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Background: The association of impaired dopaminergic neurotransmission with the development and maintenance of alcohol use disorder is well known. More specifically, reduced dopamine D2/3 receptors in the striatum of subjects with alcohol dependence (AD) compared to healthy controls have been found in previous studies. Furthermore, alterations of gamma‐aminobutyric acid (GABA) and glutamate (Glu) levels in the anterior cingulate cortex (ACC) of AD subjects have been documented in several studies. However, the interaction between cortical Glu levels and striatal dopamine D2/3 receptors has not been investigated in AD thus far. Methods: This study investigated dopamine D2/3 receptor availability via 18F‐fallypride positron emission tomography (PET) and GABA as well as Glu levels via magnetic resonance spectroscopy (MRS) in 19 detoxified AD subjects, 18 healthy controls (low risk, LR) controls and 19 individuals at high risk (HR) for developing AD, carefully matched for sex, age and smoking status. Results: We found a significant negative correlation between GABA levels in the ACC and dopamine D2/3 receptor availability in the associative striatum of LR but not in AD or HR individuals. Contrary to our expectations, we did not observe a correlation between Glu concentrations in the ACC and striatal D2/3 receptor availability. Conclusions: The results may reflect potential regulatory cortical mechanisms on mesolimbic dopamine receptors and their disruption in AD and individuals at high risk, mirroring complex neurotransmitter interactions associated with the pathogenesis of addiction. This is the first study combining 18F‐fallypride PET and MRS in AD subjects and individuals at high risk. [ABSTRACT FROM AUTHOR]

Recent research on neural and behavioral consequences of transcranial direct current stimulation (tDCS) has highlighted the impact of individual factors, such as brain anatomy which determines current field distribution and may thus significantly impact stimulation effects. Computational modeling approaches may significantly advance our understanding of such factors, but the association of simulation-based tDCS-induced fields and neurophysiological outcomes has not been investigated. To provide empirical evidence for the relationship between tDCS-induced neurophysiological outcomes and individually induced electric fields. We applied tDCS during eyes-closed resting-state functional resonance imaging (rsfMRI) and assessed pre-post magnetic resonance spectroscopy (MRS) in 24 participants. We aimed to quantify effects of 15-min tDCS using the "classical" left SM1-right supraorbital area montage on sensorimotor network (SMN) strength and gamma-aminobutyric acid (GABA) and glutamate concentrations, implementing a cross-over counterbalanced design with three stimulation conditions. Additional structural anatomical MRI sequences and recordings of individual electrode configurations allowed individual electric field simulations based on realistic head models of all participants for both conditions. On a neurophysiological level, we observed the expected reduction of GABA concentrations and increase in SMN strength, both during anodal and cathodal compared to sham tDCS, replicating previous results. The magnitudes of neurophysiological modulations induced by tDCS were significantly associated with simulation-based electric field strengths within the targeted left precentral gyrus. Our findings corroborate previous reports on tDCS-induced neurophysiological modulations and further advance the understanding of underlying mechanisms by providing first empirical evidence for the association of the injected electric field and neuromodulatory effects. • GABA concentrations were reduced after anodal and cathodal compared to sham tDCS. • Functional coupling in the sensorimotor network was increased. • Neurophysiological modulations were associated with electric field strengths. [ABSTRACT FROM AUTHOR]

In everyday life we are confronted with inputs of multisensory stimuli that need to be integrated across our senses. Individuals vary considerably in how they integrate multisensory information, yet the neurochemical foundations underlying this variability are not well understood. Neural oscillations, especially in the gamma band (> 30 Hz) play an important role in multisensory processing. Furthermore, gamma-aminobutyric acid (GABA) neurotransmission contributes to the generation of gamma band oscillations (GBO), which can be sustained by activation of metabotropic glutamate receptors. Hence, differences in the GABA and glutamate systems might contribute to individual differences in multisensory processing. In this combined magnetic resonance spectroscopy and electroencephalography study, we examined the relationships between GABA and glutamate concentrations in the superior temporal sulcus (STS), source localized GBO, and illusion rate in the sound-induced flash illusion (SIFI). In 39 human volunteers we found robust relationships between GABA concentration, GBO power, and the SIFI perception rate (r-values = 0.44 to 0.53). The correlation between GBO power and SIFI perception rate was about twofold higher when the modulating influence of the GABA level was included in the analysis as compared to when it was excluded. No significant effects were obtained for glutamate concentration. Our study suggests that the GABA level shapes individual differences in audiovisual perception through its modulating influence on GBO. GABA neurotransmission could be a promising target for treatment interventions of multisensory processing deficits in clinical populations, such as schizophrenia or autism. [ABSTRACT FROM AUTHOR]