Increasing striatal dopamine release through repeated bouts of theta burst transcranial magnetic stimulation of the left dorsolateral prefrontal cortex. A 18F-desmethoxyfallypride positron emission tomography study

IntroductionTranscranial Magnetic Stimulation (TMS) can modulate fronto-striatal connectivity in the human brain. Here Positron Emission Tomography (PET) and neuro-navigated TMS were combined to investigate the dynamics of the fronto-striatal connectivity in the human brain. Employing 18F-DesmethoxyFallypride (DMFP) – a Dopamine receptor-antagonist – the release of endogenous dopamine in the striatum in response to time-spaced repeated bouts of excitatory, intermittent theta burst stimulation (iTBS) of the Left-Dorsolateral Prefrontal Cortex (L-DLPFC) was measured.Methods23 healthy participants underwent two PET sessions, each one with four blocks of iTBS separated by 30 minutes: sham (control) and verum (90% of individual resting motor threshold). Receptor Binding Ratios were collected for sham and verum sessions across 37 time frames (about 130 minutes) in striatal sub-regions (Caudate nucleus and Putamen).ResultsVerum iTBS increased the dopamine release in striatal sub-regions, relative to sham iTBS. Dopamine levels in the verum session increased progressively across the time frames until frame number 28 (approximately 85 minutes after the start of the session and after three iTBS bouts) and then essentially remained unchanged until the end of the session.ConclusionResults suggest that the short-timed iTBS protocol performed in time-spaced blocks can effectively induce a dynamic dose dependent increase in dopaminergic fronto-striatal connectivity. This scheme could provide an alternative to unpleasant and distressing, long stimulation protocols in experimental and therapeutic settings. Specifically, it was demonstrated that three repeated bouts of iTBS, spaced by short intervals, achieve larger effects than one single stimulation. This finding has implications for the planning of therapeutic interventions, for example, treatment of major depression

Neural response to social rejection in children with early separation experiences.

Objective: Nonhuman and human studies have documented the adverse effects of early life stress (ELS) on emotion regulation and underlying neural circuitry. Less is known about how these experiences shape social processes and neural circuitry. In this study, we thus investigated how ELS affects children's perception of, and neural response to, negative social experiences in a social exclusion paradigm (Cyberball). Method: Twenty-five foster or adopted children with ELS (age 10.6 +/- 1.8 years, 13 male and 12 female) and 26 matched nonseparated controls (age 10.38 +/- 1.7 years, 12 male and 14 female) took part in a Cyberball paradigm during functional magnetic resonance imaging (fMRI). Results: During peer rejection, children with ELS reported significantly more feelings of exclusion and frustration than nonseparated controls. On the neural level, children with ELS showed reduced activation in the dorsal anterior cingulate cortex (dACC) and dorsolateral prefrontal cortex (dlPFC), and reduced connectivity between dlPFC-dACC, areas previously implicated in affect regulation. Conversely, children with ELS showed increased neural activation in brain regions involved in memory, arousal, and threat-related processing (middle temporal gyrus, thalamus, ventral tegmental area) relative to controls during social exclusion. The number of separation experiences before entering the permanent family predicted reductions in fronto-cingulate recruitment. The relationship between early separations and self-reported exclusion was mediated by dlPFC activity. Conclusion: The findings suggest that ELS leads to alterations in neural circuitry implicated in the regulation of socioemotional processes. This neural signature may underlie foster children's differential reactivity to rejection in everyday life and could increase risk for developing affective disorders

Anthropomorphic or non-anthropomorphic? Effects of biological sex in observation of actions in a digital human model and a gantry robot model

Robots are ever more relevant for everyday life, such as healthcare or rehabilitation, as well as for modern industrial environment. One important issue in this context is the way we perceive robots and their actions. From our previous study, evidence exists that sex can affect the way people perceive certain robot's actions. In our fMRI study, we analyzed brain activations of female and male participants, while they observed anthropomorphic and robotic movements performed by a human or a robot model. While lying in the scanner, participants rated the perceived level of anthropomorphic and robotic likeness of movements in the two models. The observation of the human model and the anthropomorphic movements similarly activated the biological motion coding areas in posterior temporal and parietal areas. The observation of the robot model activated predominantly areas of the ventral stream, whereas the observation of robotic movements activated predominantly the primary and higher order motor areas. To note, this later activation originated mainly from female participants, whereas male participants activated, in both robot model and robotic movements contrasts, areas in the posterior parietal cortex. Accordingly, the general contrast of sex suggests that men tend to use the ventro-dorsal stream most plausibly to rely on available previous knowledge to analyze the movements, whereas female participants use the dorso-dorsal and the ventral streams to analyze online the differences between the movement types and between the different models. The study is a first step toward the understanding of sex differences in the processing of anthropomorphic and robotic movements