Sensory and environmental uncertainty in perceptual decision-making.

In perceptual decision-making, uncertainties regarding both noisy sensory information and changing environmental regularities must be considered. We aimed to clarify the relationship between these two sources of uncertainty using a combined motion discrimination and audiovisual reversal learning task with Bayesian modeling. As predicted, the influence of learned beliefs regarding audiovisual associations on perceptual decisions was greater under high sensory uncertainty. Critically, this modulatory effect was larger under high than low environmental uncertainty. Moreover, the degree to which observers relied on learned beliefs when making perceptual decisions depended on their individual tendency to change beliefs. While these findings suggest that weighting of the available sensory information against learned beliefs is modulated by their respective uncertainties, belief learning was not found to rely on sensory uncertainty. Unraveling of these interactive effects of sensory and environmental uncertainties in perception might aid in the understanding of aberrant perceptual inference in psychopathology such as schizophrenia.

Thalamic Aphasia: a Review.

PURPOSE OF REVIEW: Thalamic aphasia is a rare language disorder resulting from lesions to the thalamus. While most patients exhibit mild symptoms with a predominance of lexical-semantic difficulties, variations in phenotype have been described. Overall, the exact mechanisms of thalamic aphasia await empirical research. The article reviews recent findings regarding phenotypes and possible underlying mechanisms of thalamic aphasia. RECENT FINDINGS: Variations in phenotype of thalamic aphasia may be related to different lesion locations. Overall, the thalamus' role in language is thought to be due to its involvement in cortico-thalamic language networks with lesioning of certain nuclei resulting in the diachisis of otherwise interconnected areas. Its possible monitoring function in such a network might be due to its different cellular firing modes. However, no specific evidence has been collected to date. While recent findings show a more distinct understanding of thalamic aphasia phenotypes and possible underlying mechanisms, further research is needed. Additionally, as standard language testing might oftentimes not pick up on its subtle symptoms, thalamic aphasia might be underdiagnosed.

Frequency and phenotype of thalamic aphasia.

BACKGROUND: Aphasia is a recognized presenting symptom of thalamic lesions. Little is known regarding its frequency and phenotype. We examined the frequency of thalamic aphasia following Isolated Acute unilateral ischemic Lesions in the Thalamus (IALT) with respect to lesion location. Furthermore, we characterized thalamic aphasia according to affected language domains and severity. METHODS: Fifty-two patients with IALT were analyzed [44% female, median age: 73 years (IQR: 60-79)]. Lesion location was determined using 3-Tesla magnetic resonance imaging and categorized as anterior, posterior, paramedian or inferolateral. Standardized language assessment was performed using the validated Aphasia checklist (ACL) directly after symptom onset. Aphasia was defined as an ACL sum score of < 135 (range: 0-148). RESULTS: Of 52 patients, 23 (44%) fulfilled the ACL diagnostic criteria for aphasia, including nearly all lesion locations and both sides. The average ACL sum score was 132 ± 11 (range: 98-147). Aphasia was characterized by deficits within domains of complex understanding of speech and verbal fluency. Patients with left anterior IALT were most severely affected, having significantly lower ACL scores than all other patients (117 ± 13 vs. 135 ± 8; p < 0.001). In particular, aphasia in patients with left anterior IALT was characterized by significantly worse performance in the rating of verbal communication, verbal fluency, and naming (all p ≤ 0.001). CONCLUSION: Aphasia occurs in almost half of patients with focal thalamic lesions. Thalamic aphasia is not confined to one predefined thalamic lesion location, but language deficits are particularly pronounced in patients with left anterior IALT presenting with a distinct pattern.

Cerebral embolisation during transcatheter edge-to-edge repair of the mitral valve with the MitraClip system: a prospective, observational study.

BACKGROUND: New ischaemic brain lesions on magnetic resonance imaging (MRI) are reported in up to 86% of patients after transcatheter edge-to-edge repair of the mitral valve (TEER-MV). Knowledge of the exact procedural step(s) that carry the highest risk for cerebral embolisation may help to further improve the procedure. AIMS: The aim of this study was to identify the procedural step(s) that are associated with an increased risk of cerebral embolisation during TEER-MV with the MitraClip system. Furthermore, the risk of overt stroke and silent brain ischaemia after TEER-MV was assessed. METHODS: In this prospective, pre-specified observational study, all patients underwent continuous transcranial Doppler examination during TEER-MV to detect microembolic signals (MES). MES were assigned to specific procedural steps: (1) transseptal puncture and placement of the guide, (2) advancing and adjustment of the clip in the left atrium, (3) device interaction with the MV, and (4) removal of the clip delivery system and the guide. Neurological examination using the National Institutes of Health Stroke Scale (NIHSS) and cerebral MRI were performed before and after TEER-MV. RESULTS: Fifty-four patients were included. The number of MES differed significantly between the procedural steps with the highest numbers observed during device interaction with the MV. Mild neurological deterioration (NIHSS ≤3) occurred in 9/54 patients. New ischaemic lesions were detected in 21/24 patients who underwent MRI. Larger infarct volume was significantly associated with neurological deterioration. CONCLUSIONS: Cerebral embolisation is immanent to TEER-MV and predominantly occurs during device interaction with the MV. Improvements to the procedure may focus on this procedural step.

