Neural implementation of computational mechanisms underlying the continuous trade-off between cooperation and competition.

Social interactions evolve continuously. Sometimes we cooperate, sometimes we compete, while at other times we strategically position ourselves somewhere in between to account for the ever-changing social contexts around us. Research on social interactions often focuses on a binary dichotomy between competition and cooperation, ignoring people's evolving shifts along a continuum. Here, we develop an economic game - the Space Dilemma - where two players change their degree of cooperativeness over time in cooperative and competitive contexts. Using computational modelling we show how social contexts bias choices and characterise how inferences about others' intentions modulate cooperativeness. Consistent with the modelling predictions, brain regions previously linked to social cognition, including the temporo-parietal junction, dorso-medial prefrontal cortex and the anterior cingulate gyrus, encode social prediction errors and context-dependent signals, correlating with shifts along a cooperation-competition continuum. These results provide a comprehensive account of the computational and neural mechanisms underlying the continuous trade-off between cooperation and competition.

Non-invasive transcranial ultrasound stimulation for neuromodulation.

Transcranial ultrasound stimulation (TUS) holds great potential as a tool to alter neural circuits non-invasively in both animals and humans. In contrast to established non-invasive brain stimulation methods, ultrasonic waves can be focused on both cortical and deep brain targets with the unprecedented spatial resolution as small as a few cubic millimeters. This focusing allows exclusive targeting of small subcortical structures, previously accessible only by invasive deep brain stimulation devices. The neuromodulatory effects of TUS are likely derived from the kinetic interaction of the ultrasound waves with neuronal membranes and their constitutive mechanosensitive ion channels, to produce short term and long-lasting changes in neuronal excitability and spontaneous firing rate. After decades of mechanistic and safety investigation, the technique has finally come of age, and an increasing number of human TUS studies are expected. Given its excellent compatibility with non-invasive brain mapping techniques, such as electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), as well as neuromodulatory techniques, such as transcranial magnetic stimulation (TMS), systemic TUS effects can readily be assessed in both basic and clinical research. In this review, we present the fundamentals of TUS for a broader audience. We provide up-to-date information on the physical and neurophysiological mechanisms of TUS, available readouts for its neural and behavioral effects, insights gained from animal models and human studies, potential clinical applications, and safety considerations. Moreover, we discuss the indirect effects of TUS on the nervous system through peripheral co-stimulation and how these confounding factors can be mitigated by proper control conditions.