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BackgroundProgressive Supranuclear Palsy (PSP) is associated with tau-protein aggregation and neuroinflammation, but it remains unclear whether these pathogenic processes are relatedin vivo.ObjectivesWe examined the relationship between tau pathology and microglial activation using [18F]AV-1451 (indexing tau burden) and [11C]PK11195 (microglial activation) PET in n=17 patients with PSP-Richardson’s syndrome.MethodsNon-displaceable binding potential (BPND) for each ligand was quantified in 83 regions of interest (ROIs). [18F]AV-1451 and [11C]PK11195 BPNDvalues were correlated across all ROIs. The anatomical patterns of [18F]AV-1451 and [11C]PK11195 binding co-localization was determined across sets of regions derived from principal component analyses (PCAs). Finally, PCA-derived brain patterns of tau pathology and neuroinflammation were linked to clinical severity.Results[18F]AV-1451 and [11C]PK11195 binding were positively related across all ROIs (r=0.577, p18F]AV-1451 and [11C]PK11195 components were found in sub-cortical (r=0.769, pConclusionsWe show that tau pathology and neuroinflammation co-localize in PSP, and that individual differences in subcortical tau pathology and neuroinflammation are linked to clinical severity. Although longitudinal studies are needed to determine how these molecular pathologies are causally linked, we suggest that the combination of tau- and immune-oriented strategies may be useful for effective disease-modifying treatments in PSP.

To bridge the gap between preclinical cellular models of disease and in vivo imaging of human cognitive network dynamics, there is a pressing need for informative biophysical models. Here we assess dynamic causal models (DCM) of cortical network responses, inverted to magnetoencephalographic observations during an auditory oddball roving paradigm in healthy adults. This paradigm induces robust perturbations that permeate frontotemporal networks, including an evoked ‘mismatch negativity’ response and transiently induced oscillations. Here, we probe GABAergic influences of the networks using double-blind placebo-controlled randomised-crossover administration of the GABA re-uptake inhibitor, tiagabine (oral, 10mg) in healthy older adults. We demonstrate the facility of conductance-based neural mass mean-field models, incorporating local synaptic connectivity, to investigate laminar-specific and GABAergic mechanisms of the auditory response. The neuronal model accurately recapitulated the observed magnetoencephalographic data. Using parametric empirical Bayes for optimal model inversion across both sessions, we identify the effect of tiagabine on GABAergic modulation of deep pyramidal and interneuronal cell populations. Moreover, in keeping with the hierarchical coding of beliefs and sensory evidence, we found a transition of the main GABAergic drug effects from auditory cortex in standard trials to prefrontal cortex in deviant trials. The successful integration of pharmaco-magnetoencephalography with dynamic causal models of frontotemporal networks provides a potential platform on which to evaluate the effects of disease and pharmacological interventions.Significance StatementUnderstanding human brain function and developing new treatments require good models of brain function. We tested a detailed generative model of cortical microcircuits that accurately reproduced human magnetoencephalography, to quantify network dynamics and connectivity in frontotemporal cortex. This approach correctly identified the effect of a test drug (tiagabine) on neuronal function (GABA-ergic dynamics), opening the way for psychopharmacological studies in health and disease with the mechanistic precision afforded by generative models of the brain.