An active role of inferior frontal cortex in conscious experience.

In the search for the neural correlates of consciousness, it has remained controversial whether prefrontal cortex determines what is consciously experienced or, alternatively, serves only complementary functions, such as introspection or action. Here, we provide converging evidence from computational modeling and two functional magnetic resonance imaging experiments that indicated a key role of inferior frontal cortex in detecting perceptual conflicts caused by ambiguous sensory information. Crucially, the detection of perceptual conflicts by prefrontal cortex turned out to be critical in the process of transforming ambiguous sensory information into unambiguous conscious experiences: in a third experiment, disruption of neural activity in inferior frontal cortex through transcranial magnetic stimulation slowed down the updating of conscious experience that occurs in response to perceptual conflicts. These findings show that inferior frontal cortex actively contributes to the resolution of perceptual ambiguities. Prefrontal cortex is thus causally involved in determining the contents of conscious experience.

Frequency, clinical presentation and outcome of vigilance impairment in patients with uni- and bilateral ischemic infarction of the paramedian thalamus.

Ischemic stroke of the paramedian thalamus is a rare differential diagnosis in sudden altered vigilance states. While efforts to describe clinical symptomatology exist, data on the frequency of paramedian thalamic stroke as a cause of sudden impaired vigilance and on accompanying clinical signs and outcome are scarce. We retrospectively analyzed consecutive patients admitted to a tertiary stroke center between 2010 and 2019 diagnosed with paramedian thalamic stroke. We evaluated frequency of vigilance impairment (VI) due to paramedian thalamic stroke, accompanying clinical signs and short-term outcome in uni- versus bilateral paramedian lesion location. Of 3896 ischemic stroke patients, 53 showed a paramedian thalamic stroke location (1.4%). VI was seen in 29/53 patients with paramedian thalamic stroke and in 414/3896 with any stroke (10.6%). Paramedian thalamic stroke was identified as causal to VI in 3.4% of all patients with initial VI in the emergency department and in 0.7% of all ischemic stroke patients treated in our center. Accompanying clinical signs were detected in 21 of these 29 patients (72.4%) and facilitated a timely diagnosis. VI was significantly more common after bilateral than unilateral lesions (92.0% vs. 21.4%; p < 0.001). Patients with bilateral paramedian lesions were more severely affected, had longer hospital stays and more frequently required in-patient rehabilitation. Paramedian thalamic lesions account for about 1 in 15 stroke patients presenting with impaired vigilance. Bilateral paramedian lesion location is associated with worse stroke severity and short-term outcome. Paying attention to accompanying clinical signs is of importance as they may facilitate a timely diagnosis.

"Thalamic aphasia" after stroke is associated with left anterior lesion location.

BACKGROUND: Aphasic symptoms are typically associated with lesions of the left fronto-temporal cortex. Interestingly, aphasic symptoms have also been described in patients with thalamic strokes in anterior, paramedian or posterolateral location. So far, systematic analyses are missing. METHODS: We conducted a retrospective analysis of consecutive patients admitted to our tertiary stroke care center between January 2016 and July 2017 with image-based (MRI) proven ischemic stroke. We evaluated stroke lesion location, using 3-T MRI, and presence of aphasic symptoms. RESULTS: Out of 1064 patients, 104 (9.8%) presented with a thalamic stroke, 52 of which (4.9%) had an isolated lesion in the thalamus (ILT). In patients with ILT, 6/52 had aphasic symptoms. Aphasic symptoms after ILT were only present in patients with left anterior lesion location (n = 6, 100% left anterior vs. 0% other thalamic location, p < 0.001). CONCLUSIONS: Aphasic symptoms in thalamic stroke are strongly associated with left anterior lesion location. In thalamo-cortical language networks, specifically the nuclei in the left anterior thalamus could play an important role in integration of left cortical information with disconnection leading to aphasic symptoms.

Maturation of interhemispheric signal propagation in autism spectrum disorder and typically developing controls: a TMS-EEG study.

Brain maturation from childhood to adulthood is associated with changes in structural and functional connectivity between remote brain regions. Altered connectivity plays an important role in the pathology of autism spectrum disorder (ASD), a severe neurodevelopmental disorder. ASD is associated with abnormal brain development and structurally altered interhemispheric connections. Cortico-cortical connectivity can be studied by a combination of transcranial magnetic stimulation (TMS) with concurrent EEG (TMS-EEG). TMS-evoked Interhemispheric Signal Propagation (ISP) is a correlate of interhemispheric connectivity related to the microstructure of the corpus callosum (CC). We used TMS-EEG to measure ISP in 22 ASD subjects (10-21 years) and 22 typically developing control subjects (9-19 years). We expected (1) maturational changes of ISP from childhood to young adulthood and also (2) reduced interhemispheric signal transfer in ASD. ISP was positively correlated with age in both ASD and typically developing control subjects. No difference in ISP between ASD and typically developing controls was found. Our findings demonstrate maturation of effective interhemispheric connectivity during adolescence. As ISP is related to the microstructure of the CC, the developmental change of ISP likely reflects maturation of the CC during the second life decade. The results support ISP as a valid parameter reflecting functional interhemispheric connectivity. Our results do not support a global deficit of interhemispheric connectivity in ASD.