Post-interaction neuroplasticity of inter-brain networks underlies the development of social relationship.

Inter-brain coupling has been increasingly recognized for its role in supporting connectedness during social communication. Here we investigate whether inter-brain coupling is plastic and persists beyond the offset of social interaction, facilitating the emergence of social closeness. Dyads were concurrently scanned using functional near infrared spectroscopy (fNIRS) while engaging in a task that involved movement synchronization. To assess post-interaction neuroplasticity, participants performed a baseline condition with no interaction before and after the interaction. The results reveal heightened inter-brain coupling in neural networks comprising the inferior frontal gyrus (IFG) and dorsomedial prefrontal cortex in the post-task compared to the pre-task baseline. Critically, the right IFG emerged as a highly connected hub, with post-task inter-brain coupling in this region predicting the levels of motivation to connect socially. We suggest that post-interactions inter-brain coupling may reflect consolidation of socially related cues, underscoring the role of inter-brain plasticity in fundamental aspects of relationship development.

Competition in context: response selection within the supervisory attentional system model.

We examined the effects of context bias and target exposure duration on error rates (ERR) and response times (RTs) in letter choice task within context. Surface Electromyography (sEMG) was recorded in both hands during context presentation, as a measure of readiness to respond. The goal was to affect the outcome of the task by manipulating relative schemata activation levels prior to target onset, as per the Supervisory Attentional System model. At short exposures, context bias and sEMG activity affected ERR, whereas at longer durations, RTs were affected. Context bias mediated the effect of sEMG activity. Increasing activity in both hands led to higher ERR and RTs in incongruent context. Non-increasing activity in the non-responding lead to lack of relationship between sEMG activity and behavior, irrespective of context. sEMG activity in both hands was found to be interrelated and context-sensitive. These results conform to the predictions of the Supervisory Attentional Model.

Interhemispheric transfer of visual information: Meaningfulness and response formation.

We examined whether Redundancy Gain (RG) can be dissociated from the response stage of a go/nogo paradigm, and whether the meaningfulness of a stimulus modulates the stage at which interhemispheric transfer occurs. Experiment 1 used a lateralized match-to-category paradigm, taken from categories with varying meaningfulness. Experiment 2 presented a novel design, which separates the perceptual stage from response formation, in examination of RG. A sequence of two stimuli was presented. Participants responded by matching the category of the second stimulus to that of the first. The redundant stimulus could appear at the first or the second stage, thus redundancy gain could be separated from the response. Experiment 1 revealed that redundancy gain occurs earlier in the process of stimulus identification for highly meaningful stimuli than for less meaningful stimuli. The results of Experiment 2 support the hypothesis that redundancy gain results from interhemispheric integration of perceptual information, rather than response-formation. Results from both experiments suggest that redundancy gain arises from interhemispheric integration in the perceptual stage, and the efficiency of this integration depends on the meaningfulness of the stimulus. These results are relevant to current hypotheses about the physiological mechanisms underlying RG.

Differential contribution of between and within-brain coupling to movement synchronization.

A fundamental characteristic of the human brain that supports behavior is its capacity to create connections between brain regions. A promising approach holds that during social behavior, brain regions not only create connections with other brain regions within a brain, but also coordinate their activity with other brain regions of an interaction partner. Here we ask whether between-brain and within-brain coupling contribute differentially to movement synchronization. We focused on coupling between the inferior frontal gyrus (IFG), a brain region associated with the observation-execution system, and the dorsomedial prefrontal cortex (dmPFC), a region associated with error-monitoring and prediction. Participants, randomly divided into dyads, were simultaneously scanned with functional near infra-red spectroscopy (fNIRS) while performing an open-ended 3D hand movement task consisting of three conditions: back-to-back movement, free movement, or intentional synchronization. Results show that behavioral synchrony was higher in the intentional synchrony compared with the back-to-back and free movement conditions. Between-brain coupling in the IFG and dmPFC was evident in the free movement and intentional synchrony conditions but not in the back-to-back condition. Importantly, between-brain coupling was found to positively predict intentional synchrony, while within-brain coupling was found to predict synchronization during free movement. These results indicate that during intentional synchronization, brain organization changes such that between-brain networks, but not within-brain connections, contribute to successful communication, pointing to shift from a within-brain feedback loop to a two-brains feedback loop.

Handedness in the presence of prior knowledge: Effects of interhemispheric configuration on performance.

The current study examined the effects of prior knowledge of the responding hand, and that of errors, on the configuration of interhemispheric balance. Prior knowledge was manipulated by instructing the participants to respond with one hand throughout a session (Blocked) or to select the responding hand according to the identity of the stimulus in each trial (Mixed). In addition, we examined how failures to inhibit responses within Logan's (1981) Stop Signal Response Task (SSRT) task affected the Response Times (RTs) of subsequent correct responses. The SSRT was modified to include visual stop signals, shown in Divided Visual Field (DVF), in order to examine the effects of errors committed by each hemisphere. The effects of prior knowledge were shown by absence of a dominant hand effect in the Blocked condition but were uniformly present in the Mixed condition. We also show that commission of an error in the peripheral VFs differentially affected subsequent RTs only in the absence of prior knowledge. We conclude that prior knowledge shifts interhemispheric configuration from the default dominance model to a more complex cooperative configuration.

The benefits of learning movement sequences in social interactions.

