Split-brain patients present a unique opportunity to address controversies regarding subcortical contributions to interhemispheric coordination. We characterized residual functional connectivity in a complete commissurotomy patient by examining patterns of low-frequency BOLD fMRI signal. Using independent components analysis (ICA) and region-of-interest (ROI) based functional connectivity analyses, we demonstrate bilateral resting state networks in a patient lacking all major cerebral commissures. Compared to a control group, the patient's interhemispheric correlation scores fell within the normal range for two out of three regions examined. Thus we provide evidence for bilateral resting state networks in a patient with complete commissurotomy. Such continued interhemispheric interaction suggests that, at least in part, cortical networks in the brain can be coordinated by subcortical mechanisms.

High-Definition transcranial Direct Current Stimulation (HD-tDCS) using specialized small electrodes has been proposed as a focal, non-invasive neuromodulatory technique. Here we provide the first evidence of a change in cortical excitability after HD-tDCS of the motor cortex, using TMS motor evoked potential (MEP) as the measure of excitability. Stimulation for 20 minutes at 1 mA with an anode centered over the hand area of the motor cortex and four surrounding return electrodes (anodal 4×1 montage) produced a significant increase in MEP amplitude and variability after stimulation, compared to sham stimulation. Stimulation was well tolerated by all subjects with adverse effects limited to transient sensation under the electrodes. A high-resolution computational model confirmed predictions of increased focality using the 4×1 HD tDCS montage compared to conventional tDCS. Simulations also indicated that variability in placement of the center electrode relative to the location of the target (central sulcus) could account for increasing variability. These results provide support for the careful use of this technique where focal tDCS is desired.

Previous evidence suggests that directional social cues (e.g., eye gaze) cause automatic shifts in attention toward gaze direction. It has been proposed that automatic attentional orienting driven by social cues (social orienting) involves a diVerent neural network from automatic orienting driven by nonsocial cues. However, previous neuroimaging studies on social orienting have only compared gaze cues to symbolic cues, which typically engage top-down mechanisms. Therefore, we directly compared the neural activity involved in social orienting to that involved in purely automatic nonsocial orienting. Twenty participants performed a spatial cueing task consisting of social (gaze) cues and automatic nonsocial (peripheral squares) cues presented at short and long stimulus (cue-totarget) onset asynchronies (SOA), while undergoing fMRI. Behaviorally, a facilitation eVect was found for both cue types at the short SOA, while an inhibitory eVect (inhibition of return: IOR) was found only for nonsocial cues at the long SOA. Imaging results demonstrated that social and nonsocial cues recruited a largely overlapping fronto-parietal network. In addition, social cueing evoked greater activity in occipito-temporal regions at both SOAs, while nonsocial cueing recruited greater subcortical activity, but only for the long SOA (when IOR was found). A control experiment, including central arrow cues, conWrmed that the occipito-temporal activity was at least in part due to the social nature of the cue and not simply to the location of presentation (central vs. peripheral). These results suggest an evolutionary trajectory for automatic orienting, from predominantly subcortical mechanisms for nonsocial orienting to predominantly cortical mechanisms for social orienting.

Feedback and monetary reward can enhance motor skill learning, suggesting reward system involvement. Continuous theta burst (cTBS) transcranial magnetic stimulation of the primary motor area (M1) disrupts processing, reduces excitability and impairs motor learning. To see whether feedback and reward can overcome the learning impairment associated with M1 cTBS, we delivered real or sham stimulation to two groups of participants before they performed a motor sequence learning task with and without feedback. Participants were trained on two intermixed sequences, one occurring 85% of the time (the “probable” sequence) and the other 15% of the time (the “improbable” sequence). We measured sequence learning as the difference in reaction time (RT) and error rate between probable and improbable trials (RT and error difference scores). Participants were also tested for sequence recall with the same indices of learning 60 min after cTBS. Real stimulation impaired initial sequence learning and sequence knowledge recall as measured by error difference scores and impaired sequence knowledge recall as measured by RT difference score. Relative to non-feedback learning, the introduction of feedback during sequence learning improved subsequent sequence knowledge recall indexed by RT difference score, in both real and sham stimulation groups and feedback reversed the RT difference score based sequence knowledge recall impairment from real cTBS that we observed in the non-feedback learning condition. Only the real cTBS group in the non-feedback condition showed no evidence of explicit sequence knowledge when tested at the end of the study. Feedback improves recall of implicit and explicit motor sequence knowledge and can protect sequence knowledge against the effect of M1 inhibition. Adding feedback and monetary reward/punishment to motor skill learning may help overcome retention impairments or accelerate training in clinical and other settings.