Reduced stereotypicality and spared use of facial expression predictions for social evaluation in autism

Background/Objective

Autism has been investigated through traditional emotion recognition paradigms, merely investigating accuracy, thereby constraining how potential differences across autistic and control individuals may be observed, identified, and described. Moreover, the use of emotional facial expression information for social functioning in autism is of relevance to provide a deeper understanding of the condition.

Method

Adult autistic individuals (n = 34) and adult control individuals (n = 34) were assessed with a social perception behavioral paradigm exploring facial expression predictions and their impact on social evaluation.

Results

Autistic individuals held less stereotypical predictions than controls. Importantly, despite such differences in predictions, the use of such predictions for social evaluation did not differ significantly between groups, as autistic individuals relied on their predictions to evaluate others to the same extent as controls.

Conclusions

These results help to understand how autistic individuals perceive social stimuli and evaluate others, revealing a deviation from stereotypicality beyond which social evaluation strategies may be intact.

Noninvasive modulation of predictive coding in humans: causal evidence for frequency-specific temporal dynamics

Increasing evidence indicates that the brain predicts sensory input based on past experiences, importantly constraining how we experience the world. Despite a growing interest on this framework, known as predictive coding, most of such approaches to multiple psychological domains continue to be theoretical or primarily provide correlational evidence. We here explored the neural basis of predictive processing using noninvasive brain stimulation and provide causal evidence of frequency-specific modulations in humans. Participants received 20 Hz (associated with top-down/predictions), 50 Hz (associated with bottom-up/prediction errors), or sham transcranial alternating current stimulation on the left dorsolateral prefrontal cortex while performing a social perception task in which facial expression predictions were induced and subsequently confirmed or violated. Left prefrontal 20 Hz stimulation reinforced stereotypical predictions. In contrast, 50 Hz and sham stimulation failed to yield any significant behavioral effects. Moreover, the frequency-specific effect observed was further supported by electroencephalography data, which showed a boost of brain activity at the stimulated frequency band. These observations provide causal evidence for how predictive processing may be enabled in the human brain, setting up a needed framework to understand how it may be disrupted across brain-related conditions and potentially restored through noninvasive methods.

A Novel Localization of METTL7A in Bergmann Glial Cells in Human Cerebellum

Methyltransferase-like protein 7A (METTL7A) is a member of the METTL family of methyltransferases.Little information is available regarding the cellular expression of METTL7A in the brain. METTL7A is commonly located in the endoplasmic reticulum and to a lesser extent, in the lipid droplets of some cells. Several studies have reported altered protein and RNA levels in different brain areas in schizophrenia. One of these studies found reduced protein levels of METTL7A in the cerebellar cortex in schizophrenia and stress murine models. Since there is limited information in the literature about METTL7A, we characterized its cellular and subcellular localizations in the human cerebellum using immunohistochemical analysis with laser confocal microscopy. Our study reveals a novel METTL7A localization in GFAP-positive cells, with higher expression in the end-feet of the Bergmann glia, which participate in the cerebrospinal fluid-brain parenchyma barrier. Further 3D reconstruction image analysis showed that METTL7A was expressed in the contacts between the Bergmann glia and Purkinje neurons. METTL7A was also detected in lipid droplets in some cells in the white matter. The localization of METTL7A in the human cerebellar glia limitans could suggest a putative role in maintaining the cerebellar parenchyma homeostasis and in the regulation of internal cerebellar circuits by modulating the synaptic activity of Purkinje neurons.

CD8 T cell nigral infiltration precedes synucleinopathy in early stages of Parkinson's disease

There is no consensus on the exact role of the adaptive immune system in Parkinson's disease pathogenesis, although there is increasing evidence that it is somehow involved. Moreover, T cell infiltration in the brain has not been thoroughly studied in Parkinson's disease and no study has assessed the infiltration in incidental Lewy body diseases cases that are considered to be early presymptomatic stages of the disease. In this study, we performed an immunohistochemistry/immunofluorescence quantitative and phenotypic assessment of T cell infiltration in human substantia nigra pars compacta and analysed the correlations with neuronal death and synucleinopathy throughout different stages of the disease. We included two groups of incidental Lewy disease in the study. One of the groups, which is believed to be the earliest stage of the disease, showed α-synuclein aggregates only in the olfactory bulb. The second group also presented α-synuclein aggregates in the substantia nigra. We also assessed the formation of different α-synuclein aggregates throughout the different stages of the unified staging system for Lewy body disorders (I to IV). We found that CD8 T cells were increased in diagnosed Parkinson's disease cases compared to the control group and their density positively correlated with neuronal death. Some of the infiltrating CD8 T cells were indeed contacting dopaminergic neurons. No differences were found regarding CD4 T cells. In the earliest stage of the disease, when substantia nigra α-synuclein aggregation is absent, we found a robust CD8 T cell infiltration and no dopaminergic neuronal death yet. Conversely, in the next stage we found neuronal loss and a milder CD8 T cell infiltration. CD8 T cell infiltration paralleled that of α-synuclein accumulation and neuronal death throughout stages II to IV. We also confirmed that CD8 T cells in charge of immune surveillance and involved in the aetiopathogenesis of the disease are equipped with cytolytic enzymes (granzyme A, B and K) and/or proinflammatory cytokines (interferon gamma), and that phenotypic differences were observed between early and late stages of the disease. We also demonstrate that a high proportion of nigral CD8 T cells are tissue resident memory T cells. Our results show that nigral cytotoxic CD8 T cell infiltration is an earlier pathogenic event than α-synuclein aggregation and neuronal death and that it parallels the progression of neuronal death and synucleinopathy in Parkinson's disease. Overall, our study suggests that CD8 T cell cytotoxic attack may initiate and propagate neuronal death and synucleinopathy in Parkinson's disease.

Validation of a Reversed Phase UPLC-MS/MS Method to Determine Dopamine Metabolites and Oxidation Intermediates in Neuronal Differentiated SH-SY5Y Cells and Brain Tissue

Dopamine is a key neurotransmitter in the pathophysiology of various neurological disorders such as addiction or Parkinson's disease. Disturbances in its metabolism could lead to dopamine accumulation in the cytoplasm and an increased production of o-quinones and their derivatives, which have neurotoxic potential and act as precursors in neuromelanin synthesis. Thus, quantification of the dopaminergic metabolism is essential for monitoring changes that may contribute to disease development. Here, we developed and validated an UPLC-MS/MS method to detect and quantify a panel of eight dopaminergic metabolites, including the oxidation product aminochrome. Our method was validated in differentiated SH-SY5Y cells and mouse brain tissue and was then employed in brain samples from humans and rats to ensure method reliability in different matrices. Finally, to prove the biological relevance of our method, we determined metabolic changes in an in vitro cellular model of dopamine oxidation/neuromelanin production and in human postmortem samples from Parkinson's disease patients. The current study provides a validated method to simultaneously monitor possible alterations in dopamine degradation and o-quinone production pathways that can be applied to in vitro and in vivo experimental models of neurological disorders and human brain samples.