Disruption and rescue of interareal theta phase coupling and adaptive behavior

Rescuing executive functions in people with neurological and neuropsychiatric disorders has been a major goal of psychology and neuroscience for decades. Innovative computer-training regimes for executive functions have made tremendous inroads, yet the positive effects of training have not always translated into improved cognitive functioning and often take many days to emerge. In the present study, we asked whether it was possible to immediately change components of executive function by directly manipulating neural activity using a stimulation technology called high-definition transcranial alternating current stimulation (HD-tACS). Twenty minutes of inphase stimulation over medial frontal cortex (MFC) and right lateral prefrontal cortex (lPFC) synchronized theta (∼6 Hz) rhythms between these regions in a frequency and spatially specific manner and rapidly improved adaptive behavior with effects lasting longer than 40 min. In contrast, antiphase stimulation in the same individuals desynchronized MFC-lPFC theta phase coupling and impaired adaptive behavior. Surprisingly, the exogenously driven impairments in performance could be instantly rescued by reversing the phase angle of alternating current. The results suggest executive functions can be rapidly up- or down-regulated by modulating theta phase coupling of distant frontal cortical areas and can contribute to the development of tools for potentially normalizing executive dysfunction in patient populations.Published versio

Frontal midline theta and N200 amplitude reflect complementary information about expectancy and outcome evaluation

Feedback ERN (fERN) and frontal midline theta have both been proposed to index a dopamine-like reinforcement learning signal in anterior cingulate cortex (ACC). We investigated these proposals by comparing fERN amplitude and theta power with respect to their sensitivities to outcome valence and probability in a previously collected EEG dataset. Bayesian model comparison revealed a dissociation between the two measures, with fERN amplitude mainly sensitive to valence and theta power mainly sensitive to probability. Further, fERN amplitude was highly correlated with the portion of theta power that is consistent in phase across trials (i.e., evoked theta power). These results suggest that although both measures provide valuable information about cognitive function of frontal midline cortex, fERN amplitude is specifically sensitive to dopamine reinforcement learning signals whereas theta power reflects the ACC response to unexpected events

Contextual novelty modulates the neural dynamics of reward anticipation

We investigated how rapidly the reward-predicting properties of visual cues are signaled in the human brain and the extent these reward prediction signals are contextually modifiable. In a magnetoencephalography study, we presented participants with fractal visual cues that predicted monetary rewards with different probabilities. These cues were presented in the temporal context of a preceding novel or familiar image of a natural scene. Starting at similar to 100 ms after cue onset, reward probability was signaled in the event-related fields (ERFs) over temporo-occipital sensors and in the power of theta (5-8 Hz) and beta (20-30 Hz) band oscillations over frontal sensors. While theta decreased with reward probability beta power showed the opposite effect. Thus, in humans anticipatory reward responses are generated rapidly, within 100 ms after the onset of reward-predicting cues, which is similar to the timing established in non-human primates. Contextual novelty enhanced the reward anticipation responses in both ERFs and in beta oscillations starting at similar to 100 ms after cue onset. This very early context effect is compatible with a physiological model that invokes the mediation of a hippocampal-VTA loop according to which novelty modulates neural response properties within the reward circuitry. We conclude that the neural processing of cues that predict future rewards is temporally highly efficient and contextually modifiable

Intra- and inter-brain synchrony oscillations underlying social adjustment

Humans naturally synchronize their behavior with other people. However, although it happens almost automatically, adjusting behavior and conformity to others is a complex phenomenon whose neural mechanisms are still yet to be understood entirely. The present experiment aimed to study the oscillatory synchronization mechanisms underlying automatic dyadic convergence in an EEG hyperscanning experiment. Thirty-six people performed a cooperative decision-making task where dyads had to guess the correct position of a point on a line. A reinforcement learning algorithm was used to model different aspects of the participants’ behavior and their expectations of their peers. Intra- and inter-connectivity among electrode sites were assessed using inter-site phase clustering in three main frequency bands (theta, alpha, beta) using a two-level Bayesian mixed-effects modeling approach. The results showed two oscillatory synchronization dynamics related to attention and executive functions in alpha and reinforcement learning in theta. In addition, inter-brain synchrony was mainly driven by beta oscillations. This study contributes preliminary evidence on the phase-coherence mechanism underlying inter-personal behavioral adjustment

A gut feeling:Noninvasive brain stimulation, gut microbiota and decision-making under risk

The majority of our daily choices include some degree of risk. This dissertation comprises a series of studies that investigate risk-taking behavior through the lens of decision neuroscience, exploring its neural processing from the brain to the gut. The first part includes studies using transcranial alternating current stimulation (tACS) and electroencephalography (EEG) to investigate the role of frontal theta-band activity in the modulation of risk-taking behavior. Part 2 explores the specific roles of the right DLPFC (rDLPFC) and the ventromedial prefrontal cortex (VMPFC) in this type of behavior and demonstrates that both areas are involved in valuation processing and the modulation of risk-taking behavior, reinforcing evidence of a strong functional interplay (Hare et al., 2009; Schiller et al., 2014). Finally, in part 3, the neural basis of risk-taking behavior was explored by looking beyond the central nervous system. The gut microbiota can influence various cognitive processes via the gut-brain axis (GBA). This study explores the effects of a probiotics manipulation on participants’ risk-taking behavior and intertemporal choices. The results show that probiotics led to a relative reduction in risk-taking behavior and increased likelihood of opting for delayed gratification, with reduced discount rates and lower risk proneness. In conclusion, this dissertation provides novel insights into the neural mechanisms underlying risk-taking behavior, both within the central nervous system and including the gut-brain axis as a potential key actor

