concentration and its receptor binding, and to reduce bile acids in enterohepatic circulation.

Association of human papillomavirus with Fanconi anemia promotes carcinogenesis in Fanconi anemia patients

Fanconi anemia (FA) is a rare recessive disorder associated with chromosomal fragility. FA patients are at very high risk of cancers, especially head and neck squamous cell carcinomas and squamous cell carcinomas caused by infection of human papillomaviruses (HPVs). By integrating into the host genome, HPV oncogenes E6 and E7 drive the genomic instability to promote DNA damage and gene mutations necessary for carcinogenesis in FA patients. Furthermore, E6 and E7 oncoproteins not only inhibit p53 and retinoblastoma but also impair the FANC/BRCA signaling pathway to prevent DNA damage repair and alter multiple signals including cell‐cycle checkpoints, telomere function, cell proliferation, and interference of the host immune system leading to cancer development in FA patients. In this review, we summarize recent advances in unraveling the molecular mechanisms of FA susceptibility to HPV‐induced cancers, which facilitate rational preventive and therapeutic strategies. Copyright