Although we frequently acquire knowledge and skills through social interactions, the focus of most research on learning is on individual learning. Here we characterize Interaction Based Learning (IBL), which represents the acquisition of knowledge or skill through social interactions, and compare it to Observational Learning (OL)-learning by observation. To that end, we designed a movement synchronization paradigm whereby participants learned Tai-Chi inspired movement sequences from trained teachers in two separated sessions. We used a motion capture system to track the movement of 40 dyads comprised of a teacher and learner, who were randomly divided into OL or IBL groups, and calculated time-varying synchrony of three-dimensional movement velocity. While in the IBL group both the learner and the teacher could see each other through a transparent glass, in the OL group dyads interacted through a one-way mirror, such that the learners observed the teacher, but the teacher could not see the learners. Results show that although the number of movements recalled was not different between groups, we found improved movement smoothness in the IBL compared to the OL group, indicating movement acquisition was better in the IBL group. In addition, we found that motor synchronization levels in dyads improved over time, indicating that movement synchronization can be learned and retained. In the first session, the IBL group, but not the OL group, showed a significant improvement in synchronization. This suggests that dyadic interaction is important for learning movement sequences, and that bidirectional communication of signals and mutual feedback are essential for the consolidation of motor learning.

Using machine learning-based analysis for behavioral differentiation between anxiety and depression.

Anxiety and depression are distinct-albeit overlapping-psychiatric diseases, currently diagnosed by self-reported-symptoms. This research presents a new diagnostic methodology, which tests rigorously for differences in cognitive biases among subclinical anxious and depressed individuals. 125 participants were divided into four groups based on the levels of their anxiety and depression symptoms. A comprehensive behavioral test battery detected and quantified various cognitive-emotional biases. Advanced machine-learning tools, developed for this study, analyzed these results. These tools detect unique patterns that characterize anxiety versus depression to predict group membership. The prediction model for differentiating between symptomatic participants (i.e., high symptoms of depression, anxiety, or both) compared to the non-symptomatic control group revealed a 71.44% prediction accuracy for the former (sensitivity) and 70.78% for the latter (specificity). 68.07% and 74.18% prediction accuracy was obtained for a two-group model with high depression/anxiety, respectively. The analysis also disclosed which specific behavioral measures contributed to the prediction, pointing to key cognitive mechanisms in anxiety versus depression. These results lay the ground for improved diagnostic instruments and more effective and focused individually-based treatment.

Asymmetric dopamine loss differentially affects effort to maximize gain or minimize loss.

BACKGROUND: Dopamine (DA) plays an important role in regulating effort expenditure for reward, but whether it is also involved in modulating effort to avoid punishment is not clear. Preference for approach towards rewarding stimuli or away from aversive stimuli is associated with asymmetric activation in anterior brain regions. Asymmetric DA signaling in subcortical-frontal circuits may therefore contribute to differentially energizing behavior towards approach or avoidance behavior. We tested this hypothesis in patients with Parkinson's disease (PD), characterized by asymmetric DA loss. METHODS: Patients with greater DA deficit in the left (n = 20) or right (n = 19) hemisphere, performed a task that measures separately effort to approach (maximize gains) versus effort to avoid (minimize loss), on and off DA replacement therapy. RESULTS: When tested off medication, patients with relatively greater DA deficit in the left hemisphere showed greater approach deficit (less effort to increase gain than to avoid loss) whereas the opposite pattern of effort expenditure was demonstrated by patients with greater DA deficit in the right hemisphere. Performing the same task when medicated revealed increased willingness to expend effort, such that increased effort to maximize gain was associated left hemisphere improved DA function (reflected by reduced symptoms), while increased effort to avoid loss was related to right hemisphere improvement. CONCLUSIONS: These results suggest that asymmetry of DA levels modulates the differential exertion of effort toward attaining rewards versus avoiding aversive consequences, providing new insights into understanding the underlying pathophysiology of behavioral syndromes such as apathy and impulsive-compulsive disorders.

Hemispheric asymmetries in meaning selection: evidence from the disambiguation of homophonic vs. heterophonic homographs.

Research investigating hemispheric asymmetries in meaning selection using homophonic homographs (e.g., bank), suggests that the left hemisphere (LH) quickly selects contextually relevant meanings, whereas the right hemisphere (RH) maintains a broader spectrum of meanings including those that are contextually irrelevant (e.g., Faust & Chiarello, 1998). The present study investigated cerebral asymmetries in maintaining the multiple meanings of two types of Hebrew homographs: homophonic homographs and heterophonic homographs (e.g., tear). Participants read homographs preceded by a biasing, or a non-biasing sentential context, and performed a lexical decision task on targets presented laterally, 1000ms after the onset of the sentence-final ambiguous prime. Targets were related to either the dominant or the subordinate meaning of the preceding homograph, or unrelated to it. When targets were presented in the LVF/RH, dominant and subordinate meanings, of both types of homographs, were retained only when they were supported by context. In a non-biasing context, only dominant meanings of homophonic homographs were retained. Alternatively, when targets were presented in the RVF/LH, priming effects for homophonic homographs were only evident when meanings were supported by both context and frequency (i.e., when context favored the dominant meaning). In contrast, heterophonic homographs resulted in activation of dominant meanings, in all contexts, and activation of subordinate meanings, only in subordinate-biasing contexts. The results challenge the view that a broader spectrum of meanings is maintained in the right than in the left hemisphere and suggest that hemispheric differences in the time course of meaning selection (or decay) may be modulated by phonology.