Reward-based decision-making in mesial temporal lobe epilepsy patients with unilateral hippocampal sclerosis pre- and post-surgery

Background: Correct functioning of the reward processing system is critical for optimizing decision-making as well as preventing the development of addictions and/or neuropsychiatric symptoms such as depression, apathy, and anhedonia. Consequently, patients with mesial temporal lobe epilepsy due to unilateral hippocampal sclerosis (mTLE-UHS) represent an excellent opportunity to study the brain networks involved in this system. Objective: The aim of the current study was to evaluate decision-making and the electrophysiological correlates of feedback processing in a sample of mTLE-UHS patients, compared to healthy controls. In addition, we assessed the impact of mesial temporal lobe surgical resection on these processes, as well as general, neuropsychological functioning. Method: 17 mTLE-UHS patients and 17 matched healthy controls completed: [1] a computerized version of the Game of Dice Task, [2] a Standard Iowa Gambling Task, and [3] a modified ERP version of a probabilistic gambling task coupled with multichannel electroencephalography. Neuropsychological scores were also obtained both pre- and post-surgery. Results: Behavioral analyses showed a pattern of increased risk for the mTLE-UHS group in decision-making under ambiguity compared to the control group. A decrease in the amplitude of the Feedback Related Negativity (FRN), a weaker effect of valence on delta power, and a general reduction of delta and theta power in the mTLE-UHS group, as compared to the control group, were also found. The beta-gamma activity associated with the delivery of positive reward was similar in both groups. Behavioral performance and electrophysiological measures did not worsen post-surgery. Conclusions: Patients with mTLE-UHS showed impairments in decision-making under ambiguity, particularly when they had to make decisions based on the outcomes of their choices, but not in decision-making under risk. No group differences were observed in decision-making when feedbacks were random. These results might be explained by the abnormal feedback processing seen in the EEG activity of patients with mTLE-UHS, and by concomitant impairments in working memory, and memory. These impairments may be linked to the disruption of mesial temporal lobe networks. Finally, feedback processing and decision-making under ambiguity were already affected in mTLE-UHS patients pre-surgery and did not show evidence of clear worsening post-surgery

Electrophysiological indices of feedback processing

xii, 76 leaves : ill. (chiefly col.) ; 29 cmAll sentient organisms use contextual information to assess the amount of reward associated with a particular behavior. Human beings have arguably evolved the most sophisticated of these mechanisms and are capable of integrating information over a long duration of time to accurately assess the expected outcome of a chosen action. This thesis used electroencephalography (EEG) to measure how the human brain processes rewarding and punishing feedback in a gambling-type game with variable risk and reward. Experiment 1 determined that phase-locked (evoked) and non-phase-locked (induced) electroencephalographic activity share only partially overlapping generators in human mediofrontal cortex. Experiment 2 determined that the magnitude of certain evoked EEG components during reward processing tracked subsequent changes in bets placed in the next round. These results extend the body of literature by assessing the overlap between induced and evoked EEG components and the role of evoked activity in affecting future decision making

Selective Theta-Synchronization of Choice-Relevant Information Subserves Goal-Directed Behavior

Theta activity reflects a state of rhythmic modulation of excitability at the level of single neuron membranes, within local neuronal groups and between distant nodes of a neuronal network. A wealth of evidence has shown that during theta states distant neuronal groups synchronize, forming networks of spatially confined neuronal clusters at specific time periods during task performance. Here, we show that a functional commonality of networks engaging in theta rhythmic states is that they emerge around decision points, reflecting rhythmic synchronization of choice-relevant information. Decision points characterize a point in time shortly before a subject chooses to select one action over another, i.e., when automatic behavior is terminated and the organism reactivates multiple sources of information to evaluate the evidence for available choices. As such, decision processes require the coordinated retrieval of choice-relevant information including (i) the retrieval of stimulus evaluations (stimulus–reward associations) and reward expectancies about future outcomes, (ii) the retrieval of past and prospective memories (e.g., stimulus–stimulus associations), (iii) the reactivation of contextual task rule representations (e.g., stimulus–response mappings), along with (iv) an ongoing assessment of sensory evidence. An increasing number of studies reveal that retrieval of these multiple types of information proceeds within few theta cycles through synchronized spiking activity across limbic, striatal, and cortical processing nodes. The outlined evidence suggests that evolving spatially and temporally specific theta synchronization could serve as the critical correlate underlying the selection of a choice during goal-directed behavior