Inhibition-excitation balance in the parietal cortex modulates volitional control for auditory and visual multistability

International audiencePerceptual organisation must select one interpretation from several alternatives to guide behaviour. Computational models suggest that this could be achieved through an interplay between inhibition and excitation across competing types of neural population coding for each interpretation. Here, to test for such models, we used magnetic resonance spectroscopy to measure non-invasively the concentrations of inhibitory γ-aminobutyric acid (GABA) and excitatory glutamate-glutamine (Glx) in several brain regions. Human participants first performed auditory and visual multistability tasks that produced spontaneous switching between percepts. Then, we observed that longer percept durations during behaviour were associated with higher GABA/Glx ratios in the sensory area coding for each modality. When participants were asked to voluntarily modulate their perception, a common factor across modalities emerged: the GABA/Glx ratio in the posterior parietal cortex tended to be positively correlated with the amount of effective volitional control. Our results provide direct evidence implicating that the balance between neural inhibition and excitation within sensory regions resolves perceptual competition. This powerful computational principle appears to be leveraged by both audition and vision, implemented independently across modalities, but modulated by an integrated control process. Perceptual multistability describes an intriguing situation, whereby an observer reports random changes in conscious perception for a physically unchanging stimulus 1,2. Multistability is a powerful tool with which to probe perceptual organisation, as it highlights perhaps the most fundamental issue faced by perception for any reasonably complex natural scene. And because the information encoded by sensory receptors is never sufficient to fully specify the state of the outside world 3 , at each instant perception must always choose between a number of competing alternatives. In realistic situations, the process produces a stable and useful representation of the world. In situations with intrinsically ambiguous information, the same process is revealed as multistable perception. A number of theoretical models have converged to pinpoint the generic computational principles likely to be required to explain multistability, and hence perceptual organisation 4-9. All of these models consider three core ingredients: inhibition between competing neural populations, adaptation within these populations, and neuronal noise. The precise role of each ingredient and their respective importance is still being debated. Noise is introduced to induce fluctuations in each population and initiate the stochastic perceptual switching in some models 7-9 , whereas switching dynamics are solely determined by inhibition in others 5,6. Functional brain imaging in humans has provided results qualitatively compatible with those computational principles at several levels of the visual processing hierarchy 10. But, for most functional imaging techniques in humans such as fMRI or MEG/EEG, change

Auditory multistability and neurotransmitter concentrations in the human brain

Multistability in perception is a powerful tool for investigating sensory–perceptual transformations, because it produces dissociations between sensory inputs and subjective experience. Spontaneous switching between different perceptual objects occurs during prolonged listening to a sound sequence of tone triplets or repeated words (termed auditory streaming and verbal transformations, respectively). We used these examples of auditory multistability to examine to what extent neurochemical and cognitive factors influence the observed idiosyncratic patterns of switching between perceptual objects. The concentrations of glutamate–glutamine (Glx) and γ-aminobutyric acid (GABA) in brain regions were measured by magnetic resonance spectroscopy, while personality traits and executive functions were assessed using questionnaires and response inhibition tasks. Idiosyncratic patterns of perceptual switching in the two multistable stimulus configurations were identified using a multidimensional scaling (MDS) analysis. Intriguingly, although switching patterns within each individual differed between auditory streaming and verbal transformations, similar MDS dimensions were extracted separately from the two datasets. Individual switching patterns were significantly correlated with Glx and GABA concentrations in auditory cortex and inferior frontal cortex but not with the personality traits and executive functions. Our results suggest that auditory perceptual organization depends on the balance between neural excitation and inhibition in different brain regions. This article is part of the themed issue ‘Auditory and visual scene analysis'

Malleability and fluidity of time perception

Time perception is inherently subjective and malleable. We experience a wide range of time scales, from less than a second to decades. In addition, our perception of time can be affected by our attentional and emotional states. Previous psychological and neuroimaging studies have used several paradigms and methods to probe factors that influence time perception. Considering these factors facilitates approaches to improve time management and to enhance sensory experiences. This Collection of time perception studies includes reports that focus on stimulus property, physiological state, cross-modal interaction, attention, learning, age, and environment. These findings help to illuminate the complex mechanisms of time perception

γδ T Cell Immunotherapy?A Review

Cancer immunotherapy utilizing Vγ9Vδ2 T cells has been developed over the past decade. A large number of clinical trials have been conducted on various types of solid tumors as well as hematological malignancies. Vγ9Vδ2 T cell-based immunotherapy can be classified into two categories based on the methods of activation and expansion of these cells. Although the in vivo expansion of Vγ9Vδ2 T cells by phosphoantigens or nitrogen-containing bisphosphonates (N-bis) has been translated to early-phase clinical trials, in which the safety of the treatment was confirmed, problems such as activation-induced Vγ9Vδ2 T cell anergy and a decrease in the number of peripheral blood Vγ9Vδ2 T cells after infusion of these stimulants have not yet been solved. In addition, it is difficult to ex vivo expand Vγ9Vδ2 T cells from advanced cancer patients with decreased initial numbers of peripheral blood Vγ9Vδ2 T cells. In this article, we review the clinical studies and reports targeting Vγ9Vδ2 T cells and discuss the development and improvement of Vγ9Vδ2 T cell-based cancer immunotherapy