RESUMEN
Although risk is prevalent in decision-making, the specific neural processes underlying risk-taking behavior remain unclear. Previous studies have suggested that frontal theta-band activity plays a crucial role in modulating risk-taking behavior. The functional relevance of theta in risk-taking behavior is yet to be clearly established and studies using noninvasive brain stimulation have yielded inconsistent findings. We aimed to investigate this relevance using transcranial alternating current stimulation (tACS) over right or left dorsolateral prefrontal cortex (DLPFC). We also studied the influence of stimulation intensity on risk-taking behavior and electrophysiological effects. We applied theta-band (6.5 Hz) tACS over the left (F3) and right (F4) DLPFC with lower (1.5 mA) and higher (3 mA) tACS intensities. We employed a single-blinded, sham-controlled, within-subject design and combined tACS with electroencephalography (EEG) measurements and the Maastricht Gambling Task (MGT) to elicit and evaluate risk-taking behavior. Our results show an increase in risk-taking behavior after left DLPFC stimulation at both intensities and a reduction of risk-taking behavior after 3 mA (and not 1.5 mA) right DLPFC stimulation compared to sham. Further analyses showed a negative correlation between resting-state frontal theta-power and risk-taking behavior. Overall, frontal theta-power was increased after left, but not right, theta-band tACS independent of stimulation intensity. Our findings confirm the functional relevance of frontal theta-band activity in decision-making under risk and the differential role of left and right DLPFC. We also were able to show that stimulation intensity did have an effect on behavioral responses, namely risk-taking behavior. Significant right hemisphere stimulation effects were observed only after high-intensity stimulation. Nevertheless, electrophysiological effects were only significant after left DLPFC stimulation, regardless of tACS intensity. Furthermore, the results indicate the role of the baseline frontal theta-power in the direction of behavioral effects after theta-band tACS.
Asunto(s)
Estimulación Transcraneal de Corriente Directa , Humanos , Electroencefalografía/métodos , Asunción de Riesgos , Estimulación Transcraneal de Corriente Directa/métodosRESUMEN
BACKGROUND: The prefrontal cortex can be partialized in various anatomical and functional sub regions. Among those regions, both right dorsolateral prefrontal cortex (rDLPFC) and ventromedial prefrontal cortex (VMPFC) have been associated with risk-taking behavior based on neuroimaging studies. Noninvasive brain stimulation (NIBS) studies aiming at demonstrating the functional relevance of neural activity in these areas almost exclusively focused on the rDLPFC, where its experimental stimulation with a (generally) inhibitory protocol lead to a measurable increase in risk-taking behavior due to reduced cognitive control. The functional relevance of VMPFC in risk-taking behavior has not yet been addressed using NIBS, although multiple neuroimaging studies correlate this area's activity with valuation. OBJECTIVE/HYPOTHESIS: Here, we used NIBS to investigate the functional relevance of both, the rDLPFC and VMPFC in risk-taking behavior. We hypothesized that, compared to sham stimulation, VMPFC suppression leads to a reduction in risk-taking behavior by reducing the appeal to higher value options and consequently the attractiveness of riskier options, whereas rDLPFC suppression leads to an increase in risk taking, replicating previous findings. METHODS: We applied continuous theta burst stimulation (cTBS), a generally inhibitory protocol, to stimulate either VMPFC or DLPFC before the execution of the computerized Maastricht Gambling Task (MGT) in a within-subject design with 30 participants. The MGT allowed the analysis of potential brain region-specific effects of cTBS on risk-taking behavior such as participants' choices of average values, probabilities, and response time. RESULTS: cTBS applied to either rDLPFC or VMPFC both led to an increase in risk-taking behavior and in the average value chosen as compared to sham transcranial magnetic stimulation. No effect on the choice of probabilities was found. A significant increase in response time was observed exclusively after suppressing rDLPFC. We speculate that these similar behavioral consequences following cTBS over DLPFC and VMPFC are likely due to the strong anatomical and functional interconnection between both brain regions.
Asunto(s)
Corteza Prefontal Dorsolateral , Juego de Azar , Humanos , Corteza Prefrontal/fisiología , Encéfalo , Estimulación Magnética Transcraneal/métodos , Asunción de RiesgosRESUMEN
Animal models, human neuroimaging and lesion studies revealed that the gut microbiota can influence the interaction between the central and the enteric nervous systems via the gut-brain axis (GBA) and can affect brain regions linked to basic emotional and cognitive processes. The role of the gut microbiota in decision-making in healthy humans thus far remains largely unknown. Our study establishes a functional relationship between the gut microbiota and healthy humans' decisions that involve risk and time. We conducted a between subjects' placebo-controlled double-blinded design, with two groups and two sessions separated by 28 days, during which participants received daily doses of probiotics or a placebo. We investigated whether the prolonged and controlled intake of probiotics affects risk-taking behavior and intertemporal choices using incentivized economic tasks. We found a significant decrease in risk-taking behavior and an increase in future-oriented choices in the probiotics group as compared to the placebo group. These findings provide the first direct experimental evidence suggesting a potential functional role on the part of the microbiota-gut-brain axis in decision-making, creating a path for potential clinical applications and allowing for a better understanding of the underlying neural mechanisms of risk-taking behavior and intertemporal choices.
Asunto(s)
Sistema Nervioso Entérico , Microbioma Gastrointestinal , Probióticos , Animales , Encéfalo/fisiología , Emociones , Sistema Nervioso Entérico/fisiología , HumanosRESUMEN
BACKGROUND: Most of our decisions involve a certain degree of risk regarding the outcomes of our choices. People vary in the way they make decisions, resulting in different levels of risk-taking behavior. These differences have been linked to prefrontal theta band activity. However, a direct functional relationship between prefrontal theta band activity and risk-taking has not yet been demonstrated. OBJECTIVE: We used noninvasive brain stimulation to test the functional relevance of prefrontal oscillatory theta activity for the regulatory control of risk-taking behavior. METHODS: In a within-subject experiment, 31 healthy participants received theta (6.5 Hertz [Hz]), gamma (40 Hz), and sham transcranial alternating current stimulation (tACS) over the left prefrontal cortex (lPFC). During stimulation, participants completed a task assessing their risk-taking behavior as well as response times and sensitivity to value and outcome probabilities. Electroencephalography (EEG) was recorded before and immediately after stimulation to investigate possible long-lasting stimulation effects. RESULTS: Theta band, but not gamma band or sham, tACS led to a significant reduction in risk-taking behavior, indicating a frequency-specific effect of prefrontal brain stimulation on the modulation of risk-taking behavior. Moreover, theta band stimulation led to increased response times and decreased sensitivity to reward values. EEG data analyses did not show an offline increase in power in the stimulated frequencies after the stimulation protocol. CONCLUSION: These findings provide direct empirical evidence for the effects of prefrontal theta band stimulation on behavioral risk-taking regulation.