L’esprit predictif : introduction à la théorie du cerveau bayésien

Efficient gaze stabilization during video Active Gaze Shift Test (vAGST) in bilateral vestibulopathy

Introduction

While most head movements in daily life are active, most tools used to assess vestibular deficits rely on passive head movements. A single gain value is not sufficient to quantify gaze stabilization efficiency during active movements in vestibular deficit patients. Moreover, during active gaze shifts, anticipatory mechanisms come into play. Our aim was to explore the extent to which previously described compensatory mechanisms are employed in patients with bilateral vestibular loss.

Methods

We used a Video Head Impulse Test (vHIT) to simultaneously record eye and head movements during a video Active Gaze Shift Test (vAGST). Thirty-eight patients with bilateral vestibular deficits and 61 control subjects were tested.

Results

Despite impaired performance on caloric tests and vHIT, most patients exhibited normal gaze stabilization (gain = 0.92 ± 0.1) during active gaze shifts up to a head speed ('stall speed') of approximately 140 ± 60°/sec, compared to 280 ± 65°/sec in controls. Our results indicate that BVD patients spontaneously adopt a head speed during active horizontal movements that significantly improves gaze stabilization compared to passive movements. The stall speed correlates with the spontaneous head speed typically adopted by BVD patients and controls in daily activities. As a consequence of the reduction in head speed and corrective saccades, patients also showed an increased delay in gaze stabilization (413 ± 105 ms in BVD patients versus 358 ± 82 ms in controls) at the end of the gaze shift, which might become disabling for certain tasks.

Discussion

Recent model suggests that compensatory eye movements, which stabilize gaze during the counter rotation phase of active gaze shifts, are predictive in nature. vAGST is not designed to provide an etiological diagnosis but rather a functional assessment of the patient's ability to generate predictive eye movements that compensate for vestibular sensor deficits. Understanding the quality of the patient's sensory predictions can also shed light on vestibular symptoms, even in cases where no vestibular sensor deficit is detected. This suggest that quality of life and oscillopsia questionnaires should distinguish between predictable and unpredictable movements.

Auditory illusions and Post-traumatic stress disorder: Sound test in a case-control study

Post-Traumatic Stress Disorder (PTSD) is a prevalent and disabling disorder with a high degree of comorbidity. Clinical studies have focused on hallucinations, which could be associated with the severity of the disorder and treatment resistance. Auditory illusions have received little attention so far, possibly because they are particularly difficult to assess. However, they may impact functioning, and underdiagnosis could impair prognosis. To provide a clearer understanding of PTSD psychopathology, this paper proposes to focus on these auditory illusions. A monocentric case-control study was conducted on 30 subjects with PTSD and 30 controls, based on an original design. False recognitions were estimated during a sound test created with a vocoder. Additionally, differences in emotional valence, dissociation, hyperarousal, and reliving were assessed. The study found that individuals with PTSD experience a higher frequency of auditory illusions compared to healthy controls (65% versus 20%, p < 0.001). Additionally, the emotional valence of these illusions was more negative in individuals with PTSD than in controls. The study also identified a correlation between dissociation symptoms, hyperarousal and reliving with auditory illusions. These findings are in line with neurobiological studies of PTSD, as well as cognitive predictive models, and support the hypothesis of a significant prevalence of auditory illusions in PTSD. Like hallucinations, auditory illusions may be influenced by dissociation. Although these results are preliminary, they suggest a need for further investigation into auditory illusions in PTSD and their effect on prognosis.

[Conspiracy theories and COVID-19: How do conspiracy beliefs arise?]

The COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 has caused an unprecedented global crisis, and a proliferation of conspiracy theories. These conspiratorial beliefs has contributed to weakening the credibility of government public health measures, limiting citizens' access to reliable sources of information, and disrupting the response of health systems to the crisis. Several hypotheses have been proposed in psychology and social science to understand the genesis of these beliefs during a pandemic, including generational, socio-cultural and political characteristics of individuals, and psychological factors such as the desire to preserve one's safety, to maintain a positive self-image, or even to strengthen its social role. However, recent discoveries in cognitive science about belief updating mechanisms offer new insights into the generation of conspiratorial beliefs across time and culture. In this paper, we offer a definition of conspiracy theory and a classification of conspiracy beliefs during the COVID-19 pandemic. We show how the mechanisms of belief updating may explain the genesis of conspiracy theories, and we propose several hypotheses supported by contemporary research in cognitive and social science.